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Stock-Based Compensation - Restricted Stock Units (Details) - Restricted stock units - USD ($)
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vested in period, fair value $ 2,500,000 $ 0
Number of Shares (in shares)    
Unvested at beginning of period (in shares) 381,952  
Granted (in shares) 413,792  
Forfeited (in shares) 0  
Vested (in shares) (174,211)  
Unvested at end of period (in shares) 621,533  
Weighted- Average Grant Date Fair Value (in dollars per share)    
Unvested at beginning of period (in dollars per share) $ 15.11  
Granted (in dollars per share) 13.95  
Forfeited (in dollars per share) 0  
Vested (in dollars per share) 14.58  
Unvested at end of period (in dollars per share) $ 14.48  
Number of vested shares recipients elected to defer settlement (in shares) 146,075  
Unrecognized compensation expense $ 6,500,000  
Unrecognized compensation expense, period for recognition (years) 1 year 9 months 18 days  
Executive Officer    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period (years) 3 years  
Board of Directors    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period (years) 1 year