Stock-Based Compensation - Restricted Stock (Details) - Restricted stock awards - $ / shares |
3 Months Ended | 12 Months Ended | |
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Awards | |||
| Outstanding, beginning of period (in shares) | 1,009,716 | ||
| Granted (in shares) | 1,029,721 | ||
| Vested (in shares) | (367,441) | ||
| Forfeited (in shares) | (136,051) | ||
| Outstanding, end of period (in shares) | 1,535,945 | 1,009,716 | |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] | |||
| Granted (in dollars per share) | $ 20.03 | $ 18.11 | $ 17.33 |
| Vested (in dollars per share) | 17.93 | ||
| Canceled (in dollar per share) | 17.70 | ||
| Outstanding, end of period (in dollars per share) | $ 17.88 | $ 17.64 | |