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Share-based compensation - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Share-based compensation        
Income tax benefit $ 0.3 $ 1.4 $ 1.5  
Long-term incentive plan (LTIP)        
Share-based compensation        
Performance period (in years) 3 years      
Exception to forfeiture, minimum requisite service period (in months) 12 months      
Payout low end of range (as percent) 0.00%      
Payout high end of range (as percent) 200.00%      
Restricted stock units        
Share-based compensation        
Fair value $ 1.4 3.7 4.2  
Income tax benefit 0.3 0.8 0.6  
Unrecognized compensation cost $ 1.1      
Weighted-average period over which unrecognized compensation cost expected to be recognized (in years) 1 year 1 month 6 days      
LTIP linked to TRS        
Share-based compensation        
Fair value $ 0.0 0.0 0.8  
Income tax benefit     0.1  
Unrecognized compensation cost $ 1.1      
Weighted-average period over which unrecognized compensation cost expected to be recognized (in years) 1 year 9 months 18 days      
LTIP awards linked to other performance conditions        
Share-based compensation        
Fair value $ 1.7 2.9 3.2  
Income tax benefit 0.3 $ 0.6 $ 0.4  
Unrecognized compensation cost $ 3.4      
Weighted-average period over which unrecognized compensation cost expected to be recognized (in years) 1 year 9 months 18 days      
Equity and Incentive Plan (EIP)        
Share-based compensation        
Shares remaining available for future issuance (in shares) 1,800,000      
Shares that can be issued upon vesting of outstanding units and achievement of performance goals (in shares) 700,000      
Equity and Incentive Plan (EIP) | Restricted shares        
Share-based compensation        
Vesting period   3 years 3 years  
Equity and Incentive Plan (EIP) | Restricted shares | Share-based Payment Arrangement, Tranche One        
Share-based compensation        
Vesting percentage 33.33% 33.33% 25.00% 25.00%
Equity and Incentive Plan (EIP) | Restricted shares | Share-based Payment Arrangement, Tranche Two        
Share-based compensation        
Vesting percentage 33.33% 33.33% 25.00% 25.00%
Equity and Incentive Plan (EIP) | Restricted shares | Share-based Payment Arrangement, Tranche Three        
Share-based compensation        
Vesting percentage 33.33% 33.33% 25.00% 25.00%
Equity and Incentive Plan (EIP) | Restricted shares | Share-Based Payment Arrangement, Tranche Four        
Share-based compensation        
Vesting percentage     25.00% 25.00%
Nonemployee Director Stock Plan        
Share-based compensation        
Shares remaining available for future issuance (in shares) 168,177