Employee Benefit Plans - Stock Activity, Weighted Average Exercise Price (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Shares      
Granted (in shares) 3,702,500 3,960,000 4,245,000
Stock options      
Shares      
Options outstanding, beginning balance (in shares) 11,700,786    
Granted (in shares) 3,702,500 3,960,000 4,246,000
Exercised (in shares) (274,000)    
Forfeited (in shares) (347,482)    
Expired (in shares) (21,750)    
Options outstanding, end balance (in shares) 14,760,054 11,700,786  
Options exercisable (in shares) 7,368,564    
Options unvested (in shares) 7,391,490    
Weighted Average Exercise Price      
Options outstanding, beginning balance, weighted-average exercise price $ 3.29    
Granted, weighted-average exercise price 1.72    
Exercised, weighted-average exercise price 0.37    
Forfeited, weighted-average exercise price 2.91    
Expired, weighted-average exercise price 49.18    
Options outstanding, end balance, weighted-average exercise price 2.90 $ 3.29  
Options exercisable, weighted-average exercise price 3.28    
Options unvested, weighted-average exercise price $ 2.52    
Stock option activity additional disclosures      
Options outstanding, weighted-average remaining contractual term 7 years 10 months 24 days 8 years 3 months 18 days  
Options exercisable, weighted-average remaining contractual term 7 years    
Options unvested, weighted-average remaining contractual term 8 years 10 months 24 days    
Options outstanding, aggregate intrinsic value $ 878    
Options exercisable, aggregate intrinsic value $ 878    
Weighted-average grant date fair value of options granted (per share) $ 1.39 $ 1.99 $ 4.05
Unrecognized compensation cost $ 11,000    
Period for recognition 3 years    
Fair value of stock options that vested during the period $ 8,600 $ 6,100  
the 2011 Plan | Stock options      
Shares      
Options outstanding, end balance (in shares) 14,800,000