Accounts receivable, unbilled revenue (contract assets) and unearned revenue or payments on account (contract liabilities) - Schedule of Unbilled Services and Unearned Revenue or Payments on Account (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Revenue from Contract with Customer [Abstract] | |||
| Unbilled revenue (Unbilled services) | $ 1,096,592 | $ 1,040,174 | $ 853,581 |
| Change in unbilled revenue (unbilled services) | $ 56,418 | $ 186,593 | |
| Percentage change in unbilled revenue (unbilled services) | 5.40% | 21.90% | |
| Unearned revenue (Payments on account ) | $ (1,550,471) | $ (1,467,671) | $ (1,566,464) |
| Change in unearned revenue (payments on account ) | $ (82,800) | $ 98,793 | |
| Percentage change in unearned revenue (payments on account ) | 5.60% | (6.30%) | |