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Stock-Based Compensation - Restricted Stock Units Narrative (Details) - USD ($)
shares in Thousands, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
RSUs and PSUs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 174    
Shares vested (in shares) 268    
Stock-based compensation expense $ 10.4 $ 8.3 $ 5.5
Remaining stock-based compensation expense for unvested shares, not yet recognized $ 23.4    
Stock-based compensation expense, weighted average recognition period (in years) 2 years 2 months 12 days    
RSUs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 160    
Vesting period 4 years    
PSUs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 14    
Percent of award target performance metric 100.00%    
Shares vested (in shares) 84    
Percent of achievement of award target performance metric   95.00%  
PSUs | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 0.00%    
PSUs | Minimum | Tranche one      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 100.00%    
Performance-based cash bonus payment, percent 100.00%    
PSUs | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 100.00%    
PSUs | Maximum | Tranche one      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 150.00%    
Performance-based cash bonus payment, percent 165.00%    
PSUs | 2016 Performance metric      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 4    
PSUs granted in 2019      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 32    
PSUs granted in 2018      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 82    
PSUs granted in 2019 and 2018      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 100.00%    
PSUs granted in 2019 and 2018 | Tranche one      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares vested (in shares) 48    
PSUs granted in 2019 and 2018 | Tranche two      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares vested (in shares) 42    
PSUs granted in 2019 and 2018 | Tranche three      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares vested (in shares) 24    
PSUs granted in 2019 and 2018 | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 0.00%    
Percent of cash bonus payment on initial targets 100.00%    
PSUs granted in 2019 and 2018 | Minimum | Tranche one      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 100.00%    
PSUs granted in 2019 and 2018 | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 100.00%    
Percent of cash bonus payment on initial targets 165.00%    
PSUs granted in 2019 and 2018 | Maximum | Tranche one      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of award target performance metric 150.00%    
Unvested RSAs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted (in shares) 5    
Vesting period 1 year    
Shares vested (in shares) 5    
Stock-based compensation expense $ 0.7 $ 0.3 $ 0.3
Fair value of shares vested 0.5    
Remaining stock-based compensation expense for unvested shares, not yet recognized $ 0.4    
Stock-based compensation expense, weighted average recognition period (in years) 8 months 12 days