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Stock-based Compensation - Stock Option and Restricted Share Activity (Details) - USD ($)
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Stock options      
Stock-based compensation expense      
Shares available for future issuance 1,458,561    
Shares      
Outstanding at the beginning of the period (in shares) 784,011    
Options granted (in shares) 192,700    
Outstanding at the end of the period (in shares) 976,711    
Exercisable at the end of the period (in shares) 153,088    
Weighted average exercise price      
Outstanding at the beginning of the period (in dollars per share) $ 10.70    
Options granted (in dollars per share) 15.96    
Outstanding at the end of the period (in dollars per share) 11.74    
Exercisable at the end of the period (in dollars per share) $ 13.06    
Additional disclosures      
Total cash received from stock option exercises $ 0 $ 0  
Weighted-average grant date fair value of options (in dollars per share) $ 12.68    
Stock options | Maximum      
Stock-based compensation expense      
Expiration period 10 years    
Restricted stock      
Shares      
Unvested restricted common stock 157,262   157,262
Weighted average grant date fair value      
Weighted average grant date fair value $ 10.06   $ 10.06