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[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 Schedule of Proforma Information of PRA Health Sciences Inc Acquisition 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) Number of operating segments Number of Operating Segments Basic (in 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 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100,000,000 shares authorized, 81,293,012 shares issued and outstanding at March 31, 2022 and 81,554,683 shares issued and outstanding at December 31, 2021 Common Stock, Value, Issued Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Outstanding at beginning of period (in USD per share) Outstanding at end of period (in 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] Lease liability Lease Liability [Member] Lease Liability 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 2021 Restructuring Plan 2021 Restructuring Plan [Member] 2021 Restructuring Plan Total costs and expenses Costs and Expenses Schedule of 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 Total long-term debt Long-term Debt, Excluding Current Maturities, Gross Long-term Debt, Excluding Current Maturities, Gross 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 and Geographical Information Segment Reporting Disclosure [Text Block] Income from operations Income from operations Operating Income (Loss) Operating lease liabilities Operating Lease, Liability, Current 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 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 Payments of debt restructuring costs Payments of Debt Restructuring Costs 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 Long-term debt at fair value Long-term Debt, Fair Value Share repurchase program (in shares) Share repurchase program, number of shares repurchased (in shares) Stock Repurchased and Retired During Period, Shares Purchase of property, plant and equipment Payments to Acquire Property, Plant, and Equipment Non-executive directors Non-Executive Director [Member] Non-executive Director [Member] Other liabilities Other Liabilities, Current Business Combinations [Abstract] Business Combinations [Abstract] Maximum Maximum [Member] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Total Liabilities Liabilities Award Type [Axis] Award Type [Axis] Granted (in USD per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Income taxes receivable Income Taxes 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Operating Lease, Liability, Noncurrent Measurement Frequency [Domain] Measurement Frequency [Domain] Debt instrument, principal amount Debt Instrument, Face Amount Interest expense Interest Expense Non-current Assets: Assets, Noncurrent [Abstract] Non-current operating lease liabilities Non-Current Operating Lease Liabilities [Member] Non-Current Operating Lease Liabilities Net assets acquired Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net Retained earnings Retained Earnings (Accumulated Deficit) Oncacare Oncacare [Member] Oncacare Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Summary of Equity Method Investments Equity Method Investments [Table Text Block] Schedule of PRA Health Sciences Inc Acquisition Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Restructuring credit Release provision Restructuring Reserve, Release Of Accrual Restructuring Reserve, Release Of Accrual Billed services (accounts receivable) Billed Contracts Receivable 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 Carrying Value Equity Method Investments Amendment Flag Amendment Flag Accounts receivable (net) Contracts Receivable, Gross Contracts Receivable Current portion of operating lease liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Operating Lease Liability Business Combination, Recognized Identifiable Assets Acquired 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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 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 Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract] Restructuring Plan [Axis] Restructuring Plan [Axis] 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 / performance 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] 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 Unearned revenue Increase (Decrease) in Contract with Customer, Liability 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 / performance share units Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Year 4 Lessee, Operating Lease, Liability, to be Paid, Year Four Debt Disclosure [Abstract] 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 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] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Operating lease 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 Other comprehensive loss, net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Payments to settle debt obligations that existed prior to acquisition date Business Combination, Consideration Transferred, Payments To Settle Debt Obligations That Existed Prior To Acquisition Date Business Combination, 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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 (in 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 Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Total comprehensive 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 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] Deferred tax liability Deferred Income Tax Liabilities, Net Shares vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Related Party Transaction [Line Items] Related Party Transaction [Line Items] Share of losses in equity method investments Loss on equity method investments Income (Loss) from Equity Method Investments Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Fixed assets 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] Additional provisions Restructuring Charges Accounts payable Accounts Payable, Current Concentration Risk Type [Axis] Concentration Risk Type [Axis] Impairment of long lived assets Impairment, Long-Lived Asset, Held-for-Use Depreciation and amortization expense Depreciation, Depletion and Amortization Performance Share Unit (PSUs) Performance Share Unit [Member] Performance Share Unit [Member] Business Combinations Business Combinations Policy [Policy Text Block] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Summary of Restructuring Charges Restructuring and Related Costs [Table Text Block] 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 Provision for income taxes (excluding restructuring) Income Tax Expense (Benefit), Excluding Other Tax Expense (Benefit) Income Tax Expense (Benefit), Excluding Other Tax Expense (Benefit) Restructuring and Related Activities [Abstract] Restructuring and Related Activities [Abstract] 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] 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 Senior Secured Credit Facility and Senior Secured Notes Senior Secured Credit Facility And Senior Secured Notes [Member] Senior Secured Credit Facility And Senior Secured Notes Non-current other liabilities Other Liabilities, Noncurrent Debt Instrument [Line Items] Debt Instrument [Line Items] Net 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 Related Party Transaction [Domain] Related Party Transaction [Domain] Revenue, remaining performance obligation percentage Revenue, Remaining Performance Obligation, Percentage Other liabilities Other Current Liabilities [Member] Rest of World Rest of World [Member] Rest of World [Member] Outstanding at beginning of period (in USD per share) Outstanding at end of period (in USD per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Sale/ (purchase) of investments in equity - long term Payments for (Proceeds from) Long-term Investments Total long-term debt, net Long-term Debt, Excluding Current Maturities Schedule of Related Party Transactions, by 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Thereafter Long-Term Debt, Maturity, Year Four And Thereafter Amortization of financing costs and debt discount 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 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 Summary of Stock Option Activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Basis spread on variable rate (in percent) Debt Instrument, Basis Spread on Variable Rate Share capital Stockholders' Equity Note Disclosure [Text Block] First lien net leverage ratio Debt Instrument, Covenant, First Lien Net Leverage Ratio Debt Instrument, Covenant, First Lien Net Leverage Ratio Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] 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: Increase (Decrease) in Operating Capital [Abstract] Other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Shares vested (in 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 Business acquisition, number of shares issued (in shares) Business Combination, Consideration Transferred, Shares Issued To Shareholders, Per Current Share Held Business Combination, Consideration Transferred, Shares Issued, Per Current Share Held To Shareholders Expected life Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Total current liabilities Liabilities, Current Fair value of cash consideration Payments to Acquire Businesses, Gross Debt instrument, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Foreign exchange movement Goodwill, Foreign Currency Translation Gain (Loss) Cash and cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Schedule of Fair Value of Intangible Assets PRA Health Sciences Inc Acquisition Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Less debt issuance costs and debt discount Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Long-lived assets Long-Lived Assets 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] Intangible assets  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 Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Statement of Financial Position [Extensible Enumeration] 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 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 Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Debt discount paid Debt Instrument, Unamortized Discount Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Bank credit lines and loan facilities Long-term Debt [Text Block] Other Liabilities