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, 2017
Dec. 31, 2016
Summary of option activity under stock plans    
Number of options outstanding, beginning balance (in shares) 34,640,514  
Number of options, granted (in shares) 2,131,500  
Number of options, exercised (in shares) (1,298,704)  
Number of options, forfeited (in shares) (2,735,813)  
Number of options, expired (in shares) (1,438,112)  
Number of options outstanding, ending balance (in shares) 31,299,385 34,640,514
Share-based Compensation Weighted Average Exercise Price [Abstract]    
Weighted average exercise price, beginning balance (in dollars per share) $ 10.18  
Weighted average exercise price, granted (in dollars per share) 7.50  
Weighted average exercise price, exercised (in dollars per share) 3.01  
Weighted average exercise price, forfeited (in dollars per share) 11.75  
Weighted average exercise price, expired (in dollars per share) 11.84  
Weighted average exercise price, ending balance (in dollars per share) $ 10.08 $ 10.18
Weighted average remaining contractual term, outstanding 6 years 4 months 15 days 6 years 9 months 15 days
Aggregate intrinsic value, outstanding $ 1,886 $ 32,984
Vested and expected to vest, number of options (in shares) 29,484,888  
Vested and expected to vest, weighted average exercise price (in dollars per share) $ 10.04  
Weighted average expected to vest, remaining contractual term 6 years 3 months 6 days  
Aggregate intrinsic value, vested and expected to vest $ 1,886  
Number of options exercisable (in shares) 18,697,466  
Weighted average exercise price exercisable (in dollars per share) $ 9.59  
Weighted average remaining contractual term, exercisable 4 years 15 months 3 days  
Exercisable, aggregate intrinsic value $ 1,886