v3.8.0.1
Stock Based Compensation - Summary of Stock Option Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Options Granted      
Outstanding at beginning of period 1,972,884 2,716,834 2,769,616
Options granted     23,000
Options exercised (1,072,000) (690,592) (62,614)
Options forfeited   (53,358) (13,168)
Outstanding at end of period 900,884 1,972,884 2,716,834
Options exercisable 900,884 1,945,032 2,599,010
Weighted Average Exercise Price      
Outstanding at beginning of period $ 6.34 $ 6.35 $ 6.34
Options granted     9.88
Options exercised 5.18 6.17 6.47
Options forfeited   9.18 8.24
Outstanding at end of period 7.73 6.34 6.35
Options exercisable $ 7.73 $ 6.30 $ 6.23
Weighted-Average Remaining Contractual Term      
Outstanding at end of period 3 years 4 months 13 days 2 years 5 months 12 days 3 years 6 months 7 days
Options exercisable 3 years 4 months 13 days 2 years 4 months 20 days 3 years 3 months 18 days
Aggregate Intrinsic Value      
Outstanding at end of period $ 9,738 $ 15,601 $ 14,782
Options exercisable $ 9,738 $ 15,457 $ 14,463