Accounts receivable, unbilled revenue (contract assets) and unearned revenue or payments on account (contract liabilities) - Schedule of Accounts Receivables and Unbilled Revenue (Details) - USD ($) $ in Thousands |
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
Dec. 31, 2022 |
|---|---|---|---|---|
| Contract Assets [Abstract] | ||||
| Accounts receivable (Billed services) | $ 1,517,217 | $ 1,428,428 | $ 1,795,937 | |
| Allowance for credit losses (Note 5) | (42,319) | (35,664) | (31,533) | $ (20,562) |
| Accounts receivable (net) | 1,474,898 | 1,392,764 | 1,764,404 | |
| Unbilled revenue (Unbilled services) | 1,096,592 | 1,040,174 | 853,581 | |
| Accounts receivable and unbilled revenue, net | $ 2,571,490 | $ 2,432,938 | $ 2,617,985 |