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Share-Based Compensation - Summary of Incentive Unit Activity (Details) - Incentive Unit Award - USD ($)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
Dec. 31, 2014
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Non-vested shares activity        
Non-vested at the beginning of the period (in shares)   987,797 604,942 435,515
Granted (in shares)   382,648 678,469 347,811
Vested (in shares)   (371,731) (256,016) (160,120)
Forfeited (in shares)   (219,453) (39,598) (18,264)
Non-vested at the end of the period (in shares) 435,515 779,261 987,797 604,942
Weighted-Average Grant-Date Fair Value        
Non-vested at the beginning of the period (in dollars per share)   $ 12.63 $ 19.64 $ 18.95
Granted (in dollars per share)   12.87 9.46 20.38
Vested (in dollars per share)   14.14 19.69 19.33
Forfeited (in dollars per share)   12.23 19.52 19.69
Non-vested at the end of the period (in dollars per share) $ 18.95 $ 12.14 $ 12.63 $ 19.64
Aggregate Intrinsic Value $ 7.3 $ 12.9 $ 10.3 $ 11.5