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Limit of Shares Issued or To Be Issued Pursuant to Options Granted

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Per Share

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Share-Based Compensation Arrangement By Share-Based Payment Award, Percentage Of Outstanding Shares Authorized

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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- Definition

Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of noncash expense for share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

The highest quantity of shares an employee can purchase under the plan per period.

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- Definition

Number of additional shares authorized for issuance under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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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
	Feb. 14, 2017	May 11, 2015	Jan. 17, 2003	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2017	May 18, 2020	May 16, 2019	May 31, 2018	Feb. 13, 2017	Sep. 23, 2013
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Weighted average contractual term of options outstanding				5 years 4 months 20 days	4 years 10 months 9 days
Exercisable - weighted average remaining contractual life				4 years 6 months 18 days	3 years 7 months 6 days
Total compensation costs				$ 133,844	$ 26,271	$ 26,819
Income tax benefit related to stock compensation				22,700	6,900	8,200
Cash tax benefit related to stock options exercised				$ 23,900	2,500	$ 1,900
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
2013 Legacy PRA Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)													2,052,909
Percentage of outstanding shares authorized													12.50%
Consultants Stock Plan, 2008 Plan
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Ordinary shares which have been reserved for issuance (in shares)	1,000,000											400,000
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 Plan, 2003 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
Maximum number of award as percentage of shares outstanding (in percent)			10.00%
Employee Stock Option \| Minimum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period				5 years
Employee Stock Option \| Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period				8 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
Employee Stock Option \| Award date, 2018 and thereafter
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Shares vesting period						12 months
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				$ 83,500	$ 14,300
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)				$ 115.11	$ 83.47		$ 83.47
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)				$ 206.71	$ 156.21		156.21
Performance Share Unit (PSUs)
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Fair value of stock units vested				$ 5,100	$ 5,300
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)				$ 115.11	$ 83.47		83.47
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)				$ 125.74	$ 90.03		$ 90.03
PSUs Based on Service and EPS Targets \| Maximum
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Stock units to be granted (in shares)				71,890