Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Payments - Stock Options (Details)

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Stock-Based Payments - Stock Options (Details) - USD ($)
$ / shares in Units, $ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Shares    
Outstanding at beginning of year (in shares) 2,543,435  
Granted (in shares) 1,091,900  
Exercised (in shares) (314,088)  
Cancelled (in shares) (550,132)  
Outstanding at end of period (in shares) 2,771,115 2,543,435
Exercisable (in shares) 860,612  
Vested and expected to vest (in shares) 2,771,115  
Weighted Average Exercise Price    
Outstanding at beginning of year (in dollars per share) $ 6.44  
Granted (in dollars per share) 11.86  
Exercised (in dollars per share) 2.91  
Cancelled (in dollars per share) 7.18  
Outstanding at end of period (in dollars per share) 8.82 $ 6.44
Exercisable (in dollars per share) 5.44  
Vested and expected to vest (in dollars per share) $ 8.82  
Remaining Contractual Life    
Outstanding 8 years 8 years 3 months 18 days
Exercisable 6 years 2 months 12 days  
Vested and expected to vest 8 years  
Aggregate Intrinsic Value    
Outstanding $ 16,544 $ 14,898
Exercisable 8,018  
Vested and expected to vest 16,544  
Intrinsic value of options exercised 4,100  
Performance-based stock options    
Stock-based payments    
Unrecognized compensation costs $ 600  
Period in which compensation costs will be recognized 2 years 8 months 12 days  
Performance-based stock options | Maximum    
Stock-based payments    
Vesting period 6 years  
Performance-based stock options | Advisor    
Stock-based payments    
Unrecognized compensation costs $ 1,000  
Period in which compensation costs will be recognized 9 years  
Shares    
Granted (in shares)   75,000