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Share Plans - Additional Information (Details)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
Jun. 30, 2021
shares
Mar. 31, 2021
shares
Sep. 30, 2020
shares
Jun. 30, 2020
shares
May 31, 2020
shares
Mar. 31, 2020
shares
Dec. 31, 2019
$ / shares
shares
May 31, 2019
shares
Mar. 31, 2019
shares
Dec. 31, 2021
USD ($)
$ / shares
Dec. 31, 2020
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
Dec. 31, 2021
£ / shares
Dec. 31, 2021
USD ($)
$ / shares
Dec. 31, 2020
£ / shares
Dec. 31, 2020
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Loan outstanding from ESOP                           $ 0.5   $ 0.6
Tax benefit realized for the tax deductions from option exercises                   $ 1.1 $ 0.6 $ 0.9        
Weighted average fair value of options granted (in USD per share) | $ / shares                   $ 20.56 $ 9.41 $ 17.65        
Total intrinsic value of options exercised                   $ 5.8 $ 3.0 $ 11.2        
Total unrecognized compensation cost related to share options                           $ 2.8   $ 2.2
Options                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Total unrecognized compensation cost related to share options, period for recognition                   1 year 10 months 24 days 1 year 3 months 18 days          
Long-Term Umbrella Incentive Plan (LTIP)                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award vesting period                   4 years            
Award expiration period                   6 years            
Long-Term Umbrella Incentive Plan (LTIP) | Tranche One                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award vesting percentage                   25.00%            
Long-Term Umbrella Incentive Plan (LTIP) | Tranche Two                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award vesting percentage                   25.00%            
Long-Term Umbrella Incentive Plan (LTIP) | Tranche Three                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award vesting percentage                   25.00%            
Long-Term Umbrella Incentive Plan (LTIP) | Tranche Four                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award vesting percentage                   25.00%            
Long-Term Umbrella Incentive Plan (LTIP) | Restricted Stock Units and Options                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award granted during period (in shares) | shares   110,000 3,892     132,900 6,000   196,320              
Award vesting period   4 years 4 years   4 years   4 years   4 years              
Award expiration period   2 years 2 years   2 years   2 years   2 years              
Non-Executive Directors Equity Incentive Plan (Director EIP)                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award vesting period                   1 year            
Non-Executive Directors Equity Incentive Plan (Director EIP) | Restricted Stock Units and Options                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award granted during period (in shares) | shares 19,000 45,000   27,280 2,000     3,981                
Non-Executive Directors Equity Incentive Plan (Director EIP) | Restricted Stock Units and Options | Tranche Two                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Award fully vested and settled period after grant date 1 year 2 years           1 year                
Ordinary shares                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Common stock, par value (in GBP per share) | (per share)             $ 0.50         $ 0.50 £ 0.50 $ 0.50 £ 0.50 $ 0.50
Ordinary shares | Employee Benefit Trust                                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Market value of shares held by ESOP (in USD per share) | $ / shares                           $ 19.31   $ 16.42