Annual report pursuant to Section 13 and 15(d)

Stock-Based Payments - Stock Options (Details)

v3.8.0.1
Stock-Based Payments - Stock Options (Details)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
Milestone
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2015
USD ($)
Shares      
Outstanding at beginning of year (in shares) | shares 2,543,435    
Granted (in shares) | shares 1,368,000    
Exercised (in shares) | shares (445,012)    
Cancelled (in shares) | shares (619,755)    
Outstanding at end of period (in shares) | shares 2,846,668 2,543,435  
Exercisable (in shares) | shares 858,927    
Vested and expected to vest (in shares) | shares 2,846,668    
Weighted Average Exercise Price      
Outstanding at beginning of year (in dollars per share) | $ / shares $ 6.44    
Granted (in dollars per share) | $ / shares 11.87    
Exercised (in dollars per share) | $ / shares 4.03    
Cancelled (in dollars per share) | $ / shares 7.22    
Outstanding at end of period (in dollars per share) | $ / shares 9.25 $ 6.44  
Exercisable (in dollars per share) | $ / shares 6.06    
Vested and expected to vest (in dollars per share) | $ / shares $ 9.25    
Remaining Contractual Life      
Outstanding 8 years 2 months 12 days 8 years 3 months 18 days  
Exercisable 7 years    
Vested and expected to vest 8 years 2 months 12 days    
Aggregate Intrinsic Value      
Outstanding | $ $ 5,713 $ 14,898  
Exercisable | $ 3,827    
Vested and expected to vest | $ 5,713    
Intrinsic value of options exercised | $ 4,600 2,400 $ 2,000
Cash received from option exercises | $ 1,800 400 $ 400
Performance-based stock options      
Stock-based payments      
Additional stock-based compensation expense recorded related to achievement of certain performance-based milestones | $ 0 $ 200  
Unrecognized compensation costs | $ $ 1,000    
Performance-based stock options | Advisor      
Stock-based payments      
Number of milestones achieved during the period | Milestone 0    
Unrecognized compensation costs | $ $ 600    
Period in which compensation costs will be recognized 8 years 8 months 12 days    
Shares      
Granted (in shares) | shares   75,000