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Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense $ 3.1 $ 2.5
Stock options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense 0.6 0.6
Time-based restricted share units    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense 1.8 0.9
Performance-based restricted share units    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense 0.6 0.9
Employee stock purchase plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense $ 0.1 $ 0.1