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Share-based payments - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of options granted in the period $ 1.3 $ 3.4  
Number of options granted in the period (in shares) 140,600 647,800  
Average grant price (in usd per share) $ 9.24 $ 5.32  
Grant price (in usd per share) $ 53.24 $ 39.76  
Intrinsic Value $ 1.7    
Remaining contractual term 7 years 3 months 18 days    
Fair value of vested shares $ 9.6 $ 6.9  
Compensation costs 11.5 12.0 $ 5.8
Restricted stock and restricted stock units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Aggregate fair values at grant date $ 11.9 $ 13.1 $ 4.1
Granted (in shares) 188,300 240,800 104,200
Average grant price (in usd per share) $ 62.99 $ 54.45 $ 39.78
Restricted stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Tax benefits related to vesting of awards $ 1.2 $ 0.8 $ 0.6
Compensation costs not yet recognized $ 10.1    
Compensation costs not yet recognized, period for recognition 1 year 10 months 24 days    
Time-based shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years    
Performance-based shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years    
Stock options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expiration period 10 years    
Stock options | First anniversary      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting percentage 20.00%    
Stock options | Second anniversary      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting percentage 30.00%    
Stock options | Third anniversary      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting percentage 50.00%