Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Clinical Research Management Inc. Clinical Research Management, Inc. [Member] Clinical Research Management Inc. [Member] Finite-Lived Intangible Assets by Major Class Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Customer lists Customer Lists [Member] Order backlog Order or Production Backlog [Member] Brand Brand [Member] Brand [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Cash Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Property, plant and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Goodwill Goodwill Intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles Accounts receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Unbilled revenue Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Unbilled Revenue Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Unbilled Revenue Prepayments and other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets Accounts payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Other liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Non-current other liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Net assets acquired Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net Total consideration Business Combination, Consideration Transferred Restructuring and Related Activities [Abstract] Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Restructuring Program [Axis] Restructuring Program [Axis] Restructuring Program [Axis] Restructuring Program [Domain] Restructuring Program [Domain] Restructuring Program [Domain] Workforce Reduction Workforce Reduction [Member] Workforce Reduction [Member] Onerous Lease Onerous Lease [Member] Onerous Lease [Member] Restructuring Plan Restructuring Plan [Axis] Restructuring Plan [Domain] Restructuring Plan [Domain] Resource Rationalizations Resource Rationalizations [Member] Resource Rationalizations [Member] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Restructuring Reserve [Roll Forward] Restructuring Reserve [Roll Forward] Beginning provision Restructuring Reserve Total provision recognized Restructuring Charges Utilized Restructuring Reserve Utilizations Restructuring Reserve Utilizations Foreign exchange Restructuring Reserve, Foreign Currency Translation Gain (Loss) Closing provision Revenue from Contract with Customer [Abstract] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Top client Top Client [Member] Top Client [Member] Clients 2-5 Clients 2-5 [Member] Clients 2-5 [Member] Clients 6-10 Clients 6-10 [Member] Clients 6-10 [Member] Clients 11-25 Clients 11-25 [Member] Clients 11-25 [Member] Other Other Customers [Member] Other Customers [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Revenue Revenue from Contract with Customer, Excluding Assessed Tax Accounting Policies [Abstract] New Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Earnings Per Share [Abstract] Weighted average number of ordinary shares outstanding for basic net income per ordinary share (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive share options outstanding (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Weighted average number of ordinary shares outstanding for diluted net income per ordinary share (in shares) Weighted Average Number of Shares Outstanding, Diluted Subsequent Events [Abstract] Mapi Group [Member] Mapi Group [Member] Mapi group. Other receivables Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Other Receivables Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Other Receivables Income taxes receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Income Taxes Receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Income Taxes Receivable Payments on account Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Payments on Account Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Payments on Account Non-current deferred tax liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent Cash outflows Payments to Acquire Businesses, Gross Working capital adjustment Business Acquisition Purchase Price Allocation To Working Capital Increase (Decrease) Business Acquisition Purchase Price Allocation To Working Capital Increase (Decrease) Income Tax Disclosure [Abstract] Provision for income taxes Income Tax Expense Benefit Before Restructuring And Other Items Income Tax Expense Benefit Before Restructuring And Other Items Tax impact of restructuring and other items Other Tax Expense (Benefit) Tax impact of restructuring and other items Income Tax Expense (Benefit) Segment Reporting [Abstract] Number of operating segments Number of Operating Segments Contracts Receivable [Abstract] Trade accounts receivable, unbilled services and payments on account Revenue from Contract with Customer [Text Block] Segment Reporting Disclosure Segment Reporting Disclosure [Text Block] Statement of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Net income Net Income (Loss) Attributable to Parent Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Loss on disposal of property, plant and equipment Gain (Loss) on Disposition of Property Plant Equipment Depreciation expense Depreciation Amortization of intangibles Amortization of Intangible Assets Amortization of government grants Recovery of Amortization of Government Grants Amortization of Government Grants. Interest on short term investments Accrued Interest On Short Term Bank Deposits Accrued Interest On Short Term Bank Deposits Stock compensation expense Share-based Compensation Amortization of gain on interest rate hedge Amortization Of Gain On Interest Rate Hedge Amortization Of Gain On Interest Rate Hedge Amortization of financing costs Amortization of Debt Issuance Costs Deferred taxes Deferred Income Taxes and Tax Credits Changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] (Increase)/decrease in accounts receivable Increase (Decrease) in Accounts Receivable Increase in unbilled revenue Increase (Decrease) in Contract with Customer, Asset Increase (Decrease) in Contract with Customer, Asset Increase in other receivables Increase (Decrease) in Other Receivables Decrease/(increase) in prepayments and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Increase in other non-current assets Increase (Decrease) in Other Noncurrent Assets Increase/(decrease) in payments on account Increase (Decrease) In Contract With Customer Liability Increase (Decrease) In Contract With Customer Liability Decrease in other current liabilities Increase (Decrease) in Other Current Liabilities Decrease in other non-current liabilities Increase (Decrease) in Other Noncurrent Liabilities (Decrease)/increase in income taxes payable Increase (Decrease) in Income Taxes Payable Decrease in accounts payable Increase (Decrease) in Accounts Payable Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Purchase of property, plant and equipment Payments to Acquire Property, Plant, and Equipment Purchase of subsidiary undertakings Purchase of short term investments Payments to Acquire Short-term Investments Sale of short term investments Proceeds from Sale of Short-term Investments Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Financing costs Payments of Financing Costs Proceeds from exercise of equity compensation Proceeds from Stock Options Exercised Share issue costs Payments of Stock Issuance Costs Repurchase of ordinary shares Payments for Repurchase of Common Stock Share repurchase costs Payments for Share Repurchase Costs Payments for Share Repurchase Costs Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Effect of exchange rate movements on cash Effect of Exchange Rate on Cash and Cash Equivalents Net increase in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Initial Application Period Cumulative Effect Transition [Table] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Initial Application Period Cumulative Effect Transition [Domain] Difference between Revenue Guidance in Effect before and after Topic 606 Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Calculated under Revenue Guidance in Effect before Topic 606 Calculated under Revenue Guidance in Effect before Topic 606 [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Cash flows from operating activities [Abstract] Net Cash Provided by (Used in) Operating Activities [Abstract] Loss on disposal of property, plant and equipment Depreciation expense Amortization of government grants Interest on short term investments Stock compensation expense Amortization of financing costs Deferred taxes Increase in accounts receivable Increase (Decrease) in Contract with Customer, Asset Increase in unbilled revenue Increase (Decrease) in Unbilled Receivables (Increase)/decrease in other receivables Decrease in prepayments and other current assets Increase in other non-current assets Decrease in income taxes payable Cash flows from investing activities [Abstract] Net Cash Provided by (Used in) Investing Activities [Abstract] Purchase of property, plant and equipment Purchase of subsidiary undertakings Purchase of short term investments Sale of short term investments Cash flows from financing activities [Abstract] Net Cash Provided by (Used in) Financing Activities [Abstract] Share issue costs Repurchase of ordinary shares Share repurchase costs Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock [Member] Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Other Undenominated Capital Other Undenominated Capital [Member] Other undenominated capital. AOCI Attributable to Parent [Member] AOCI Attributable to Parent [Member] Retained Earnings [Member] Retained Earnings [Member] Ordinary shares, shares issued (in shares) Common Stock, Shares, Issued Beginning balance Stockholders' Equity Attributable to Parent Currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Currency impact of long term funding Other Comprehensive Income Foreign Currency Transaction And Translation Adjustment, Before Tax, Long Term Funding Adjustment that results from the process of translating the impact of long-term funding into the functional currency of the reporting entity. Tax on currency impact of long term funding Other Comprehensive Income Foreign Currency Transaction And Translation Adjustment Long Term Funding Tax Tax impact on the adjustment that results from the process of translating the impact of long-term funding into the functional currency of the reporting entity. Unrealized capital gain – investments Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Amortization of interest rate hedge Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Fair value of cash flow hedge Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Total comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Exercise of share options (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Exercise of share options Stock Issued During Period, Value, Stock Options Exercised Issue of restricted share units (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Issue of restricted share units Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Non-cash stock compensation expense Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Share issuance costs Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Share repurchase program (in shares) Stock Repurchased and Retired During Period, Shares Share repurchase program Stock Repurchased and Retired During Period, Value Share repurchase costs Adjustment to Retained Earning Share Repurchase costs Adjustment to Retained Earning Share Repurchase costs Ending balance Business Combinations Business Combination Disclosure [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Share-based Awards Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Ordinary Shares Accumulated Other Comprehensive Income (Loss) Retained Earnings Statement [Line Items] Statement [Line Items] Balance (in shares) Cumulative effect adjustment from adoption of ASC 606 Cumulative Effect of New Accounting Principle in Period of Adoption Currency translation adjustment Currency impact of long term funding (net of tax) Unrealized capital gain – investments Fair value of cash flow hedge (net of tax) Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax Exercise of share options Issue of restricted share units Non-cash stock compensation expense Share issuance costs Share repurchase program Share repurchase costs Balance (in shares) Significant Accounting Policies Significant Accounting Policies [Text Block] Income Taxes Income Tax Disclosure [Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Geographical Geographical [Axis] Geographical [Domain] Geographical [Domain] Ireland IRELAND Rest of Europe Rest Of Europe [Member] Rest Of Europe [Member] U.S. UNITED STATES Rest of World Rest of World [Member] Rest of World [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Revenue Contracts Revenue Schedule of summary of recognized identified assets acquired and liabilities assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Assets Assets Schedule of components of income tax expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule of share option activity Share-based Compensation, Stock Options, Activity [Table Text Block] Schedule of movement in non-vested share options Schedule of Nonvested Share Activity [Table Text Block] Schedule of weighted average fair values and assumptions used Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of RSU and PSU activity Schedule Of Share Based Compensation Restricted Stock Units Performance Stock Units Award Activity [Table Text Block] Schedule Of Share Based Compensation Restricted Stock Units Performance Stock Units Award Activity [Table Text Block] Schedule of non-cash stock compensation expense Schedule of Non Cash Stock Compensation Expense [Table Text Block] Schedule of Non Cash Stock Compensation Expense. Schedule of New Accounting Pronouncements and Changes in Accounting Principles Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Goodwill and Intangible Assets Disclosure [Abstract] Goodwill [Roll Forward] Goodwill [Roll Forward] Opening balance Current period acquisitions (Note 6) Goodwill, Acquired During Period Prior period acquisitions (Note 6) Goodwill, Purchase Accounting Adjustments Foreign exchange movement Goodwill, Foreign Currency Translation Gain (Loss) Closing balance Equity [Abstract] Share Capital Stockholders' Equity Note Disclosure [Text Block] Reconciliation of Number of Shares Used in Computation of Basic and Diluted Net Income Per Ordinary Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Net income per ordinary share Earnings Per Share [Text Block] Impact fo change in accounting policy New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Current Assets: Assets, Current [Abstract] Cash and cash equivalents Short term investments - available for sale Available-for-sale Securities, Debt Securities, Current Accounts receivable, net Accounts Receivable, Net, Current Unbilled revenue Unbilled Contracts Receivable Other receivables Nontrade Receivables, Current Prepayments and other current assets Prepaid Expense and Other Assets, Current Income taxes receivable Income Taxes Receivable, Current Total current assets Assets, Current Other Assets: Assets, Noncurrent [Abstract] Property, plant and equipment, net Property, Plant and Equipment, Net Other non-current assets Other Assets, Noncurrent Non-current income taxes receivable Income Taxes Receivable, Noncurrent Non-current deferred tax asset Deferred Income Tax Assets, Net Intangible assets Finite-Lived Intangible Assets, Net Total Assets LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities and Equity [Abstract] Current Liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Payments on account Contract with Customer, Liability, Current Other liabilities Other Liabilities, Current Income taxes payable Accrued Income Taxes, Current Total current liabilities Liabilities, Current Other Liabilities: Liabilities, Noncurrent [Abstract] Non-current bank credit lines and loan facilities Long-term Line of Credit, Noncurrent Non-current other liabilities Other Liabilities, Noncurrent Non-current government grants Capital Government Grants Noncurrent Noncurrent capital government grants, which are amortized and recognized in earnings over the grant period. Non-current income taxes payable Accrued Income Taxes, Noncurrent Non-current deferred tax liability Deferred Income Tax Liabilities, Net Commitments and contingencies Commitments and Contingencies Total Liabilities Liabilities Shareholders' Equity: Stockholders' Equity Attributable to Parent [Abstract] Ordinary shares Common Stock, Value, Issued Additional paid‑in capital Additional Paid in Capital, Common Stock Other undenominated capital Other Undenominated Capital Other undenominated capital. Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total Shareholders' Equity Total Liabilities and Shareholders' Equity Liabilities and Equity Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Performance Share Unit (PSUs) Performance Share Unit [Member] Performance Share Unit [Member] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Outstanding Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Outstanding at beginning of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Shares vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Outstanding at ending of period (in share) Weighted Average Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Outstanding at beginning of period (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Shares vested (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Forfeited (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Outstanding at end of period (USD per share) Weighted Average Remaining Contractual Life Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Outstanding at end of period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms Compensation Related Costs Share Based Payments Disclosure [Table] Compensation Related Costs Share Based Payments Disclosure [Table] Compensation Related Costs Share Based Payments Disclosure [Table] PSUs Based on Service and EPS Targets Performance Based Grants [Member] Performance Based Grants [Member] Employee Stock Plan, 2008 Plan Employee Stock Plan, 2008 Plan [Member] Employee Stock Plan, 2008 Plan [Member] Employee Stock Plan, 2003 Plan Employee Stock Plan, 2003 Plan [Member] Employee Stock Plan, 2003 Plan [Member] Employee Stock Option Employee Stock Option [Member] Restricted Stock Units 2008 Restricted Stock Units Twenty Zero Eight [Member] Restricted Stock Units Twenty Zero Eight [Member] Restricted Stock Units 2013 Restricted Stock Units Twenty Thirteen [Member] Restricted Stock Units Twenty Thirteen [Member] Range Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Plan Name Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Individual Employee Employee [Member] Employee [Member] Compensation Related Costs Share Based Payments Disclosure [Line Items] Compensation Related Costs Share Based Payments Disclosure [Line Items] Compensation Related Costs Share Based Payments Disclosure [Line Items] Additional number of ordinary shares which have been reserved for issuance Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Ordinary shares which have been reserved for issuance Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Limit of shares issued or to be issued pursuant to options granted Limit of Shares Issued or To Be Issued Pursuant to Options Granted Limit of Shares Issued or To Be Issued Pursuant to Options Granted Percentage of option price for fair value of ordinary share Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent Maximum number of award as percentage of shares outstanding Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Outstanding Stock Maximum Shares vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Shares expiration period Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Weighted average contractual term of options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Options outstanding fair value Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Option Price Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Option Price Weighted average fair value per option Share Based Compensation Arrangement by Share Based Payment Award, Options, Grants in Period, Weighted Average Option Price Share Based Compensation Arrangement by Share Based Payment Award, Options, Grants in Period, Weighted Average Option Price Exercisable - number of shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Exercisable - weighted average remaining contractual life Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Exercisable - weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Fully vested total intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Intrinsic value of option exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Fair value of stock units vested Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Stock units granted Stock units to be granted Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Cumulative EPS vesting period Share Based Compensation Arrangement by Share Based Payment Award Other Than Options Expected Vesting Period Share Based Compensation Arrangement by Share Based Payment Award Other Than Options Expected Vesting Period Non-cash stock compensation expense not yet recognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Unrecognized stock-based compensation expense, weighted average period (years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Revenues [Abstract] Revenues [Abstract] Revenue Revenue from Contract with Customer, Excluding Assessed Tax, Gross Revenue from Contract with Customer, Excluding Assessed Tax, Gross Reimbursable expenses Revenue from Contract with Customer, Excluding Assessed Tax, Reimbursable Expenses Revenue from Contract with Customer, Excluding Assessed Tax, Reimbursable Expenses Total Revenue Costs and expenses [Abstract] Operating Expenses [Abstract] Direct costs Direct Operating Costs Direct Costs, Reimbursable Expenses Direct Costs, Reimbursable Expenses Direct Costs, Reimbursable Expenses Direct Costs, Other Direct Costs, Other Direct Costs, Other Selling, general and administrative expense Selling, General and Administrative Expense Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Restructuring charges Total costs and expenses Costs and Expenses Income from operations Operating Income (Loss) Interest income Investment Income, Interest Interest expense Interest Expense, Debt Income before provision for income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Provision for income taxes Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Table] Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Table] Tax Period [Axis] Tax Period [Axis] Tax Period [Domain] Tax Period [Domain] Earliest Tax Year Earliest Tax Year [Member] Latest Tax Year Latest Tax Year [Member] Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] Liability for unrecognized tax benefit Unrecognized Tax Benefits Items generating unrecognized tax benefits Unrecognized Tax Benefits, Current Year Tax Positions Unrecognized Tax Benefits, Current Year Tax Positions Interest and related penalties Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued Tax year subject to examination by major tax jurisdictions Open Tax Year Weighted average grant date fair value Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Assumptions: Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Expected life Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Class of Treasury Stock [Table] Class of Treasury Stock [Table] Share Repurchase Program Share Repurchase Program [Axis] Share Repurchase Program [Domain] Share Repurchase Program [Domain] Buyback Program Buyback Program [Member] Buyback Program [Member] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Stock repurchase program, authorized amount Stock Repurchase Program, Authorized Amount Share repurchase program, authorized percentage Stock Repurchase Program Authorized Percentage Stock Repurchase Program Authorized Percentage Ordinary shares repurchased Treasury Stock, Shares, Acquired Ordinary shares repurchased, value Treasury Stock, Value, Acquired, Cost Method Schedule of Contracts with Customers, Asset and Liabilities Contract with Customer, Asset and Liability [Table Text Block] Goodwill Goodwill Disclosure [Text Block] Schedule of Goodwill Schedule of Goodwill [Table Text Block] Billed services (accounts receivable) Billed Contracts Receivable Trade accounts receivable and unbilled revenue Contracts Receivable, Gross Contracts Receivable Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Trade accounts receivable and unbilled revenue, net Contracts Receivable, Net Contracts Receivable, Net Unearned revenue (payments on account) Contract with Customer, Liability Change in unbilled receivables Change in Unbilled Receivables Change in Unbilled Receivables Change in unbilled receivables, percent Change in Unbilled Receivables, Percent Change in Unbilled Receivables, Percent Change in customer advances and deposits Change in Customer Advances and Deposits Change in Customer Advances and Deposits Change in customer advances and deposits, percent Change in Customer Advances and Deposits, Percent Change in Customer Advances and Deposits, Percent Net balance Advance Payments Netted Against Unbilled Contracts Receivable Advance Payments Netted Against Unbilled Contracts Receivable Change in advance payments netted against unbilled contracts receivable Change in Advance Payments Netted Against Unbilled Contracts Receivable Change in Advance Payments Netted Against Unbilled Contracts Receivable Change in advance payments netted against unbilled contracts receivable, percent Change in Advance Payments Netted Against Unbilled Contracts Receivable, Percent Change in Advance Payments Netted Against Unbilled Contracts Receivable, Percent Distribution of Net Revenue by Geographical Area Revenue from External Customers by Geographic Areas [Table Text Block] Distribution of Income from Operations by Geographical Area Operating Income by Geography [Table Text Block] Operating Income by Geography. Distribution of Property, Plant and Equipment, Net, by Geographical Area Long-lived Assets by Geographic Areas [Table Text Block] Distribution of Depreciation and Amortization by Geographical Area Schedule Of Depreciation And Amortization Expense By Geographical Area [Table Text Block] Schedule Of Depreciation And Amortization Expense By Geographical Area. Distribution of Total Assets by Geographical Area Reconciliation of Assets from Segment to Consolidated [Table Text Block] Income Statement [Abstract] Revenue: Costs and expenses: Cost of Revenue [Abstract] Selling, general and administrative expense Depreciation and amortization Restructuring Interest income Interest expense Provision for income taxes Net income Net income per Ordinary Share: Basic (USD per share) Earnings Per Share, Basic Diluted (USD per share) Earnings Per Share, Diluted Weighted average number of Ordinary Shares outstanding: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Diluted (in shares) Ordinary shares, par value (in EUR per share) Common Stock, Par or Stated Value Per Share Ordinary shares, shares authorized (in shares) Common Stock, Shares Authorized Ordinary shares, shares outstanding (in shares) Common Stock, Shares, Outstanding Options Outstanding Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward] Beginning Balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares Ending Balance (in shares) Weighted Average Exercise Price Share Based Compensation Arrangement By Share Based Payment Award Nonvested Options Outstanding Exercise Price Abstract Share Based Compensation Arrangement By Share Based Payment Award Nonvested Options Outstanding Exercise Price Abstract Beginning balance (USD per share) Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Outstanding Weighted Average Exercise Price Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Outstanding Weighted Average Exercise Price Granted (USD per share) Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Granted in Period Weighted Average Exercise Price Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Granted in Period Weighted Average Exercise Price Vested (USD per share) Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Vested in Period Weighted Average Exercise Price Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Vested in Period Weighted Average Exercise Price Forfeited (USD per share) Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Forfeited in Period Weighted Average Exercise Price Share Based Compensation Arrangement by Share Based Payment Award, Nonvested Options, Forfeited in Period Weighted Average Exercise Price Ending balance (USD per share) Weighted Average Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Beginning Balance (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value Granted (USD per share) Vested (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value Forfeited (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Weighted Average Grant Date Fair Value Ending Balance (USD per share) Income from operations Income from operations excluding restructuring Operating Income (Loss) Excluding Restructuring Operating Income (Loss) Excluding Restructuring Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Direct costs Cost of Sales [Member] Selling, general and administrative Selling, General and Administrative Expenses [Member] Prior period workforce reduction Prior period workforce reduction [Member] Prior period workforce reduction [Member] Workforce Reduction Onerous Lease Utilization Short term investments - available for sale Accounts receivable, net Unbilled revenue Other receivables Income taxes receivable Other non-current assets Intangible assets Accounts payable Other liabilities Income taxes payable Non-current bank credit lines and loan facilities Non-current government grants Shareholders' Equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Common Stock, Value, Issued Accumulated other comprehensive income Retained earnings Options Outstanding Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Outstanding at beginning of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (in shares) Exercised (in shares) Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Outstanding at end of period (in shares) Exercisable at end of period Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Outstanding at beginning of period (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted (USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Exercised (USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Forfeited (USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Outstanding at end of period (USD per share) Exercisable at end of period (USD per share) Weighted Average Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Grant Date Fair Value [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Grant Date Fair Value [Abstract] Outstanding at beginning of period (USD per share) Share Based Compensation Arrangement by Share Based Payment Award, Options, Weighted Average Grant Date Fair Value Share Based Compensation Arrangement by Share Based Payment Award, Options, Weighted Average Grant Date Fair Value Exercised (USD per share) Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Weighted Average Grant Date Fair Value Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Weighted Average Grant Date Fair Value Forfeited (USD per share) Share Based Compensation Arrangement by Share Based Payment Award, Forfeited in Period, Weighted Average Grant Date Fair Value Share Based Compensation Arrangement by Share Based Payment Award, Forfeited in Period, Weighted Average Grant Date Fair Value Outstanding at end of period (USD per share) Exercisable at end of period (USD per share) Share Based Compensation Arrangement by Share Based Payment Award, Options, Exercisable, Weighted Average Grant Date Fair Value Share Based Compensation Arrangement by Share Based Payment Award, Options, Exercisable, Weighted Average Grant Date Fair Value Weighted Average Remaining Contractual Life Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Remaining Contractual Term [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Remaining Contractual Term [Abstract] Outstanding at end of period Exercisable at end of period Restructuring Restructuring and Related Activities Disclosure [Text Block] Revenue, remaining performance obligation Revenue, Remaining Performance Obligation Revenue, remaining performance obligation, percent Revenue, Remaining Performance Obligation, Percent Revenue, Remaining Performance Obligation, Percent Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Restructuring Charges Restructuring and Related Costs [Table Text Block] Details of Movement in Restructuring Provisions Recognized Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Revenue Asset Impairment Asset Impairment [Member] Asset Impairment [Member] Restructuring Plan [Axis] Manchester Facility Manchester Facility [Member] Manchester Facility [Member] Asset write off Asset Impairment Charges Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Current Liabilities Other Current Liabilities [Member] Other Noncurrent Liabilities Other Noncurrent Liabilities [Member] Restructuring Plan [Axis] Resource Rationalizations Asset impairment charges Restructuring reserve, current Restructuring Reserve, Current Restructuring reserve, noncurrent Restructuring Reserve, Noncurrent Restructuring Reserve Business Acquisition [Axis] Income Statement Location [Axis] Selling, General and Administrative Expenses [Member] Cash outflows on acquisition Payments to Acquire Businesses, Net of Cash Acquired Estimate of intangible assets acquired Certain payments made on behalf of business acquired Business Combination, Consideration Transferred, Liabilities Incurred Contingent consideration Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High Fair value of contingent consideration liability Business Combination, Contingent Consideration, Liability Contingent consideration recorded in SG&A costs Business Combination, Acquisition Related Costs Fair value adjustments made to unbilled revenue Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Unbilled Revenue Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Unbilled Revenue Fair value adjustments made to other liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities, Other Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities, Other Fair value adjustments made to AR acquired Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Receivables Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Receivables Fair value of adjustments made to accounts payable Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Payable Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Payable Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block]