Summary of Siginificant Accounting Policies - Stock-Based Compensation, Per Share Amounts (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2016
Jan. 31, 2014
Feb. 28, 2013
May 31, 2011
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 22, 2016
May 16, 2013
Dec. 31, 2011
Stock-Based Compensation                                      
Tax benefit (expense) for stock-based compensation                         $ 0 $ 0 $ 0        
Numerator                                      
Net loss attributable to common shareholders         $ (19,237) $ (13,420) $ (13,154) $ (11,780) $ (25,227) $ (10,238) $ (9,253) $ (11,077) $ (57,591) $ (55,795) $ (88,644)        
Denominator                                      
Weighted Average Number of Shares Outstanding, Basic and Diluted                         180,619,860 176,067,231 159,228,815        
Number of dilutive potential common shares                         46,765,065 21,652,391 18,614,650        
Granted (in shares)                         3,702,500 3,960,000 4,245,000        
Number of warrants exercised (in shares)                         119,879 26,882 23,918,429        
Weighted average exercise price of warrants (in dollars per share) $ 1.50       $ 1.50               $ 1.50            
Warrants outstanding (in shares) 14,501,600       14,501,600       4,192,567       14,501,600 4,192,567          
Stock options                                      
Denominator                                      
Number of dilutive potential common shares                         14,760,054 11,700,786 8,367,271        
Restricted stock                                      
Denominator                                      
Number of dilutive potential common shares                         13,333 204,444 473,336        
Warrants                                      
Denominator                                      
Number of dilutive potential common shares                         14,501,600 4,192,567 4,219,449        
Preferred stock                                      
Denominator                                      
Number of dilutive potential common shares                         17,490,078 5,554,594 5,554,594        
Warrants issued in May, 2011                                      
Denominator                                      
Number of warrants issued (in shares)       7,128,563                              
Weighted average exercise price of warrants (in dollars per share)       $ 0.93                              
Warrants outstanding (in shares) 0       0       192,467       0 192,467 219,349       22,995,365
Warrants issued in February, 2013                                      
Denominator                                      
Number of warrants issued (in shares)     23,637,500                                
Weighted average exercise price of warrants (in dollars per share)     $ 0.15                                
Warrants outstanding (in shares) 100       100       100       100 100 100        
Warrants issued in February, 2013 | Minimum                                      
Denominator                                      
Weighted average exercise price of warrants (in dollars per share)                               $ 0.15      
Warrants issued in January, 2014                                      
Denominator                                      
Number of warrants issued (in shares)   4,000,000                                  
Number of warrants exercised (in shares)                         0 0 0        
Weighted average exercise price of warrants (in dollars per share) $ 1.025 $ 4.00     $ 1.025               $ 1.025   $ 4.00        
Warrants issued in December 2016                                      
Denominator                                      
Number of warrants issued (in shares) 10,501,500                                    
Number of warrants exercised (in shares)                         0            
Weighted average exercise price of warrants (in dollars per share) $ 1.50       $ 1.50               $ 1.50            
Series C Redeemable Convertible Preferred Stock                                      
Denominator                                      
Redeemable convertible Preferred Stock, shares issued 5,231       5,231       5,231       5,231 5,231       10,431  
Shares issued upon conversion of redeemable stock (in shares)                               5,200      
Series D Redeemable Convertible Preferred Stock                                      
Denominator                                      
Redeemable convertible Preferred Stock, shares issued 18,500       18,500       0       18,500 0     18,500    
Shares issued upon conversion of redeemable stock (in shares)                         0