Deferred tax assets Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Customer [Domain] Customer [Domain] Percentage change in unbilled services (unbilled revenue) Increase (Decrease) In Contract with Customer, Asset, Gross, Current, Percent Increase (Decrease) In Contract with Customer, Asset, Gross, Current, Percent Shares vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period PSUs Based on Service and EPS Targets Performance Based Grants [Member] Performance Based Grants [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Net (loss) income attributable to the Group Net (loss)/income attributable to the Group Net income (loss) Net Income (Loss) Attributable to Parent Operating right-of-use assets Operating Lease, Right-of-Use Asset Schedule of Business Acquisitions, by Acquisition Schedule of Business Acquisitions, by Acquisition [Table Text Block] Available for sale investments Debt Securities, Available-for-sale, Current Income Statement Location [Axis] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line Income Statement Location [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Goodwill Goodwill Disclosure [Text Block] Transaction and integration-related expenses Business Combination, Acquisition Related Costs Schedule of Maturities of Long-term Debt Schedule of Maturities of Long-term Debt [Table Text Block] Unbilled revenue Increase (Decrease) in Contract with Customer, Asset Customer A Customer A [Member] Customer A 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 Variable Rate Component [Axis] Variable Rate Component [Axis] Variable Rate Component Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Schedule of Contracts with Customers, Asset and Liabilities Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Additional paid-in capital Additional Paid in Capital, Common Stock Accrued expenses and other current liabilities Other liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Restructuring Type [Axis] Restructuring Type [Axis] Weighted average remaining lease term Operating Lease, Weighted Average Remaining Lease Term Other non-current assets Other Assets, Noncurrent Share repurchase costs Adjustment to Retained Earning Share Repurchase costs Adjustment to Retained Earning Share Repurchase costs Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of 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Recognition Entity number of employees Entity Number of Employees Prior period acquisitions Goodwill, Purchase Accounting Adjustments Canceled/expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period 2021 (remaining) Long-Term Debt, Maturity, Remainder of Fiscal Year Document fiscal year focus Document Fiscal Year Focus Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Non-current deferred tax liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Details of movement in restructuring charge Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Financing related costs Payments of Financing Costs Weighted average discount rate Operating Lease, Weighted Average Discount Rate, Percent Net income of acquiree since acquisition date Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Diluted shares adjustment if in profit position (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment If In Profit Position Weighted Average Number Diluted Shares Outstanding Adjustment If In Profit Position 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 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 Business Acquisition [Axis] Business Acquisition [Axis] Title of Individual [Domain] Title of Individual [Domain] Award Type [Domain] Award Type [Domain] Share Repurchase Program [Domain] Share Repurchase Program [Domain] Credit Facility [Domain] Credit Facility [Domain] ASSETS Assets [Abstract] 2024 Long-Term Debt, Maturity, Year Three Fair value, nonrecurring Fair Value, Nonrecurring [Member] Exercisable at end of period (in shares) Exercisable - number of shares (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Accumulated impairment loss Goodwill, Impaired, Accumulated Impairment Loss Other liabilities Other Liabilities [Member] Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Customer concentration risk Concentration Risk, Percentage Outstanding at beginning of period (in shares) Outstanding at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Trade names & brands Trade names Trade Names [Member] Retained Earnings Retained Earnings [Member] Debt Instrument [Axis] Debt Instrument [Axis] Unearned revenue Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Contract With Customer, Liability, Current Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Contract With Customer, Liability, Current Other Liabilities: Liabilities, Noncurrent [Abstract] Senior Secured Notes Senior Secured Notes [Member] Senior Secured Notes Share repurchase program Share repurchase program Stock Repurchased and Retired During Period, Value Secured debt Secured Debt [Member] Accounts receivable Increase (Decrease) in Accounts Receivable Right-of-use assets obtained in exchange for lease obligations Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Business Acquisition, Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Senior Secured Notes Senior Subordinated Notes [Member] Other non-current liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Tax impact of restructuring Other Tax Expense (Benefit) Unearned revenue Increase (Decrease) in Deferred Revenue Working capital adjustment paid Business Combination, Consideration Transferred, Working Capital Adjustments Business Combination, Consideration Transferred, Working Capital Adjustments Unearned revenue Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deferred Revenue Number of operating segments Number of Operating Segments Basic (USD per share) Earnings Per Share, Basic Year 3 Lessee, Operating Lease, Liability, to be Paid, Year Three Revenue Accounts receivable, unbilled revenue (contract assets) and unearned revenue or payments on account (contract liabilities) Revenue from Contract with Customer [Text Block] Income from sub-leases Sublease Income Outstanding at beginning of period (in shares) Outstanding at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Foreign exchange movement Restructuring Reserve, Foreign Currency Translation Gain (Loss) Document type Document Type 2022 Long-Term Debt, Maturity, Year One Deferred financing cost Deferred Costs Interest expense Interest Expense, Debt Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Percentage change in net balance Change in Advance Payments Netted Against Unbilled Contracts Receivable, Percent Change in Advance Payments Netted Against Unbilled Contracts Receivable, Percent Outstanding Number of Shares Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Intangible assets, net Estimated Fair Value Customer relationships/ Order backlog Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles Compensation Related Costs Share Based Payments Disclosure [Table] Compensation Related Costs Share Based Payments Disclosure [Table] Compensation Related Costs Share Based Payments Disclosure [Table] Ordinary shares which have been reserved for issuance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Other non-cash items Other Noncash Income (Expense) Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Non-current government grants Capital Government Grants Noncurrent Noncurrent capital government grants, which are amortized and recognized in earnings over the grant period. 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Net income per ordinary share Earnings Per Share [Text Block] Non-current lease liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Operating Lease Liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Operating Lease Liability Impairment of right-of-use assets Operating Lease, Impairment Loss Equity method investment, ownership percentage Equity Method Investment, Ownership Percentage Exercise of share options Stock Issued During Period, Value, Stock Options Exercised Minimum Minimum [Member] Basis of presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Replacement share-based awards issued to acquiree employees Fair value of replacement share-based awards issued to acquiree employees Shares Issued, Shares, Share-Based Payment Arrangement, Acquisitions Shares Issued, Shares, Share-Based Payment Arrangement, Acquisitions Income taxes receivable Income Taxes Receivable, Current Other assets and liabilities Increase (Decrease) in Other Operating Assets and Liabilities, Net Assumed through business combinations (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Assumed Through Business Combination, Share-based Compensation Arrangement by Share-based Payment Award, Options, Assumed Through Business Combination, Year 2 Lessee, Operating Lease, Liability, to be Paid, Year Two Effect of exchange rate movements on cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Balance Sheet Location [Domain] Balance Sheet Location [Domain] Loss on issuance of debt Gain (Loss) On Issuance Of Debt Gain (Loss) On Issuance Of Debt Selling, general and administrative expense Selling, General and Administrative Expense Canceled/expired (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Less debt issuance costs and debt discount Debt Issuance Costs, Net Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Reclassification Reclassification, Comparability Adjustment [Policy Text Block] Liability for unrecognized tax benefit Unrecognized Tax Benefits Opening provision Ending provision Provision balance Restructuring Reserve Percentage of share capital acquired Business Acquisition, Percentage of Voting Interests Acquired (Loss) income before share of earnings from equity method investments Income (Loss) from Continuing Operations before Equity Method Investments, Noncontrolling Interest Income (Loss) from Continuing Operations before Equity Method Investments, Noncontrolling Interest Non-current deferred tax asset Deferred Income Tax Assets, Net Issue of shares associated with a business combination Stock Issued During Period, Value, Acquisitions Current Liabilities: Liabilities, Current [Abstract] Exercisable at end of period (USD per share) Exercisable - weighted average exercise price (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Schedule of Components of Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Line of credit Line of Credit [Member] Share-based awards Share-based Payment Arrangement [Text Block] 2020 Senior Notes Senior Notes [Member] Fair value, inputs, level 3 Fair Value, Inputs, Level 3 [Member] 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. Interest and related penalties Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued Accounting Policies [Abstract] Accounting Policies [Abstract] Outstanding at end of period Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Share issue costs Payments of Stock Issuance Costs Clients 1-5 Clients 1-5 [Member] Clients 2-5 [Member] Costs and expenses: Cost of Revenue [Abstract] Other assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Total Operating Lease, Liability Beginning balance Ending balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Variable rate floor percentage Debt Instrument, Basis Spread on Variable Rate, Variable Rate Floor Debt Instrument, Basis Spread on Variable Rate, Variable Rate Floor Ordinary shares, par value 6 euro cents per share; 100,000,000 shares authorized, 52,958,063 shares issued and outstanding at June 30, 2021 and 52,788,093 shares issued and outstanding at December 31, 2020 Common Stock, Value, Issued Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Outstanding at beginning of period (USD per share) Outstanding at end 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 Customer concentration risk Customer Concentration Risk [Member] Current period acquisitions (Note 7) Goodwill, Acquired During Period Commitments and contingencies Commitments and Contingencies Operating leases Lessee, Operating Leases [Text Block] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Class of Treasury Stock [Table] Class of Treasury Stock [Table] Non-current income taxes payable Accrued Income Taxes, Noncurrent Business combinations Business Combination Disclosure [Text Block] Schedule of Weighted Average Fair Values and Assumptions Used Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Net balance Advance Payments Netted Against Unbilled Contracts Receivable Advance Payments Netted Against Unbilled Contracts Receivable Share repurchase program, authorized percentage Stock Repurchase Program Authorized Percentage Stock Repurchase Program Authorized Percentage Amortization of interest rate hedge Other Comprehensive Income (Loss), Cash Flow Hedge, Adjustment, Amortization, After Tax Other Comprehensive Income (Loss), Cash Flow Hedge, Adjustment, Amortization, After Tax Document period end date Document Period End Date Other receivables Nontrade Receivables, Current Total costs and expenses Costs and Expenses Distribution of Revenue by Geographical Area Revenue from External Customers by Geographic Areas [Table Text Block] Net income/(loss) Business Acquisition, Pro Forma Net Income (Loss) Entity registrant name Entity Registrant Name Lease imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Equity method investment, period majority voting share capital can be sold to the company Equity Method Investment, Period Majority Voting Share Capital Can Be Sold To The Company Equity Method Investment, Period Majority Voting Share Capital Can Be Sold To The Company Prepayments and other current assets Prepaid Expense and Other Assets, Current Selling, general and administration costs Selling, general and administrative Selling, General and Administrative Expenses [Member] Revenue Revenue from Contract with Customer, Excluding Assessed Tax Employee Stock Option Share-based Payment Arrangement, Option [Member] Share issuance costs Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Equity [Abstract] Equity [Abstract] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Utilization Payments for Restructuring Ordinary Shares Common Stock [Member] Interest income Investment Income, Interest Variable Rate [Axis] Variable Rate [Axis] Business segment information Segment Reporting Disclosure [Text Block] Income from operations Income from operations, including restructuring Operating Income (Loss) Purchase of investments in equity - long term Payments to Acquire Long-term Investments Number of tranches Issue Of Senior Notes, Number Of Tranches Issue Of Senior Notes, Number Of Tranches Operating lease liabilities Operating Lease, Liability, Current Noncontrolling interest adjustment to redemption amount Temporary Equity, Accretion to Redemption Value, Adjustment Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Stock compensation expense Share-based Payment Arrangement, Noncash Expense Variable Rate [Domain] Variable Rate [Domain] Restructuring Restructuring and Related Activities Disclosure [Text Block] Additional Paid-in Capital Additional Paid-in Capital [Member] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Technology assets Technology-Based Intangible Assets [Member] Variable rate component two Variable Rate Component Two [Member] Variable Rate Component Two Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Goodwill at fair value Goodwill, Fair Value Disclosure Revenue of acquiree since acquisition date Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Customer B Customer B [Member] Customer B Other undenominated capital Other Undenominated Capital Other undenominated capital. Unbilled revenue Unbilled services (unbilled revenue) Contract with Customer, Asset, before Allowance for Credit Loss, Current Drawdown of bank credit lines and loan facilities, net of debt issuance costs and debt discount withheld Proceeds from Lines of Credit Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Debt at fair value Long-term Debt, Fair Value Share repurchase program (in shares) Shares redeemed (in shares) Stock Repurchased and Retired During Period, Shares Purchase of property, plant and equipment Payments to Acquire Property, Plant, and Equipment Other liabilities Other Liabilities, Current Change in unbilled services (unbilled revenue) Increase in unbilled services (unbilled revenue) Increase (Decrease) In Contract with Customer, Asset, Gross, Current Increase (Decrease) In Contract with Customer, Asset, Gross, Current Business Combinations [Abstract] Business Combinations [Abstract] Maximum Maximum [Member] Line of credit facility, interest rate at period end Line of Credit Facility, Interest Rate at Period End Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Total Liabilities Liabilities Net income Temporary Equity, Net Income Award Type [Axis] Award Type [Axis] Granted (USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Non-current income taxes receivable Income Taxes Receivable, Noncurrent Schedule of Operating Lease Maturity Lessee, Operating Lease, Liability, Maturity [Table Text Block] Total Shareholders' Equity Beginning balance Ending balance Stockholders' Equity Attributable to Parent Common Stock, Shares, Issued Ordinary shares, shares issued (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Issued Term loan Senior Secured Bridge Loan Facility [Member] Senior Secured Bridge Loan Facility Prepayments and other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets Equity method investments Equity Method Investments and Joint Ventures Disclosure [Text Block] Assumed through business combinations (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Through Business Combination Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Through Business Combination Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Ireland IRELAND Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Noncontrolling interest redemption adjustment Noncontrolling interest redemption adjustment Redeemable Noncontrolling Interest, Increase From Business Combination Redeemable Noncontrolling Interest, Increase From Business Combination Intangible assets Intangible Assets Disclosure [Text Block] Repurchase of ordinary shares Payments for Repurchase of Common Stock Shareholders' Equity: Stockholders' Equity Attributable to Parent [Abstract] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Non-current operating lease liabilities Operating Lease, Liability, Noncurrent Measurement Frequency [Domain] Measurement Frequency [Domain] Debt instrument, principal amount Debt Instrument, Face Amount Interest expense Interest Expense Other Assets: Assets, Noncurrent [Abstract] Non-current operating lease liabilities Non-Current Operating Lease Liabilities [Member] Non-Current Operating Lease Liabilities Effective interest rate Debt Instrument, Interest Rate, Effective Percentage Net assets acquired Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net Retained earnings Retained Earnings (Accumulated Deficit) Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Equity method investments Equity Method Investments [Table Text Block] Schedule of Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Redeemable Noncontrolling Interest Redeemable Noncontrolling Interest [Member] Redeemable Noncontrolling Interest [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Clients 11-25 Clients 11-25 [Member] Clients 11-25 [Member] Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Share Repurchase Program Share Repurchase Program [Axis] Order backlog Order or Production Backlog [Member] Income Statement [Abstract] Income Statement [Abstract] Equity method investments Oncacare Limited Equity Method Investments Amendment flag Amendment Flag Series B notes Series B Notes [Member] Series B Notes Accounts receivable and unbilled revenue Contracts Receivable, Gross Contracts Receivable Current lease liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Operating Lease Liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Operating Lease Liability Number of countries in which entity operates Number of Countries in which Entity Operates Accounts receivable and unbilled revenue Accounts receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Repayment of bank credit lines and loan facilities Repayments of Lines of Credit Proceeds from exercise of equity compensation Proceeds from Stock Options Exercised Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Benefit arising (provision) for income taxes Provision for income taxes Income Tax Expense (Benefit) Accounts receivable, net of allowance for credit losses Accounts Receivable, after Allowance for Credit Loss, Current Equity Components [Axis] Equity Components [Axis] Fair Value Disclosures [Abstract] Write off of loss on interest rate hedge Other Comprehensive Income (Loss), Cash Flow Hedge, Adjustment, Write Off Of Loss, after Reclassification and Tax Other Comprehensive Income (Loss), Cash Flow Hedge, Adjustment, Write Off Of Loss, After Tax Total current assets Assets, Current Total future minimum lease payments Lessee, Operating Lease, Liability, to be Paid Concentration Risk Type [Domain] Concentration Risk Type [Domain] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Distribution of income from operations by geographical area Schedule of Segment Reporting Information, by Segment [Table Text Block] Office consolidation Office Consolidation [Member] Office Consolidation Share-based compensation Share-based Payment Arrangement [Policy Text Block] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Equity Method Investments and Joint Ventures [Abstract] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Less current portion of long-term debt Long-term Debt, Current Maturities Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Revenue benchmark Revenue Benchmark [Member] 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 PRA Health Sciences Inc PRA Health Sciences Inc [Member] PRA Health Sciences Inc Equity Component [Domain] Equity Component [Domain] Issue of restricted share units (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Year 1 Lessee, Operating Lease, Liability, to be Paid, Year One Currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Fair value of ordinary shares issued to acquiree stockholders Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Statement [Line Items] Statement [Line Items] Write off of loss on interest rate hedge Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax Non-current bank credit lines and loan facilities Long-term Line of Credit, Noncurrent Issue of shares associated with a business combination (in shares) Stock Issued During Period, Shares, Acquisitions Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Revenue, remaining performance obligation Revenue, Remaining Performance Obligation, Amount Issue of restricted share units Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Contingent consideration, maximum amount Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High Transaction and integration-related expenses Transaction And Integration Related Expenses [Member] Transaction And Integration Related Expenses Year 4 Lessee, Operating Lease, Liability, to be Paid, Year Four Debt Disclosure [Abstract] (Loss) income before provision for income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Loss/(gain) on interest rate hedge Derivative, Gain (Loss) on Derivative, Net Segment Reporting [Abstract] Segment Reporting [Abstract] Type of Restructuring [Domain] Type of Restructuring [Domain] Estimated Useful Life Finite-Lived Intangible Asset, Useful Life Customer [Axis] Customer [Axis] Current bank credit lines and loan facilities Line of Credit, Current Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Variable rate component one Variable Rate Component One [Member] Variable Rate Component One Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Change in net balance Decrease in net balance Change in Advance Payments Netted Against Unbilled Contracts Receivable Change in Advance Payments Netted Against Unbilled Contracts Receivable Operating lease right-of-use assets Operating right of use assets Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Operating Lease, Right-Of-Use Asset Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease, Right-of-Use Asset Business acquisition, number of shares issued (in shares) Business Combination, Consideration Transferred, Shares Issued To Shareholders, Per Share Held Business Combination, Consideration Transferred, Shares Issued, Per Current Share Held To Shareholders Other comprehensive income, net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Total Assets Assets Deferred taxes Deferred Income Taxes and Tax Credits Ordinary shares, shares authorized (in shares) Common Stock, Shares Authorized Variable rate, step down percentage Debt Instrument, Basis Spread on Variable Rate, Step Down Percentage Debt Instrument, Basis Spread on Variable Rate, Step Down Percentage Investments in equity-long term Other Long-term Investments Geographical [Domain] Geographical [Domain] Comprehensive (loss) income: Net Income (Loss) Attributable to Parent [Abstract] Repayments of secured debt Repayments of Secured Debt Title of Individual [Axis] Title of Individual [Axis] Net income attributable to the Group (including NCI redemption adjustment) Net Income (Loss) Available to Common Stockholders, Basic Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Debt instrument, interest rate as of period end Amortization rate of debt instrument Debt Instrument, Interest Rate, Stated Percentage Contingent consideration Business Combination, Contingent Consideration, Liability Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Revolving loan facility Revolving Credit Facility [Member] Assumed through business combinations (in USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Assumed In Business Combination, Weighted Average Exercise Price Share-based Compensation Arrangements by Share-based Payment Award, Options, Assumed In Business Combination, Weighted Average Exercise Price Significant accounting policies Significant Accounting Policies [Text Block] Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Measurement Frequency [Axis] Measurement Frequency [Axis] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Transfer to realized capital gain Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Schedule of Debt Schedule of Debt [Table Text Block] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Lease Costs Lease, Cost [Table Text Block] Geographical [Axis] Geographical [Axis] Currency impact of long term funding (net of tax) Other Comprehensive Income (Loss), Foreign Currency Transaction And Translation Adjustment, Net Of 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. Basic (in shares) Weighted average number of ordinary shares outstanding for basic net income per ordinary share (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (USD per share) Earnings Per Share, Diluted Reduction in carrying value of operating right-of-use assets Operating Lease, Right-of-Use Asset, Amortization Expense Effect of dilutive share options and other awards outstanding under share based compensation programs (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Total comprehensive (loss) income attributable to the group Comprehensive Income (Loss), Net of Tax, Attributable to Parent Employee severance Employee Severance [Member] Patient database Database Rights [Member] Goodwill expected to be tax deductible Business Acquisition, Goodwill, Expected Tax Deductible Amount Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Weighted average number of Ordinary Shares outstanding (note 14): Weighted Average Number of Shares Outstanding, Diluted [Abstract] Debt issuance costs Debt, Policy [Policy Text Block] Non-current deferred tax liability Deferred Income Tax Liabilities, Net Shares vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Share of equity method investments Loss on equity method investments Loss from equity method investments Income (Loss) from Equity Method Investments Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Fixed assets, net Property, plant and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Consultants Restricted Stock Units 2019 Consultants Restricted Stock Units Twenty Nineteen [Member] Consultants Restricted Stock Units Twenty Nineteen [Member] Fair value measurements Fair Value Disclosures [Text Block] Restructuring Additional provisions Restructuring Charges Accounts payable Accounts Payable, Current Concentration Risk Type [Axis] Concentration Risk Type [Axis] Depreciation and amortization expense Depreciation, Depletion and Amortization Performance Share Unit (PSUs) Performance Share Unit [Member] Performance Share Unit [Member] Business combinations and Transaction and integration-related expenses Business Combinations Policy [Policy Text Block] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Ordinary shares, shares outstanding (in shares) Common Stock, Shares, Outstanding Accounts payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Increase (Decrease) in Temporary Equity [Roll Forward] Increase (Decrease) in Temporary Equity [Roll Forward] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Provision for income taxes (excluding restructuring) Income Tax Expense (Benefit), Excluding Other Tax Expense (Benefit) Income Tax Expense (Benefit), Excluding Other Tax Expense (Benefit) Periodic interest payment Debt Instrument, Periodic Payment, Interest Restructuring and Related Activities [Abstract] Restructuring and Related Activities [Abstract] Share repurchase program, number of shares authorized to be repurchased (in shares) Stock Repurchase Program, Number of Shares Authorized to be Repurchased Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Schedule of Non-cash Stock Compensation Expense Schedule of Non Cash Stock Compensation Expense [Table Text Block] Schedule of Non Cash Stock Compensation Expense. Options Outstanding Number of Shares  Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract] Net operating lease costs Total lease cost Lease, Cost Income Statement Location [Domain] Income Statement Location [Domain] Investments at fair value Investments, Fair Value Disclosure Customer relationships Customer Relationships [Member] Other Other Customers [Member] Other Customers [Member] Rest of Europe Rest Of Europe [Member] Rest Of Europe [Member] Property, plant and equipment, net Property, Plant and Equipment, Net Non-current other liabilities Other Liabilities, Noncurrent Change in unearned revenue (payments on account) Increase in unearned revenue (payments on account) Increase (Decrease) In Contract With Customer, Liability, Current Increase (Decrease) In Contract With Customer, Liability, Current Repayments of long-term debt Repayments of Long-term Debt Debt Instrument [Line Items] Debt Instrument [Line Items] Net (loss) income per Ordinary Share attributable to the Group (note 14): Earnings Per Share [Abstract] Revolving loan facility Senior Secured Revolving Credit Facility [Member] Senior Secured Revolving Credit Facility Revenue Business Acquisition, Pro Forma Revenue Allowance for credit losses Accounts Receivable, Allowance for Credit Loss 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] Revenue, remaining performance obligation percentage Revenue, Remaining Performance Obligation, Percentage Sale of available for sale investments Proceeds from Sale of Debt Securities, Available-for-sale Rest of World Rest of World [Member] Rest of World [Member] Outstanding at beginning of period (USD per share) Outstanding at end of period (USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Total long-term debt Long-term Debt, Excluding Current Maturities Repayment of term loan obligations and accrued interest Business Combination, Consideration Transferred, Liabilities Incurred Exercisable at end of period Exercisable - weighted average remaining contractual life Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Net income/(loss) per Ordinary Share attributable to the Group (including NCI redemption adjustment): Earnings Per Share, Basic and Diluted [Abstract] Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Document fiscal period focus Document Fiscal Period Focus Net income Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Billed services (accounts receivable) Accounts Receivable, before Allowance for Credit Loss, Current 2025 and thereafter Long-Term Debt, Maturity, Year Four And Thereafter Long-Term Debt, Maturity, Year Four And Thereafter Amortization of financing costs Amortization of Debt Issuance Costs Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents U.S. UNITED STATES Ordinary shares, par value (in EUR cents per share) Common Stock, Par or Stated Value Per Share Statement of Comprehensive Income [Abstract] Current Assets: Assets, Current [Abstract] 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] Total cost Finite-Lived Intangible Assets, Gross Leases [Abstract] Leases [Abstract] Entity central index key Entity Central Index Key Schedule of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] London Interbank Offered Rate (LIBOR) London Interbank Offered Rate (LIBOR) [Member] Intangible assets Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block] Revenue recognition Revenue from Contract with Customer [Policy Text Block] Exercise of share options (in shares) Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Diluted (in shares) Weighted average number of ordinary shares outstanding for diluted net income per ordinary share (in shares) Weighted Average Number of Shares Outstanding, Diluted Fair value, recurring Fair Value, Recurring [Member] Income taxes Income Tax Disclosure [Text Block] Buyback Program Buyback Program [Member] Buyback Program [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Business acquisition, share price (in USD per share) Business Combination, Consideration Transferred, Cash Payment To Shareholders, Per Share Held Business Combination, Consideration Transferred, Cash Payment To Shareholders, Per Share Held Current fiscal year end date Current Fiscal Year End Date Schedule of Share Option Activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Share capital Stockholders' Equity Note Disclosure [Text Block] Disclosure of fair value of financial instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Purchase of equity method investments Payments to Acquire Equity Method Investments Credit Facility [Axis] Credit Facility [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities 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] Changes in operating assets and liabilities, net of acquired assets and assumed liabilities: Increase (Decrease) in Operating Capital [Abstract] Senior Notes 2020 Senior Notes 2020 [Member] Senior Notes 2020 Other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other 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 Expected life Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Total current liabilities Liabilities, Current Purchase of subsidiary undertakings, net of cash acquired Fair value of cash consideration Cash outflows Payments to Acquire Businesses, Gross Line of credit facility, principal amount Line of Credit Facility, Maximum Borrowing Capacity Foreign exchange movement Goodwill, Foreign Currency Translation Gain (Loss) Exercise of call option on noncontrolling interest Temporary Equity, Accretion to Redemption Value Cash & cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Variable Rate Component [Domain] Variable Rate Component [Domain] Variable Rate Component [Domain] Early termination options reasonably certain to be exercised Early Termination Options Reasonably Certain To Be Exercised, Right Of Use Asset Obtained In Exchange For Operating Lease Liability Early Termination Options Reasonably Certain To Be Exercised, Right Of Use Asset Obtained In Exchange For Operating Lease Liability Statement [Table] Statement [Table] Percentage change in unearned revenue (payments on account) Increase (Decrease) In Contract With Customer, Liability, Gross, Current, Percent Increase (Decrease) In Contract with Customer, Liability, Gross, Current, Percent Assumptions: Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Direct costs (excluding depreciation and amortization) Cost of Goods and Service, Excluding Depreciation, Depletion, and Amortization Statistical Measurement [Axis] Statistical Measurement [Axis] Cover [Abstract] First lien net leverage ratio Debt Instrument, Covenant, Net Leverage Ratio, Maximum Debt Instrument, Covenant, Net Leverage Ratio, Maximum Non-executive directors Non-executive Director [Member] Non-executive Director [Member] Intangible assets, net  Net book value Finite-Lived Intangible Assets, Net Goodwill Opening balance Closing balance Goodwill Direct costs Cost of Sales [Member] Income taxes payable Accrued Income Taxes, Current Schedule of Goodwill Schedule of Goodwill [Table Text Block] 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] Operating lease costs Operating Lease, Cost Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Debt discount Debt Instrument, Unamortized Discount Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Non-current bank credit lines and loan facilities Long-term Debt [Text Block]