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Stock-based Compensation - Time-Based RSUs (Details)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Weighted-average grant date fair value per unit:      
Compensation expense recorded during the year | $ $ 24,771 $ 25,251 $ 20,697
Time-based RSUs      
Stock-Based Compensation      
Percentage of the award vesting at each of the three anniversaries 33.00%    
Summary of equity award grants, RSUs      
Balance at beginning of year (in units) 627,000 600,000 382,000
Granted (in units) 334,000 328,000 408,000
Vested (in units) (300,000) (254,000) (173,000)
Forfeited or canceled (in units) (19,000) (47,000) (17,000)
Balance at end of year (in units) 642,000 627,000 600,000
Weighted-average grant date fair value per unit:      
Outstanding at beginning of year (in dollars per share) | $ / shares $ 20.39 $ 16.37 $ 13.71
Granted (in dollars per share) | $ / shares 22.88 24.25 18.02
Vested (in dollars per share) | $ / shares 18.73 16.08 14.66
Forfeited (in dollars per share) | $ / shares 22.29 19.40 14.87
Outstanding at end of year (in dollars per share) | $ / shares $ 22.40 $ 20.39 $ 16.37
Compensation expense recorded during the year | $ $ 6,659 $ 6,608 $ 4,768
Unamortized compensation cost | $ $ 4,107    
Number of shares expected to vest (in units) 570,000    
Weighted average remaining vesting period (in months) 10 months    
Time-based RSUs | Minimum      
Stock-Based Compensation      
Turnover rates (as a percent) 0.0    
Time-based RSUs | Maximum      
Stock-Based Compensation      
Turnover rates (as a percent) 22.7    
Time-based RSUs | Common Stock      
Stock-Based Compensation      
Number of share awarded for each RSU (in shares) 1