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Share-based Compensation - Summary of Company's Stock Option Activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Shares    
Outstanding at beginning of period (in shares) 6,989,856 6,829,097.00
Granted (in shares) 662,769.00 331,616
Exercised (in shares) (274,037) (134,539)
Forfeited (in shares) (60,293)  
Expired (in shares) (157,434) (36,318)
Outstanding at end of period (in shares) 7,160,861.00 6,989,856
Eligible for exercise (in shares) 5,877,428.00  
Weighted Average Exercise Price    
Outstanding at beginning of period (in usd per share) $ 6.57 $ 6.58
Granted (in usd per share) 5.45 5.50
Exercised (in usd per share) 4.37 3.53
Forfeited (in usd per share) 5.50  
Expired (in usd per share) 9.00 9.00
Outstanding at end of period (in usd per share) 6.51 $ 6.57
Eligible for exercise (in usd per share) $ 6.31