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Equity Incentive Schemes and Stock Compensation Charges - Schedule of Non-cash Stock Compensation Expense (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total compensation costs | $ 133,844 | $ 26,271 | $ 26,819
Direct costs |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total compensation costs | 18,551 | 8,557 | 14,777
Selling, general and administrative |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total compensation costs | 41,457 | 17,714 | 12,042
Transaction and integration related * |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total compensation costs | $ 73,836 | $ 0 | $ 0

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