Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Payments - Stock Options (Details)

v3.8.0.1
Stock-Based Payments - Stock Options (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Shares      
Outstanding at beginning of year (in shares) 2,846,668    
Granted (in shares) 1,101,550    
Exercised (in shares) (74,982)    
Cancelled (in shares) (120,211)    
Outstanding at end of period (in shares) 3,753,025   2,846,668
Exercisable (in shares) 1,128,846    
Weighted Average Exercise Price      
Outstanding at beginning of year (in dollars per share) $ 9.25    
Granted (in dollars per share) 10.61    
Exercised (in dollars per share) 3.23    
Cancelled (in dollars per share) 10.14    
Outstanding at end of period (in dollars per share) 9.74   $ 9.25
Exercisable (in dollars per share) $ 7.29    
Remaining Contractual Life      
Outstanding 8 years 6 months   8 years 2 months 12 days
Exercisable 7 years 2 months 12 days    
Aggregate Intrinsic Value      
Outstanding $ 12,930   $ 5,713
Exercisable 6,556    
Intrinsic value of options exercised 700 $ 500  
Performance-based stock options      
Stock-based payments      
Additional stock-based compensation expense recorded related to achievement of certain performance-based milestones 200 $ 0  
Unrecognized compensation costs $ 1,200    
Period in which compensation costs will be recognized 3 years 6 months 26 days    
Performance-based stock options | Maximum      
Stock-based payments      
Vesting period 6 years    
Performance-based stock options | Advisor      
Stock-based payments      
Unrecognized compensation costs $ 800    
Period in which compensation costs will be recognized 8 years 6 months    
Shares      
Granted (in shares) 0   75,000