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Stock-based Compensation Plans (Details)
shares in Thousands, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
USD ($)
Jun. 30, 2021
USD ($)
Mar. 31, 2021
USD ($)
Sep. 30, 2020
USD ($)
Jun. 30, 2020
USD ($)
Mar. 31, 2020
USD ($)
Sep. 30, 2021
USD ($)
performanceCondition
shares
Sep. 30, 2020
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation | $ $ 7.8 $ 7.1 $ 5.5 $ 6.9 $ 6.1 $ 4.3    
Stock-based compensation expense | $ 7.8     6.9     $ 20.4 $ 17.3
Common Stock                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation | $ $ 7.8 $ 7.1 $ 5.5 $ 6.9 $ 6.1 $ 4.3    
Performance Shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Service period vested             3 years  
Number of performance conditions | performanceCondition             2  
Number of Units Awarded (in shares) | shares             27  
Share-based Compensation Award, Tranche One | Restricted Stock Units (RSUs)                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of Units Awarded (in shares) | shares             63  
Award vesting period             3 years  
Share-based Compensation Award, Tranche Two | Restricted Stock Units (RSUs)                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Service period vested             1 year  
Number of Units Awarded (in shares) | shares             5