Annual report pursuant to Section 13 and 15(d)

Equity-Based Compensation - Summary of Option Activity (Details)

Equity-Based Compensation - Summary of Option Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Summary of option activity under stock plans    
Number of options outstanding, beginning balance (in shares) 31,299,385  
Number of options, granted (in shares) 5,880,900  
Number of options, exercised (in shares) (540,000)  
Number of options, forfeited (in shares) (1,533,025)  
Number of options, expired (in shares) (2,075,962)  
Number of options outstanding, ending balance (in shares) 33,031,298 31,299,385
Share-based Compensation Weighted Average Exercise Price [Abstract]    
Weighted average exercise price, beginning balance (in dollars per share) $ 10.08  
Weighted average exercise price, granted (in dollars per share) 4.30  
Weighted average exercise price, exercised (in dollars per share) 3.69  
Weighted average exercise price, forfeited (in dollars per share) 8.14  
Weighted average exercise price, expired (in dollars per share) 8.48  
Weighted average exercise price, ending balance (in dollars per share) $ 9.31 $ 10.08
Weighted average remaining contractual term, outstanding 5 years 11 months 4 days 6 years 4 months 13 days
Aggregate intrinsic value, outstanding $ 232 $ 1,886
Vested and expected to vest, number of options (in shares) 31,317,632  
Vested and expected to vest, weighted average exercise price (in dollars per share) $ 9.39  
Weighted average expected to vest, remaining contractual term 5 years 9 months 18 days  
Aggregate intrinsic value, vested and expected to vest $ 206  
Number of options exercisable (in shares) 21,451,856  
Weighted average exercise price exercisable (in dollars per share) $ 10.18  
Weighted average remaining contractual term, exercisable 4 years 7 months 20 days  
Exercisable, aggregate intrinsic value $ 58