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Stock-Based Compensation - Restricted Stock Units (Details) - Restricted Stock Units (RSUs) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 8.0 $ 8.7 $ 8.9
Fair value of awards vested 9.6 7.1 6.7
Unamortized stock compensation expense $ 9.0    
Compensation cost not yet recognized, period for recognition 1 year 3 months 18 days    
LTIP      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average grant date fair value $ 9.9 $ 11.4 $ 9.5
LTIP | Primary Vesting Category | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 1 year    
LTIP | Primary Vesting Category | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years