Quarterly report pursuant to Section 13 or 15(d)

Common Stock Warrants - Summary of Common Stock Warrants Outstanding (Details)

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Common Stock Warrants - Summary of Common Stock Warrants Outstanding (Details) - $ / shares
shares in Thousands
 3 Months Ended
Mar. 31, 2016
Feb. 29, 2016
Dec. 31, 2015
Class Of Warrant Or Right [Line Items]      
Exercise price of warrants (in dollars per share)   $ 0.77  
Warrant outstanding (in shares) 18,330   18,165
Five Year Warrants Issued in December 2011 [Member] | Stockholders' Deficit [Member]      
Class Of Warrant Or Right [Line Items]      
Issuance Date 2011-12    
Expiration Date 2016-12    
Exercise price of warrants (in dollars per share) $ 1.14    
Warrant outstanding (in shares) 263   263
Five Year Warrants Issued in March 2012 [Member] | Warrant Liabilities [Member]      
Class Of Warrant Or Right [Line Items]      
Issuance Date 2012-03    
Expiration Date 2017-03    
Exercise price of warrants (in dollars per share) $ 1.76    
Warrant outstanding (in shares) 9,585   9,585
Five Year Warrants Issued in September 2012 [Member] | Stockholders' Deficit [Member]      
Class Of Warrant Or Right [Line Items]      
Issuance Date 2012-09    
Expiration Date 2017-09    
Exercise price of warrants (in dollars per share) $ 3.54    
Warrant outstanding (in shares) 39   39
Two Year Warrants Issued in December 2014 [Member] | Warrant Liabilities [Member]      
Class Of Warrant Or Right [Line Items]      
Issuance Date 2014-12    
Expiration Date 2016-12    
Exercise price of warrants (in dollars per share) $ 7.90    
Warrant outstanding (in shares) 8,097   8,097
Five Year Warrants Issued in February 2015 [Member] | Stockholders' Deficit [Member]      
Class Of Warrant Or Right [Line Items]      
Issuance Date 2015-02    
Expiration Date 2020-02    
Exercise price of warrants (in dollars per share) $ 3.31    
Warrant outstanding (in shares) 181   181
Five Year Warrants Issued in February 2016 [Member] | Stockholders' Deficit [Member]      
Class Of Warrant Or Right [Line Items]      
Issuance Date 2016-02    
Expiration Date 2021-02    
Exercise price of warrants (in dollars per share) $ 0.77    
Warrant outstanding (in shares) 165