Annual report pursuant to Section 13 and 15(d)

Stock-based Compensation Plans and Awards - Schedule of stock option activity (Details)

v3.8.0.1
Stock-based Compensation Plans and Awards - Schedule of stock option activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Outstanding Stock Options    
Expired (in shares) 1,469,714  
Stock options    
Outstanding Stock Options    
Balance at the beginning of the period (in shares) 9,436,380  
Granted (in shares) 2,226,938 0
Exercised (in shares) (4,968,577)  
Forfeited (in shares) (903,112)  
Expired (in shares) 1,469,714  
Balance at the end of the period (in shares) 4,321,915 9,436,380
Vested and exercisable at the end of the period (in shares) 2,616,163  
Expected to vest at the end of the period (in shares) 1,705,752  
Weighted-Average Exercise Price    
Balance at the beginning of the period (in dollars per share) $ 5.74  
Granted (in dollars per share) 9.80  
Exercised (in dollars per share) 1.97  
Forfeited (in dollars per share) 7.69  
Expired (in dollars per share) 16.15  
Balance at the end of the period (in dollars per share) 8.90 $ 5.74
Vested and exercisable at the end of the period (in dollars per share) 8.55  
Expected to vest at the end of the period (in dollars per share) $ 9.45  
Weighted-Average Remaining Contractual Term (in years)    
Outstanding at the beginning of the period 5 years 10 months 2 days 14 days
Outstanding at the end of the period 5 years 10 months 2 days 14 days
Vested and exercisable at the end of the period 3 years 5 months 4 days  
Expected to vest at the end of the period 9 years 6 months 10 days  
Aggregate Intrinsic Value    
Aggregate intrinsic value beginning of the period $ 2,922 $ 77,752
Aggregate intrinsic value end of the period 2,922 $ 77,752
Vested and exercisable at the end of the period 2,918  
Expected to vest at the end of the period $ 4  
Fair value per share of common stock (in dollars per share) $ 4.82 $ 13.04