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Equity Incentive Schemes and Stock Compensation Charges - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands |  |  | 12 Months Ended | 24 Months Ended | 252 Months Ended |  |  |  |
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Feb. 14, 2017 | May 11, 2015 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2017 | May 18, 2020 | May 16, 2019 | May 31, 2018 | Feb. 13, 2017
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Weighted average contractual term of options outstanding |  |  | 4 years 5 months 1 day | 4 years 8 months 8 days |  |  |  |  |  |  |
Exercisable - weighted average remaining contractual life |  |  | 3 years 10 months 20 days | 4 years 3 months |  |  |  |  |  |  |
Total compensation costs |  |  | $ 55,667 | $ 70,523 | $ 133,844 |  |  |  |  |  |
Income tax benefit related to stock compensation |  |  | 20,000 | 12,900 | 22,700 |  |  |  |  |  |
Cash tax benefit related to stock options exercised |  |  | $ 10,900 | 7,700 | $ 23,900 |  |  |  |  |  |
The 2020 Legacy PRA Plan |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  |  |  |  |  |  | 2,500,000 |  |  |
The 2018 Legacy PRA Plan |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  |  |  |  |  |  |  |  | 2,000,000 |
Consultants Stock Plan, 2008 Plan |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) | 400,000 |  |  |  |  |  |  |  |  |  | 1,000,000
Limit of shares issued or to be issued pursuant to options granted (in shares) | 1,000,000 |  |  |  |  |  |  |  |  |  |
Employee Stock Plan, 2008 Plan |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) | 6,000,000 |  |  |  |  |  |  |  |  |  |
Maximum number of shares per employee (in shares) | 400,000 |  |  |  |  |  |  |  |  |  |
Option Plans 2008 | Minimum |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percentage of option price for fair value of ordinary share (in percent) | 100.00% |  |  |  |  |  |  |  |  |  |
Employee Stock Option |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  | 5 years |  |  |  |  |  |  |  |
Employee Stock Option | Award date, prior to 2018 |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  |  |  |  |  | 5 years |  |  |  |
Shares expiration period |  |  |  |  |  |  | 8 years |  |  |  |
Restricted Stock Units 2013 |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  | 4,100,000 |  |  |  |  |  |  |  |  |
Additional number of ordinary shares which have been reserved for issuance (in shares) |  | 2,500,000 |  |  |  |  |  |  |  |  |
Consultants Restricted Stock Units 2019 |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  |  |  |  |  |  |  | 250,000 |  |
Consultants Restricted Stock Units 2019 | Non-executive director |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  |  |  |  | 12 months |  |  |  |  |
Restricted Stock Units (RSUs) |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fair value of stock units vested |  |  | $ 35,400 | $ 34,100 |  |  |  |  |  |  |
Restricted Stock Units (RSUs) | Minimum |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Share price of equity instruments other than options, vested in period (in USD per share) |  |  | $ 159.33 | $ 137.47 |  |  |  |  |  |  |
Restricted Stock Units (RSUs) | Maximum |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Share price of equity instruments other than options, vested in period (in USD per share) |  |  | $ 265.96 | $ 265.96 |  |  |  |  |  |  |
Performance Share Unit (PSUs) |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fair value of stock units vested |  |  | $ 7,500 | $ 6,500 |  |  |  |  |  |  |
Performance Share Unit (PSUs) | Minimum |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Share price of equity instruments other than options, vested in period (in USD per share) |  |  | $ 159.33 | $ 137.47 |  |  |  |  |  |  |
Performance Share Unit (PSUs) | Maximum |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Share price of equity instruments other than options, vested in period (in USD per share) |  |  | $ 166.51 | $ 166.51 |  |  |  |  |  |  |
PSUs Based on Service and EPS Targets | Maximum |  |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stock units to be granted (in shares) |  |  | 49,340 |  |  |  |  |  |  |  |

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