Other receivables Nontrade Receivables, Current Total costs and expenses Costs and Expenses Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Revision of Prior Period [Axis] Revision of Prior Period [Axis] Share issuance costs Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Deferred tax benefit Deferred Income Taxes and Tax Credits Revision of Prior Period [Domain] Revision of Prior Period [Domain] Additional Paid-in Capital Additional Paid-in Capital [Member] Loss on equity method investments Loss on equity method investments Income (Loss) from Equity Method Investments Schedule of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Purchase of subsidiary undertakings (net of cash acquired) Payments to Acquire Businesses, Gross Issue of restricted share units Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Clients 11-25 Clients 11-25 [Member] Clients 11-25 [Member] 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to Parent Comprehensive income (net of tax): Other comprehensive income, net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Ordinary shares, shares authorized (in shares) Common Stock, Shares Authorized Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Current assets: Assets, Current [Abstract] Total Liabilities and Shareholders' Equity Liabilities and Equity LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities and Equity [Abstract] Schedule of Distribution of Income from Operations by Geographical Area Schedule Of Operating Income By Geography [Table Text Block] Schedule Of Operating Income By Geography Cover [Abstract] Current bank credit lines, loan facilities and notes Line of Credit, Current Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Share repurchase costs Stock Repurchased During Period, Cost, Equity Stock Repurchased During Period, Cost, Equity Non-current assets: Assets, Noncurrent [Abstract] Intangible assets, net  Net book value Finite-Lived Intangible Assets, Net Costs and expenses: Cost of Revenue [Abstract] Prior period acquisition Goodwill, Measurement Period Adjustment Accounts payable Accounts Payable, Current Acquisition-related gain Business Combination, Bargain Purchase, Gain Recognized, Amount Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction 76,567,325 shares issued and outstanding at December 31, 2025, (2024: 80,756,860 and 2023: 82,495,086) Common Stock, Value, Issued Income taxes receivable Income Taxes Receivable, Noncurrent Goodwill [Roll Forward] Goodwill [Roll Forward] Contract Assets [Abstract] Contract Assets [Abstract] Contract Assets Non-current other liabilities Other Liabilities, Noncurrent Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted 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Contracts Receivable, Net Contracts Receivable, Net Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income tax (expense) / benefit Income Tax Expense (Benefit) Clients 6-10 Clients 6-10 [Member] Clients 6-10 [Member] Investments in equity Equity Securities, FV-NI and without Readily Determinable Fair Value Net income per ordinary share: Earnings Per Share [Abstract] Other Undenominated Capital Other Undenominated Capital [Member] Other undenominated capital. Consolidation Items [Domain] Consolidation Items [Domain] Purchase of investments in equity Payments to Acquire Long-Term Investments Available for sale investments Debt Securities, Available-for-Sale, Current Repurchase of ordinary shares Stock Repurchased and Retired During Period, Value Unearned revenue Increase (Decrease) in Contract with Customer, Liability Reduction in carrying value of operating right-of-use assets Operating Lease, Right-of-Use Asset, Periodic Reduction Proceeds from exercise of equity compensation Proceeds from Stock Options Exercised Other Other Customers [Member] Other Customers [Member] Schedule of Accounts Receivables and Unbilled Revenue, and Unbilled Services and Unearned Revenue Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Rest of Europe Rest Of Europe [Member] Rest Of Europe [Member] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation 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