Document and Entity Information	12 Months Ended
Document and Entity Information	Dec. 31, 2017 shares
Document And Entity Information [Abstract]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	ICLR
Entity Registrant Name	ICON PLC
Entity Central Index Key	0001060955
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	54,081,601

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 282,859	$ 192,541
Short term investments - available for sale (Note 3)	77,589	68,046
Accounts receivable, net	379,501	416,229
Unbilled revenue	268,509	192,687
Other receivables	33,798	32,044
Prepayments and other current assets	34,377	35,170
Income taxes receivable (Note 13)	24,385	21,241
Total current assets	1,101,018	957,958
Other Assets:
Property, plant and equipment, net (Note 6)	163,051	148,967
Goodwill (Note 4)	769,058	616,088
Other non-current assets	15,393	13,831
Non-current income taxes receivable (Note 13)	18,396	12,698
Non-current deferred tax asset (Note 13)	8,074	19,691
Intangible assets (Note 5)	71,628	56,610
Total Assets	2,146,618	1,825,843
Current Liabilities:
Accounts payable	18,590	8,696
Payments on account	298,992	272,757
Other liabilities (Note 7)	233,503	190,727
Income taxes payable (Note 13)	14,973	22,226
Total current liabilities	566,058	494,406
Other Liabilities:
Non-current bank credit lines and loan facilities (Note 20)	348,888	348,511
Non-current other liabilities (Note 8)	17,111	23,752
Non-current government grants (Note 11)	966	887
Non-current income taxes payable (Note 13)	14,879	8,482
Non-current deferred tax liability (Note 13)	7,716	4,631
Commitments and contingencies (Note 16)	0	0
Total Liabilities	955,618	880,669
Ordinary shares, par value 6 euro cents per share; 100,000,000 shares authorized, (Note 12)
54,081,601 shares issued and outstanding at December 31, 2017 and 54,530,843 shares issued and outstanding at December 31, 2016.	4,664	4,692
Additional paid-in capital	481,337	438,126
Other undenominated capital (Note 12 (a))	912	809
Accumulated other comprehensive income (Note 19)	(38,713)	(86,300)
Retained earnings	742,800	587,847
Total Shareholders' Equity	1,191,000	945,174
Total Liabilities and Shareholders' Equity	$ 2,146,618	$ 1,825,843

Consolidated Balance Sheets (Parenthetical) - € / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Ordinary shares, par value (euro per share)	€ 0.06	€ 0.06
Ordinary shares, shares authorized (in shares)	100,000,000	100,000,000
Ordinary shares, shares issued (in shares)	54,081,601	54,530,843
Ordinary shares, shares outstanding (in shares)	54,081,601	54,530,843

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Gross revenue	$ 2,402,321	$ 2,364,956	$ 2,161,618
Reimbursable expenses	(643,882)	(698,469)	(586,640)
Net revenue	1,758,439	1,666,487	1,574,978
Costs and expenses:
Direct costs	1,027,310	961,333	908,979
Selling, general and administrative	323,741	325,726	326,786
Depreciation and amortization	61,297	59,575	57,677
Restructuring and other items, net (Note 14)	7,753	8,159	0
Total costs and expenses	1,420,101	1,354,793	1,293,442
Income from operations	338,338	311,694	281,536
Interest income	2,346	1,484	1,306
Interest expense	(12,627)	(13,006)	(3,992)
Income before provision for income taxes	328,057	300,172	278,850
Provision for income taxes (Note 13)	(46,569)	(37,993)	(39,311)
Net income	$ 281,488	$ 262,179	$ 239,539
Net income per ordinary share:
Basic (dollars per share)	$ 5.20	$ 4.75	$ 4.08
Diluted (dollars per share)	$ 5.13	$ 4.65	$ 3.97
Weighted average number of ordinary shares outstanding:
Basic (in shares)	54,129,439	55,248,900	58,746,935
Diluted (in shares)	54,849,046	56,407,136	60,290,033

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 281,488	$ 262,179	$ 239,539
Currency translation adjustment	33,966	(12,839)	(35,105)
Currency impact of long-term funding	13,730	(8,428)	3,768
Unrealized capital (loss)/gain– investments	(272)	11	(54)
Actuarial gain/(loss) on defined benefit pension plan	50	(2,485)	2,693
Realized gain on interest rate hedge	0	0	4,658
Amortization of interest rate hedge	(923)	(923)	(41)
Fair value of cash flow hedge	1,036	0	0
Total comprehensive income	$ 329,075	$ 237,515	$ 215,458

Consolidated Statements of Shareholders' Equity and Comprehensive Income - USD ($) $ in Thousands	Total	Ordinary Shares	Additional Paid-in Capital	Other Undenominated Capital	Accumulated Other Comprehensive Income	Retained Earnings
Balance (in shares) at Dec. 31, 2014		60,106,780
Balance at Dec. 31, 2014	$ 950,206	$ 5,059	$ 327,212	$ 305	$ (37,555)	$ 655,185
Comprehensive Income:
Net income	239,539					239,539
Currency translation adjustment	(35,105)				(35,105)
Currency impact of long-term funding	3,768				3,768
Unrealized capital loss - investments	(54)				(54)
Actuarial gain on defined benefit pension plan	2,693				2,693
Net gain on interest rate hedge	4,617				4,617
Total comprehensive income	215,458
Exercise of share options (in shares)		773,753
Exercise of share options	20,981	$ 52	20,929
Issue of restricted share units / performance share units (in shares)		276,860
Issue of restricted share units / performance share units	18	$ 18	0
Share based compensation expense	33,317		33,317
Share issue costs	(8)		(8)
Repurchase of ordinary shares (in shares)		(6,198,481)
Repurchase of ordinary shares	(457,892)	$ (410)		410		(457,892)
Share repurchase costs	(889)					(889)
Excess income tax benefit on exercise of equity compensation (net of deferred tax)	1,905		1,905
Balance (in shares) at Dec. 31, 2015		54,958,912
Balance at Dec. 31, 2015	763,096	$ 4,719	383,355	715	(61,636)	435,943
Comprehensive Income:
Net income	262,179					262,179
Currency translation adjustment	(12,839)				(12,839)
Currency impact of long-term funding	(8,428)				(8,428)
Unrealized capital loss - investments	11				11
Actuarial gain on defined benefit pension plan	(2,485)				(2,485)
Amortization of interest rate hedge	(923)				(923)
Total comprehensive income	237,515
Exercise of share options (in shares)		393,240
Exercise of share options	10,139	$ 26	10,113
Issue of restricted share units / performance share units (in shares)		607,878
Issue of restricted share units / performance share units	41	$ 41	0
Share based compensation expense	40,343		40,343
Share issue costs	(17)		(17)
Repurchase of ordinary shares (in shares)		(1,429,187)
Repurchase of ordinary shares	(110,000)	$ (94)		94		(110,000)
Share repurchase costs	(275)					(275)
Excess income tax benefit on exercise of equity compensation (net of deferred tax)	$ 4,332		4,332
Balance (in shares) at Dec. 31, 2016	54,530,843	54,530,843
Balance at Dec. 31, 2016	$ 945,174	$ 4,692	438,126	809	(86,300)	587,847
Comprehensive Income:
Cumulative effect adjustment from adoption of ASU 2016-09	6,677		0			6,677
Net income	281,488					281,488
Currency translation adjustment	33,966				33,966
Currency impact of long-term funding	13,730				13,730
Unrealized capital loss - investments	(272)				(272)
Actuarial gain on defined benefit pension plan	50				50
Amortization of interest rate hedge	(923)				(923)
Fair value of cash flow hedge	1,036				1,036
Total comprehensive income	329,075
Exercise of share options (in shares)		458,243
Exercise of share options	13,906	$ 31	13,875
Issue of restricted share units / performance share units (in shares)		681,742
Issue of restricted share units / performance share units	44	$ 44
Share based compensation expense	29,351		29,351
Share issue costs	(15)		(15)
Repurchase of ordinary shares (in shares)		(1,589,227)
Repurchase of ordinary shares	(133,106)	$ (103)		103		(133,106)
Share repurchase costs	$ (106)					(106)
Balance (in shares) at Dec. 31, 2017	54,081,601	54,081,601
Balance at Dec. 31, 2017	$ 1,191,000	$ 4,664	$ 481,337	$ 912	$ (38,713)	$ 742,800

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 281,488	$ 262,179	$ 239,539
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on disposal of property, plant and equipment	228	151	55
Depreciation expense	43,436	42,125	40,210
Amortization of intangibles	17,861	17,450	17,467
Amortization of government grants	(44)	(44)	53
Interest on short term investments	(1,088)	(823)	(571)
Realized (gain)/loss on sale of short term investments	(112)	(50)	113
Amortization of gain on interest rate hedge	(923)	(923)	(41)
Amortization of financing costs	556	566	0
Stock compensation expense	30,573	40,343	33,317
Deferred taxes	10,729	1,545	3,157
Changes in assets and liabilities:
Decrease/(increase) in accounts receivable	57,747	2,526	(18,671)
Increase in unbilled revenue	(62,491)	(16,753)	(29,281)
Decrease/(increase) in other receivables	1,771	(1,829)	(14,519)
Decrease/(increase) in prepayments and other current assets	4,359	1,872	(8,631)
Increase in other non-current assets	(1,524)	(2,157)	(55)
(Decrease)/increase in payments on account	(7,174)	(45,754)	34,644
Increase/(decrease) in other current liabilities	6,679	(44,713)	(26,266)
(Decrease)/increase in other non-current liabilities	(3,710)	3,008	6,378
Decrease in income taxes payable	(2,293)	(690)	(949)
Increase in accounts payable	7,014	1,175	3,124
Net cash provided by operating activities	383,082	259,204	279,073
Cash flows from investing activities:
Purchase of property, plant and equipment	(44,717)	(42,601)	(49,730)
Purchase of subsidiary undertakings	(144,131)	(54,209)	(166,292)
Cash acquired with subsidiary undertaking	19,649	3,168	194
Sale of short term investments	33,086	40,858	25,708
Purchase of short term investments	(41,701)	(22,030)	(14,194)
Net cash used in investing activities	(177,814)	(74,814)	(204,314)
Cash flows from financing activities:
Drawdown of credit lines and facilities	0	73,000	851,500
Repayment of credit lines and facilities	0	(73,000)	(501,500)
Proceeds from the exercise of equity compensation	13,950	10,180	20,999
Share issue costs	(15)	(17)	(8)
Excess tax benefit on exercise of equity compensation	0	6,402	1,905
Repurchase of ordinary shares	(133,106)	(110,000)	(457,892)
Share repurchase costs	(106)	(275)	(889)
Repayment of government grant	0	0	(159)
Proceeds from interest rate hedge	0	0	4,658
Net cash used in financing activities	(119,277)	(93,710)	(81,386)
Effect of exchange rate movements on cash	4,327	(2,050)	(8,362)
Net increase/(decrease) in cash and cash equivalents	90,318	88,630	(14,989)
Cash and cash equivalents at beginning of year	192,541	103,911	118,900
Cash and cash equivalents at end of year	$ 282,859	$ 192,541	$ 103,911

Description of business	12 Months Ended
Description of business	Dec. 31, 2017
Accounting Policies [Abstract]
Description of business	Description of business ICON plc and its subsidiaries ("the Company" or "ICON") is a clinical research organization ("CRO"), providing outsourced development services on a global basis to the pharmaceutical, biotechnology and medical device industries. We specialize in the strategic development, management and analysis of programs that support all stages of the clinical development process from compound selection to Phase I-IV clinical studies. Our vision is to be the Global CRO partner of choice in drug development by delivering best in class information, solutions and performance in clinical and outcomes research. We believe that we are one of a select group of CROs with the expertise and capability to conduct clinical trials in most major therapeutic areas on a global basis and have the operational flexibility to provide development services on a stand-alone basis or as part of an integrated "full service" solution. At December 31, 2017 we had approximately 13,250 employees, in 98 locations in 38 countries. During the year ended December 31, 2017, we derived approximately 45.0%, 43.3% and 11.7% of our net revenue in the United States, Europe and Rest of World, respectively. We began operations in 1990 and have expanded our business predominately through internal growth, together with a number of strategic acquisitions to enhance our capabilities and expertise in certain areas of the clinical development process. We are incorporated in Ireland and our principal executive office is located at: South County Business Park, Leopardstown, Dublin 18, Republic of Ireland. The contact telephone number of this office is +353 1 2912000.

Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Significant Accounting Policies

The accounting policies noted below were applied in the preparation of the accompanying financial statements of the Company and are in conformity with accounting principles generally accepted in the United States.

(a) Basis of consolidation

The consolidated financial statements include the financial statements of the Company and all of its subsidiaries. All significant intercompany profits, transactions and account balances have been eliminated. The results of subsidiary undertakings acquired in the period are included in the Consolidated Statement of Operations from the date of acquisition.

(b) Use of estimates

The preparation of financial statements in conformity with generally accepted accounting principles in the United States requires management to make estimates and judgments that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reported period. Actual results could differ from those estimates. The principal management estimates and judgments used in preparing the financial statements relate to revenue recognition and taxation.

The Company primarily earns revenues by providing a number of different services to its customers. These services, which are integral elements of the clinical development process, include clinical trials management, biometric activities, consulting, imaging, contract staffing, informatics and laboratory services. Contracts range in duration from a number of months to several years. Revenue for services, as rendered, is recognized only after persuasive evidence of an arrangement exists, the sales price is fixed or determinable and collectability is reasonably assured.

Clinical trials management revenue is recognized on a proportional performance method. Depending on the contractual terms revenue is either recognized on the percentage of completion method based on the relationship between hours incurred and the total estimated hours of the trial or on the unit of delivery method. Contract costs equate to the product of labor hours incurred and compensation rates. For the percentage of completion method, the input (effort expended) method has been used to measure progress towards completion as there is a direct relationship between input and productivity. Contract revenue is the product of the aggregated labor hours required to complete the specified contract tasks at the agreed contract rates. The Company regularly reviews the estimate of total contract time to ensure such estimates remain appropriate taking into account actual contract stage of completion, remaining time to complete and any identified changes to the contract scope. Remaining time to complete depends on the specific contract tasks, the complexity of the contract and can include geographical site selection and initiation, patient enrollment, patient testing and level of results analysis required. While the Company may routinely adjust time estimates, the Company's estimates and assumptions historically have been accurate in all material respects in the aggregate. Where revenue is recognized on the unit of delivery method, the basis applied is the number of units completed as a percentage of the total number of contractual units.

Biometrics revenue is recognized on a fee-for-service method as each unit of data is prepared on the basis of the number of units completed in a period as a percentage of the total number of contracted units. Imaging revenue is recognized on a fee-for-service basis recognizing revenue for each image completed. Consulting revenue is recognized on a fee-for-service basis as each hour of the related service is performed. Contract staffing revenue is recognized on a fee-for-service basis, over the time the related service is performed, or in the case of permanent placement, once the candidate has been placed with the client. Informatics revenue is recognized on a fee-for-service basis. Informatics contracts are treated as multiple element arrangements, with contractual elements comprising license fee revenue, support fee revenue and revenue from software services, each of which can be sold separately. Sales prices for contractual elements are determined by reference to objective and reliable evidence of their sales price. License and support fee revenues are recognized rateably over the period of the related agreement. Revenue from software services is recognized using the percentage of completion method based on the relationship between hours incurred and the total estimated hours required to perform the service.

Laboratory service revenue is recognized on a fee-for-service basis. The Company accounts for laboratory service contracts as multiple element arrangements, with contractual elements comprising laboratory kits and laboratory testing, each of which can be sold separately. Sales prices for contractual elements are determined by reference to objective and reliable evidence of their sales price. Revenues for contractual elements are recognized on the basis of the number of deliverable units completed in the period.

Contracts generally contain provisions for renegotiation in the event of changes in the scope, nature, duration, or volume of services of the contract. Renegotiated amounts are recognized as revenue by revision to the total contract value arising as a result of an authorized customer change order.

The difference between the amount of revenue recognized and the amount billed on a particular contract is included in the Consolidated Balance Sheet as unbilled revenue or payments on account. Normally, amounts become billable upon the achievement of certain milestones, for example, target patient enrollment rates, clinical testing sites initiated or case report forms completed. Once the milestone target is reached, amounts become billable in accordance with pre-agreed payment schedules included in the contract or on submission of appropriate billing detail. Such cash payments are not representative of revenue earned on the contract as revenues are recognized over the period in which the specified contractual obligations are fulfilled. Amounts included in unbilled revenue are expected to be collected within one year and are included within current assets. Advance billings to customers, for which revenue has not been recognized, are recognized as payments on account within current liabilities.

In the event of contract termination, if the value of work performed and recognized as revenue is greater than aggregate milestone billings at the date of termination, cancellation clauses usually ensure that the Company is paid for all work performed to the termination date.

(d) Reimbursable expenses

Reimbursable expenses comprise investigator payments and certain other costs which are reimbursed by clients under terms specific to each contract and are deducted from gross revenue in arriving at net revenue. Investigator payments are accrued based on patient enrollment over the life of the contract. Investigator payments are made based on predetermined contractual arrangements, which may differ from the accrual of the expense.

(e) Direct costs

Direct costs consist of compensation, associated employee benefits and share-based payments for project-related employees and other direct project-related costs.

(f) Advertising costs

All costs associated with advertising and promotion are expensed as incurred. The advertising and promotion costs were $6,744,333, $7,167,050 and $4,513,750 for the years ended December 31, 2017, December 31, 2016 and December 31, 2015 respectively.

(g) Foreign currencies and translation of subsidiaries

The Company's financial statements are prepared in United States dollars. Transactions in currencies other than United States dollars are recorded at the rate ruling at the date of the transaction. Monetary assets and liabilities denominated in currencies other than United States dollars are translated into United States dollars at exchange rates prevailing at the Balance Sheet date. Adjustments resulting from these translations are charged or credited to income. Amounts charged or credited to the Consolidated Statement of Operations for the years ended December 31, 2017, December 31, 2016 and December 31, 2015 were as follows:



	Year ended December 31, (in thousands)
	2017		2016		2015
Amounts charged/(credited)	$	7,760	$	2,094	$	(3,608	)

The financial statements of subsidiaries with other functional currencies are translated at period end rates for the Consolidated Balance Sheet and average rates for the Consolidated Statement of Operations. Translation gains and losses arising are reported as a movement on accumulated other comprehensive income. Foreign currency transaction gains and losses are reporting in other comprehensive income rather than through income where the foreign currency transaction is 'long-term investment' in nature i.e. settlement is not planned or anticipated in the foreseeable future.

(h) Disclosure about fair value of financial instruments

Cash, cash equivalents, unbilled revenue, other receivables, short term investments, prepayments and other current assets, accounts receivable, accounts payable, investigator payments, payments on account, accrued liabilities, accrued bonuses and income taxes payable have carrying amounts that approximate fair value due to the short term maturities of these instruments. Other liabilities' carrying amounts approximate fair value based on net present value of estimated future cash flows.

Financial instruments are measured in the Consolidated Balance Sheet fair value using a fair value hierarchy of valuation inputs. The hierarchy prioritizes the inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market. Each fair value measurement is reported in one of three levels, which is determined by the lowest level input that is significant to the fair value measurement in its entirety. These levels are:



Level 1:	Inputs are based upon unadjusted quoted prices for identical instruments traded in active markets.

Level 2:	Inputs are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3:	Inputs are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability.

The Company classifies its short term investments as available for sale, as it does not actively trade such securities nor does it intend to hold them to maturity. The fair value of short term investments are represented by level 1 fair value measurements – quoted prices in active markets for identical assets. The unrealized movements in fair value are recognized in equity until disposal or sale, at which time, those unrealized movements from prior periods are recognized in Consolidated Statement of Operations. Losses other than temporary, which reduce the carrying amount below cost are recognized in Consolidated Statement of Operations.

(i) Business combinations

The cost of a business combination is measured as the aggregate of the fair values at the date of exchange of assets given, liabilities incurred or assumed and equity instruments issued in exchange for control. Where a business combination agreement provides for an adjustment to the cost of the acquisition which is contingent upon future events, the amount of the estimated adjustment is recognized at the acquisition date at the fair value of the contingent consideration. Any changes to this estimate outside the measurement period will depend on the classification of the contingent consideration. If the contingent consideration is classified as equity it shall not be re-measured and the settlement shall be accounted for within equity. If the contingent consideration is classified as a liability any adjustments will be accounted for through the Consolidated Statement of Operations or Other Comprehensive Income depending on whether the liability is considered a financial instrument.

The assets, liabilities and contingent liabilities of businesses acquired are measured at their fair values at the date of acquisition. In the case of a business combination which is completed in stages, the fair values of the identifiable assets, liabilities and contingent liabilities are determined at the date of each exchange transaction. When the initial accounting for a business combination is determined provisionally, any subsequent adjustments to the provisional values allocated to the identifiable assets, liabilities and contingent liabilities are made within twelve months of the acquisition date and presented as adjustments to goodwill in the reporting period in which the adjustments are determined.

(j) Goodwill and Impairment

Goodwill represents the excess of the cost of acquired entities over the net amounts assigned to assets acquired and liabilities assumed. Goodwill primarily comprises acquired workforce in place which does not qualify for recognition as an asset apart from goodwill. Goodwill is stated net of any provision for impairment. The Company tests goodwill annually for any impairments or whenever events occur which may indicate impairment. The first step is to compare the carrying amount of the reporting unit's assets to the fair value of the reporting unit. If the carrying amount exceeds the fair value then a second step is completed which involves the fair value of the reporting unit being allocated to each asset and liability with the excess being goodwill. The impairment loss is the amount by which the recorded goodwill exceeds the implied goodwill. No impairment was recognized as a result of the impairment testing carried out for the years ended December 31, 2017, December 31, 2016 and December 31, 2015.

(k) Intangible assets

Intangible assets are amortized on a straight line basis over their estimated useful life.

(l) Cash and cash equivalents

Cash and cash equivalents include cash and highly liquid investments with initial maturities of three months or less and are stated at cost, which approximates market value.

(m) Short term investments - available for sale

The Company classifies short-term investments as available for sale in accordance with the terms of FASB ASC 320, Investments – Debt and Equity Securities. Realized gains and losses are determined using specific identification. The investments are reported at fair value, with unrealized gains or losses reported in a separate component of shareholders' equity. Any differences between the cost and fair value of the investments are represented by accrued interest and unrealized gains/losses.

(n) Accounts receivable, net

Accounts receivable are recorded at fair value less an allowance for doubtful accounts. The allowance is an estimate based on historical collection experience, current economic and market conditions, and a review of the current status of each customer's trade accounts receivable. Account balances are written-off against the allowance when the Group determines that it is probable that the receivable will not be recovered.

(o) Inventory

Inventory is valued at the lower of cost and net realizable value and after provisions for obsolescence. The cost of inventories comprises the purchase price and attributable costs, less trade discounts. At December 31, 2017 the carrying value of inventory, included within prepayments and other current assets on the Consolidated Balance Sheet, was $2.2 million (2016: $2.4 million).

(p) Property, plant and equipment

Property, plant and equipment is stated at cost less accumulated depreciation. Depreciation of property, plant and equipment is computed using the straight line method based on the estimated useful lives of the assets as listed below:



	Years
Building	40
Computer equipment and software	2-8
Office furniture and fixtures	8
Laboratory equipment	5
Motor vehicles	5

Leasehold improvements are amortized using the straight-line method over the estimated useful life of the asset or the lease term, whichever is shorter.

(q) Leased assets

Costs in respect of operating leases are charged to the Consolidated Statement of Operations on a straight line basis over the lease term.

Assets acquired under capital finance leases are included in the Consolidated Balance Sheet at the present value of the future minimum lease payments and are depreciated over the shorter of the lease term and their remaining useful lives. The corresponding liabilities are recorded in the Consolidated Balance Sheet and the interest element of the capital lease rental is charged to interest expense.

(r) Income taxes

The Company applies the asset and liability method of accounting for income taxes. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which these temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Deferred tax assets are reduced by a valuation allowance to the amount more likely than not to be realized. The Company recognizes the effect of income tax positions only if those positions will more likely than not be sustained. Recognized income tax positions are measured at the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement. Interest and penalties related to income taxes are included in income tax expense and classified with the related liability on the Consolidated Balance Sheet. The Company intends to account for the impact of GILTI (“global intangible low-taxed income”) as a period item in the period it arises and has therefore not provided for deferred taxes in respect of this item.

(s) Government grants

Government grants received relating to capital expenditures are shown as deferred income and credited to income on a basis consistent with the depreciation policy of the relevant assets. Grants relating to categories of operating expenditures are credited to income in the period in which the expenditure to which they relate is charged.

Under the grant agreements amounts received may become repayable in full should certain circumstances specified within the grant agreements occur, including downsizing by the Company, disposing of the related assets, ceasing to carry on its business or the appointment of a receiver over any of its assets. The Company has not recognized any loss contingency having assessed as remote the likelihood of these events arising.

(t) Research and development credits

Research and development credits are available to the Company under the tax laws in certain jurisdictions, based on qualifying research and development spend as defined under those tax laws. Research and development credits are generally recognized as a reduction of income tax expense. However, certain tax jurisdictions provide refundable credits that are not wholly dependent on the Company's ongoing income tax status or income tax position. In these circumstances the benefit of these credits is not recorded as a reduction to income tax expense, but rather as a reduction of operating expenditure.

(u) Pension costs

The Company contributes to defined contribution plans covering all eligible employees. The Company contributes to these plans based upon various fixed percentages of employee compensation and such contributions are expensed as incurred.

The Company operates, through two subsidiaries, a defined benefit plan for certain of its United Kingdom and Swiss employees. The Company accounts for the costs of these plans using actuarial models required by FASB ASC 715-30 and these plans are presented in accordance with the requirements of FASB ASC 715-60 Defined Benefit Plans – Other Post retirement.

(v) Net income per ordinary share

Basic net income per ordinary share has been computed by dividing net income available to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period. Diluted net income per ordinary share is computed by adjusting the weighted average number of ordinary shares outstanding during the period for all potentially dilutive ordinary shares outstanding during the period and adjusting net income for any changes in income or loss that would result from the conversion of such potential ordinary shares.

There is no difference in net income used for basic and diluted net income per ordinary share. The reconciliation of the number of shares used in the computation of basic and diluted net income per ordinary share is as follows:



	Year Ended December 31,
	2017	2016	2015
Weighted average number of ordinary shares outstanding for basic net income per ordinary share	54,129,439	55,248,900	58,746,935
Effect of dilutive share options outstanding	719,607	1,158,236	1,543,098
Weighted average number of ordinary shares outstanding for diluted net income per ordinary share	54,849,046	56,407,136	60,290,033

(w) Share-based compensation

The Company accounts for its share options, restricted share units ("RSUs") and performance share units ("PSUs") in accordance with the provisions of FASB ASC 718, Compensation – Stock Compensation. Share-based compensation expense for equity-settled awards made to employees and Directors is measured and recognized based on estimated grant date fair values. These equity-settled awards include employee share options, RSUs and PSUs.

Share-based compensation expense for share options awarded to employees and Directors is estimated at the grant date based on each option's fair value as calculated using the Black-Scholes option-pricing model. Share-based compensation for RSUs and PSUs awarded to employees and Directors is calculated based on the market value of the Company's shares on the date of award of the RSUs and PSUs. The value of awards expected to vest is recognized as an expense over the requisite service periods. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs materially from original estimates.

Estimating the grant date fair value of share options as of the grant date using an option-pricing model, such as the Black-Scholes model, is affected by the Company's share price as well as assumptions regarding a number of complex variables. These variables include, but are not limited to, the expected share price volatility over the term of the awards, risk-free interest rates and the expected term of the awards.

Liability classified awards are measured at the fair value of the award on the grant date and remeasured at each reporting period at fair value until the award is settled.

(x) Impairment of long-lived assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of the asset to future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured at the amount by which the carrying amount of the asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount of the asset or fair value less selling costs.

(y) Derivative financial instruments

We enter into transactions in the normal course of business using various financial instruments in order to hedge against exposure to fluctuating exchange and interest rates. We use derivative financial instruments to reduce exposure to fluctuations in interest rates. A derivative is a financial instrument or other contract whose value changes in response to some underlying variable, which has an initial net investment smaller than would be required for other instruments that have a similar response to the variable and that will be settled at a future date. We do not enter into derivative financial instruments for trading or speculative purposes. We did not hold any interest rate swap contracts or forward currency contracts at December 31, 2016 or December 31, 2015.

We use derivative financial instruments to reduce exposure to fluctuations in foreign exchange rates. During the year-ended December 31, 2017, we entered into forward currency contracts in respect of identified exposure arising from euro payments. The fair value of the derivative asset at December 31, 2017 was $1.2 million (included in other receivables). The forward currency contracts expire within 12 months of year-end.

Our accounting policies for derivative financial instruments are based on whether they meet the criteria for designation as cash flow or fair value hedges. A designated hedge of the exposure to variability in the future cash flows of an asset or a liability, or of a forecasted transaction, is referred to as a cash flow hedge. A designated hedge of the exposure to changes in fair value of an asset or a liability is referred to as a fair value hedge. The criterion for designating a derivative as a hedge includes the assessment of the instrument's effectiveness in risk reduction, matching of the derivative instrument to its underlying transaction and the probability that the underlying transaction will occur. For derivatives with cash flow hedge accounting designation, we report the gain or loss from the effective portion of the hedge as a component of Other Comprehensive Income and reclassify it into earnings in the same period or periods in which the hedged transaction affects earnings and within the same income statement line item as the impact of the hedged transaction. For derivatives with fair value hedge accounting designation, we recognize gains or losses from the change in fair value of these derivatives, as well as the offsetting change in the fair value of the underlying hedged item, in earnings. Fair value gains and losses arising on derivative financial instruments not qualifying for hedge accounting are reported in our Consolidated Statement of Operations.

(z) Financing costs and gain on interest rate hedge

The interest rate in respect of the Senior Notes is fixed at 3.64% for the five year term of the agreement. The associated interest cost is recognized in interest expense in the period since drawdown in December 2015.

On October 5, 2015, the Company entered into an interest rate hedge in respect of the planned issuance of the Senior Notes in December 2015. The interest rate hedge matured on November 17, 2015 when the interest rate on the Senior Notes was fixed. The interest rate hedge was effective in accordance with Financial Accounting Standards Board ("FASB") ASC 815, "Derivatives and Hedging". The cash proceeds ($4.6 million), representing the realized gain on the interest rate hedge, were received on maturity in November 2015 and are recorded within Other Comprehensive Income. The realized gain will be amortized to the Consolidated Statement of Operations, net against interest payable, over the period of the Senior Notes.

Deferred financing costs (including issue costs relating to the Senior Notes) are reported at cost less accumulated amortization and the related amortization expense is included in interest expense, in our Consolidated Statement of Operations.

(aa) Reclassifications

Certain amounts in the consolidated financial statements have been reclassified where necessary to conform to the current year presentation.

Short term investments - available for sale

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Short term investments - available for sale



	December 31, 2017			December 31, 2016
	(in thousands)
At start of year	$	68,046		$	85,990
Purchases	41,701			22,030
Sales and maturities	(33,086		)	(40,858		)
Interest on short term investments	1,088			823
Realized gain on sale of short term investments	112			50
Unrealized capital (loss)/gain – investments	(272		)	11
At end of year	$	77,589		$	68,046

The Company classifies its short term investments as available for sale. Short term investments comprise highly liquid investments with maturities of greater than three months and minimum "A-" rated fixed and floating rate securities. Short term investments at December 31, 2017 have an average maturity of 1.58 years compared to 1.37 years at December 31, 2016. The investments are reported at fair value with unrealized gains or losses reported in a separate component of shareholders' equity. Any differences between the cost and fair value of investments are represented by accrued interest and unrealized gains/losses. The fair value of short term investments are represented by level 1 fair value measurements – quoted prices in active markets for identical assets.

The following table represents our available for sale short term investments by major security type as of December 31, 2017:



								Maturity by period
	Cost Total		Unrealized gains / (losses)			Fair Value Total		Less than 1 year		1 to 5 years
	(U.S.$ in millions)
US government debt securities	13.95		(0.11		)	13.84		1.99		11.85
Corporate securities	62.61		(0.19		)	62.42		23.06		39.36
Term deposits	1.33		—			1.33		1.33		—
Total (U.S.$ in millions)	$	77.89	$	(0.30	)	$	77.59	$	26.38	$	51.21

The contractual maturity of certain of the portfolio is greater than 12 months, however classification as short-term investments reflects the Company practice and intention in respect of these investments. The company recognizes the unrealized losses in fair value in equity as these unrealized losses on short term investments have been considered as temporary.

Goodwill

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill



	December 31, 2017		December 31, 2016
	(in thousands)
Opening goodwill	$	616,088	$	588,434
Current year acquisitions (note 4 (a))	129,222		34,576
Prior period acquisition (note 4 (b))	1,393		7,689
Foreign exchange movement	22,355		(14,611		)
Closing goodwill	$	769,058	$	616,088

The Company has made a number of strategic acquisitions since inception to enhance its capabilities and experience in certain areas of the clinical development process. Goodwill arising on acquisition represents the excess of the cost of acquired entities over the net amounts assigned to assets acquired and liabilities assumed. Goodwill primarily comprises of the acquired workforce in place which does not qualify for recognition as an asset apart from goodwill.

The Company acquired Mapi Developments SAS ('Mapi') during the year-ended December 31, 2017 resulting in the recognition of goodwill of $129.2 million (note 4 (a)).

The Company tests goodwill annually for impairment or whenever events occur which may indicate impairment. The results of the Company's goodwill impairment testing (assessed at September 30, 2017) during the year ended December 31, 2017 provided no evidence of impairment and indicated the existence of sufficient headroom such that a reasonably possible change to the key assumptions used would be unlikely to result in an impairment of the related goodwill.

(a) Acquisitions - Mapi Group

On July 27, 2017, a subsidiary of the Company, ICON Clinical Research Limited, acquired Mapi Group. Mapi Group is a leading patient-centered health outcomes research and commercialization company. Cash outflows on acquisition were $144.1 million.

The acquisition of Mapi has been accounted for as a business combination in accordance with FASB ASC 805 Business Combinations. The Company has made a provisional assessment of the fair value of assets acquired and liabilities assumed as at that date. The table following summarizes the Company’s provisional estimates of the fair values of the assets acquired and liabilities assumed:



	July 27,
	2017
	(in thousands)
Cash	$	19,649
Property, plant and equipment	3,410
Goodwill*	129,222
Intangible assets**	32,305
Accounts receivable	15,467
Unbilled revenue	8,484
Prepayments and other current assets	3,160
Other receivables	1,430
Income taxes receivable	4,262
Accounts payable	(3,166		)
Payments on account	(31,341		)
Other liabilities	(26,586		)
Non-current other liabilities	(1,061		)
Non-current deferred tax liability	(11,104		)
Net assets acquired	$	144,131

Cash outflows	$	144,131
Total consideration	$	144,131

*Goodwill represents the acquisition of an established workforce with experience in late phase commercialization, analytics, real world evidence generation and strategic regulatory services in clinical trial services for biologics, drugs and devices. Goodwill related to the business acquired is not tax deductible.

**The Company has made an initial estimate of separate intangible assets acquired of $32.3 million, being customer relationships and order book assets. This assessment is under review and will be finalized within 12 months of the date of acquisition.

The proforma effect of the Mapi acquisition if completed on January 1, 2016 would have resulted in net revenue, net income and earnings per share for the fiscal years ending December 31, 2017 and December 31, 2016 as follows:



	Year Ended
	December 31,
	2017		2016
	(in thousands)
Net revenue	$	1,811,018	$	1,750,643
Net income	$	284,903	$	263,101
Basic earnings per share	$	5.26	$	4.76
Diluted earnings per share	$	5.19	$	4.66

(b) Acquisition of ClinicalRM

On September 15, 2016, a subsidiary of the Company, ICON US Holdings Inc. acquired Clinical Research Management, Inc. ("ClinicalRM") which resulted in net cash outflows of $52.4 million (including certain payments made on behalf of ClinicalRM totaling $9.2 million). ClinicalRM is a full-service CRO specializing in preclinical through Phase IV support of clinical research and clinical trial services for biologics, drugs and devices. The organization helps customers progress their products to market faster with a wide array of research, regulatory and sponsor services within the U.S. and around the globe. ClinicalRM provide full service and functional research solutions to a broad range of US government agencies. Their extensive expertise extends across basic and applied research, infectious diseases, vaccines development, testing and the response to bio-threats. They have worked in collaboration with government and commercial customers to respond to the threat of global viral epidemics. Further consideration of up to $12.0 million is payable if certain performance milestones are achieved in respect of periods up to December 31, 2017. The fair value of the contingent consideration on acquisition and at March 31, 2017, was estimated at $6.0 million. The evaluation of the performance and forecast performance of ClinicalRM against performance milestones was updated as required at June 30, 2017. Arising from that evaluation, the fair value of the contingent consideration liability was determined as $Nil, resulting in a net credit of $6.0 million being recorded within selling, general & administrative expenses in the Consolidated Statement of operations. The fair value of the contingent consideration at December 31, 2017 is $Nil.

The acquisition of ClinicalRM has been accounted for as a business combination in accordance with FASB ASC 805 Business Combinations. The table following summarizes the fair values of the assets acquired and liabilities assumed:



	September 15,
	2016
	(in thousands)
Cash	$	3,168
Property, plant and equipment	939
Goodwill*	35,969
Customer lists	4,012
Order backlog	1,668
Brand	1,409
Accounts receivable	11,431
Unbilled revenue	3,868
Prepayments and other current assets	1,673
Accounts payable	(165		)
Other liabilities	(5,569		)
Non-current other liabilities	(7		)

Net assets acquired	$	58,396



Cash outflows (including other liabilities assumed of $9.2 million)	$	52,396
Assessment of valuation of contingent consideration at acquisition	6,000
Net purchase consideration	$	58,396

*Goodwill represents the acquisition of an established workforce with experience in preclinical through Phase IV support of clinical research and clinical trial services for biologics, drugs and devices. Goodwill related to the US portion of the business acquired is tax deductible. In finalizing the goodwill on acquisition of CRM in the twelve month period from acquisition, fair value adjustments were made which resulted in an increase to unbilled revenue ($1.1 million) and other liabilities ($1.1 million) and in a decrease to accounts receivable ($0.3 million) and accounts payable ($0.5 million). Customer list, order backlog and brand intangible asset values were also finalized.

The proforma effect of the ClinicalRM acquisition if completed on January 1, 2015 would have resulted in net revenue, net income and earnings per share for the fiscal years ended December 31, 2016 and December 31, 2015 as follows:



	Year Ended December 31,
	2016		2015
	(in thousands)
Net revenue	$	1,713,245	$	1,639,085
Net income	$	266,148	$	244,167
Basic earnings per share	$	4.82	$	4.16
Diluted earnings per share	$	4.72	$	4.05

On December 4, 2015, a subsidiary of the Company, ICON Clinical Research LLC. acquired PMG for cash consideration of $65.4 million, including certain payments on behalf of PMG totaling $10.1 million. PMG is an integrated network of 52 clinical research sites in North Carolina, South Carolina, Tennessee, Illinois and Iowa. The site network includes wholly owned facilities and dedicated clinical research sites. PMG conducts clinical trials in all major therapeutic areas and has particular expertise in vaccine, gastroenterology, cardiovascular, neurology and endocrinology studies. It has a proprietary database of clinical trial participants. It also has access to in excess of 2 million active patients via electronic medical records through its partnerships with health care institutions and community physical practices.

The acquisition of PMG has been accounted for as a business combination in accordance with FASB ASC 805 Business Combinations. The table following summarizes the fair values of the assets acquired and liabilities assumed;



	December 4, 2015
	(in thousands)
Cash	$	194
Property, plant and equipment	712
Goodwill*	48,728
Customer lists	6,938
Order backlog	2,948
Accounts receivable	11,597
Prepayments and other current assets	1,329
Accounts payable	(530		)
Other liabilities	(3,456		)
Non-current deferred tax liability	(3,106		)
Net assets acquired	$	65,354



Cash consideration	$	53,681
Other liabilities assumed	10,060
Working capital adjustment	1,613
Total cash outflows	$	65,354

*Goodwill represents the acquisition of an established workforce with experience in clinical trial consulting and regulatory support for the development of drugs, medical devices and diagnostics, with a specific focus on strategy to increase efficiency and productivity in product development. In finalizing the goodwill on acquisition of PMG in the twelve month period from acquisition, fair value adjustments of $7.7 million were made to deferred tax liabilities ($3.1 million), accounts receivable acquired ($1.4 million), other liabilities ($1.2 million) and the value of the customer list and order backlog assets acquired ($0.4 million). Additional consideration of $1.6 million was provided on completion of the contractual working capital process.

The proforma effect of the PMG acquisition if completed on January 1, 2014 would have resulted in net revenue, net income and earnings per share for the fiscal years ended December 31, 2015 and December 31, 2014 as follows:



	Year Ended December 31,
	2015		2014
	(in thousands)
Net revenue	$	1,601,891	$	1,527,685
Net income	$	243,004	$	172,390
Basic earnings per share	$	4.14	$	2.80
Diluted earnings per share	$	4.03	$	2.73

(d) Acquisition of MediMedia Pharma Solutions

On February 27, 2015, a subsidiary of the Company, ICON Holdings Unlimited Company (formerly ICON Holdings), acquired MediMedia Pharma Solutions for cash consideration of $104.7 million (net of working capital adjustments of $4.0 million). In addition to the cash consideration, certain payments were made on behalf of MediMedia Pharma Solutions on completion totaling $11.3 million. Headquartered in Yardley, Pennsylvania, MediMedia Pharma Solutions includes MediMedia Managed Markets and Complete Healthcare Communications. MediMedia Managed Markets is a leading provider of strategic payer-validated market access solutions. Complete Healthcare Communications is one of the leading medical and scientific communication agencies working with medical affairs, commercial and brand development teams within life science companies. The acquisition agreement provides for certain working capital targets to be achieved by MediMedia Pharma Solutions.

The acquisition of MediMedia Pharma Solutions has been accounted for as a business combination in accordance with FASB ASC 805 Business Combinations. The following table summarizes the fair values of the assets acquired and liabilities assumed on acquisition:



	February 27, 2015
	(in thousands)
Property, plant and equipment	$	1,049
Goodwill*	92,084
Customer lists	22,752
Order backlog	2,521
Accounts receivable	5,240
Unbilled Revenue	4,324
Prepayments and other current assets	621
Accounts payable	(749		)
Payments on account	(4,186		)
Deferred tax liability	(2,171		)
Other liabilities	(5,483		)
Net assets acquired	$	116,002



Cash consideration	$	108,717
Other liabilities assumed**	11,283
Gross cash outflows	120,000
Working capital adjustment	(3,998		)
Net cash outflows	$	116,002

Goodwill represents the acquisition of an established workforce with experience in the provision of strategic payer-validated market access solutions while the acquisition of Complete Healthcare Communications comprises an established workforce with significant communication experience working with medical affairs, commercial and brand development teams within the life science industry. Goodwill related to the US portion of the business acquired is tax deductible.


**	Payments made at acquisition date of $11.3 million were in respect of certain one-time liabilities at the acquisition date which have subsequently been discharged.

The proforma effect of the MediMedia Pharma Solutions acquisition if completed on January 1, 2014 would have resulted in net revenue, net income and earnings per share for the fiscal years ended December 31, 2015 and December 31, 2014 as follows:



	Year Ended December 31,
	2015		2014
	(in thousands)
Net revenue	$	1,581,816	$	1,556,936
Net income	$	239,361	$	179,289
Basic earnings per share	$	4.07	$	2.92
Diluted earnings per share	$	3.97	$	2.84

Intangible Assets

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets



	December 31, 2017			December 31, 2016
Cost	(in thousands)
Customer relationships acquired	$	91,230		$	92,110
Technology asset acquired	11,169			11,169
Order backlog	18,208			18,574
Trade names/ brands acquired	2,766			3,075
Volunteer list acquired	1,325			1,325
Non-compete arrangements	489			489
Mapi intangible asset	32,305			—
Foreign exchange movement	(2,389		)	(6,578		)
Total cost	155,103			120,164
Accumulated amortization	(84,898		)	(67,037		)
Foreign exchange movement	1,423			3,483
Net book value	$	71,628		$	56,610

On July 27, 2017, a subsidiary of the Company, ICON Clinical Research Limited acquired Mapi Group. Mapi is a leading patient-centered health outcomes research and commercialization company. The acquisition of Mapi strengthens ICON’s existing commercialization and outcomes research business adding significant commercialization presence, analytics, real world evidence generation and strategic regulatory services. The value of intangible assets provisionally identified is $32.3 million. These intangible assets are being amortized over approximately 6 years, the estimated period of benefit. In total, $3.3 million has been amortized in the period since the date of acquisition.

On September 15, 2016, a subsidiary of the Company, ICON US Holdings Inc., acquired ClinicalRM, a full-service CRO specializing in preclinical through Phase IV support of clinical research and clinical trial services for biologics, drugs and devices. The organization helps customers progress their products to market faster with a wide array of research, regulatory and sponsor services within the U.S. and around the globe. ClinicalRM provide full service and functional research solutions to a broad range of US government agencies. The value of certain customer relationship, order backlog and brand assets identified of $4.0 million, $1.7 million and $1.4 million respectively are being amortized over approximately 7 years, 2 years and 5 years respectively, the estimated period of benefit. In total, $2.3 million has been amortized in the period since the date of acquisition.

On December 4, 2015, a subsidiary of the Company, ICON Clinical Research LLC, acquired PMG, an integrated network of 52 clinical research sites in North Carolina, South Carolina, Tennessee, Illinois and Iowa. The site network includes wholly owned facilities and dedicated clinical research sites. PMG conducts clinical trials in all major therapeutic areas and has particular expertise in vaccine, gastroenterology, cardiovascular, neurology and endocrinology studies. The value of certain customer relationship and order backlog assets identified of $6.9 million and $3.0 million respectively are being amortized over approximately 7 years and 2 years respectively, the estimated period of benefit. In total, $5.0 million has been amortized in the period since the date of acquisition. The order backlog is fully amortized at December 31, 2017.

On February 27, 2015, a subsidiary of the Company, ICON Holdings Unlimited Company (formerly ICON Holdings), acquired MediMedia Pharma Solutions. Headquartered in Yardley, Pennsylvania, MediMedia Pharma Solutions includes MediMedia Managed Markets and Complete Healthcare Communications. MediMedia Managed Markets is a leading provider of strategic payer-validated market access solutions. Complete Healthcare Communications is one of the leading medical and scientific communication agencies working with medical affairs, commercial and brand development teams within life science companies. The value of certain customer relationships and order backlog identified of $22.8 million and $2.5 million respectively are being amortized over approximately 7 years and 1 year, the estimated period of benefit. $11.7 million has been amortized in the period since the date of acquisition. The order backlog is fully amortized at December 31, 2017.

On May 7, 2014, a subsidiary of the Company, ICON US Holdings Inc., acquired Aptiv Solutions, Inc. ("Aptiv"), a global biopharmaceutical and medical device development services company and leader in adaptive clinical trials. Aptiv offers full-service clinical trial consulting and regulatory support for drugs, medical devices and diagnostics with a specific focus on strategy to increase product development efficiency and productivity. The value of certain customer relationships and order backlog identified of $21.4 million and $7.9 million respectively are being amortized over approximately 7 years and 3 years, the estimated period of benefit. In total, $19.1 million has been amortized in the period since the date of acquisition. The order backlog is fully amortized at December 31, 2017.

On February 15, 2013, subsidiaries of the Company, ICON Clinical Research LLC (formerly ICON Clinical Research, Inc.) and ICON Clinical Research (U.K.) Limited, acquired the Clinical Trial Services division of Cross Country Healthcare, Inc. Cross Country Healthcare's Clinical Trial Services division includes US resourcing providers, ClinForce and Assent Consulting, whose services include contract staffing, permanent placement and functional service provision ("FSP"). The value of certain customer relationships and order backlog identified of $3.3 million and $0.6 million respectively are being amortized over approximately 3 years and 1 year, the estimated period of benefit. The full $3.9 million has been amortized in the period since the date of acquisition.

On February 28, 2012, a subsidiary of the Company, ICON Clinical Research LLC (formerly ICON Clinical Research, Inc.), acquired PriceSpective, a strategy consulting company. The value of certain customer relationships identified of $10.2 million is being amortized over approximately 10 years, the estimated period of benefit. The value of order backlog and certain non-compete arrangements identified of $0.4 million and $0.4 million respectively are being amortized over approximately 0.8 years and 3 years, the estimated period of benefit. In total, $6.8 million has been amortized in the period since the date of acquisition.

On February 15, 2012, a subsidiary of the Company, ICON Clinical Research Limited, acquired BeijingWits Medical, a Chinese CRO. The value of certain customer relationships and order backlog identified of $1.8 million and $0.4 million respectively are being amortized over approximately 10 years and 4 years, the estimated period of benefit. The value of certain non-compete arrangements identified of $0.01 million are being amortized over approximately 5 years, the estimated period of benefit. In total, $1.5 million has been amortized in the period since the date of acquisition.

On July 14, 2011, a subsidiary of the Company, ICON Clinical Research Limited, acquired Firecrest Clinical Limited, a provider of technology solutions that boost investigator site performance and study management. The value of certain technology assets and customer relationships identified of $11.2 million and $5.2 million respectively are being amortized over approximately 7.5 years, the estimated period of benefit. The value of the Firecrest trade name and order backlog identified of $1.4 million and $1.2 million respectively are being amortized over approximately 4.5 years and 1.2 years, the estimated period of benefit. In total, $14.5 million has been amortized in the period since the date of acquisition.

On January 14, 2011, a subsidiary of the Company, ICON Clinical Research (U.K.) Limited, acquired Oxford Outcomes Limited, an international health outcomes consultancy business. The value of certain customer relationships and order backlog identified of $6.6 million and $0.6 million respectively were amortized over approximately 6.5 years and 2 years, the estimated period of benefit. The intangible assets identified have been fully amortized at December 31, 2017.

On November 14, 2008, subsidiaries of the Company, ICON Holdings Clinical Research International Limited and ICON Clinical Research LLC (formerly ICON Clinical Research, Inc.), acquired Prevalere Life Sciences, a US provider of bioanalytical and immunoassay laboratory services. The value of certain customer relationships identified of $7.4 million is being amortized over periods ranging from approximately 7 to 11 years, the estimated period of the benefit. In total, $6.8 million has been amortized in the period since the date of acquisition.

On February 11, 2008, a subsidiary of the Company, ICON Clinical Research LLC (formerly ICON Clinical Research, Inc.), acquired Healthcare Discoveries, a US provider of Phase I clinical trial services. The value of certain client relationships identified of $1.6 million was amortized over periods ranging from approximately 2 to 9 years, the estimated periods of benefit. The value of certain volunteer lists identified of $1.3 million was amortized over approximately 6 years, the estimated period of benefit. The intangible assets identified have been fully amortized at December 31, 2017.

Future intangible asset amortization expense for the years ended December 31, 2018 to December 31, 2022 is as follows:



	Year Ended December 31,(in thousands)
2018	$	19,788
2019	16,217
2020	13,867
2021	11,906
2022	6,580
	$	68,358

Property, Plant and Equipment, net

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment, net



	December 31, 2017			December 31, 2016
	(in thousands)
Cost
Land	$	3,464		$	3,464
Building	88,411			77,950
Computer equipment and software	358,874			315,984
Office furniture and fixtures	78,372			70,218
Laboratory equipment	34,918			31,487
Leasehold improvements	24,097			20,933
Motor vehicles	42			43
	588,178			520,079
Less accumulated depreciation and asset write offs	(425,127		)	(371,112		)
Property, plant and equipment (net)	$	163,051		$	148,967

Employee Benefits

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Employee Benefits

Certain Company employees are eligible to participate in a defined contribution plan (the "Plan"). Participants in the Plan may elect to defer a portion of their pre-tax earnings into a pension plan, which is run by an independent party. The Company matches participant's contributions typically at 6% of the participant's annual compensation. Contributions to the plan are recorded as an expense in the selling, general and administrative line in the Consolidated Statement of Operations. Contributions for the years ended December 31, 2017, December 31, 2016 and December 31, 2015 were $20,355,000, $20,952,000 and $20,439,000 respectively.

The Company's United States operations maintain a retirement plan (the "U.S. Plan") that qualifies as a deferred salary arrangement under Section 401(k) of the Internal Revenue Code. Participants in the U.S. Plan may elect to defer a portion of their pre-tax earnings, up to the Internal Revenue Service annual contribution limit. The Company matches 50% of each participant's contributions; each participant can contribute up to 6% of their annual compensation. Contributions to this U.S. Plan are recorded, in the year contributed, as an expense in the Consolidated Statement of Operations. Contributions for the years ended December 31, 2017, December 31, 2016 and December 31, 2015 were $14,946,000, $15,223,000 and $12,802,000 respectively.

One of the Company's subsidiaries, ICON Development Solutions Limited, operates a defined benefit pension plan in the United Kingdom for its employees. The plan is managed externally and the related pension costs and liabilities are assessed in accordance with the advice of a professionally qualified actuary. Plan assets at December 31, 2017, December 31, 2016 and December 31, 2015, consist of units held in independently administered funds. The pension costs of this plan are presented in the following tables in accordance with the requirements of ASC 715-60, Defined Benefit Plans – Other Postretirement. The plan has been closed to new entrants with effect from July 1, 2003.



Funded status	December 31, 2017			December 31, 2016
	(in thousands)
Projected benefit obligation	$	(37,759	)	$	(32,906	)
Fair value of plan assets	32,423			24,876
Funded status	$	(5,336	)	$	(8,030	)
Non-current other liabilities (note 8)	$	(5,336	)	$	(8,030	)



Change in benefit obligation	December 31, 2017			December 31, 2016
	(in thousands)
Benefit obligation at beginning of year	$	32,906		$	27,369
Service cost	112			75
Interest cost	929			1,017
Plan participants' contributions	22			22
Expenses	(8		)	8
Benefits paid	(68		)	(104		)
Actuarial loss	658			10,057
Foreign currency exchange rate changes	3,208			(5,538		)
Benefit obligation at end of year	$	37,759		$	32,906



Change in plan assets	December 31, 2017			December 31, 2016
	(in thousands)
Fair value of plan assets at beginning of year	$	24,876		$	23,367
Actual return on plan assets	979			5,861
Employer contributions	4,008			108
Plan participants' contributions	22			22
Benefits paid	(68		)	(104		)
Foreign currency exchange rate changes	2,606			(4,378		)
Fair value of plan assets at end of year	$	32,423		$	24,876

The fair values of the assets above do not include any of the Company's own financial instruments, property occupied by, or other assets used by, the Company.

The following amounts were recorded in the Consolidated Statement of Operations as components of the net periodic benefit cost:



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Service cost	$	112		$	75		$	78
Interest cost	929			1,017			1,140
Expected return on plan assets	(586		)	(646		)	(661		)
Amortization of net loss	250			—			224
Expenses	(8		)	8			—
Net periodic benefit cost	$	697		$	454		$	781

The following assumptions were used at the commencement of the year in determining the net periodic pension benefit cost for the years ended December 31, 2017, December 31, 2016 and December 31, 2015:



	December 31, 2017		December 31, 2016		December 31, 2015
Discount rate	2.7	%	4.0	%	3.6	%
Rate of compensation increase	3.9	%	3.7	%	3.6	%
Expected rate of return on plan assets	2.1	%	3.0	%	2.7	%



Other comprehensive income	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Actuarial loss/(gain) - benefit obligation	$	658		$	10,057		$	(3,992	)
Actuarial (gain)/loss – plan assets	(393		)	(5,215		)	384
Actuarial gain recognized in net periodic benefit cost	(250		)	—			(224		)
Total	$	15		$	4,842		$	(3,832	)

The estimated net loss and prior service cost for the defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year are $0.3 million and $Nil respectively.

Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows:



	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Net actuarial loss	$	7,138	$	7,123	$	2,281
Total	$	7,138	$	7,123	$	2,281

Benefit Obligation

The following assumptions were used in determining the benefit obligation at December 31, 2017 and December 31, 2016:



	December 31, 2017		December 31, 2016
Discount rate	2.5	%	2.7	%
Rate of compensation increase	3.7	%	3.9	%

The discount rate is determined by reference to UK long dated government and corporate bond yields at the Balance Sheet date. This is represented by the iboxx corporate bond over 15 year index plus 10 basis points.

Plan Assets

The assets of the scheme are invested with Legal and General and held in a combination of the Active Corporate Bond over 10 Year fund, Gilt and Index Linked Gilt funds. The overall investment strategy is that approximately 75% of investments are in government bonds (both fixed interest and index linked), approximately 25% of investments are held in corporate bonds. There is no self-investment in employer related assets. The expected long-term rate of return on assets at December 31, 2017 of 2.0% was calculated as the value of the fund after application of a market value reduction factor. The expected long term rates of return on different asset classes are as follows:



Asset Category	Expected long-term return per annum
Corporate Bonds	2.5	%
Gilts	1.8	%
Cash	2.5	%

The long-term expected return on corporate bonds and gilts (fixed interest and index linked) is determined by reference to bond yields and gilt yields at the Balance Sheet date.

The underlying asset split of the fund is shown below.



Asset Category	December 31, 2017		December 31, 2016
Corporate Bonds	22	%	25	%
Gilts	65	%	75	%
Cash	13	%	—	%
	100	%	100	%

Applying the above expected long term rates of return to the asset distribution at December 31, 2017, gives rise to an expected overall rate of return of scheme assets of approximately 2.0% per annum.

Plan Asset Fair Value Measurements



	Quoted Prices in Active Markets for Identical Assets Level 1 (in thousands)
	December 31, 2017		December 31, 2016
Cash	$	4,086	$	16
Fixed Income Securities
Legal and General Active Corporate Bond – Over 10 Year	7,188		6,095
Legal and General Gilt Funds	7,611		6,725
Legal and General Index Linked Gilt Funds	13,539		12,040
	$	32,424	$	24,876

Cash Flows

The Company expects to contribute $0.1 million to the pension fund in the year ending December 31, 2018.

The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid.



	(in thousands)
2018	336
2019	312
2020	330
2021	405
2022	436
Years 2023 - 2027	$	3,297

The expected cash flows are estimated figures based on the members expected to retire over the next 10 years assuming no early retirements plus an additional amount based on recent average withdrawal experience. At the present time it is not clear whether annuities will be purchased when members reach retirement or whether pensions will be paid each month out of scheme assets. The cash flows above have been estimated on the assumption that pensions will be paid monthly out of scheme assets. If annuities are purchased, then the expected benefit payments will be significantly different from those shown above.

On May 7, 2014 the Company acquired 100% of the common stock of Aptiv Solutions ("Aptiv"). The acquisition of Aptiv was accounted for as a business combination in accordance with FASB ASC 805 Business Combinations. The Company has a defined benefit plan covering its employees in Switzerland as mandated by the Swiss government. Benefits are based on the employee's years of service and compensation. Benefits are paid directly by the Company when they become due, in conformity with the funding requirements of applicable government regulations. The plan is managed externally and the related pension costs and liabilities are assessed in accordance with the advice of a professionally qualified actuary. Plan assets at December 31, 2017 and December 31, 2016 consist of units held in independently administered funds. The pension costs of this plan are presented in the following tables in accordance with the requirements of ASC 715-60, Defined Benefit Plans – Other Postretirement.



Funded status	December 31, 2017			December 31, 2016
	(in thousands)
Projected benefit obligation	$	(5,927	)	$	(6,928	)
Fair value of plan assets	5,202			6,006
Funded status	$	(725	)	$	(922	)
Non-current other liabilities (note 8)	$	(725	)	$	(922	)



Change in benefit obligation	December 31, 2017			December 31, 2016
	(in thousands)
Benefit obligation at beginning of year	$	6,928		$	8,537
Service cost	243			352
Interest cost	54			82
Plan participants' contributions	120			150
Settlement	(1,019		)	(909		)
Prior service cost	—			(88		)
Transferred (benefits paid)/balances	(76		)	53
Actuarial gain	(626		)	(1,157		)
Foreign currency exchange rate changes	303			(92		)
Benefit obligation at end of year	$	5,927		$	6,928



Change in plan assets	December 31,			December 31,
	2017			2016
	(in thousands)
Fair value of plan assets at beginning of year	$	6,006		$	5,350
Expected return on plan assets	47			48
Actual return on plan assets	(296		)	1,233
Scheme contributions	157			195
Plan participants' contributions	120			150
Transferred (benefits paid)/balances	(76		)	53
Settlement	(1,019		)	(909		)
Foreign currency exchange rate changes	263			(114		)
Fair value of plan assets at end of year	$	5,202		$	6,006

The fair values of the assets above do not include any of the Company's own financial instruments, property occupied by, or other assets used by, the Company.



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Service cost	$	243		$	352		$	402
Interest cost	54			82			159
Expected return on plan assets	(47		)	(48		)	(119		)
Amortization of net (gain)/loss	(43		)	22			—
Amortization of prior service credit	(8		)	(8		)	—
Settlement	(214		)	(136		)	—
Curtailment	—			—			18
Net periodic benefit cost	$	(15	)	$	264		$	460



	December 31, 2017		December 31, 2016		December 31, 2015
Discount rate	0.75	%	0.95	%	1.35	%
Rate of compensation increase	2.0	%	2.0	%	2.00	%
Expected rate of return on plan assets	0.75	%	0.95	%	1.35	%



Other comprehensive income	December 31, 2017			December 31, 2016			December 31, 2015
Actuarial (gain)/loss - benefit obligation	$	(626	)	$	(1,157	)	$	81
Actuarial loss/(gain) – plan assets	296			(1,233		)	1,075
Prior service credit/(cost) recognized in net periodic benefit cost	215			136			(17		)
Actuarial gain/(loss) recognized in net periodic benefit cost	43			(22		)	—
Amortization of net prior service credit	8			8			—
Net prior service credit occurring during the year	(1		)	(89		)	—
Total	$	(65	)	$	(2,357	)	$	1,139

The estimated net gain and prior service credit for the defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year are $69,000 and $8,000 respectively.

Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows:



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Net actuarial (gain)/loss	$	(1,283	)	$	(1,218	)	$	1,139
Total	$	(1,283	)	$	(1,218	)	$	1,139

Benefit Obligation

The following assumptions were used in determining the benefit obligation at December 31, 2017 and December 31, 2016:



	December 31, 2017		December 31, 2016
Discount rate	0.80	%	0.75	%
Rate of compensation increase	2.0	%	2.0	%

The discount rate is determined by reference to Swiss corporate bond yields at the Balance Sheet date.

Plan Assets

The pension plan is an insured arrangement with Swiss Life. The assets are an insurance contract whose value depends on the amount saved by employees and the interest granted by Swiss Life. The value of assets does not depend on the performance of any underlying assets. There is no self-investment in employer related assets.

Cash Flows

The Company expects to contribute $0.1 million to its pension fund in the year ending December 31, 2018.

The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid.



	(in thousands)

2018	286
2019	224
2020	204
2021	201
2022	197
Years 2023 - 2027	$	878

Equity Incentive Schemes and Stock Compensation Charges

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Equity Incentive Schemes and Stock Compensation Charges

Share Options

On July 21, 2008 the Company adopted the Employee Share Option Plan 2008 (the "2008 Employee Plan") pursuant to which the Compensation and Organization Committee of the Company's Board of Directors may grant options to any employee, or any Director holding a salaried office or employment with the Company or a Subsidiary for the purchase of ordinary shares. On the same date, the Company also adopted the Consultants Share Option Plan 2008 (the "2008 Consultants Plan"), pursuant to which the Compensation and Organization Committee of the Company's Board of Directors may grant options to any consultant, adviser or non-executive Director retained by the Company or any Subsidiary for the purchase of ordinary shares.

On February 14, 2017 both the 2008 Employee Plan and the 2008 Consultants Plan (together the "2008 Option Plans") were amended and restated in order to increase the number of options that can be issued under the 2008 Consultants Plan from 400,000 to 1 million and to extend the date for options to be granted under the 2008 Option Plans.

An aggregate of 6.0 million ordinary shares have been reserved under the 2008 Employee Plan, as reduced by any shares issued or to be issued pursuant to options granted under the 2008 Consultants Plan, under which a limit of 1 million shares applies. Further, the maximum number of ordinary shares with respect to which options may be granted under the 2008 Employee Option Plan, during any calendar year to any employee shall be 400,000 ordinary shares. There is no individual limit under the 2008 Consultants Plan. No options may be granted under the 2008 Option Plans after February 14, 2027.

Each option granted under the 2008 Option Plans will be an employee stock option, or NSO, as described in Section 422 or 423 of the Internal Revenue Code. Each grant of an option under the 2008 Options Plans will be evidenced by a Stock Option Agreement between the optionee and the Company. The exercise price will be specified in each Stock Option Agreement, however option prices will not be less than 100% of the fair market value of an ordinary share on the date the option is granted.

On January 17, 2003 the Company adopted the Share Option Plan 2003 (the "2003 Share Option Plan") pursuant to which the Compensation and Organization Committee of the Board could grant options to officers and other employees of the Company or its subsidiaries for the purchase of ordinary shares. An aggregate of 6.0 million ordinary shares were reserved under the 2003 Share Option Plan; and in no event could the number of ordinary shares issued pursuant to options awarded under this plan exceed 10% of the outstanding shares, as defined in the 2003 Share Option Plan, at the time of the grant, unless the Board expressly determined otherwise. Further, the maximum number of ordinary shares with respect to which options could be granted under the 2003 Share Option Plan during any calendar year to any employee was 400,000 ordinary shares. The 2003 Share Option Plan expired on January 17, 2013. No new options may be granted under this plan.

Share option awards are granted with an exercise price equal to the market price of the Company's shares at date of grant. Share options typically vest over a period of five years from date of grant and expire eight years from date of grant. The maximum contractual term of options outstanding at December 31, 2017 is eight years.

The following table summarizes the transactions for the Company's share option plans for the years ended December 31, 2017, December 31, 2016 and December 31, 2015:



	Options Granted Under Plans		Number of Shares		Weighted Average Exercise Price		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2014	2,227,700		2,227,700		$	28.00	$	10.40
Granted	259,059		259,059		$	68.25	$	19.75
Exercised	(773,753	)	(773,753	)	$	27.13	$	10.31
Cancelled	(86,424	)	(86,424	)	$	27.32	$	10.31
Outstanding at December 31, 2015	1,626,582		1,626,582		$	34.87	$	11.94
Granted	256,191		256,191		$	69.61	$	20.10
Exercised	(393,240	)	(393,240	)	$	25.79	$	9.84
Cancelled	(23,089	)	(23,089	)	$	29.74	$	11.19
Outstanding at December 31, 2016	1,466,444		1,466,444		$	43.45	$	13.94
Granted	219,113		219,113		$	85.98	$	25.06
Exercised	(458,243	)	(458,243	)	$	30.35	$	10.72
Cancelled	(55,921	)	(55,921	)	$	54.35	$	16.76
Outstanding at December 31, 2017	1,171,393		1,171,393		$	56.02	$	17.15
Vested and exercisable at December 31, 2017	476,666		476,666		$	38.47	$	12.95

The weighted average remaining contractual life of options outstanding and options exercisable at December 31, 2017, was 4.86 years and 3.4 years respectively (2016: 4.67 years and 3.30 years respectively). 255,198 options are expected to vest during the year ended December 31, 2018 (333,433 options were expected to vest during the year ended December 31, 2017).

The intrinsic value of options exercised during the year ended December 31, 2017 amounted to $31.8 million. The intrinsic value of options outstanding and options exercisable at December 31, 2017 amounted to $65.8 million and $35.1 million respectively. Intrinsic value is calculated based on the market value versus strike price of the Company's shares at the date of exercise.

Non-vested shares outstanding as at December 31, 2017 are as follows:



	Options Outstanding Number of Shares		Weighted Average Exercise Price		Weighted Average Fair Value
Non-vested outstanding at December 31, 2016	814,870		$	54.37	$	16.55

Granted	219,113		85.98		25.06
Vested	(292,630	)	44.54		14.39
Forfeited	(46,626	)	60.73		18.22

Non-vested outstanding at December 31, 2017	694,727		$	68.06	$	20.03

Outstanding and exercisable share options:

The following table summarizes information concerning outstanding and exercisable share options as of December 31, 2017:



Options Outstanding						Options Exercisable
Range Exercise Price		Number of Shares	Weighted Average Remaining Contractual Life	Weighted Average Exercise Price		Number of Shares	Weighted Average Exercise Price
$	20.28	63,824	1.16	$	20.28	63,824	$	20.28
$	20.59	8,800	2.14	$	20.59	8,800	$	20.59
$	22.30	84,137	2.32	$	22.30	84,137	$	22.30
$	23.66	1,711	2.57	$	23.66	1,711	$	23.66
$	24.46	7,692	0.17	$	24.46	7,692	$	24.46
$	26.20	450	0.38	$	26.20	450	$	26.20
$	26.71	4,450	2.69	$	26.71	4,450	$	26.71
$	32.37	159,686	3.33	$	32.37	124,476	$	32.37
$	36.22	5,923	3.46	$	36.22	3,323	$	36.22
$	37.90	2,520	3.93	$	37.90	460	$	37.90
$	40.83	72,634	4.39	$	40.83	37,026	$	40.83
$	47.03	39,477	4.17	$	47.03	9,626	$	47.03
$	48.67	80,039	4.21	$	48.67	21,160	$	48.67
$	51.35	2,030	4.60	$	51.35	418	$	51.35
$	65.60	91,549	6.38	$	65.60	26,161	$	65.60
$	66.47	6,717	5.39	$	66.47	1,698	$	66.47
$	66.97	1,872	5.45	$	66.97	—	$	66.97
$	68.39	190,821	5.18	$	68.39	65,178	$	68.39
$	71.95	133,256	6.17	$	71.95	16,076	$	71.95
$	83.47	130,836	7.17	$	83.47	—	$	83.47
$	90.03	82,969	7.38	$	90.03	—	$	90.03
$20.28 - $90.03		1,171,393	4.86	$	56.02	476,666	$	38.47

Options outstanding include both vested and unvested options as at December 31, 2017. Options exercisable represent options which have vested at December 31, 2017. From the date of grant, substantially all options vest over a five year period at 20% per annum.

Fair value of Stock Options Assumptions

The weighted average fair value of options granted during the years ended December 31, 2017, December 31, 2016 and December 31, 2015 was calculated using the Black-Scholes option pricing model. The weighted average fair values and assumptions were as follows:



	Year Ended
	December 31, 2017			December 31, 2016			December 31, 2015
Weighted average fair value	$	25.06		$	20.10		$	19.75

Assumptions:
Expected volatility	29		%	30		%	30		%
Dividend yield	—		%	—		%	—		%
Risk-free interest rate	1.93		%	1.39		%	1.58		%
Expected life	5.0 years			5.0 years			5.0 years

Expected volatility is based on the historical volatility of our common stock over a period equal to the expected term of the options; the expected life represents the weighted average period of time that options granted are expected to be outstanding given consideration to vesting schedules and our historical experience of past vesting and termination patterns. The risk-free rate is based on the U.S. government zero-coupon bonds yield curve in effect at time of the grant for periods corresponding with the expected life of the option.

Restricted Share Units and Performance Share Units

On July 21, 2008 the Company adopted the 2008 Employees Restricted Share Unit Plan (the "2008 RSU Plan") pursuant to which the Compensation and Organization Committee of the Company's Board of Directors may select any employee, or any Director holding a salaried office or employment with the Company, or a Subsidiary to receive an award under the plan. An aggregate of 1.0 million ordinary shares have been reserved for issuance under the 2008 RSU Plan.

On April 23, 2013 the Company adopted the 2013 Employees Restricted Share Unit and Performance Share Unit Plan (the "2013 RSU Plan") pursuant to which the Compensation and Organization Committee of the Company's Board of Directors may select any employee, or any Director holding a salaried office or employment with the Company, or a Subsidiary to receive an award under the plan. On May 11, 2015 the 2013 RSU Plan was amended and restated in order to increase the number of shares that can be issued under the RSU Plan by 2.5 million shares. Accordingly, an aggregate of 4.1 million ordinary shares have been reserved for issuance under the 2013 RSU Plan. The shares are awarded at par value and vest over a service period. Awards under the 2013 RSU Plan may be settled in cash or shares at the option of the Company.

The Company has awarded RSUs and PSUs to certain key individuals of the Group. The following table summarizes RSU and PSU activity for the year ended December 31, 2017:



	PSU Outstanding Number of Shares		PSU Weighted Average Fair Value		PSU Weighted Average Remaining Contractual Life	RSU Outstanding Number of Shares		RSU Weighted Average Fair Value		RSU Weighted Average Remaining Contractual Life
Outstanding at December 31, 2016	830,523		$	60.73	1.11	1,025,484		$	58.64	1.40

Granted	68,040		$	84.10		186,102		$	89.60
Shares vested	(320,640	)	$	46.63		(367,177	)	$	45.18
Forfeited	(66,897	)	$	67.16		(128,439	)	$	63.89

Outstanding at December 31, 2017	511,026		$	72.07	0.93	715,970		$	72.65	1.28

The fair value of RSUs vested for the year ended December 31, 2017 totaled $16.6 million (2016: $10.8 million).

The fair value of PSUs vested for the year ended December 31, 2017 totaled $15.0 million (2016: $10.3 million).

The PSUs vest based on service and specified EPS targets over the period 2014 – 2017, 2015 – 2018, 2016 - 2019 and 2017 - 2020. Since 2013, 270,858 PSUs (net of forfeitures) have been granted. Depending on the actual amount of EPS from 2014 to 2020, up to an additional 240,168 PSUs may also be granted.

Non-cash stock compensation expense

Income from operations for the year ended December 31, 2017 is stated after charging $30.6 million in respect of non-cash stock compensation expense. Non-cash stock compensation expense has been allocated as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Direct costs	$	18,020	$	21,903	$	18,358
Selling, general and administrative	$	12,553	$	18,440	$	14,959
Total compensation costs	$	30,573	$	40,343	$	33,317

Total non-cash stock compensation expense not yet recognized at December 31, 2017 amounted to $49.3 million. The weighted average period over which this is expected to be recognized is 2.04 years.

The amendments required by Accounting Standards Update (‘ASU’) 2016-09 ‘Improvements to Employee Share-Based Payment Accounting’ require the Company to record all tax effects related to share-based payments through the income statement rather than additional paid in capital. The Company has applied the updated standard prospectively in the twelve months of the year ended December 31, 2017. Total tax benefit recognized in additional paid in capital related to the non-cash compensation expense amounted to $Nil for the year ended December 31, 2017 (2016: $4.3 million, 2015: $1.9 million).

The income tax expense for the year ended December 31, 2017 reflects a net income tax benefit of $9.3 million in connection with stock compensation (including excess benefits) and the total tax benefit realized in connection with stock options exercised during 2017 was $3.2 million. The income tax expense for the year ended December 31, 2016 reflects a net income tax benefit of $3.5 million in connection with stock compensation and the cash tax benefit realized in connection with stock options exercised during 2016 was $3.4 million. The income tax expense for the year ended December 31, 2015 reflects a net income tax benefit of $1.5 million in connection with stock compensation and the cash tax benefit realized in connection with stock options exercised during 2016 was $5.6 million.

Government Grants

12 Months Ended

Dec. 31, 2017

Deferred Revenue Disclosure [Abstract]

Government Grants



	December 31, 2017			December 31, 2016
	(in thousands)
Received	$	3,539		$	3,539
Less accumulated amortization	(2,745		)	(2,701		)
Foreign exchange translation adjustment	207			103
Total government grants	1,001			941
Less current portion	(35		)	(54		)
Non-current government grants	$	966		$	887

Capital grants received may be refundable in full if certain events occur. Such events, as set out in the related grant agreements, include sale of the related asset, liquidation of the Company or failure to comply with other conditions of the grant agreements. No loss contingency has been recognized as the likelihood of such events arising has been assessed as remote. Government grants amortized to the profit and loss account amounted to $44,000 for the year ended December 31, 2017. A net charge of $44,000 was recorded in respect of government grants during the year ended December 31, 2016. As at December 31, 2017 the Company had $1.2 million in restricted retained earnings, pursuant to the terms of grant agreements.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

The Company's United States and Irish based subsidiaries file tax returns in the United States and Ireland respectively. Other foreign subsidiaries are taxed separately under the laws of their respective countries.

The components of income before provision for income taxes are as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	218,306	$	201,221	$	184,643
United States	28,426		11,466		15,436
Other	81,325		87,485		78,771
Income before provision for income taxes	$	328,057	$	300,172	$	278,850

The components of provision for income taxes are as follows:



	Year ended
	December 31, 2017		December 31, 2016			December 31, 2015
	(in thousands)
Provision for income taxes:
Current tax expense:
Ireland	$	20,084	$	22,931		$	21,769
United States	5,792		7,768			684
Other	9,964		5,749			13,701
Total current tax expense	35,840		36,448			36,154

Deferred tax expense/(benefit):
Ireland	261		1,284			26
United States	8,980		613			2,896
Other	1,488		(352		)	235
Total deferred tax expense	10,729		1,545			3,157

Provision for income taxes	46,569		37,993			39,311

Impact on shareholders equity and other comprehensive income of the tax consequence of :
Excess tax benefit on stock compensation	—		(4,332		)	(1,905		)
Currency impact on long term funding	973		(396		)	3,574
Fair value of cash flow hedge	148		—			—

Total	$	47,690	$	33,265		$	40,980

Ireland's statutory income tax rate is 12.5%. The Company's consolidated reported provision for income taxes differed from the amount that would result from applying the Irish statutory rate as set forth below:



	Year ended
	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Taxes at Irish statutory rate of 12.5% (2016:12.5%; 2015:12.5%)	$	41,007		$	37,522		$	34,856
Foreign and other income taxed at higher rates	6,324			4,642			4,614
Research & development tax incentives	(830		)	(907		)	(695		)
Movement in valuation allowance	1,329			1,208			(4,133		)
Effects of change in tax rates	925			576			(16		)
Increase/(decrease) in unrecognized tax benefits	933			(1,521		)	5,085
Impact of stock compensation	(9,917		)	(4,121		)	(3,468		)
Impact of mandatory repatriation under US Tax Reform	7,694			—			—
Other	(896		)	594			3,068
Provision for income taxes	$	46,569		$	37,993		$	39,311

In 2017, the provision for income taxes includes non-recurring items related to US Tax Reform (H.R.1). The income tax expense recognized in respect of mandatory deemed repatriation of historic earnings of non-U.S. subsidiaries owned by our U.S. subsidiaries

is $7.7 million. The income tax expense recognized in respect of the change in the US federal income tax rate from 35% to 21% is $0.5 million (included in “Effects of change in tax rates” above).

The income tax effects of US Tax Reform are provisional in respect of the Mapi Group acquisition in July 2017 (see Note 4 Goodwill for further information). The Company has made provisional estimates of the fair value of net assets acquired and liabilities assumed. The non-current deferred tax liability recognized as at December 31, 2017 in respect of US-based intangible assets is $5.8 million. To the extent there are purchase accounting adjustments made in a subsequent period, there may be additional income tax effects of US Tax Reform (i.e. impact of the change in rates) to be recognized at such time.

The tax effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities are presented below:



	December 31, 2017			December 31, 2016
	(in thousands)
Deferred tax liabilities:
Property, plant and equipment	$	1,139		$	979
Goodwill	22,655			26,617
Other intangible assets	11,801			6,700
Other	4,139			1,441
Total deferred tax liabilities recognized	39,734			35,737

Deferred tax assets:
Operating loss and tax credits carryforwards	24,962			22,705
Property, plant and equipment	4,062			3,121
Accrued expenses and payments on account	24,433			28,904
Stock compensation	5,786			13,062
Deferred compensation expense	2,548			3,327
Other	740			15
Total deferred tax assets	62,531			71,134
Valuation allowance for deferred tax assets	(22,439		)	(20,337		)
Deferred tax assets recognized	40,092			50,797
Overall net deferred tax asset	$	358		$	15,060

At December 31, 2017 Ireland subsidiaries had tax credit carryforwards for income tax purposes that may be carried forward indefinitely, available for offset against future tax liabilities, if any, of $4.5 million (2016: $3.3 million).

At December 31, 2017 U.S. subsidiaries had U.S. federal and state net operating loss ("NOL") carry forwards of approximately $25.0 million and $43.6 million, respectively. These NOLs are available for offset against future taxable income and expire between 2018 and 2037. Of the $25.0 million U.S. federal NOLs, approximately $5.9 million of which is available for offset against future U.S. federal taxable income within 12 months of the balance sheet date. The subsidiary's ability to use the U.S. federal and state NOL carry forwards is limited on an annual basis due to changes of ownership in 2000, 2010, 2014 and 2017, as defined by Section 382 of the Internal Revenue Code of 1986, as amended. Of the U.S. federal NOLs, $22.8 million are limited by Section 382. Of the $22.8 million of losses, the amounts are available as follows: $11.8 million for the years 2018 – 2020, $10.1 million in 2021-2025, $0.9 million for the years 2026 – 2035.

At December 31, 2017 other than those in the U.S. and Ireland had operating loss carryforwards for income tax purposes that be carried forward indefinitely, available to offset against future taxable income, if any, of approximately $77.2 million (2016: $70.1 million). In addition at December 31, 2017 those subsidiaries had tax credit carryforwards for income tax purposes that may be carried forward indefinitely, available to offset against future tax liabilities, if any, of $4.8 million (2016: $3.9 million). At December 31, 2017 those subsidiaries also had additional operating loss carry forwards of $4.7 million which are due to expire between 2018 and 2024.

The expected expiry dates of these losses are as follows:



	Federal NOL's		State NOL's
	(in thousands)
2018	113		—
2021-2034	24,041		14,945
2035-2036	812		28,703

	$	24,966	$	43,648

In addition, US subsidiaries have alternative minimum tax credit carry forwards of approximately $0.4 million that are available to reduce future U.S. federal regular income taxes through 2020. Any remaining alternative minimum tax credits will be fully refundable in 2021. We also have general business credit carry forwards of approximately $0.3 million that are available to offset future U.S. federal income taxes.

The valuation allowance at December 31, 2017 was approximately $22.4 million. The valuation allowance for deferred tax assets as of December 31, 2016 and December 31, 2015 was $20.3 million and $17.2 million respectively. The net change in the total valuation allowance was an increase of $2.1 million during 2017 and an increase of $3.1 million during 2016. Of the total increase of $2.1 million in 2017, $0.5 million resulted in a current year income tax expense and $1.6 million was recognized in Other Comprehensive Income. Of the total increase of $3.1 million in 2016, $1.2 million resulted in a current year income tax expense, $2.4 million was acquired and impacted goodwill, and these were offset by a decrease of $0.5 million recognized in Other Comprehensive Income.

The valuation allowances at December 31, 2017 and December 31, 2016 were primarily related to operating losses and tax credits carried forward that, in the judgment of management, are not more likely than not to be realized. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considers the scheduled reversal of deferred tax liabilities and projected future taxable income in making this assessment. In respect of deferred tax assets not subject to a valuation allowance, management considers that it is more likely than not that these deferred tax assets will be realized on the basis that there will be sufficient reversals of deferred tax liabilities and taxable income in future periods. During 2016, there were no movements in the valuation allowance that had a material impact on the effective tax rate. During 2017, there were no movements in the valuation allowance that had a material impact on the effective tax rate.

The Company has recognized a deferred tax liability of $3.1 million (2016: $Nil) for the undistributed earnings of foreign subsidiaries where the Company does not consider the earnings to be indefinitely reinvested. It is not practicable to calculate the exact unrecognized deferred tax liability, however it is not expected to be material as Ireland allows a tax credit in respect of distributions from foreign subsidiaries at the statutory tax rate in the jurisdiction of the subsidiary so that no material tax liability would be expected to arise in the event these earnings were ever remitted. In addition, withholding taxes applicable to remittances from foreign subsidiaries would not be expected to be material given Ireland’s tax treaty network and the EU parent subsidiary directive.

A reconciliation of the beginning and ending amount of total unrecognized tax benefits is as follows:



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Unrecognized tax benefits at start of year	$	26,620		$	28,166		$	23,201
Increase related to acquired tax positions	—			—			778
Increase related to prior year tax positions	—			1,151			1,482
Decrease related to prior year tax positions	(3,050		)	(2,483		)	(315		)
Increase related to current year tax positions	4,765			1,104			3,063
Settlements	(2,523		)	(837		)	—
Lapse of statute of limitations	(2,092		)	(481		)	(43		)
Unrecognized tax benefits at end of year	$	23,720		$	26,620		$	28,166

The relevant statute of limitations for unrecognized tax benefits totaling $3.4 million could potentially expire during 2018.

Included in the balance of total unrecognized tax benefits at December 31, 2017 were potential benefits of $23.7 million, which if recognized, would affect the effective rate on income tax from continuing operations. The balance of total unrecognized tax benefits at December 31, 2016 and December 31, 2015 included potential benefits which, if recognized, would affect the effective rate of income tax from continuing operations of $26.6 million and $28.2 million respectively.

Interest and penalties recognized as a net benefit during the year ended December 31, 2017 amounted to $0.9 million (2016: net expense of $0.1 million, 2015: net expense of $0.9 million) and are included within the provision for income taxes. Total accrued interest and penalties as of December 31, 2017 and December 31, 2016 were $2.4 million and $3.3 million respectively and are included in closing income taxes payable at those dates.

Our major tax jurisdictions are the United States and Ireland. We may potentially be subjected to tax audits in both our major jurisdictions. In the United States tax periods open to audit include the years ended December 31, 2014, December 31, 2015, December 31, 2016 and December 31, 2017. In Ireland, tax periods open to audit include the years ended December 31, 2013, December 31, 2014, December 31, 2015, December 31, 2016 and December 31, 2017. During such audits, local tax authorities may challenge the positions taken by us in our tax returns.

Share Capital

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Share Capital

Holders of ordinary shares will be entitled to receive such dividends as may be recommended by the Board of Directors of the Company and approved by the shareholders and/or such interim dividends as the Board of Directors of the Company may decide. On liquidation or a winding up of the Company, the par value of the ordinary shares will be repaid out of the assets available for distribution among the holders of the ordinary shares of the Company. Holders of ordinary shares have no conversion or redemption rights. On a show of hands, every holder of an ordinary share present in person or proxy at a general meeting of shareholders shall have one vote, for each ordinary share held with no individual having more than one vote.

During the year ended December 31, 2017, 458,243 options were exercised by employees at an average exercise price of $30.35 per share for total proceeds of $13.9 million. During the year ended December 31, 2017, 361,102 ordinary shares were issued in respect of certain RSUs and 320,640 ordinary shares were issued in respect of PSUs previously awarded by the Company.

During the year ended December 31, 2016, 393,240 options were exercised by employees at an average exercise price of $25.79 per share for total proceeds of $10.1 million. During the year ended December 31, 2016, 296,386 ordinary shares were issued in respect of certain RSUs and 311,492 ordinary shares were issued in respect of PSUs previously awarded by the Company.

During the year ended December 31, 2015, 773,753 options were exercised by employees at an average exercise price of $27.13 per share for total proceeds of $21.0 million. During the year ended December 31, 2015, 268,870 ordinary shares were issued in respect of certain RSUs and 7,990 ordinary shares were issued in respect of PSUs previously awarded by the Company.


(a)	Share Repurchase Program

On October 3, 2016 the Company commenced a previously announced share buyback program of up to $400 million. During the year ended December 31, 2017, the Company redeemed a total of 1,589,227 ordinary shares under this program for total consideration of $133.1 million. At December 31, 2017 a total of 3,018,414 ordinary shares were redeemed by the Company under this buyback program for a total consideration of $243.1 million. All ordinary shares that were redeemed under the buyback program were canceled in accordance with the Constitution of the Company and the nominal value of these shares transferred to a other undenominated capital fund as required under Irish Company Law.

On May 1, 2015 the Company commenced a buyback program of up to $60 million under which the Company could acquire its outstanding ordinary shares (by way of redemption), in accordance with Irish law, the United States securities laws and the Company's constitutional documents through open market share acquisitions. A total of 882,419 ordinary shares were redeemed by the Company under this buyback program for a total consideration of $57.9 million. All ordinary shares that were redeemed under the buyback program were canceled in accordance with the Constitution of the Company and the nominal value of these shares transferred to a other undenominated capital fund as required under Irish Company Law.

On July 31, 2015 the Company commenced a further buyback program of up to $400 million under which the Company could acquire its outstanding ordinary shares (by way of redemption), in accordance with Irish law, the United States securities laws and the Company's constitutional documents through open market share acquisitions. A total of 5,316,062 ordinary shares were redeemed by the Company under this buyback program for a total consideration of $400 million. All ordinary shares that were redeemed under the buyback program were canceled in accordance with the Constitution of the Company and the nominal value of these shares transferred to a other undenominated capital reserve as required under Irish Company Law. The share buyback program was completed in December 31, 2015, with a total of 6,198,481 ordinary shares redeemed during the year ended December 31, 2015 for total consideration of $457.9 million.

Under the repurchase program, a broker purchased the Company's shares from time to time on the open market or in privately negotiated transactions in accordance with agreed terms and limitations. The program was designed to allow share repurchases during periods when the Company would ordinarily not be permitted to do so because it may be in possession of material non-public or price-sensitive information or due to applicable insider trading laws or self-imposed trading blackout periods. The Company's instructions to the broker were irrevocable and the trading decisions in respect of the repurchase program were made independently of and uninfluenced by the Company. The Company confirms that on entering the share repurchase plans it had no material non-public, price-sensitive or inside information regarding the Company or its securities. Furthermore, the Company will not enter into additional plans whilst in possession of such information. The timing and actual number of shares acquired by way of the redemption will be dependent on market conditions, legal and regulatory requirements and the other terms and limitations contained in the program. In addition, acquisitions under the program may be suspended or discontinued in certain circumstances in accordance with the agreed terms. Therefore, there can be no assurance as to the timing or number of shares that may be acquired under the program.

Restructuring and other items

12 Months Ended

Dec. 31, 2017

Restructuring and Related Activities [Abstract]

Restructuring and other items

Restructuring and other items recognized during the year ended December 31, 2017 comprise:



	Year Ended
	December 31, 2017		December 31, 2016	December 31, 2015
	(in thousands)
Restructuring charges	$	7,753	8,159	$	—
Net charge	$	7,753	8,159	$	—

Restructuring Charges

A restructuring charge of $7.8 million was recognized during the year ended December 31, 2017, under a restructuring plan adopted following a review of operations. The restructuring plan reflected resource rationalization across the business to improve resource utilization.



	Workforce reductions
	(in thousands)
Total provision recognized	$	7,753
Utilized	(4,656		)
Foreign exchange	—
Provision at December 31, 2017	$	3,097

Prior Period Restructuring Charges

A restructuring charge of $8.2 million was recognized during the year ended December 31, 2016, under a restructuring plan adopted following a review by the Company of its operations. The restructuring plan includes resource rationalizations in certain areas of the business to improve resource utilization, resulting in charge of $6.2 million and office consolidation resulting in the recognition of an onerous lease of $2.0 million during the twelve months ended December 31, 2016. No additional charge was recorded during the twelve months ended December 31, 2017.



	Workforce Reductions			Onerous Lease			Total
	(in thousands)
Total provision recognized	$	6,190		$	1,969		$	8,159
Utilized	(5,734		)	(571		)	(6,305		)
Foreign exchange	$	(63	)	—			$	(63	)
Provision at December 31, 2016	$	393		$	1,398		$	1,791
Utilized	(393		)	(1,081		)	(1,474		)
Provision at December 31, 2017	$	—		$	317		$	317

A restructuring charge of $8.8 million was recognized during the year ended December 31, 2014. Following the closure of the Company’s European Phase 1 services in 2013, the Company recognized a charge in 2014 in relation to its Manchester, United Kingdom facility; $5.6 million in relation to asset impairments and $3.2 million in relation to an onerous lease charge associated with this facility. We expect this to be paid by 2024.



	Onerous Lease			Asset Impairment			Total
	(in thousands)
Total provision recognized	$	3,167		$	5,629		$	8,796
Asset write off	—			(5,629		)	(5,629		)
Provision at December 31, 2014	$	3,167		$	—		$	3,167
Utilized	(1,167		)	—			(1,167		)
Provision at December 31, 2015	$	2,000		$	—		$	2,000
Utilized	(1,359		)	—			(1,359		)
Provision at December 31, 2016	$	641		$	—		$	641
Utilized	(441		)	—			(441		)
Provision at December 31, 2017	$	200		$	—		$	200

At December 31, 2017, $3.2 million is included within other liabilities and $0.4 million within non-current other liabilities.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Litigation

The Company is not party to any litigation or other legal proceedings that the Company believes could reasonably be expected to have a material adverse effect on the Company's business, results of operations and financial condition.

Operating Leases

The Company has several non-cancelable operating leases, primarily for facilities, that expire over the next 10 years. These leases generally contain renewal options and require the Company to pay all executory costs such as maintenance and insurance. The Company recognized $44.0 million, $44.0 million and $49.9 million in rental expense, including rates, for the years ended December 31, 2017, December 31, 2016 and December 31, 2015 respectively. Future minimum rental commitments for operating leases with non-cancelable terms in excess of one year are as follows:



	Minimum rental payments
	(in thousands)
2018	38,111
2019	32,575
2020	26,336
2021	19,079
2022	13,389
Thereafter	36,692
Total	$	166,182

Business Segment and Geographical Information

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Business Segment and Geographical Information

The Company is a clinical research organization ("CRO"), providing outsourced development services on a global basis to the pharmaceutical, biotechnology and medical device industries. It specializes in the strategic development, management and analysis of programs that support all stages of the clinical development process - from compound selection to Phase I-IV clinical studies. The Company has the expertise and capability to conduct clinical trials in most major therapeutic areas on a global basis and has the operational flexibility to provide development services on a stand-alone basis or as part of an integrated "full service" solution. The Company has expanded predominately through internal growth, together with a number of strategic acquisitions to enhance its expertise and capabilities in certain areas of the clinical development process.

The Company determines and presents operating segments based on the information that is internally provided to the chief operating decision maker, together the ('CODM') in accordance with FASB ASC 280-10 Disclosure about Segments of an Enterprise and Related Information. The Chief Executive Officer, Chief Financial Officer and Chief Operating Officer, were together considered the Company's CODM in the period up to and including March 1, 2017. On March 1, 2017, Mr Ciaran Murray transitioned from his role as Chief Executive Officer to the role of Executive Chairman of the Board of Directors and Dr. Steve Cutler was appointed as Chief Executive Officer. As of March 1, 2017, the Company determined that the CODM was comprised of the Chief Executive Officer and the Chief Financial Officer in accordance with the requirements of FASB ASC 280-10 Disclosures about Segments of an Enterprises and Related Information.

The Company operates as one business segment, which is the provision of outsourced development services on a global basis to the pharmaceutical, biotechnology and medical devices industries.

Revenues are allocated to individual entities based on where the work is performed in accordance with the Company's global transfer pricing model. Revenues and income from operations in Ireland are a function of this transfer pricing model.

Given ICON Clinical Research Limited's ("ICON Ireland") role in the development and management of the group, it's ownership of key intellectual property, customer relationships, its key role in the mitigation of risks faced by the group, plus the responsibility for maintaining the group's global network, ICON Ireland acts as the group entrepreneur and enters into the majority of the Company's customer contracts. As such, ICON Ireland remunerates most of the other operating entities ("cost plus service providers") in the ICON Group on the basis of a guaranteed cost plus mark up for the services they perform in each of their local territories.

The cost plus mark up for each ICON entity is established to ensure that each of ICON Ireland and the ICON entities in the various geographical areas that are involved in the conduct of services for customers, earn an appropriate arms-length return having regard to the assets owned, risks borne and functions performed by each entity from these intercompany transactions. The cost plus mark-up policy is reviewed annually to ensure that it is market appropriate.

Under this method, the residual operating profits (or losses) of the group, once the cost plus service providers have been paid their respective intercompany service fee, are retained by ICON Ireland. The geographic split of revenue disclosed for each region outside Ireland is the cost plus revenue attributable to these entities. The revenues disclosed as relating to Ireland are the net revenues after deducting the cost plus revenues attributable to the activities performed outside Ireland.

The Company's areas of operation outside of Ireland include the United States, United Kingdom, Belgium, France, Germany, Italy, Spain, The Netherlands, Sweden, Turkey, Poland, Czech Republic, Latvia, Russia, Ukraine, Hungary, Israel, Romania, Switzerland, Canada, Mexico, Brazil, Colombia, Argentina, Chile, Peru, India, China, South Korea, Japan, Thailand, Taiwan, Singapore, The Philippines, Australia, New Zealand, and South Africa.

There have been no changes to the basis of segmentation or the measurement basis for the segment results since the prior year.

Reportable segment information at December 31, 2017 and December 31, 2016 and for the years ended December 31, 2017, December 31, 2016 and December 31, 2015 is as follows:

a) The distribution of net revenue by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	424,292	$	410,572	$	429,631
Rest of Europe	337,105		313,185		330,487
U.S.	791,543		763,821		650,941
Other	205,499		178,909		163,919
Total	$	1,758,439	$	1,666,487	$	1,574,978

b) The distribution of income from operations, including restructuring and other items, by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	232,032	$	216,149	$	189,035
Rest of Europe	26,493		34,200		38,166
U.S.	58,322		41,348		45,320
Other	21,491		19,997		9,015
Total	$	338,338	$	311,694	$	281,536

c) The distribution of income from operations, excluding restructuring and other items, by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	240,115	$	218,334	$	189,035
Rest of Europe	26,351		36,509		38,166
U.S.	58,164		44,590		45,320
Other	21,461		20,420		9,015
Total	$	346,091	$	319,853	$	281,536

d) The distribution of property, plant and equipment, net, by geographical area was as follows:



	December 31, 2017		December 31, 2016
	(in thousands)
Ireland	$	111,329	$	105,684
Rest of Europe	9,026		6,231
U.S.	27,797		29,428
Other	14,899		7,624
Total	$	163,051	$	148,967

e) The distribution of depreciation and amortization by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	26,277	$	25,766	$	22,100
Rest of Europe	6,857		6,914		11,055
U.S.	24,246		23,462		20,106
Other	3,917		3,433		4,416
Total	$	61,297	$	59,575	$	57,677

f) The distribution of total assets by geographical area was as follows:



	December 31, 2017		December 31, 2016
	(in thousands)
Ireland	$	880,378	$	766,120
Rest of Europe	504,418		337,062
U.S.	650,681		651,160
Other	111,141		71,501
Total	$	2,146,618	$	1,825,843

g) The distribution of capital expenditures by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	24,468	$	27,670	$	30,900
Rest of Europe	2,819		2,851		1,916
U.S.	11,027		8,432		15,256
Other	6,403		3,648		1,658
Total	$	44,717	$	42,601	$	49,730

h) The following table sets forth the clients which represented 10% or more of the Company's net revenue in each of the periods set out below.

i) The distribution of interest income by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	1,084	$	407	$	102
Rest of Europe	1,222		1,040		1,151
U.S.	16		2		4
Other	24		35		49
Total	$	2,346	$	1,484	$	1,306

j) The distribution of the income tax charge by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016			December 31, 2015
	(in thousands)
Ireland	$	20,345	$	24,215		$	21,795
Rest of Europe	1,921		5,528			8,007
U.S.	14,772		8,381			3,580
Other	9,531		(131		)	5,929
Total	$	46,569	$	37,993		$	39,311

Supplemental Disclosure of Cash Flow Information

12 Months Ended

Dec. 31, 2017

Supplemental Cash Flow Elements [Abstract]

Supplemental Disclosure of Cash Flow Information



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Cash paid for interest	$	13,094	$	13,615	$	2,175
Cash paid for income taxes	$	12,305	$	10,205	$	14,829

Long-Term Debt - Senior Notes	12 Months Ended
Long-Term Debt - Senior Notes	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Debt - Senior Notes	Long-Term Debt – Senior Notes In December 2015 the Company issued $350 million in the private placement market which is due for repayment in 2020. The interest rate in respect of the Senior Notes is fixed at 3.64% for the five year term of the agreement. The associated interest cost is recognized in interest expense in the period since drawdown in December 2015. In October 2015, the Company entered into an interest rate hedge in respect of the planned issuance of the Senior Notes in December 2015. The interest rate hedge matured in November 2015 when the interest rate on the Senior Notes was fixed. The interest rate hedge was effective in accordance with Financial Accounting Standards Board ("FASB") ASC 815, "Derivatives and Hedging". The cash proceeds ($4.6 million), representing the realized gain on the interest rate hedge, were received on maturity in November 2015 and are recorded within Other Comprehensive Income. The realized gain is being amortized to the income statement, net against interest payable, over the period of the Senior Notes. The Senior Notes agreement also includes certain financial covenants that require compliance with a consolidated leverage ratio, a minimum EBIT to consolidated net interest charge ratio and a maximum amount of priority debt, each of which are defined in the Note Purchase and Guarantee Agreement. The Company was in compliance with these covenants at December 31, 2017. The Senior Notes have not been, and will not be, registered under the Securities Act of 1933, as amended, and may not be offered or sold in the United States absent registration or an applicable exemption from registration requirements.

Impact of New Accounting Pronouncements

12 Months Ended

Dec. 31, 2017

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Impact of New Accounting Pronouncements

Impact of new accounting pronouncements adopted during fiscal year-ended December 31, 2017

Accounting Standards Update (‘ASU’) 2016-09 ‘Improvements to Employee Share-Based Payment Accounting’ was issued in March 2016 which simplifies various aspects related to the accounting and presentation of share-based payments. The amendments require entities to record all tax effects related to share-based payments at settlement or expiration through the income statement and the windfall tax benefit to be recorded when it arises, subject to normal valuation allowance considerations. All tax-related cash flows resulting from share-based payments are required to be reported as operating activities in the statement of cash flows. The effective date of the new standard for public companies is for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years. The Company has applied the modified retrospective approach, as required by the amendment to the standard, in determining the cumulative increase in retained earnings at January 1, 2017. This resulted in the recognition within non-current deferred tax assets of previously unrecognized excess tax benefits, as a credit to retained earnings, of $6.7 million. The Company has adopted the cash flow presentation prospectively.

In July 2015, the FASB issued ASU 2015-11, which, for entities that do not measure inventory using the last-in, first-out (LIFO) or retail inventory method, changes the measurement principle for inventory from the lower of cost or market to lower of cost and net realizable value. The ASU also eliminates the requirement for these entities to consider replacement cost or net realizable value less an approximately normal profit margin when measuring inventory. This ASU is effective for public business entities in fiscal years beginning after December 15, 2016. The adoption of ASU 2015-11 did not impact on the financial statements.

In January 2017, the FASB issued 'Accounting changes and error corrections and Investments - Equity method and joint ventures: Amendments to SEC paragraphs pursuant to staff announcements at the September 22, 2016 and November 17, 2016 EITF meetings (SEC update)' which incorporates into the FASB Accounting Standards Codification recent SEC guidance about disclosing, under SEC SAB Top 11.M, the effect on financial statements of adopting the revenue, leases, and credit losses standards. The Company has adopted the ASU in its December 31, 2017 financial statements. See the sections following.

In October 2016, the FASB issued ASU 2016-17, 'Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control', which requires a single decision maker or service provider, in evaluating whether it is the primary beneficiary, to consider on a proportionate basis indirect interests held through related parties under common control. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2016. The adoption of ASU 2016-17 did not have an impact on the financial statements.

Financial statement effects of tax reform

H.R.1 was enacted on December 22, 2017. The effective date of the law for most provisions is January 1, 2018 however the effects are required to be recognized in December 2017 financial statements. In response, the SEC staff issued SAB 118, which allows registrants to record provisional amounts during a 'measurement period'. See Note 13 for assessment of impact of H.R.1 on the December 31, 2017 financial statements.

Impact of new accounting pronouncements which will be adopted during fiscal year-ended December 31, 2018

ASC 606 'Revenue from Contracts with Customers'

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which provides that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The updated standard will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. To achieve the core principle of the new standard, an entity should apply the following steps: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. Early adoption is permitted for annual periods beginning after December 16, 2016. Subsequent to issuing ASU 2014-09, the FASB issued the following amendments concerning clarification of ASU 2014-09. In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers (Topic 606), Principal versus Agent Considerations (Reporting Revenue Gross versus Net) (“ASU 2016-08”), which further clarifies the implementation guidance on principal versus agent considerations. The new guidance requires either a retrospective or a modified retrospective approach to adoption. In April 2016, the FASB issued ASU 2016-10, Revenue from Contracts with Customers (Topic 606), Identifying Performance Obligations and Licensing (“ASU 2016-10”), which clarifies the identification of performance obligations and the licensing implementation guidance, while retaining the related principles for those areas. In May 2016, the FASB issued ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”), which provides clarification on assessing the collectability criterion, presentation of sales taxes, measurement date for non-cash consideration and completed contracts at transition.

The updated standard is effective for ICON in the first quarter of the year ended December 31, 2018. ICON has elected to adopt the updated standard using the cumulative effect transition method. Under this transition method, ICON will apply the new standard as of the date of initial application (i.e. January 1, 2018), without restatement of comparative period amounts. ICON will record the cumulative effect of initially applying the new standard (to revenue and cost) as an adjustment to the opening balance of equity at the date of initial application. While we continue to assess all potential impacts of the new standard, we believe the most significant impact relates to our assessment of measurement of performance and percentage of completion in respect of our clinical trials service revenue. ICON will apply the requirements of the new standard to those contracts not completed at the date of initial application. The adoption of the new standard is expected to result in a cumulative reduction in shareholder's equity at January 1, 2018 (date of initial application) of an amount in the range of $40 million to $80 million reflecting cumulative adjustments to life to date revenue and associated costs. The full impact of adoption of the new standard, including the indirect impact (taxation and cost deferral adjustments) will be finalized in the first quarter of 2018 and is therefore subject to change.

Under current GAAP, the revenue attributable to performance is determined based on both input and output methods of measurement based on the relationship between hours incurred and the total estimated hours of the trial, or on the unit of delivery method. We have evaluated the application of the requirements of ASC 606 to ‘recognize revenue when or as the entity satisfies a performance obligation’ to its business. We have concluded that under the revised standard, clinical trial service is a single performance obligation satisfied over time i.e. the full service obligation in respect of a clinical trial (including services provided by investigators and other parties) is considered a single performance obligation in respect of the clinical services revenue stream. Promises offered to the customer are not distinct within the context of the contract.

We have also concluded that ICON is the contract principal in respect of both direct services and in the use of third parties (principally investigator services) that support the clinical research project. The transaction price is determined by reference to the contract or change order value (total service revenue and pass-through) adjusted to reflect historical experience to determine a realizable contract value. Revenue will be recognized as the single performance obligation is satisfied. The progress towards completion for clinical service contracts will be measured on an input measure of progress toward completion based on total project costs (inclusive of third party costs) at each reporting period.

The revised standard includes additional disclosure requirements related to revenue. Our results for the first quarter of the year ended December 31, 2018, being the quarter ended March 31, 2018, will include expanded disclosure in respect of (i) disaggregated revenue disclosures from contracts with customers (ii) separate disclosure of contract assets and liabilities (iii) disclosure of retrospective revenue and (iv) disclosure of the remaining performance obligations by product/service (or backlog).

Due to the complexity of certain of our contracts, the actual revenue recognition treatment required under the new standard for these arrangements may be dependent on contract-specific terms and vary in some instances.

In May 2017, the FASB issued ASU 2017-10 'Service Concession Arrangements (Topic 853): Determining the Customer of the Operation Services' which clarifies that the customer in a service concession arrangement is always the grantor.

This ASU is effective at the same time as ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (the new revenue standard).


•	If an entity had early adopted the new revenue standard before this ASU was issued (May 16, 2017), the entity may adopt this ASU on its effective date with certain specific transition provisions.


•	If an entity early adopts the new revenue standard after this ASU was issued, the entity must adopt this ASU at the same time as the new revenue standard with certain specific transition provisions.


•	An entity may elect to early adopt this ASU before the adoption of the new revenue standard with certain specific transition provisions.

The adoption of the ASU is not expected to have a significant impact on the financial statements.

In January 2017, the FASB issued ASU 2017-01 'Business combinations - Clarifying the definition of a business' to provide a new framework for determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. The ASU may be early adopted. The adoption of ASU 2017-01 is not expected to have a significant impact on the financial statements.

In March 2017, the FASB issued ASU 2017-07 'Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost' which requires companies to present the service cost component of net benefit cost in the same line items in which they report compensation cost. Companies will present all other components of net benefit cost outside operating income, if this subtotal is presented. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. The adoption of ASU 2017-07 is not expected to have a significant impact on the financial statements.

In January 2016, the FASB issued ASU 2016-01 'Financial Instruments- Overall (Subtopic 825-10): Recognition and Measurement of the Financial Assets and Financial Liabilities' which will significantly change the income statement impact of equity investments and the recognition of changes in fair value of financial liabilities when the fair value option is elected. The ASU is effective for public business entities for interim and annual periods in fiscal years beginning after December 15, 2017. The adoption of ASU 2016-01 is not expected to have a significant impact on the financial statements.

In March 2016, the FASB issued ASU 2016-04 , 'Recognition of Breakage for Certain Prepaid Stored-Value Products', which allows entities to recognize breakage on prepaid stored-value products consistent with how breakage is recognized under the new revenue standard. The exception applies to prepaid stored-value products in physical or digital form, with stored monetary values that are redeemable for goods and services, including those that can be redeemed for cash (e.g. prepaid gift cards issued on a specific payment network and redeemable at network-accepting merchant locations, prepaid telecommunication cards, and traveler's checks). The ASU is effective for public business entities for interim and annual periods in fiscal years beginning after December 15, 2017. The adoption of ASU 2016-04 is not expected to have a significant impact on the financial statements.

In August 2016, the FASB issued ASU 2016-15, 'Classification of Certain Cash Receipts and Cash Payments', which addresses eight classification issues related to the statement of cash flows:


•	Debt prepayment or debt extinguishment costs;


•	Settlement of zero-coupon bonds;


•	Contingent consideration payments made after a business combination;


•	Proceeds from the settlement of insurance claims;


•	Proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies;


•	Distributions received from equity method investees;


•	Beneficial interests in securitization transactions; and


•	Separately identifiable cash flows and application of the predominance principle.

The ASU is effective for public business entities for interim and annual periods in fiscal years beginning after December 15, 2017. The adoption of ASU 2016-15 is not expected to have a significant impact on the financial statements. Any contingent consideration payment arrangements arising on business combinations effected in the future will be reviewed for cash flow statement classification in line with ASU 2016-15.

In October 2016, the FASB issued ASU 2016-16, 'Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory', which requires entities to recognize at the transaction date the income tax consequences of intercompany asset transfers other than inventory. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. For all other entities, the ASU is effective for annual periods in fiscal years beginning after December 15, 2018, and interim periods in fiscal years beginning after December 15, 2019. The adoption of ASU 2016-16 is not expected to have a significant impact on the financial statements.

In November 2016, the FASB issued ASU 2016-18, 'Statement of Cash Flows (Topic 230): Restricted Cash', which requires companies to include cash and cash equivalents that have restrictions on withdrawal or use in total cash and cash equivalents on the statement of cash flows. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. For all other entities, the ASU is effective for annual periods in fiscal years beginning after December 15, 2018, and interim periods in fiscal years beginning after December 15, 2019. The adoption of ASU 2016-18 is not expected to have a material impact on the financial statements.

Impact of other new accounting pronouncements

In January 2017, the FASB issued ASU 2017-04 'Intangibles - Goodwill and Other: Simplifying the test for goodwill impairment' which requires an entity to no longer perform a hypothetical purchase price allocation to measure goodwill impairment. Instead, impairment will be measured using the difference between the carrying amount and the fair value of the reporting unit. The ASU is effective for public businesses, that are SEC filers, for annual and interim periods in fiscal years beginning after December 15, 2019. The adoption of ASU 2017-04 is not expected to have a significant impact on the financial statements.

In February 2017, the FASB issued ASU 2017-05 'Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets'. In February 2017, the FASB issued ASU 2017-05, which clarifies the guidance in Subtopic 610-20 on accounting for derecognition of a nonfinancial asset. The ASU also defines in-substance nonfinancial assets and includes guidance on partial sales of non-financial assets. The adoption of ASU 2017-05 is not expected to have an impact on the financial statements.

In July 2017, the FASB issued ASU 2017-11 'Earnings Per Share (Topic 260); Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (Part I) Accounting for Certain Financial Instruments with Down Round Features, (Part II) Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception' under which down round features will not cause certain equity-linked financial instruments to be accounted for as derivatives. A company that presents EPS information will reflect the effect of a down round feature of free-standing equity-linked financial instruments in EPS only if it is triggered. The ASU is effective for public business entities, for annual and interim periods in fiscal years beginning after December 15, 2018. The adoption of the ASU is not expected to have a significant impact on the financial statements.

In August 2017, the FASB issue ASU 2017-12 'Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities' which changes the recognition and presentation requirements of hedge accounting, including:


•	Eliminating the requirement to separately measure and report hedge ineffectiveness; and


•	Presenting all items that affect earnings in the same income statement line item as the hedged item.

The ASU also provides new alternatives for:


•	Applying hedge accounting to additional hedging strategies;


•	Measuring the hedged item in fair value hedges of interest rate risk;


•	Reducing the cost and complexity of applying hedge accounting by easing the requirements for effectiveness testing, hedge documentation and application of the critical terms match method; and


•	Reducing the risk of material error correction if a company applies the shortcut method inappropriately.

This ASU is effective for public business entities, for annual and interim periods in fiscal years beginning after December 15, 2018. Early adoption is permitted any time after the issuance of the ASU, including in an interim period. If adopted at other than the beginning of a fiscal year, cumulative effect adjustments are reflected as of the beginning of the fiscal year. The adoption of the ASU is not expected to have a significant impact on the financial statements.

In February 2016, the FASB issued ASU 2016-02, 'Leases', requiring lessees to recognize a right-of-use asset and a lease liability on the Consolidated Balance Sheet for all leases with the exception of short-term leases. For lessees, leases will continue to be classified as either operating or finance leases in the income statement. Lessor accounting is similar to the current model but updated to align with certain changes to the lessee model. Lessors will continue to classify leases as operating, direct financing or sales-type leases. The effective date of the new standard for public companies is for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption is permitted. The new standard must be adopted using a modified retrospective transition and requires application of the new guidance at the beginning of the earliest comparative period presented. The updated standard is effective for us beginning in the first quarter of the year-ended December 31, 2019. We are currently evaluating the effect that the updated standard will have on our consolidated financial statements and related disclosures. See Note 16 Commitments and Contingencies for details of operating leases held during year-ended December 31, 2017. A lease liability and right-of-use asset will be recorded on the Consolidated Balance Sheet at December 31, 2019 and comparative periods will be restated to reflect the lease liabilities and right-of use assets.

In June 2016, the FASB issued ASU 2016-13, 'Measurement of Credit Losses on Financial Instruments', which significantly changes the way entities recognize impairment of many financial assets by requiring immediate recognition of estimated credit losses expected to occur over their remaining life. The ASU is effective for public business entities that are SEC filers for interim and annual periods in fiscal years beginning after December 15, 2019. The adoption of ASU 2016-13 is not expected to have a significant impact on the financial statements.

Related Parties	12 Months Ended
Related Parties	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Parties	Related Parties Subsidiaries of the Company earned revenue of $743,000 (2016: $100,000) from DS Biopharma Limited (formerly Dignity Sciences Limited) during the year. Dr. John Climax is Chief Executive Officer and both Dr. John Climax and Dr. Ronan Lambe are Directors and shareholders of DS Biopharma Limited. $220,000 was recorded as due from DS Biopharma Limited at December 31, 2017. The contract terms were agreed on an arm’s length basis. On July 22, 2016, Mr. Thomas Lynch retired as a Director of the Company, having previously resigned as Chairman of the Company in March 2016. A charge of €231,750 was recorded during 2017 in respect of consultancy services provided by a company controlled by Mr. Lynch. $64,000 was recorded as due to Mr. Lynch under the terms of the agreement at December 31, 2017. During the year ended December 31, 2017, personal expenses totaling $178,000 were settled by the Company on behalf of Mr Ciaran Murray. Payment was received in advance from Mr Murray in respect of these expenses. The Company transferred ownership of an asset at fair value ($77,000) to Mr Ciaran Murray effective November 1, 2017. Payment was received in full in January 2018.

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Consolidation

Basis of consolidation

Use of Estimates

Use of estimates

Revenue Recognition

Revenue recognition

Reimbursable Expenses

Reimbursable expenses

Direct Costs

Direct costs

Direct costs consist of compensation, associated employee benefits and share-based payments for project-related employees and other direct project-related costs.

Advertising Costs

Advertising costs

All costs associated with advertising and promotion are expensed as incurred.

Foreign Currencies and Translation of Subsidiaries

Foreign currencies and translation of subsidiaries

Disclosure About Fair Value of Financial Instruments

Disclosure about fair value of financial instruments



Level 1:	Inputs are based upon unadjusted quoted prices for identical instruments traded in active markets.

Level 2:	Inputs are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques for which all significant assumptions are observable in the market or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3:	Inputs are generally unobservable and typically reflect management’s estimates of assumptions that market participants would use in pricing the asset or liability.

Business Combinations

Business combinations

Goodwill and Impairment

Intangible Assets

Intangible assets

Intangible assets are amortized on a straight line basis over their estimated useful life.

Cash and Cash Equivalents

Cash and cash equivalents

Cash and cash equivalents include cash and highly liquid investments with initial maturities of three months or less and are stated at cost, which approximates market value.

Short Term Investments - Available for Sale

Short term investments - available for sale

Accounts Receivable, net

Accounts receivable, net

Inventory

Property, Plant and Equipment

Property, plant and equipment



	Years
Building	40
Computer equipment and software	2-8
Office furniture and fixtures	8
Laboratory equipment	5
Motor vehicles	5

Leasehold improvements are amortized using the straight-line method over the estimated useful life of the asset or the lease term, whichever is shorter.

Leased Assets

Leased assets

Costs in respect of operating leases are charged to the Consolidated Statement of Operations on a straight line basis over the lease term.

Income Taxes

Income taxes

Government Grants

Government grants

Research and Development Credits

Research and development credits

Pension Costs

Pension costs

Net Income per Ordinary Share

Net income per ordinary share

Share-Based Compensation

Share-based compensation

Impairment of Long-Lived Assets

Impairment of long-lived assets

Derivative Financial Instruments

Derivative financial instruments

Financing Costs and Gain on Interest Rate Hedge

Financing costs and gain on interest rate hedge

Reclassifications

Certain amounts in the consolidated financial statements have been reclassified where necessary to conform to the current year presentation.

New Accounting Pronouncements, Policy

Impact of new accounting pronouncements adopted during fiscal year-ended December 31, 2017

Financial statement effects of tax reform

Impact of new accounting pronouncements which will be adopted during fiscal year-ended December 31, 2018

ASC 606 'Revenue from Contracts with Customers'

This ASU is effective at the same time as ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (the new revenue standard).


•	If an entity had early adopted the new revenue standard before this ASU was issued (May 16, 2017), the entity may adopt this ASU on its effective date with certain specific transition provisions.


•	If an entity early adopts the new revenue standard after this ASU was issued, the entity must adopt this ASU at the same time as the new revenue standard with certain specific transition provisions.


•	An entity may elect to early adopt this ASU before the adoption of the new revenue standard with certain specific transition provisions.

The adoption of the ASU is not expected to have a significant impact on the financial statements.

In August 2016, the FASB issued ASU 2016-15, 'Classification of Certain Cash Receipts and Cash Payments', which addresses eight classification issues related to the statement of cash flows:


•	Debt prepayment or debt extinguishment costs;


•	Settlement of zero-coupon bonds;


•	Contingent consideration payments made after a business combination;


•	Proceeds from the settlement of insurance claims;


•	Proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies;


•	Distributions received from equity method investees;


•	Beneficial interests in securitization transactions; and


•	Separately identifiable cash flows and application of the predominance principle.

Impact of other new accounting pronouncements


•	Eliminating the requirement to separately measure and report hedge ineffectiveness; and


•	Presenting all items that affect earnings in the same income statement line item as the hedged item.

The ASU also provides new alternatives for:


•	Applying hedge accounting to additional hedging strategies;


•	Measuring the hedged item in fair value hedges of interest rate risk;


•	Reducing the cost and complexity of applying hedge accounting by easing the requirements for effectiveness testing, hedge documentation and application of the critical terms match method; and


•	Reducing the risk of material error correction if a company applies the shortcut method inappropriately.

Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Adjustments Resulting From Foreign Currency Translations

Amounts charged or credited to the Consolidated Statement of Operations for the years ended December 31, 2017, December 31, 2016 and December 31, 2015 were as follows:



	Year ended December 31, (in thousands)
	2017		2016		2015
Amounts charged/(credited)	$	7,760	$	2,094	$	(3,608	)

Estimated Useful Lives of Assets

Depreciation of property, plant and equipment is computed using the straight line method based on the estimated useful lives of the assets as listed below:



	Years
Building	40
Computer equipment and software	2-8
Office furniture and fixtures	8
Laboratory equipment	5
Motor vehicles	5

Reconciliation of Number of Shares Used in Computation of Basic and Diluted Net Income Per Ordinary Share

The reconciliation of the number of shares used in the computation of basic and diluted net income per ordinary share is as follows:



	Year Ended December 31,
	2017	2016	2015
Weighted average number of ordinary shares outstanding for basic net income per ordinary share	54,129,439	55,248,900	58,746,935
Effect of dilutive share options outstanding	719,607	1,158,236	1,543,098
Weighted average number of ordinary shares outstanding for diluted net income per ordinary share	54,849,046	56,407,136	60,290,033

Short term investments - available for sale (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Cost and Fair Value of Investments



	December 31, 2017			December 31, 2016
	(in thousands)
At start of year	$	68,046		$	85,990
Purchases	41,701			22,030
Sales and maturities	(33,086		)	(40,858		)
Interest on short term investments	1,088			823
Realized gain on sale of short term investments	112			50
Unrealized capital (loss)/gain – investments	(272		)	11
At end of year	$	77,589		$	68,046

Available For Sale Short Term Investments by Major Security Type

The following table represents our available for sale short term investments by major security type as of December 31, 2017:



								Maturity by period
	Cost Total		Unrealized gains / (losses)			Fair Value Total		Less than 1 year		1 to 5 years
	(U.S.$ in millions)
US government debt securities	13.95		(0.11		)	13.84		1.99		11.85
Corporate securities	62.61		(0.19		)	62.42		23.06		39.36
Term deposits	1.33		—			1.33		1.33		—
Total (U.S.$ in millions)	$	77.89	$	(0.30	)	$	77.59	$	26.38	$	51.21

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Goodwill (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Goodwill



	December 31, 2017		December 31, 2016
	(in thousands)
Opening goodwill	$	616,088	$	588,434
Current year acquisitions (note 4 (a))	129,222		34,576
Prior period acquisition (note 4 (b))	1,393		7,689
Foreign exchange movement	22,355		(14,611		)
Closing goodwill	$	769,058	$	616,088

Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed

The table following summarizes the Company’s provisional estimates of the fair values of the assets acquired and liabilities assumed:



	July 27,
	2017
	(in thousands)
Cash	$	19,649
Property, plant and equipment	3,410
Goodwill*	129,222
Intangible assets**	32,305
Accounts receivable	15,467
Unbilled revenue	8,484
Prepayments and other current assets	3,160
Other receivables	1,430
Income taxes receivable	4,262
Accounts payable	(3,166		)
Payments on account	(31,341		)
Other liabilities	(26,586		)
Non-current other liabilities	(1,061		)
Non-current deferred tax liability	(11,104		)
Net assets acquired	$	144,131

Cash outflows	$	144,131
Total consideration	$	144,131

The following table summarizes the fair values of the assets acquired and liabilities assumed on acquisition:



	February 27, 2015
	(in thousands)
Property, plant and equipment	$	1,049
Goodwill*	92,084
Customer lists	22,752
Order backlog	2,521
Accounts receivable	5,240
Unbilled Revenue	4,324
Prepayments and other current assets	621
Accounts payable	(749		)
Payments on account	(4,186		)
Deferred tax liability	(2,171		)
Other liabilities	(5,483		)
Net assets acquired	$	116,002



Cash consideration	$	108,717
Other liabilities assumed**	11,283
Gross cash outflows	120,000
Working capital adjustment	(3,998		)
Net cash outflows	$	116,002


**	Payments made at acquisition date of $11.3 million were in respect of certain one-time liabilities at the acquisition date which have subsequently been discharged.

The table following summarizes the fair values of the assets acquired and liabilities assumed:



	September 15,
	2016
	(in thousands)
Cash	$	3,168
Property, plant and equipment	939
Goodwill*	35,969
Customer lists	4,012
Order backlog	1,668
Brand	1,409
Accounts receivable	11,431
Unbilled revenue	3,868
Prepayments and other current assets	1,673
Accounts payable	(165		)
Other liabilities	(5,569		)
Non-current other liabilities	(7		)

Net assets acquired	$	58,396



Cash outflows (including other liabilities assumed of $9.2 million)	$	52,396
Assessment of valuation of contingent consideration at acquisition	6,000
Net purchase consideration	$	58,396

The table following summarizes the fair values of the assets acquired and liabilities assumed;



	December 4, 2015
	(in thousands)
Cash	$	194
Property, plant and equipment	712
Goodwill*	48,728
Customer lists	6,938
Order backlog	2,948
Accounts receivable	11,597
Prepayments and other current assets	1,329
Accounts payable	(530		)
Other liabilities	(3,456		)
Non-current deferred tax liability	(3,106		)
Net assets acquired	$	65,354



Cash consideration	$	53,681
Other liabilities assumed	10,060
Working capital adjustment	1,613
Total cash outflows	$	65,354

Summary of Proforma Effect in Net Revenue Net Income and Earnings Per Share



	Year Ended December 31,
	2015		2014
	(in thousands)
Net revenue	$	1,601,891	$	1,527,685
Net income	$	243,004	$	172,390
Basic earnings per share	$	4.14	$	2.80
Diluted earnings per share	$	4.03	$	2.73



	Year Ended
	December 31,
	2017		2016
	(in thousands)
Net revenue	$	1,811,018	$	1,750,643
Net income	$	284,903	$	263,101
Basic earnings per share	$	5.26	$	4.76
Diluted earnings per share	$	5.19	$	4.66



	Year Ended December 31,
	2015		2014
	(in thousands)
Net revenue	$	1,581,816	$	1,556,936
Net income	$	239,361	$	179,289
Basic earnings per share	$	4.07	$	2.92
Diluted earnings per share	$	3.97	$	2.84



	Year Ended December 31,
	2016		2015
	(in thousands)
Net revenue	$	1,713,245	$	1,639,085
Net income	$	266,148	$	244,167
Basic earnings per share	$	4.82	$	4.16
Diluted earnings per share	$	4.72	$	4.05

Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Intangible Assets



	December 31, 2017			December 31, 2016
Cost	(in thousands)
Customer relationships acquired	$	91,230		$	92,110
Technology asset acquired	11,169			11,169
Order backlog	18,208			18,574
Trade names/ brands acquired	2,766			3,075
Volunteer list acquired	1,325			1,325
Non-compete arrangements	489			489
Mapi intangible asset	32,305			—
Foreign exchange movement	(2,389		)	(6,578		)
Total cost	155,103			120,164
Accumulated amortization	(84,898		)	(67,037		)
Foreign exchange movement	1,423			3,483
Net book value	$	71,628		$	56,610

Schedule of Future Intangible Asset Amortization Expense

Future intangible asset amortization expense for the years ended December 31, 2018 to December 31, 2022 is as follows:



	Year Ended December 31,(in thousands)
2018	$	19,788
2019	16,217
2020	13,867
2021	11,906
2022	6,580
	$	68,358

Property, Plant and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Schedule of Property Plant and Equipment Net



	December 31, 2017			December 31, 2016
	(in thousands)
Cost
Land	$	3,464		$	3,464
Building	88,411			77,950
Computer equipment and software	358,874			315,984
Office furniture and fixtures	78,372			70,218
Laboratory equipment	34,918			31,487
Leasehold improvements	24,097			20,933
Motor vehicles	42			43
	588,178			520,079
Less accumulated depreciation and asset write offs	(425,127		)	(371,112		)
Property, plant and equipment (net)	$	163,051		$	148,967

Employee Benefits (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Schedule of Pension Costs

The pension costs of this plan are presented in the following tables in accordance with the requirements of ASC 715-60, Defined Benefit Plans – Other Postretirement. The plan has been closed to new entrants with effect from July 1, 2003.



Funded status	December 31, 2017			December 31, 2016
	(in thousands)
Projected benefit obligation	$	(37,759	)	$	(32,906	)
Fair value of plan assets	32,423			24,876
Funded status	$	(5,336	)	$	(8,030	)
Non-current other liabilities (note 8)	$	(5,336	)	$	(8,030	)



Change in benefit obligation	December 31, 2017			December 31, 2016
	(in thousands)
Benefit obligation at beginning of year	$	32,906		$	27,369
Service cost	112			75
Interest cost	929			1,017
Plan participants' contributions	22			22
Expenses	(8		)	8
Benefits paid	(68		)	(104		)
Actuarial loss	658			10,057
Foreign currency exchange rate changes	3,208			(5,538		)
Benefit obligation at end of year	$	37,759		$	32,906



Change in plan assets	December 31, 2017			December 31, 2016
	(in thousands)
Fair value of plan assets at beginning of year	$	24,876		$	23,367
Actual return on plan assets	979			5,861
Employer contributions	4,008			108
Plan participants' contributions	22			22
Benefits paid	(68		)	(104		)
Foreign currency exchange rate changes	2,606			(4,378		)
Fair value of plan assets at end of year	$	32,423		$	24,876

The pension costs of this plan are presented in the following tables in accordance with the requirements of ASC 715-60, Defined Benefit Plans – Other Postretirement.



Funded status	December 31, 2017			December 31, 2016
	(in thousands)
Projected benefit obligation	$	(5,927	)	$	(6,928	)
Fair value of plan assets	5,202			6,006
Funded status	$	(725	)	$	(922	)
Non-current other liabilities (note 8)	$	(725	)	$	(922	)



Change in benefit obligation	December 31, 2017			December 31, 2016
	(in thousands)
Benefit obligation at beginning of year	$	6,928		$	8,537
Service cost	243			352
Interest cost	54			82
Plan participants' contributions	120			150
Settlement	(1,019		)	(909		)
Prior service cost	—			(88		)
Transferred (benefits paid)/balances	(76		)	53
Actuarial gain	(626		)	(1,157		)
Foreign currency exchange rate changes	303			(92		)
Benefit obligation at end of year	$	5,927		$	6,928



Change in plan assets	December 31,			December 31,
	2017			2016
	(in thousands)
Fair value of plan assets at beginning of year	$	6,006		$	5,350
Expected return on plan assets	47			48
Actual return on plan assets	(296		)	1,233
Scheme contributions	157			195
Plan participants' contributions	120			150
Transferred (benefits paid)/balances	(76		)	53
Settlement	(1,019		)	(909		)
Foreign currency exchange rate changes	263			(114		)
Fair value of plan assets at end of year	$	5,202		$	6,006

Schedule of Funded Status



Funded status	December 31, 2017			December 31, 2016
	(in thousands)
Projected benefit obligation	$	(5,927	)	$	(6,928	)
Fair value of plan assets	5,202			6,006
Funded status	$	(725	)	$	(922	)
Non-current other liabilities (note 8)	$	(725	)	$	(922	)



Funded status	December 31, 2017			December 31, 2016
	(in thousands)
Projected benefit obligation	$	(37,759	)	$	(32,906	)
Fair value of plan assets	32,423			24,876
Funded status	$	(5,336	)	$	(8,030	)
Non-current other liabilities (note 8)	$	(5,336	)	$	(8,030	)

Schedule of Components of Net Periodic Benefit Cost

The following amounts were recorded in the Consolidated Statement of Operations as components of the net periodic benefit cost:



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Service cost	$	112		$	75		$	78
Interest cost	929			1,017			1,140
Expected return on plan assets	(586		)	(646		)	(661		)
Amortization of net loss	250			—			224
Expenses	(8		)	8			—
Net periodic benefit cost	$	697		$	454		$	781



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Service cost	$	243		$	352		$	402
Interest cost	54			82			159
Expected return on plan assets	(47		)	(48		)	(119		)
Amortization of net (gain)/loss	(43		)	22			—
Amortization of prior service credit	(8		)	(8		)	—
Settlement	(214		)	(136		)	—
Curtailment	—			—			18
Net periodic benefit cost	$	(15	)	$	264		$	460

Summary of Assumptions Used in Calculating Net Periodic Benefit Cost



	December 31, 2017		December 31, 2016		December 31, 2015
Discount rate	0.75	%	0.95	%	1.35	%
Rate of compensation increase	2.0	%	2.0	%	2.00	%
Expected rate of return on plan assets	0.75	%	0.95	%	1.35	%



Other comprehensive income	December 31, 2017			December 31, 2016			December 31, 2015
Actuarial (gain)/loss - benefit obligation	$	(626	)	$	(1,157	)	$	81
Actuarial loss/(gain) – plan assets	296			(1,233		)	1,075
Prior service credit/(cost) recognized in net periodic benefit cost	215			136			(17		)
Actuarial gain/(loss) recognized in net periodic benefit cost	43			(22		)	—
Amortization of net prior service credit	8			8			—
Net prior service credit occurring during the year	(1		)	(89		)	—
Total	$	(65	)	$	(2,357	)	$	1,139



	December 31, 2017		December 31, 2016		December 31, 2015
Discount rate	2.7	%	4.0	%	3.6	%
Rate of compensation increase	3.9	%	3.7	%	3.6	%
Expected rate of return on plan assets	2.1	%	3.0	%	2.7	%



Other comprehensive income	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Actuarial loss/(gain) - benefit obligation	$	658		$	10,057		$	(3,992	)
Actuarial (gain)/loss – plan assets	(393		)	(5,215		)	384
Actuarial gain recognized in net periodic benefit cost	(250		)	—			(224		)
Total	$	15		$	4,842		$	(3,832	)

Summary of Amounts Recognized in Accumulated Other Comprehensive Income Which Have Not Yet Been Recognized as Components of Net Periodic Benefit Cost

Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows:



	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Net actuarial loss	$	7,138	$	7,123	$	2,281
Total	$	7,138	$	7,123	$	2,281

Amounts recognized in accumulated other comprehensive income that have not yet been recognized as components of net periodic benefit cost are as follows:



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Net actuarial (gain)/loss	$	(1,283	)	$	(1,218	)	$	1,139
Total	$	(1,283	)	$	(1,218	)	$	1,139

Summary of Assumptions Used in Calculating Pension Benefit Obligations

The following assumptions were used in determining the benefit obligation at December 31, 2017 and December 31, 2016:



	December 31, 2017		December 31, 2016
Discount rate	0.80	%	0.75	%
Rate of compensation increase	2.0	%	2.0	%

The following assumptions were used in determining the benefit obligation at December 31, 2017 and December 31, 2016:



	December 31, 2017		December 31, 2016
Discount rate	2.5	%	2.7	%
Rate of compensation increase	3.7	%	3.9	%

Summary of Expected Long Term Rates of Return on Different Asset Classes

The expected long term rates of return on different asset classes are as follows:



Asset Category	Expected long-term return per annum
Corporate Bonds	2.5	%
Gilts	1.8	%
Cash	2.5	%

Schedule of underlying asset split of fund

The underlying asset split of the fund is shown below.



Asset Category	December 31, 2017		December 31, 2016
Corporate Bonds	22	%	25	%
Gilts	65	%	75	%
Cash	13	%	—	%
	100	%	100	%

The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid.



	(in thousands)

2018	286
2019	224
2020	204
2021	201
2022	197
Years 2023 - 2027	$	878

Schedule of Plan Asset Fair Value Measurements



	Quoted Prices in Active Markets for Identical Assets Level 1 (in thousands)
	December 31, 2017		December 31, 2016
Cash	$	4,086	$	16
Fixed Income Securities
Legal and General Active Corporate Bond – Over 10 Year	7,188		6,095
Legal and General Gilt Funds	7,611		6,725
Legal and General Index Linked Gilt Funds	13,539		12,040
	$	32,424	$	24,876

Schedule of Annual Benefit Payments which Reflect Expected Future Service

The following annual benefit payments, which reflect expected future service as appropriate, are expected to be paid.



	(in thousands)
2018	336
2019	312
2020	330
2021	405
2022	436
Years 2023 - 2027	$	3,297

Equity Incentive Schemes and Stock Compensation Charges (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Transactions for Company's Share Option Plans

The following table summarizes the transactions for the Company's share option plans for the years ended December 31, 2017, December 31, 2016 and December 31, 2015:



	Options Granted Under Plans		Number of Shares		Weighted Average Exercise Price		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2014	2,227,700		2,227,700		$	28.00	$	10.40
Granted	259,059		259,059		$	68.25	$	19.75
Exercised	(773,753	)	(773,753	)	$	27.13	$	10.31
Cancelled	(86,424	)	(86,424	)	$	27.32	$	10.31
Outstanding at December 31, 2015	1,626,582		1,626,582		$	34.87	$	11.94
Granted	256,191		256,191		$	69.61	$	20.10
Exercised	(393,240	)	(393,240	)	$	25.79	$	9.84
Cancelled	(23,089	)	(23,089	)	$	29.74	$	11.19
Outstanding at December 31, 2016	1,466,444		1,466,444		$	43.45	$	13.94
Granted	219,113		219,113		$	85.98	$	25.06
Exercised	(458,243	)	(458,243	)	$	30.35	$	10.72
Cancelled	(55,921	)	(55,921	)	$	54.35	$	16.76
Outstanding at December 31, 2017	1,171,393		1,171,393		$	56.02	$	17.15
Vested and exercisable at December 31, 2017	476,666		476,666		$	38.47	$	12.95

Schedule of Non Vested Shares Outstanding

Non-vested shares outstanding as at December 31, 2017 are as follows:



	Options Outstanding Number of Shares		Weighted Average Exercise Price		Weighted Average Fair Value
Non-vested outstanding at December 31, 2016	814,870		$	54.37	$	16.55

Granted	219,113		85.98		25.06
Vested	(292,630	)	44.54		14.39
Forfeited	(46,626	)	60.73		18.22

Non-vested outstanding at December 31, 2017	694,727		$	68.06	$	20.03

Summary of Information Concerning Outstanding and Exercisable Share Options

The following table summarizes information concerning outstanding and exercisable share options as of December 31, 2017:



Options Outstanding						Options Exercisable
Range Exercise Price		Number of Shares	Weighted Average Remaining Contractual Life	Weighted Average Exercise Price		Number of Shares	Weighted Average Exercise Price
$	20.28	63,824	1.16	$	20.28	63,824	$	20.28
$	20.59	8,800	2.14	$	20.59	8,800	$	20.59
$	22.30	84,137	2.32	$	22.30	84,137	$	22.30
$	23.66	1,711	2.57	$	23.66	1,711	$	23.66
$	24.46	7,692	0.17	$	24.46	7,692	$	24.46
$	26.20	450	0.38	$	26.20	450	$	26.20
$	26.71	4,450	2.69	$	26.71	4,450	$	26.71
$	32.37	159,686	3.33	$	32.37	124,476	$	32.37
$	36.22	5,923	3.46	$	36.22	3,323	$	36.22
$	37.90	2,520	3.93	$	37.90	460	$	37.90
$	40.83	72,634	4.39	$	40.83	37,026	$	40.83
$	47.03	39,477	4.17	$	47.03	9,626	$	47.03
$	48.67	80,039	4.21	$	48.67	21,160	$	48.67
$	51.35	2,030	4.60	$	51.35	418	$	51.35
$	65.60	91,549	6.38	$	65.60	26,161	$	65.60
$	66.47	6,717	5.39	$	66.47	1,698	$	66.47
$	66.97	1,872	5.45	$	66.97	—	$	66.97
$	68.39	190,821	5.18	$	68.39	65,178	$	68.39
$	71.95	133,256	6.17	$	71.95	16,076	$	71.95
$	83.47	130,836	7.17	$	83.47	—	$	83.47
$	90.03	82,969	7.38	$	90.03	—	$	90.03
$20.28 - $90.03		1,171,393	4.86	$	56.02	476,666	$	38.47

Summary of Weighted Average Fair Values and Assumptions Used

The weighted average fair values and assumptions were as follows:



	Year Ended
	December 31, 2017			December 31, 2016			December 31, 2015
Weighted average fair value	$	25.06		$	20.10		$	19.75

Assumptions:
Expected volatility	29		%	30		%	30		%
Dividend yield	—		%	—		%	—		%
Risk-free interest rate	1.93		%	1.39		%	1.58		%
Expected life	5.0 years			5.0 years			5.0 years

Summary of RSU and PSU Activity

The following table summarizes RSU and PSU activity for the year ended December 31, 2017:



	PSU Outstanding Number of Shares		PSU Weighted Average Fair Value		PSU Weighted Average Remaining Contractual Life	RSU Outstanding Number of Shares		RSU Weighted Average Fair Value		RSU Weighted Average Remaining Contractual Life
Outstanding at December 31, 2016	830,523		$	60.73	1.11	1,025,484		$	58.64	1.40

Granted	68,040		$	84.10		186,102		$	89.60
Shares vested	(320,640	)	$	46.63		(367,177	)	$	45.18
Forfeited	(66,897	)	$	67.16		(128,439	)	$	63.89

Outstanding at December 31, 2017	511,026		$	72.07	0.93	715,970		$	72.65	1.28

Schedule of Non-cash Stock Compensation Expense

Non-cash stock compensation expense has been allocated as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Direct costs	$	18,020	$	21,903	$	18,358
Selling, general and administrative	$	12,553	$	18,440	$	14,959
Total compensation costs	$	30,573	$	40,343	$	33,317

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Summary of Components of Income Before Provision for Income Taxes

The components of income before provision for income taxes are as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	218,306	$	201,221	$	184,643
United States	28,426		11,466		15,436
Other	81,325		87,485		78,771
Income before provision for income taxes	$	328,057	$	300,172	$	278,850

Summary of Components of Provision for Income Taxes

The components of provision for income taxes are as follows:



	Year ended
	December 31, 2017		December 31, 2016			December 31, 2015
	(in thousands)
Provision for income taxes:
Current tax expense:
Ireland	$	20,084	$	22,931		$	21,769
United States	5,792		7,768			684
Other	9,964		5,749			13,701
Total current tax expense	35,840		36,448			36,154

Deferred tax expense/(benefit):
Ireland	261		1,284			26
United States	8,980		613			2,896
Other	1,488		(352		)	235
Total deferred tax expense	10,729		1,545			3,157

Provision for income taxes	46,569		37,993			39,311

Impact on shareholders equity and other comprehensive income of the tax consequence of :
Excess tax benefit on stock compensation	—		(4,332		)	(1,905		)
Currency impact on long term funding	973		(396		)	3,574
Fair value of cash flow hedge	148		—			—

Total	$	47,690	$	33,265		$	40,980

Schedule of Reconciliation of Consolidated Reported Provision for Income Taxes and Statutory Rate

The Company's consolidated reported provision for income taxes differed from the amount that would result from applying the Irish statutory rate as set forth below:



	Year ended
	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Taxes at Irish statutory rate of 12.5% (2016:12.5%; 2015:12.5%)	$	41,007		$	37,522		$	34,856
Foreign and other income taxed at higher rates	6,324			4,642			4,614
Research & development tax incentives	(830		)	(907		)	(695		)
Movement in valuation allowance	1,329			1,208			(4,133		)
Effects of change in tax rates	925			576			(16		)
Increase/(decrease) in unrecognized tax benefits	933			(1,521		)	5,085
Impact of stock compensation	(9,917		)	(4,121		)	(3,468		)
Impact of mandatory repatriation under US Tax Reform	7,694			—			—
Other	(896		)	594			3,068
Provision for income taxes	$	46,569		$	37,993		$	39,311

Schedule of Tax Effects of Temporary Differences that Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities

The tax effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities are presented below:



	December 31, 2017			December 31, 2016
	(in thousands)
Deferred tax liabilities:
Property, plant and equipment	$	1,139		$	979
Goodwill	22,655			26,617
Other intangible assets	11,801			6,700
Other	4,139			1,441
Total deferred tax liabilities recognized	39,734			35,737

Deferred tax assets:
Operating loss and tax credits carryforwards	24,962			22,705
Property, plant and equipment	4,062			3,121
Accrued expenses and payments on account	24,433			28,904
Stock compensation	5,786			13,062
Deferred compensation expense	2,548			3,327
Other	740			15
Total deferred tax assets	62,531			71,134
Valuation allowance for deferred tax assets	(22,439		)	(20,337		)
Deferred tax assets recognized	40,092			50,797
Overall net deferred tax asset	$	358		$	15,060

Schedule of Expected Expiry Dates of NOL's

The expected expiry dates of these losses are as follows:



	Federal NOL's		State NOL's
	(in thousands)
2018	113		—
2021-2034	24,041		14,945
2035-2036	812		28,703

	$	24,966	$	43,648

Schedule of Reconciliation of Beginning and Ending Amount of Total Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of total unrecognized tax benefits is as follows:



	December 31, 2017			December 31, 2016			December 31, 2015
	(in thousands)
Unrecognized tax benefits at start of year	$	26,620		$	28,166		$	23,201
Increase related to acquired tax positions	—			—			778
Increase related to prior year tax positions	—			1,151			1,482
Decrease related to prior year tax positions	(3,050		)	(2,483		)	(315		)
Increase related to current year tax positions	4,765			1,104			3,063
Settlements	(2,523		)	(837		)	—
Lapse of statute of limitations	(2,092		)	(481		)	(43		)
Unrecognized tax benefits at end of year	$	23,720		$	26,620		$	28,166

Restructuring and other items (Tables)

12 Months Ended

Dec. 31, 2017

Restructuring and Related Activities [Abstract]

Schedule of Recognized Restructuring and Other Items, Net

Restructuring and other items recognized during the year ended December 31, 2017 comprise:



	Year Ended
	December 31, 2017		December 31, 2016	December 31, 2015
	(in thousands)
Restructuring charges	$	7,753	8,159	$	—
Net charge	$	7,753	8,159	$	—

Schedule of Restructuring Charges



	Workforce reductions
	(in thousands)
Total provision recognized	$	7,753
Utilized	(4,656		)
Foreign exchange	—
Provision at December 31, 2017	$	3,097



	Workforce Reductions			Onerous Lease			Total
	(in thousands)
Total provision recognized	$	6,190		$	1,969		$	8,159
Utilized	(5,734		)	(571		)	(6,305		)
Foreign exchange	$	(63	)	—			$	(63	)
Provision at December 31, 2016	$	393		$	1,398		$	1,791
Utilized	(393		)	(1,081		)	(1,474		)
Provision at December 31, 2017	$	—		$	317		$	317

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Rental Commitments for Operating Leases with Non-cancelable Terms

Future minimum rental commitments for operating leases with non-cancelable terms in excess of one year are as follows:



	Minimum rental payments
	(in thousands)
2018	38,111
2019	32,575
2020	26,336
2021	19,079
2022	13,389
Thereafter	36,692
Total	$	166,182

Business Segment and Geographical Information (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of Distribution of Net Revenue by Geographical Area

The distribution of net revenue by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	424,292	$	410,572	$	429,631
Rest of Europe	337,105		313,185		330,487
U.S.	791,543		763,821		650,941
Other	205,499		178,909		163,919
Total	$	1,758,439	$	1,666,487	$	1,574,978

Schedule of Distribution of Income from Operations by Geographical Area

The distribution of income from operations, including restructuring and other items, by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	232,032	$	216,149	$	189,035
Rest of Europe	26,493		34,200		38,166
U.S.	58,322		41,348		45,320
Other	21,491		19,997		9,015
Total	$	338,338	$	311,694	$	281,536

c) The distribution of income from operations, excluding restructuring and other items, by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	240,115	$	218,334	$	189,035
Rest of Europe	26,351		36,509		38,166
U.S.	58,164		44,590		45,320
Other	21,461		20,420		9,015
Total	$	346,091	$	319,853	$	281,536

Schedule of Distribution of Property, Plant and Equipment, Net, by Geographical Area

The distribution of property, plant and equipment, net, by geographical area was as follows:



	December 31, 2017		December 31, 2016
	(in thousands)
Ireland	$	111,329	$	105,684
Rest of Europe	9,026		6,231
U.S.	27,797		29,428
Other	14,899		7,624
Total	$	163,051	$	148,967

Schedule of Distribution of Depreciation and Amortization by Geographical Area

The distribution of depreciation and amortization by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	26,277	$	25,766	$	22,100
Rest of Europe	6,857		6,914		11,055
U.S.	24,246		23,462		20,106
Other	3,917		3,433		4,416
Total	$	61,297	$	59,575	$	57,677

Schedule of Distribution of Total Assets by Geographical Area

The distribution of total assets by geographical area was as follows:



	December 31, 2017		December 31, 2016
	(in thousands)
Ireland	$	880,378	$	766,120
Rest of Europe	504,418		337,062
U.S.	650,681		651,160
Other	111,141		71,501
Total	$	2,146,618	$	1,825,843

Schedule of Distribution of Capital Expenditures by Geographical Area

The distribution of capital expenditures by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	24,468	$	27,670	$	30,900
Rest of Europe	2,819		2,851		1,916
U.S.	11,027		8,432		15,256
Other	6,403		3,648		1,658
Total	$	44,717	$	42,601	$	49,730

Schedule of Clients Representing Company's Net Revenue

The following table sets forth the clients which represented 10% or more of the Company's net revenue in each of the periods set out below.

Schedule of Distribution of Interest Income by Business Segment

The distribution of interest income by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016		December 31, 2015
	(in thousands)
Ireland	$	1,084	$	407	$	102
Rest of Europe	1,222		1,040		1,151
U.S.	16		2		4
Other	24		35		49
Total	$	2,346	$	1,484	$	1,306

Schedule of Distribution of Tax Charge by Geographical Area

The distribution of the income tax charge by geographical area was as follows:



	Year ended
	December 31, 2017		December 31, 2016			December 31, 2015
	(in thousands)
Ireland	$	20,345	$	24,215		$	21,795
Rest of Europe	1,921		5,528			8,007
U.S.	14,772		8,381			3,580
Other	9,531		(131		)	5,929
Total	$	46,569	$	37,993		$	39,311

Description of Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 Employee Country Location
Product Information [Line Items]
Number of employees \| Employee	13,250
Number of locations in which company operates \| Location	98
Number of countries in which company operates \| Country	38
Geographic Concentration Risk \| United States \| Net Revenue
Product Information [Line Items]
Percentage of company revenue	45.00%
Geographic Concentration Risk \| Europe \| Net Revenue
Product Information [Line Items]
Percentage of company revenue	43.30%
Geographic Concentration Risk \| Rest of World \| Net Revenue
Product Information [Line Items]
Percentage of company revenue	11.70%

Significant Accounting Policies - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Nov. 30, 2015	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Advertising and promotion costs			$ 6,744,333	$ 7,167,050	$ 4,513,750
Goodwill impairment charge			0	0	0
Carrying value of inventory		$ 2,200,000	2,200,000	2,400,000
Cash proceeds from interest rate hedge			$ 0	$ 0	$ 4,658,000
Derivative remaining maturity			12 months
Senior Notes
Significant Accounting Policies [Line Items]
Debt instrument, interest rate		3.64%	3.64%
Debt instrument, term		5 years	5 years
Interest rate hedge, inception date			Oct. 05, 2015
Interest rate hedge, maturity date			Nov. 17, 2015
Cash proceeds from interest rate hedge	$ 4,600,000		$ 4,600,000
Other receivable
Significant Accounting Policies [Line Items]
Fair value of derivative asset		$ 1,200,000	$ 1,200,000

Estimated Useful Lives of Assets (Detail)	12 Months Ended
Estimated Useful Lives of Assets (Detail)	Dec. 31, 2017
Building
Property, Plant and Equipment [Line Items]
Estimated useful lives	40 years
Computer equipment and software \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Computer equipment and software \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	8 years
Office furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful lives	8 years
Laboratory equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Motor vehicles
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years

Reconciliation of Number of Shares Used in Computation of Basic and Diluted Net Income Per Ordinary Share (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Weighted average number of ordinary shares outstanding for basic net income per ordinary share (in shares)	54,129,439	55,248,900	58,746,935
Effect of dilutive share options outstanding (in shares)	719,607	1,158,236	1,543,098
Weighted average number of ordinary shares outstanding for diluted net income per ordinary share (in shares)	54,849,046	56,407,136	60,290,033

Cost and Fair Value of Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
At start of year	$ 68,046	$ 85,990
Purchases	41,701	22,030
Sales and maturities	(33,086)	(40,858)
Interest on short term investments	1,088	823	$ 571
Realized gain on sale of short term investments	112	50	(113)
Unrealized capital (loss)/gain – investments	(272)	11
At end of year	$ 77,589	$ 68,046	$ 85,990

Available For Sale Short Term Investments by Major Security Type (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Cost Total	$ 77,890
Unrealized gains / (losses)	(300)
Fair Value Total	77,590
Maturity by period, less than 1 year	26,380
Maturity by period, 1 to 5 years	51,210
US government debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost Total	13,950
Unrealized gains / (losses)	(110)
Fair Value Total	13,840
Maturity by period, less than 1 year	1,990
Maturity by period, 1 to 5 years	11,850
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Cost Total	62,610
Unrealized gains / (losses)	(190)
Fair Value Total	62,420
Maturity by period, less than 1 year	23,060
Maturity by period, 1 to 5 years	39,360
Term deposits
Schedule of Available-for-sale Securities [Line Items]
Cost Total	1,330
Unrealized gains / (losses)	0
Fair Value Total	1,330
Maturity by period, less than 1 year	1,330
Maturity by period, 1 to 5 years	$ 0

Schedule of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
Schedule of Goodwill (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Opening goodwill	$ 616,088	$ 588,434
Current year acquisitions (note 4 (a))	129,222	34,576
Prior period acquisition (note 4 (b))	1,393	7,689
Foreign exchange movement	22,355	(14,611)
Closing goodwill	$ 769,058	$ 616,088

Goodwill - Additional Information (Detail) $ in Thousands					12 Months Ended
Goodwill - Additional Information (Detail) $ in Thousands	Jul. 27, 2017 USD ($)	Sep. 15, 2016 USD ($)	Dec. 04, 2015 USD ($) Patient Site	Feb. 27, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill					$ 769,058	$ 616,088	$ 588,434
Total cash outflows					144,131	$ 54,209	$ 166,292
Assessment of valuation of contingent consideration at acquisition								$ 6,000	$ 6,000
Mapi Development SAS
Business Acquisition [Line Items]
Goodwill					129,200
Mapi
Business Acquisition [Line Items]
Goodwill	$ 129,222
Total cash outflows	144,131
Intangible assets	$ 32,305
Clinical Research Management Inc.
Business Acquisition [Line Items]
Goodwill		$ 35,969
Total cash outflows		52,396
Net cash outflows		52,400
Other liabilities assumed		9,200
Maximum additional consideration that might be payable		12,000
Assessment of valuation of contingent consideration at acquisition		$ 6,000			$ 0			$ 0
PMG
Business Acquisition [Line Items]
Goodwill			$ 48,728
Total cash outflows			65,354
Other liabilities assumed			$ 10,060
Number of clinical research sites acquired \| Site			52
Working capital adjustment			$ (1,613)
PMG \| Minimum
Business Acquisition [Line Items]
Number of active patients via electronic medical records acquired \| Patient			2,000,000
MediMedia Pharma Solutions
Business Acquisition [Line Items]
Goodwill				$ 92,084
Net cash outflows				116,002
Other liabilities assumed				11,283
Cash consideration, net of working capital adjustment				104,700
Working capital adjustment				$ 3,998

Goodwill Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands					12 Months Ended
	Jul. 27, 2017	Sep. 15, 2016	Dec. 04, 2015	Feb. 27, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017	Mar. 31, 2017
Business Acquisition [Line Items]
Goodwill					$ 769,058	$ 616,088	$ 588,434
Total cash outflows					144,131	$ 54,209	$ 166,292
Assessment of valuation of contingent consideration at acquisition								$ 6,000	$ 6,000
Mapi
Business Acquisition [Line Items]
Cash	$ 19,649
Property, plant and equipment	3,410
Goodwill	129,222
Intangible assets	32,305
Accounts receivable	15,467
Unbilled revenue	8,484
Prepayments and other current assets	3,160
Other receivables	1,430
Income taxes receivable	4,262
Accounts payable	(3,166)
Payments on account	(31,341)
Other liabilities	(26,586)
Non-current other liabilities	(1,061)
Non-current deferred tax liability	(11,104)
Net assets acquired	144,131
Total cash outflows	$ 144,131
Clinical Research Management Inc.
Business Acquisition [Line Items]
Cash		$ 3,168
Property, plant and equipment		939
Goodwill		35,969
Accounts receivable		11,431
Unbilled revenue		3,868
Prepayments and other current assets		1,673
Accounts payable		(165)
Other liabilities		(5,569)
Non-current other liabilities		(7)
Net assets acquired		58,396
Other liabilities assumed		9,200
Total cash outflows		52,396
Assessment of valuation of contingent consideration at acquisition		6,000			0			$ 0
Net cash outflows		52,400
Accounts receivable acquired		300
Unbilled revenue		1,100
Other liabilities acquired		1,100
Accounts payable		500
PMG
Business Acquisition [Line Items]
Cash			$ 194
Property, plant and equipment			712
Goodwill			48,728
Accounts receivable			11,597
Prepayments and other current assets			1,329
Accounts payable			(530)
Other liabilities			(3,456)
Non-current deferred tax liability			(3,106)
Net assets acquired			65,354
Cash consideration			53,681		$ 1,600
Other liabilities assumed			10,060
Working capital adjustment			1,613
Total cash outflows			65,354
Acquisition fair value adjustment			7,700
Deferred tax liabilities			3,100
Accounts receivable acquired			1,400
Other liabilities acquired			1,200
MediMedia Pharma Solutions
Business Acquisition [Line Items]
Property, plant and equipment				$ 1,049
Goodwill				92,084
Accounts receivable				5,240
Unbilled revenue				4,324
Prepayments and other current assets				621
Accounts payable				(749)
Payments on account				(4,186)
Deferred tax liability				(2,171)
Other liabilities				(5,483)
Net assets acquired				116,002
Cash consideration				108,717
Other liabilities assumed				11,283
Gross cash outflows				120,000
Working capital adjustment				(3,998)
Net cash outflows				116,002
Customer lists \| Clinical Research Management Inc.
Business Acquisition [Line Items]
Intangible assets		4,012
Customer lists \| PMG
Business Acquisition [Line Items]
Intangible assets			6,938
Customer lists \| MediMedia Pharma Solutions
Business Acquisition [Line Items]
Intangible assets				22,752
Order backlog \| Clinical Research Management Inc.
Business Acquisition [Line Items]
Intangible assets		1,668
Order backlog \| PMG
Business Acquisition [Line Items]
Intangible assets			2,948
Order backlog \| MediMedia Pharma Solutions
Business Acquisition [Line Items]
Intangible assets				$ 2,521
Brand \| Clinical Research Management Inc.
Business Acquisition [Line Items]
Intangible assets		$ 1,409
Customer lists and order or production backlog \| PMG
Business Acquisition [Line Items]
Customer list and order backlog assets acquired			$ 400

Summary of Proforma Effect in Net Revenue, Net Income and Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Mapi
Business Acquisition [Line Items]
Net revenue	$ 1,811,018	$ 1,750,643
Net income	$ 284,903	$ 263,101
Basic earnings per share (dollars per share)	$ 5.26	$ 4.76
Diluted earnings per share (dollars per share)	$ 5.19	$ 4.66
Clinical Research Management Inc.
Business Acquisition [Line Items]
Net revenue		$ 1,713,245	$ 1,639,085
Net income		$ 266,148	$ 244,167
Basic earnings per share (dollars per share)		$ 4.82	$ 4.16
Diluted earnings per share (dollars per share)		$ 4.72	$ 4.05
PMG
Business Acquisition [Line Items]
Net revenue			$ 1,601,891	$ 1,527,685
Net income			$ 243,004	$ 172,390
Basic earnings per share (dollars per share)			$ 4.14	$ 2.80
Diluted earnings per share (dollars per share)			$ 4.03	$ 2.73
MediMedia Pharma Solutions
Business Acquisition [Line Items]
Net revenue			$ 1,581,816	$ 1,556,936
Net income			$ 239,361	$ 179,289
Basic earnings per share (dollars per share)			$ 4.07	$ 2.92
Diluted earnings per share (dollars per share)			$ 3.97	$ 2.84

Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cost
Total cost	$ 155,103	$ 120,164
Foreign exchange movement	(2,389)	(6,578)
Accumulated amortization	(84,898)	(67,037)
Foreign exchange movement Accumulated Amortization	1,423	3,483
Net book value	71,628	56,610
Customer relationships acquired
Cost
Total cost	91,230	92,110
Technology asset acquired
Cost
Total cost	11,169	11,169
Order backlog
Cost
Total cost	18,208	18,574
Trade names/ brands acquired
Cost
Total cost	2,766	3,075
Volunteer list acquired
Cost
Total cost	1,325	1,325
Non-compete arrangements
Cost
Total cost	489	489
Mapi intangible asset
Cost
Total cost	$ 32,305	$ 0

Intangible Assets - Additional Information (Detail) $ in Thousands	Jul. 27, 2017 USD ($)	Sep. 15, 2016 USD ($)	Dec. 04, 2015 USD ($) Site	Feb. 27, 2015 USD ($)	May 07, 2014 USD ($)	Feb. 15, 2013 USD ($)	Feb. 28, 2012 USD ($)	Feb. 15, 2012 USD ($)	Jul. 14, 2011 USD ($)	Jan. 14, 2011 USD ($)	Nov. 14, 2008 USD ($)	Feb. 11, 2008 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													$ 84,898	$ 67,037
Mapi
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired	$ 32,300
Amortization period	6 years
Amount amortized since date of acquisition													3,300
Clinical Research Management Inc.
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													2,300
Clinical Research Management Inc. \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired		$ 4,000
Amortization period		7 years
Clinical Research Management Inc. \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired		$ 1,700
Amortization period		2 years
Clinical Research Management Inc. \| Brand
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired		$ 1,400
Amortization period		5 years
PMG
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													5,000
Number of clinical research sites acquired \| Site			52
PMG \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired			$ 6,900
Amortization period			7 years
PMG \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired			$ 3,000
Amortization period			2 years
MediMedia Pharma Solutions
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													11,700
MediMedia Pharma Solutions \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired				$ 22,800
Amortization period				7 years
MediMedia Pharma Solutions \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired				$ 2,500
Amortization period				1 year
Aptiv Solutions
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													19,100
Aptiv Solutions \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired					$ 21,400
Amortization period					7 years
Aptiv Solutions \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired					$ 7,900
Amortization period					3 years
Clinical Trial Services of Cross Country Healthcare Inc.
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													3,900
Clinical Trial Services of Cross Country Healthcare Inc. \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired						$ 3,300
Amortization period						3 years
Clinical Trial Services of Cross Country Healthcare Inc. \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired						$ 600
Amortization period						1 year
PriceSpective
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													6,800
PriceSpective \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired							$ 10,200
Amortization period							10 years
PriceSpective \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired							$ 400
Amortization period							9 months 18 days
PriceSpective \| Non-compete arrangements
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired							$ 400
Amortization period							3 years
BeijingWits Medical
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													1,500
BeijingWits Medical \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired								$ 1,800
Amortization period								10 years
BeijingWits Medical \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired								$ 400
Amortization period								4 years
BeijingWits Medical \| Non-compete arrangements
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired								$ 10
Amortization period								5 years
Firecrest Clinical Limited
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													14,500
Firecrest Clinical Limited \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired									$ 5,200
Amortization period									7 years 6 months
Firecrest Clinical Limited \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired									$ 1,200
Amortization period									1 year 2 months 12 days
Firecrest Clinical Limited \| Technology asset acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired									$ 11,200
Amortization period									7 years 6 months
Firecrest Clinical Limited \| Trade names acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired									$ 1,400
Amortization period									4 years 6 months
Oxford Outcomes Limited \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired										$ 6,600
Amortization period										6 years 6 months
Oxford Outcomes Limited \| Order backlog
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired										$ 600
Amortization period										2 years
Prevalere Life Sciences
Indefinite-lived Intangible Assets [Line Items]
Amount amortized since date of acquisition													$ 6,800
Prevalere Life Sciences \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired											$ 7,400
Prevalere Life Sciences \| Minimum \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Amortization period											7 years
Prevalere Life Sciences \| Maximum \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Amortization period											11 years
Healthcare Discoveries \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired												$ 1,600
Healthcare Discoveries \| Volunteer list acquired
Indefinite-lived Intangible Assets [Line Items]
Value of amortizable intangible asset acquired												$ 1,300
Healthcare Discoveries \| Minimum \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Amortization period												2 years
Healthcare Discoveries \| Minimum \| Volunteer list acquired
Indefinite-lived Intangible Assets [Line Items]
Amortization period												6 years
Healthcare Discoveries \| Maximum \| Customer relationships acquired
Indefinite-lived Intangible Assets [Line Items]
Amortization period												9 years

Future Intangible Asset Amortization Expense (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2018	$ 19,788
2019	16,217
2020	13,867
2021	11,906
2022	6,580
Finite Lived Intangible Assets, Amortization Expense, Net, Total	$ 68,358

Property, Plant and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Land	$ 3,464	$ 3,464
Building	88,411	77,950
Computer equipment and software	358,874	315,984
Office furniture and fixtures	78,372	70,218
Laboratory equipment	34,918	31,487
Leasehold improvements	24,097	20,933
Motor vehicles	42	43
Property, Plant and Equipment, Gross, Total	588,178	520,079
Less accumulated depreciation and asset write offs	(425,127)	(371,112)
Property, plant and equipment (net)	$ 163,051	$ 148,967

Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Liabilities Disclosure [Abstract]
Personnel related liabilities	$ 168,964	$ 135,349
Facility related liabilities	13,061	14,182
General overhead liabilities	41,789	31,126
Other liabilities	4,628	7,584
Short term government grants (note 11)	35	54
Restructuring and other items (note 14)	5,026	2,432
Other liabilities	$ 233,503	$ 190,727

Non-Current Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Defined benefit pension obligations, net (note 9)	$ 6,061	$ 8,952
Other non-current liabilities	11,050	14,800
Non-current other liabilities	$ 17,111	$ 23,752

Employee Benefits - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 07, 2014
Defined Benefit Plan Contributions
Defined Benefit Plan Disclosure [Line Items]
Contributions percentage of annual compensation	6.00%
Employer contributions	$ 20,355	$ 20,952	$ 20,439
Defined Contribution Pension Plan 401(k)
Defined Benefit Plan Disclosure [Line Items]
Participant's contributions percentage matches	50.00%
Participant's contributions percentage of annual compensation	6.00%
Deferred salary arrangement employer contribution	$ 14,946	$ 15,223	$ 12,802
Foreign Plan \| Pension Plan \| United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Net loss for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	(300)
Net prior service cost for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ 0
Retirement period used as a basis to estimate expected cash flows	10 years
Expected long-term rate of return after application of a market value reduction factor (per annum)	2.00%
Contribution to pension fund in the year ending December 31, 2018	$ 100
Foreign Plan \| Pension Plan \| United Kingdom \| iboxx Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan bond maturity period	15 years
Basis point increase in benefits obligation discount rate	10.00%
Foreign Plan \| Pension Plan \| United Kingdom \| Gilts
Defined Benefit Plan Disclosure [Line Items]
Percentage of investments	75.00%
Foreign Plan \| Pension Plan \| United Kingdom \| Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Percentage of investments	25.00%
Foreign Plan \| Pension Plan \| Switzerland
Defined Benefit Plan Disclosure [Line Items]
Net loss for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ 69
Net prior service cost for defined benefit pension plan that will be amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ 8
Retirement period used as a basis to estimate expected cash flows	10 years
Contribution to pension fund in the year ending December 31, 2018	$ 100
Foreign Plan \| Pension Plan \| Switzerland \| Aptiv Solutions
Defined Benefit Plan Disclosure [Line Items]
Percentage of common stock acquired				100.00%

Change in Benefit Obligations (Detail) - Foreign Plan - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	$ 32,906	$ 27,369
Service cost	112	75	$ 78
Interest cost	929	1,017	1,140
Plan participants' contributions	22	22
Expenses	(8)	8	0
Benefits paid	(68)	(104)
Actuarial loss	658	10,057
Foreign currency exchange rate changes	3,208	(5,538)
Benefit obligation at end of year	37,759	32,906	27,369
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	6,928	8,537
Service cost	243	352
Interest cost	54	82
Plan participants' contributions	120	150
Settlement	(1,019)	(909)
Prior service cost	0	(88)
Transferred (benefits paid)/balances	(76)	53
Actuarial loss	(626)	(1,157)
Foreign currency exchange rate changes	303	(92)
Benefit obligation at end of year	$ 5,927	$ 6,928	$ 8,537

Change in Plan Assets (Detail) - Foreign Plan - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
United Kingdom
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 24,876	$ 23,367
Expected return on plan assets	586	646	$ 661
Actual return on plan assets	979	5,861
Employer contributions	4,008	108
Plan participants' contributions	22	22
Benefits paid	(68)	(104)
Foreign currency exchange rate changes	2,606	(4,378)
Fair value of plan assets at end of year	32,423	24,876	23,367
Switzerland
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	6,006	5,350
Expected return on plan assets	47	48
Actual return on plan assets	(296)	1,233
Scheme contributions	157	195
Plan participants' contributions	120	150
Transferred (benefits paid)/balances	(76)	53
Settlement	(1,019)	(909)
Foreign currency exchange rate changes	263	(114)
Fair value of plan assets at end of year	$ 5,202	$ 6,006	$ 5,350

Funded Status (Detail) - Foreign Plan - Pension Plan - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ (37,759)	$ (32,906)
Fair value of plan assets	32,423	24,876	$ 23,367
Funded status	(5,336)	(8,030)
Non-current other liabilities (note 8)	(5,336)	(8,030)
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	(5,927)	(6,928)
Fair value of plan assets	5,202	6,006	$ 5,350
Funded status	(725)	(922)
Non-current other liabilities (note 8)	$ (725)	$ (922)

Components of Net Periodic Benefit Cost (Detail) - Foreign Plan - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 112	$ 75	$ 78
Interest cost	929	1,017	1,140
Expected return on plan assets	(586)	(646)	(661)
Amortization of net loss	250	0	224
Expenses	(8)	8	0
Net periodic benefit cost	697	454	781
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Service cost	243	352
Interest cost	54	82
Expected return on plan assets	(47)	(48)
Amortization of prior service credit	0	88
Settlement	1,019	909
Switzerland \| Includes Financial Instruments, Property Occupied by, or Other Assets
Defined Benefit Plan Disclosure [Line Items]
Service cost	243	352	402
Interest cost	54	82	159
Expected return on plan assets	(47)	(48)	(119)
Amortization of net loss	(43)	22	0
Amortization of prior service credit	(8)	(8)	0
Settlement	(214)	(136)	0
Curtailment	0	0	18
Net periodic benefit cost	$ (15)	$ 264	$ 460

Net Periodic Pension Benefit Cost Assumptions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total	$ (50)	$ 2,485	$ (2,693)
Foreign Plan \| Pension Plan \| United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.70%	4.00%	3.60%
Rate of compensation increase	3.90%	3.70%	3.60%
Expected rate of return on plan assets	2.10%	3.00%	2.70%
Actuarial loss/(gain) - benefit obligation	$ 658	$ 10,057	$ (3,992)
Actuarial (gain)/loss – plan assets	(393)	(5,215)	384
Actuarial gain recognized in net periodic benefit cost	(250)	0	(224)
Total	$ 15	$ 4,842	$ (3,832)
Foreign Plan \| Pension Plan \| Switzerland
Defined Benefit Plan Disclosure [Line Items]
Discount rate	0.75%	0.95%	1.35%
Rate of compensation increase	2.00%	2.00%	2.00%
Expected rate of return on plan assets	0.75%	0.95%	1.35%
Actuarial loss/(gain) - benefit obligation	$ (626)	$ (1,157)	$ 81
Actuarial (gain)/loss – plan assets	296	(1,233)	1,075
Prior service credit/(cost) recognized in net periodic benefit cost	215	136	(17)
Actuarial gain recognized in net periodic benefit cost	43	(22)	0
Amortization of net prior service credit	8	8	0
Net prior service credit occurring during the year	(1)	(89)	0
Total	$ (65)	$ (2,357)	$ 1,139

Amounts recognized in accumulated other comprehensive income that have not been recognized (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total	$ (5,855)	$ (5,905)
Foreign Plan \| Pension Plan \| United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	7,138	7,123	$ 2,281
Total	7,138	7,123	2,281
Foreign Plan \| Pension Plan \| Switzerland
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	(1,283)	(1,218)
Total	$ (1,283)	$ (1,218)	$ 1,139

Assumptions Used in Determining Benefit Obligation (Detail) - Foreign Plan - Pension Plan	Dec. 31, 2017	Dec. 31, 2016
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.50%	2.70%
Rate of compensation increase	3.70%	3.90%
Switzerland
Defined Benefit Plan Disclosure [Line Items]
Discount rate	0.80%	0.75%
Rate of compensation increase	2.00%	2.00%

Expected Long Term Rates of Return on Different Asset Classes (Detail) - Foreign Plan - Pension Plan - United Kingdom	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.10%	3.00%	2.70%
Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.50%
Gilts
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	1.80%
Cash
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return per annum	2.50%

Actual Plan Asset Allocation (Detail) - Foreign Plan - Pension Plan - United Kingdom	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	100.00%	100.00%
Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	22.00%	25.00%
Gilts
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	65.00%	75.00%
Cash
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocations	13.00%	0.00%

Plan Asset Fair Value Measurements (Detail) - Foreign Plan - Pension Plan - United Kingdom - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 32,423	$ 24,876	$ 23,367
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,424	24,876
Fair Value, Inputs, Level 1 \| Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,086	16
Fair Value, Inputs, Level 1 \| Fixed Income Securities \| Legal and General Active Corporate Bond – Over 10 Year
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,188	6,095
Fair Value, Inputs, Level 1 \| Fixed Income Securities \| Legal and General Gilt Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,611	6,725
Fair Value, Inputs, Level 1 \| Fixed Income Securities \| Legal and General Index Linked Gilt Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 13,539	$ 12,040

Annual Benefit Payments (Detail) - Foreign Plan - Pension Plan $ in Thousands	Dec. 31, 2017 USD ($)
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
2018	$ 336
2019	312
2020	330
2021	405
2022	436
Years 2023 - 2027	3,297
Switzerland
Defined Benefit Plan Disclosure [Line Items]
2018	286
2019	224
2020	204
2021	201
2022	197
Years 2023 - 2027	$ 878

Equity Incentive Schemes and Stock Compensation Charges - Additional Information (Detail) - USD ($) $ in Thousands			12 Months Ended			48 Months Ended
	Feb. 14, 2017	May 11, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2018	Jul. 21, 2008
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Weighted average contractual term of options outstanding			4 years 10 months 10 days	4 years 8 months 1 day
Exercisable - weighted average remaining contractual life			3 years 5 months 9 days	3 years 3 months 18 days
Options expected to vest (in shares)			333,433			333,433
Intrinsic value of option exercised			$ 31,800
Intrinsic value of option outstanding			65,800			$ 65,800
Intrinsic value of option exercisable			35,100			35,100
Total compensation costs			30,573	$ 40,343	$ 33,317
Non-cash stock compensation expense not yet recognized			$ 49,300			$ 49,300
Unrecognized stock-based compensation expense, weighted average period (years)			2 years 15 days
Tax benefit on exercise of options			$ 0	4,300	1,900
Income tax benefit related to stock compensation			9,300	3,500	1,500
Cash tax benefit related to stock options exercised			$ 3,200	3,400	$ 5,600
Scenario, Forecast
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options expected to vest (in shares)							255,198
Employee Stock Plan, 2008 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)			6,000,000			6,000,000		1,000,000.0
Employee Stock Plan, 2008 Plan \| Individual Employee
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)			400,000			400,000
Employee Stock Plan, 2008 Plan \| Minimum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Additional number of ordinary shares which have been reserved for issuance (in shares)	400,000
Percentage of option price for fair value of ordinary share			100.00%
Employee Stock Plan, 2008 Plan \| Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Additional number of ordinary shares which have been reserved for issuance (in shares)	1,000,000
Restricted Stock Units 2008
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)			1,000,000			1,000,000
Employee Stock Plan, 2003 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)			6,000,000			6,000,000
Maximum number of award as percentage of shares outstanding			10.00%
Employee Stock Plan, 2003 Plan \| Individual Employee
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)			400,000			400,000
Employee Stock Option
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period			5 years
Shares expiration period			8 years
Employee Stock Option \| Vested and Unvested Options
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Options vesting percentage			20.00%
Employee Stock Option \| Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Weighted average contractual term of options outstanding			8 years
Restricted Stock Units 2013
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Additional number of ordinary shares which have been reserved for issuance (in shares)		2,500,000
Ordinary shares which have been reserved for issuance (in shares)		4,100,000
Restricted Stock Units (RSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Fair value of stock units vested			$ 16,600	10,800
Stock units granted (in shares)			186,102
Performance Share Unit (PSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Fair value of stock units vested			$ 15,000	$ 10,300
Stock units granted (in shares)			68,040
PSUs Based on Service and EPS Targets
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Stock units granted (in shares)						270,858
PSUs Based on Service and EPS Targets \| Minimum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Cumulative EPS vesting period			2014
PSUs Based on Service and EPS Targets \| Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Cumulative EPS vesting period			2020
Stock units to be granted (in shares)			240,168			240,168

Summary of Stock Option Activity (Detail) - Stock Option And Award Plans - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options Granted Under Plans
Beginning balance (in shares)	1,466,444	1,626,582	2,227,700
Granted (in shares)	219,113	256,191	259,059
Exercised (in shares)	(458,243)	(393,240)	(773,753)
Cancelled (in shares)	(55,921)	(23,089)	(86,424)
Ending Balance (in shares)	1,171,393	1,466,444	1,626,582
Vested and exercisable at end of period (in shares)	476,666
Number of Shares
Beginning balance (in shares)	1,466,444	1,626,582	2,227,700
Granted (in shares)	219,113	256,191	259,059
Exercised (in shares)	(458,243)	(393,240)	(773,753)
Cancelled (in shares)	(55,921)	(23,089)	(86,424)
Ending balance (in shares)	1,171,393	1,466,444	1,626,582
Vested and exercisable at end of period (in shares)	476,666
Weighted Average Exercise Price
Beginning balance (usd per shares)	$ 43.45	$ 34.87	$ 28.00
Granted (usd per share)	85.98	69.61	68.25
Exercised (usd per share)	30.35	25.79	27.13
Cancelled (usd per share)	54.35	29.74	27.32
Ending balance (usd per shares)	56.02	43.45	34.87
Vested and exercisable at end of period (usd per share)	38.47
Weighted Average Grant Date Fair Value
Beginning balance (usd per share)	13.94	11.94	10.40
Granted (usd per share)	25.06	20.10	19.75
Exercised (usd per share)	10.72	9.84	10.31
Cancelled (usd per share)	16.76	11.19	10.31
Ending balance (usd per share)	17.15	$ 13.94	$ 11.94
Vested and exercisable at end of period (usd per share)	$ 12.95

Summary of Movement in Non-Vested Share Options (Detail) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options Outstanding Number of Shares
Beginning Balance (in shares)	814,870
Granted (in shares)	219,113
Vested (in shares)	(292,630)
Forfeited (in shares)	(46,626)
Ending Balance (in shares)	694,727	814,870
Weighted Average Exercise Price
Beginning balance (usd per share)	$ 54.37
Granted (usd per share)	85.98
Vested (usd per share)	44.54
Forfeited (usd per share)	60.73
Ending balance (usd per share)	68.06	$ 54.37
Weighted Average Fair Value
Beginning Balance (usd per share)	16.55
Granted (usd per share)	25.06	20.10	$ 19.75
Vested (usd per share)	14.39
Forfeited (usd per share)	18.22
Ending Balance (usd per share)	$ 20.03	$ 16.55

Outstanding and Exercisable Share Options (Detail)	12 Months Ended
Outstanding and Exercisable Share Options (Detail)	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 90.03
Number of Shares \| shares	1,171,393
Weighted Average Remaining Contractual Life	4 years 10 months 10 days
Weighted Average Exercise Price (usd per share)	$ 56.02
Number of Shares \| shares	476,666
Weighted Average Exercise Price (usd per share)	$ 38.47
Minimum Range Exercise Price (usd per share)	20.28
Range 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 20.28
Number of Shares \| shares	63,824
Weighted Average Remaining Contractual Life	1 year 1 month 28 days
Weighted Average Exercise Price (usd per share)	$ 20.28
Number of Shares \| shares	63,824
Weighted Average Exercise Price (usd per share)	$ 20.28
Range 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 20.59
Number of Shares \| shares	8,800
Weighted Average Remaining Contractual Life	2 years 1 month 21 days
Weighted Average Exercise Price (usd per share)	$ 20.59
Number of Shares \| shares	8,800
Weighted Average Exercise Price (usd per share)	$ 20.59
Range 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 22.30
Number of Shares \| shares	84,137
Weighted Average Remaining Contractual Life	2 years 3 months 26 days
Weighted Average Exercise Price (usd per share)	$ 22.30
Number of Shares \| shares	84,137
Weighted Average Exercise Price (usd per share)	$ 22.30
Range 4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 23.66
Number of Shares \| shares	1,711
Weighted Average Remaining Contractual Life	2 years 6 months 26 days
Weighted Average Exercise Price (usd per share)	$ 23.66
Number of Shares \| shares	1,711
Weighted Average Exercise Price (usd per share)	$ 23.66
Range 5
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 24.46
Number of Shares \| shares	7,692
Weighted Average Remaining Contractual Life	2 months 1 day
Weighted Average Exercise Price (usd per share)	$ 24.46
Number of Shares \| shares	7,692
Weighted Average Exercise Price (usd per share)	$ 24.46
Range 6
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 26.20
Number of Shares \| shares	450
Weighted Average Remaining Contractual Life	4 months 17 days
Weighted Average Exercise Price (usd per share)	$ 26.20
Number of Shares \| shares	450
Weighted Average Exercise Price (usd per share)	$ 26.20
Range 7
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 26.71
Number of Shares \| shares	4,450
Weighted Average Remaining Contractual Life	2 years 8 months 9 days
Weighted Average Exercise Price (usd per share)	$ 26.71
Number of Shares \| shares	4,450
Weighted Average Exercise Price (usd per share)	$ 26.71
Range 8
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 32.37
Number of Shares \| shares	159,686
Weighted Average Remaining Contractual Life	3 years 3 months 29 days
Weighted Average Exercise Price (usd per share)	$ 32.37
Number of Shares \| shares	124,476
Weighted Average Exercise Price (usd per share)	$ 32.37
Range 9
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 36.22
Number of Shares \| shares	5,923
Weighted Average Remaining Contractual Life	3 years 5 months 16 days
Weighted Average Exercise Price (usd per share)	$ 36.22
Number of Shares \| shares	3,323
Weighted Average Exercise Price (usd per share)	$ 36.22
Range 10
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 37.90
Number of Shares \| shares	2,520
Weighted Average Remaining Contractual Life	3 years 11 months 5 days
Weighted Average Exercise Price (usd per share)	$ 37.90
Number of Shares \| shares	460
Weighted Average Exercise Price (usd per share)	$ 37.90
Range 11
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 40.83
Number of Shares \| shares	72,634
Weighted Average Remaining Contractual Life	4 years 4 months 21 days
Weighted Average Exercise Price (usd per share)	$ 40.83
Number of Shares \| shares	37,026
Weighted Average Exercise Price (usd per share)	$ 40.83
Range 12
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 47.03
Number of Shares \| shares	39,477
Weighted Average Remaining Contractual Life	4 years 2 months 1 day
Weighted Average Exercise Price (usd per share)	$ 47.03
Number of Shares \| shares	9,626
Weighted Average Exercise Price (usd per share)	$ 47.03
Range 13
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 48.67
Number of Shares \| shares	80,039
Weighted Average Remaining Contractual Life	4 years 2 months 16 days
Weighted Average Exercise Price (usd per share)	$ 48.67
Number of Shares \| shares	21,160
Weighted Average Exercise Price (usd per share)	$ 48.67
Range 14
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 51.35
Number of Shares \| shares	2,030
Weighted Average Remaining Contractual Life	4 years 7 months 6 days
Weighted Average Exercise Price (usd per share)	$ 51.35
Number of Shares \| shares	418
Weighted Average Exercise Price (usd per share)	$ 51.35
Range 15
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 65.60
Number of Shares \| shares	91,549
Weighted Average Remaining Contractual Life	6 years 4 months 17 days
Weighted Average Exercise Price (usd per share)	$ 65.60
Number of Shares \| shares	26,161
Weighted Average Exercise Price (usd per share)	$ 65.60
Range 16
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 66.47
Number of Shares \| shares	6,717
Weighted Average Remaining Contractual Life	5 years 4 months 21 days
Weighted Average Exercise Price (usd per share)	$ 66.47
Number of Shares \| shares	1,698
Weighted Average Exercise Price (usd per share)	$ 66.47
Range 17
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 66.97
Number of Shares \| shares	1,872
Weighted Average Remaining Contractual Life	5 years 5 months 12 days
Weighted Average Exercise Price (usd per share)	$ 66.97
Number of Shares \| shares	0
Weighted Average Exercise Price (usd per share)	$ 66.97
Range 18
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 68.39
Number of Shares \| shares	190,821
Weighted Average Remaining Contractual Life	5 years 2 months 5 days
Weighted Average Exercise Price (usd per share)	$ 68.39
Number of Shares \| shares	65,178
Weighted Average Exercise Price (usd per share)	$ 68.39
Range 19
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 71.95
Number of Shares \| shares	133,256
Weighted Average Remaining Contractual Life	6 years 2 months 1 day
Weighted Average Exercise Price (usd per share)	$ 71.95
Number of Shares \| shares	16,076
Weighted Average Exercise Price (usd per share)	$ 71.95
Range 20
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 83.47
Number of Shares \| shares	130,836
Weighted Average Remaining Contractual Life	7 years 2 months 1 day
Weighted Average Exercise Price (usd per share)	$ 83.47
Number of Shares \| shares	0
Weighted Average Exercise Price (usd per share)	$ 83.47
Range 21
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum Range Exercise Price (usd per share)	$ 90.03
Number of Shares \| shares	82,969
Weighted Average Remaining Contractual Life	7 years 4 months 17 days
Weighted Average Exercise Price (usd per share)	$ 90.03
Number of Shares \| shares	0
Weighted Average Exercise Price (usd per share)	$ 90.03

Schedule of Weighted Average Fair Values and Assumptions Used (Detail) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value (usd per share)	$ 25.06	$ 20.10	$ 19.75
Assumptions:
Expected volatility	29.00%	30.00%	30.00%
Dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate	1.93%	1.39%	1.58%
Expected life	5 years	5 years	5 years

Summary of RSU and PSU Activity (Detail) - $ / shares	12 Months Ended
Summary of RSU and PSU Activity (Detail) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Performance Share Unit (PSUs)
Outstanding Number of Shares
Outstanding at beginning of period (in shares)	830,523
Granted (in shares)	68,040
Shares vested	(320,640)
Forfeited (in shares)	(66,897)
Outstanding at ending of period (in shares)	511,026	830,523
Weighted Average Fair Value
Outstanding at beginning of period (usd per share)	$ 60.73
Granted (usd per share)	84.10
Shares vested	46.63
Forfeited (usd per share)	67.16
Outstanding at end of period (usd per share)	$ 72.07	$ 60.73
Weighted Average Remaining Contractual Life
Outstanding at end of period (usd per share)	11 months 5 days	1 year 1 month 10 days
Restricted Stock Units (RSUs)
Outstanding Number of Shares
Outstanding at beginning of period (in shares)	1,025,484
Granted (in shares)	186,102
Shares vested	(367,177)
Forfeited (in shares)	(128,439)
Outstanding at ending of period (in shares)	715,970	1,025,484
Weighted Average Fair Value
Outstanding at beginning of period (usd per share)	$ 58.64
Granted (usd per share)	89.60
Shares vested	45.18
Forfeited (usd per share)	63.89
Outstanding at end of period (usd per share)	$ 72.65	$ 58.64
Weighted Average Remaining Contractual Life
Outstanding at end of period (usd per share)	1 year 3 months 11 days	1 year 4 months 24 days

Schedule of Non-cash Stock Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation costs	$ 30,573	$ 40,343	$ 33,317
Direct costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation costs	18,020	21,903	18,358
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation costs	$ 12,553	$ 18,440	$ 14,959

Government Grants (Detail) - USD ($) $ in Thousands	12 Months Ended
Government Grants (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Disclosure [Abstract]
Received	$ 3,539	$ 3,539
Less accumulated amortization	(2,745)	(2,701)
Foreign exchange translation adjustment	207	103
Total government grants	1,001	941
Less current portion	(35)	(54)
Non-current government grants	$ 966	$ 887

Government Grants - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Revenue Disclosure [Abstract]
Amortization of government grants	$ 44	$ 44	$ (53)
Restricted retained earnings	$ 1,200

Share Capital - Additional Information (Detail) - USD ($)			12 Months Ended			15 Months Ended
	Jul. 31, 2015	May 01, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Oct. 03, 2016
Equity, Class of Treasury Stock [Line Items]
Total proceeds from exercise of stock options by employees			$ 13,950,000	$ 10,180,000	$ 20,999,000
Ordinary shares redeemed, value			$ 133,106,000	$ 110,000,000	$ 457,892,000
Employee Stock Option
Equity, Class of Treasury Stock [Line Items]
Options exercised by employees (in shares)			458,243	393,240	773,753
Average exercise price of Option per share			$ 30.35	$ 25.79	$ 27.13
Total proceeds from exercise of stock options by employees			$ 13,900,000	$ 10,100,000	$ 21,000,000
Restricted Stock Units (RSUs)
Equity, Class of Treasury Stock [Line Items]
Ordinary shares issued in respect of certain RSUs previously awarded by the Company			361,102	296,386	268,870
Performance Share Unit (PSUs)
Equity, Class of Treasury Stock [Line Items]
Ordinary shares issued in respect of certain PSUs previously awarded by the Company			320,640	311,492	7,990
Buyback Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount	$ 400,000,000	$ 60,000,000					$ 400,000,000
Ordinary shares redeemed	5,316,062	882,419	1,589,227		6,198,481	3,018,414
Ordinary shares redeemed, value	$ 400,000,000	$ 57,900,000	$ 133,100,000		$ 457,900,000	$ 243,100,000

Components of Income Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before provision for income taxes	$ 328,057	$ 300,172	$ 278,850
Ireland
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before provision for income taxes	218,306	201,221	184,643
United States
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before provision for income taxes	28,426	11,466	15,436
Other
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items]
Income before provision for income taxes	$ 81,325	$ 87,485	$ 78,771

Components of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax expense:
Current tax expense	$ 35,840	$ 36,448	$ 36,154
Deferred tax expense/(benefit):
Deferred tax expense/(benefit)	10,729	1,545	3,157
Provision for income taxes	46,569	37,993	39,311
Impact on shareholders equity and other comprehensive income of the tax consequence of :
Excess tax benefit on stock compensation	0	(4,332)	(1,905)
Currency impact on long term funding	973	(396)	3,574
Fair value of cash flow hedge	148	0	0
Total	47,690	33,265	40,980
Ireland
Current tax expense:
Current tax expense	20,084	22,931	21,769
Deferred tax expense/(benefit):
Deferred tax expense/(benefit)	261	1,284	26
Provision for income taxes	20,345	24,215	21,795
United States
Current tax expense:
Current tax expense	5,792	7,768	684
Deferred tax expense/(benefit):
Deferred tax expense/(benefit)	8,980	613	2,896
Provision for income taxes	14,772	8,381	3,580
Other
Current tax expense:
Current tax expense	9,964	5,749	13,701
Deferred tax expense/(benefit):
Deferred tax expense/(benefit)	$ 1,488	$ (352)	$ 235

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Irish statutory rate	12.50%	12.50%	12.50%
Impact of mandatory repatriation under US Tax Reform	$ 7,694	$ 0	$ 0
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit)	500
Tax cuts and jobs act of 2017, incomplete accounting, change in tax rate, deferred tax liability, provisional income tax benefit	5,800
Valuation allowance for deferred tax assets	22,439	20,337	17,200
Net change in the total valuation allowance	2,100	3,100
Deferred tax liabilities, undistributed foreign earnings	3,100	0
Unrecognized tax benefit, potentially expire in 2018	3,400
Total unrecognized tax benefits net of potential benefits	23,700	26,600	28,200
Interest and penalties recognized as an expense	900	100	$ 900
Total accrued interest and penalties	2,400	3,300
Provision for income taxes
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net change in the total valuation allowance	500	1,200
Goodwill
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net change in the total valuation allowance		2,400
Other Comprehensive Income
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Net change in the total valuation allowance	1,600	(500)
Foreign Country
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Ireland subsidiaries additional tax credit carryforward for income tax	4,500	3,300
Additional operating loss carryforward	4,700
Other non-U.S subsidiaries operating loss carryforwards for income tax	77,200	70,100
Other non-U.S subsidiaries tax credit carryforwards for income tax	$ 4,800	$ 3,900
Ireland
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Irish statutory rate	12.50%
United States
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. Federal net operating loss carry forwards currently available for offset	$ 5,900
Alternative minimum tax credit carry forwards	400
Business credit carry forwards that are available to offset	300
United States \| Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Additional operating loss carryforward	24,966
U.S. federal net operating loss carry forwards	22,800
United States \| 2018 - 2020 \| Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. federal net operating loss carry forwards	11,800
United States \| 2021 - 2025 \| Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. federal net operating loss carry forwards	10,100
United States \| 2026 - 2035 \| Federal NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
U.S. federal net operating loss carry forwards	900
United States \| State NOL's
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Additional operating loss carryforward	$ 43,648

Consolidated Reported Provision for Income Taxes Differed from Statutory Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Taxes at Irish statutory rate of 12.5% (2016:12.5%; 2015:12.5%)	$ 41,007	$ 37,522	$ 34,856
Foreign and other income taxed at higher rates	6,324	4,642	4,614
Research & development tax incentives	(830)	(907)	(695)
Movement in valuation allowance	1,329	1,208	(4,133)
Effects of change in tax rates	925	576	(16)
Increase/(decrease) in unrecognized tax benefits	933	(1,521)	5,085
Impact of stock compensation	(9,917)	(4,121)	(3,468)
Impact of mandatory repatriation under US Tax Reform	7,694	0	0
Other	(896)	594	3,068
Provision for income taxes	$ 46,569	$ 37,993	$ 39,311
Irish statutory rate	12.50%	12.50%	12.50%

Tax Effects of Temporary Differences That Gives Rise to Significant Portions of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities:
Property, plant and equipment	$ 1,139	$ 979
Goodwill	22,655	26,617
Other intangible assets	11,801	6,700
Other	4,139	1,441
Total deferred tax liabilities recognized	39,734	35,737
Deferred tax assets:
Operating loss and tax credits carryforwards	24,962	22,705
Property, plant and equipment	4,062	3,121
Accrued expenses and payments on account	24,433	28,904
Stock compensation	5,786	13,062
Deferred compensation expense	2,548	3,327
Other	740	15
Total deferred tax assets	62,531	71,134
Valuation allowance for deferred tax assets	(22,439)	(20,337)	$ (17,200)
Deferred tax assets recognized	40,092	50,797
Overall net deferred tax asset	$ 358	$ 15,060

Expected Expiry Dates of NOI's (Detail) - United States $ in Thousands	Dec. 31, 2017 USD ($)
Federal NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	$ 24,966
Federal NOL's \| 2018
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	113
Federal NOL's \| 2021-2034
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	24,041
Federal NOL's \| 2035-2036
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	812
State NOL's
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	43,648
State NOL's \| 2018
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	0
State NOL's \| 2021-2034
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	14,945
State NOL's \| 2035-2036
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	$ 28,703

Reconciliation of Beginning and Ending Amount of Total Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at start of year	$ 26,620	$ 28,166	$ 23,201
Increase related to acquired tax positions	0	0	778
Increase related to prior year tax positions	0	1,151	1,482
Decrease related to prior year tax positions	(3,050)	(2,483)	(315)
Increase related to current year tax positions	4,765	1,104	3,063
Settlements	(2,523)	(837)	0
Lapse of statute of limitations	(2,092)	(481)	(43)
Unrecognized tax benefits at end of year	$ 23,720	$ 26,620	$ 28,166

Recognized Restructuring and Other Items, Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Restructuring charges	$ 7,753	$ 8,159	$ 0
Net charge	$ 7,753	$ 8,159	$ 0

Restructuring and Other Items - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 7,753	$ 8,159	$ 0
Restructuring reserve, current	3,200
Restructuring reserve, noncurrent	400
Resource Rationalizations 2017 \| Workforce Reductions
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 7,753
Resource Rationalizations 2016
Restructuring Cost and Reserve [Line Items]
Restructuring charges		8,159
Resource Rationalizations 2016 \| Workforce Reductions
Restructuring Cost and Reserve [Line Items]
Restructuring charges		6,190
Resource Rationalizations 2016 \| Onerous Lease
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 1,969
Resource Rationalizations 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 8,796
Resource Rationalizations 2015 \| Asset Impairment
Restructuring Cost and Reserve [Line Items]
Restructuring charges				5,629
Resource Rationalizations 2015 \| Onerous Lease
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 3,167

Restructuring Charges (Detail) - USD ($) $ in Thousands	12 Months Ended
Restructuring Charges (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restructuring Reserve [Roll Forward]
Restructuring charges	$ 7,753	$ 8,159	$ 0
Resource Rationalizations 2017 \| Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring charges	7,753
Utilized	(4,656)
Foreign exchange	0
Closing provision	3,097
Resource Rationalizations 2016
Restructuring Reserve [Roll Forward]
Closing provision	1,791
Restructuring charges		8,159
Utilized	(1,474)	(6,305)
Foreign exchange		(63)
Closing provision	317	1,791
Resource Rationalizations 2016 \| Workforce Reductions
Restructuring Reserve [Roll Forward]
Closing provision	393
Restructuring charges		6,190
Utilized	(393)	(5,734)
Foreign exchange		(63)
Closing provision	0	393
Resource Rationalizations 2016 \| Onerous Lease
Restructuring Reserve [Roll Forward]
Closing provision	1,398
Restructuring charges		1,969
Utilized	(1,081)	(571)
Foreign exchange		0
Closing provision	317	1,398
Resource Rationalizations 2015
Restructuring Reserve [Roll Forward]
Closing provision	641	2,000	3,167
Restructuring charges				$ 8,796
Asset write off				(5,629)
Utilized	(441)	(1,359)	(1,167)
Closing provision	200	641	2,000	3,167
Resource Rationalizations 2015 \| Onerous Lease
Restructuring Reserve [Roll Forward]
Closing provision	641	2,000	3,167
Restructuring charges				3,167
Asset write off				0
Utilized	(441)	(1,359)	(1,167)
Closing provision	200	641	2,000	3,167
Resource Rationalizations 2015 \| Asset Impairment
Restructuring Reserve [Roll Forward]
Closing provision	0	0	0
Restructuring charges				5,629
Asset write off				(5,629)
Utilized	0	0	0
Closing provision	$ 0	$ 0	$ 0	$ 0

Provision for Doubtful Debts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Opening provision	$ 9,450	$ 10,383
Amounts used during the year	(2,733)	(3,782)
Amounts provided during the year	5,116	4,651
Amounts released during the year	(3,106)	(1,814)
Foreign exchange	203	12
Closing provision	$ 8,930	$ 9,450

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Non-cancelable operating leases for facilities expiration period	10 years
Operating leases rental expense	$ 44.0	$ 44.0	$ 49.9

Future Minimum Rental Commitments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2018	$ 38,111
2019	32,575
2020	26,336
2021	19,079
2022	13,389
Thereafter	36,692
Total	$ 166,182

Distribution of Net Revenue by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net Revenue	$ 1,758,439	$ 1,666,487	$ 1,574,978
Ireland
Segment Reporting Information [Line Items]
Net Revenue	424,292	410,572	429,631
Rest of Europe
Segment Reporting Information [Line Items]
Net Revenue	337,105	313,185	330,487
U.S.
Segment Reporting Information [Line Items]
Net Revenue	791,543	763,821	650,941
Other
Segment Reporting Information [Line Items]
Net Revenue	$ 205,499	$ 178,909	$ 163,919

Distribution of Income from operations, including Restructuring, by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Income from operations	$ 338,338	$ 311,694	$ 281,536
Ireland
Segment Reporting Information [Line Items]
Income from operations	232,032	216,149	189,035
Rest of Europe
Segment Reporting Information [Line Items]
Income from operations	26,493	34,200	38,166
United States
Segment Reporting Information [Line Items]
Income from operations	58,322	41,348	45,320
Other
Segment Reporting Information [Line Items]
Income from operations	$ 21,491	$ 19,997	$ 9,015

Distribution of Income from operations, excluding Restructuring, by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	$ 346,091	$ 319,853	$ 281,536
Ireland
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	240,115	218,334	189,035
Rest of Europe
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	26,351	36,509	38,166
United States
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	58,164	44,590	45,320
Other
Segment Reporting Information [Line Items]
Income from operations, excluding restructuring and other items	$ 21,461	$ 20,420	$ 9,015

Distribution of Property, Plant and Equipment, Net, by Geographical Area (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 163,051	$ 148,967
Ireland
Segment Reporting Information [Line Items]
Property, plant and equipment, net	111,329	105,684
Rest of Europe
Segment Reporting Information [Line Items]
Property, plant and equipment, net	9,026	6,231
United States
Segment Reporting Information [Line Items]
Property, plant and equipment, net	27,797	29,428
Other
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 14,899	$ 7,624

Distribution of Depreciation and Amortization by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Depreciation and amortization	$ 61,297	$ 59,575	$ 57,677
Ireland
Segment Reporting Information [Line Items]
Depreciation and amortization	26,277	25,766	22,100
Rest of Europe
Segment Reporting Information [Line Items]
Depreciation and amortization	6,857	6,914	11,055
United States
Segment Reporting Information [Line Items]
Depreciation and amortization	24,246	23,462	20,106
Other
Segment Reporting Information [Line Items]
Depreciation and amortization	$ 3,917	$ 3,433	$ 4,416

Distribution of Total Assets by Geographical Area (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Assets	$ 2,146,618	$ 1,825,843
Ireland
Segment Reporting Information [Line Items]
Assets	880,378	766,120
Rest of Europe
Segment Reporting Information [Line Items]
Assets	504,418	337,062
United States
Segment Reporting Information [Line Items]
Assets	650,681	651,160
Other
Segment Reporting Information [Line Items]
Assets	$ 111,141	$ 71,501

Distribution of Capital Expenditure by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Capital expenditures	$ 44,717	$ 42,601	$ 49,730
Ireland
Segment Reporting Information [Line Items]
Capital expenditures	24,468	27,670	30,900
Rest of Europe
Segment Reporting Information [Line Items]
Capital expenditures	2,819	2,851	1,916
United States
Segment Reporting Information [Line Items]
Capital expenditures	11,027	8,432	15,256
Other
Segment Reporting Information [Line Items]
Capital expenditures	$ 6,403	$ 3,648	$ 1,658

Clients Representing Company's Net Revenue (Detail)	12 Months Ended
Clients Representing Company's Net Revenue (Detail)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Customer Concentration Risk \| Net Revenue \| Client A
Revenue, Major Customer [Line Items]
Clients which represented 10% or more of the company's net revenue	18.00%	26.00%	31.00%

Distribution of Interest Income by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Interest income	$ 2,346	$ 1,484	$ 1,306
Ireland
Segment Reporting Information [Line Items]
Interest income	1,084	407	102
Rest of Europe
Segment Reporting Information [Line Items]
Interest income	1,222	1,040	1,151
United States
Segment Reporting Information [Line Items]
Interest income	16	2	4
Other
Segment Reporting Information [Line Items]
Interest income	$ 24	$ 35	$ 49

Distribution of Income Tax Charge by Geographical Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Income tax charge	$ 46,569	$ 37,993	$ 39,311
Ireland
Segment Reporting Information [Line Items]
Income tax charge	20,345	24,215	21,795
Rest of Europe
Segment Reporting Information [Line Items]
Income tax charge	1,921	5,528	8,007
United States
Segment Reporting Information [Line Items]
Income tax charge	14,772	8,381	3,580
Other
Segment Reporting Information [Line Items]
Income tax charge	$ 9,531	$ (131)	$ 5,929

Supplemental Disclosure of Cash Flow Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest	$ 13,094	$ 13,615	$ 2,175
Cash paid for income taxes	$ 12,305	$ 10,205	$ 14,829

Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation adjustments	$ (36,188)	$ (70,154)
Currency impact on long term funding (Net of tax)	(182)	(13,912)
Actuarial loss on defined benefit pension plan (note 9)	(5,855)	(5,905)
Unrealized capital loss – investments (note 3)	(295)	(23)
Total	(38,713)	(86,300)
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Hedges	4,658	4,658
Amortization of interest rate hedge	(1,887)	(964)
Foreign Exchange Forward [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Hedges	$ 1,036	$ 0

Long-Term Debt - Senior Notes - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Nov. 30, 2015	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long term debt		$ 348,888	$ 348,888	$ 348,511
Cash proceeds from interest rate hedge			$ 0	$ 0	$ 4,658
Senior Notes
Debt Instrument [Line Items]
Long term debt					$ 350,000
Stated interest rate		3.64%	3.64%
Debt instrument, term		5 years	5 years
Interest rate hedge, inception date			Oct. 05, 2015
Cash proceeds from interest rate hedge	$ 4,600		$ 4,600

- Definition

The carrying value as of the balance sheet date of the noncurrent portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Impact of New Accounting Pronouncements Impact of New Accounting Pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Cumulative effect adjustment from adoption of ASU			$ 6,677
Retained Earnings
Cumulative effect adjustment from adoption of ASU			$ 6,677
Accounting Standards Update 2016-09 \| Retained Earnings
Cumulative effect adjustment from adoption of ASU		$ 6,700
Subsequent Event \| Minimum \| Accounting Standards Update 2014-09 \| Retained Earnings
Cumulative effect adjustment from adoption of ASU	$ 40,000
Subsequent Event \| Maximum \| Accounting Standards Update 2014-09 \| Retained Earnings
Cumulative effect adjustment from adoption of ASU	$ 80,000

Related Parties - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2016 USD ($)	Nov. 01, 2017 USD ($)
Subsidiaries \| DS Biopharma Limited
Related Party Transaction [Line Items]
Revenue earned from related parties	$ 743		$ 100
Amounts due from related parties	220
Mr. Thomas Lynch
Related Party Transaction [Line Items]
Related party transaction amounts \| €		€ 231,750
Amounts due to related parties	64
Mr. Ciaran Murray
Related Party Transaction [Line Items]
Expenses incurred from related Party	$ 178
Fair value of asset transferred to related party				$ 77

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events from the balance sheet date through February 28, 2018, the date at which the consolidated financial statements were available to be issued. The Company has determined that there are no items to disclose.

Business Segment and Geographical Information Business Segment and Geographical Information Narrative (Details)	12 Months Ended
	Dec. 31, 2017 segment
Segment Reporting [Abstract]
Number of Operating Segments	1

Year ended

December 31, 2017

December 31, 2016

December 31, 2015