Stockholders' (Deficit) Equity - Preferred Stock (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended
Feb. 28, 2017
Oct. 31, 2016
Mar. 31, 2014
Mar. 31, 2018
Dec. 31, 2017
Class of Stock [Line Items]          
Shares Authorized       76,894,620 76,894,620
Shares Issued       76,235,050 76,235,050
Shares Outstanding       76,235,050 76,235,050
Carrying Value       $ 119,106 $ 119,106
Dividend Rate Percentage       8.00%  
Series A convertible preferred stock          
Class of Stock [Line Items]          
Shares Authorized       5,375,507 5,375,507
Shares Issued       5,375,507 5,375,507
Shares Outstanding       5,375,507 5,375,507
Carrying Value       $ 5,037 $ 5,037
Liquidation Preference Per Share       $ 1.00  
8% Dividend Per Share       0.08  
Conversion Price Per Share       6.65  
Shares issue price (in dollars per share)       $ 1.00  
Convertible preferred stock, conversion shares       0.1504  
Series B convertible preferred stock          
Class of Stock [Line Items]          
Shares Authorized       8,706,909 8,706,909
Shares Issued       8,706,909 8,706,909
Shares Outstanding       8,706,909 8,706,909
Carrying Value       $ 15,913 $ 15,913
Liquidation Preference Per Share       $ 1.84  
8% Dividend Per Share       0.12  
Conversion Price Per Share       9.91  
Shares issue price (in dollars per share)       $ 1.84  
Convertible preferred stock, conversion shares       0.1855  
Series C convertible preferred stock          
Class of Stock [Line Items]          
Shares Authorized       14,091,589 14,091,589
Shares Issued       13,829,906 13,829,906
Shares Outstanding       13,829,906 13,829,906
Carrying Value       $ 14,949 $ 14,949
Liquidation Preference Per Share       $ 1.07  
8% Dividend Per Share       0.09  
Conversion Price Per Share       7.12  
Shares issue price (in dollars per share)       $ 1.07  
Convertible preferred stock, conversion shares       0.1504  
Series D convertible preferred stock          
Class of Stock [Line Items]          
Shares Authorized       5,683,292 5,683,292
Shares Issued       5,683,292 5,683,292
Shares Outstanding       5,683,292 5,683,292
Carrying Value       $ 6,043 $ 6,043
Liquidation Preference Per Share       $ 1.07  
8% Dividend Per Share       0.09  
Conversion Price Per Share       7.12  
Shares issue price (in dollars per share)       $ 1.07  
Convertible preferred stock, conversion shares       0.1504  
Series E convertible preferred stock          
Class of Stock [Line Items]          
Shares Authorized       15,373,091 15,373,091
Shares Issued       15,267,175 15,267,175
Shares Outstanding       15,267,175 15,267,175
Carrying Value       $ 39,848 $ 39,848
Liquidation Preference Per Share       $ 2.62  
8% Dividend Per Share       0.21  
Conversion Price Per Share       $ 15.16  
Shares issued     15,267,175    
Shares issue price (in dollars per share)     $ 2.62    
Convertible preferred stock, conversion shares     0.1728    
Proceeds from issuance of convertible preferred stock     $ 39,800    
Series F convertible preferred stock          
Class of Stock [Line Items]          
Shares Authorized       27,664,232 27,664,232
Shares Issued       27,372,261 27,372,261
Shares Outstanding       27,372,261 27,372,261
Carrying Value       $ 37,316 $ 37,316
Liquidation Preference Per Share       $ 1.37  
8% Dividend Per Share       0.11  
Conversion Price Per Share       $ 9.11  
Shares issued 18,248,177 9,124,084      
Shares issue price (in dollars per share) $ 1.37 $ 1.37      
Convertible preferred stock, conversion shares 0.1504        
Proceeds from issuance of convertible preferred stock $ 25,000 $ 12,300