Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt - Hercules Term Loan - Additional Information (Details)

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Long-Term Debt - Hercules Term Loan - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended
Feb. 27, 2015
Feb. 29, 2016
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Debt Instrument [Line Items]          
Aggregate number of unregistered shares of common stock called by warrants (in shares)   165,000      
Exercise price of warrants (in dollars per share)   $ 0.77      
Estimated fair value of warrants   $ 100,000      
Exercisable period of warrants   5 years      
Warrants expiration period   2021-02      
Carrying value of the loan     $ 46,251,000   $ 48,667,000
Hercules Loan [Member]          
Debt Instrument [Line Items]          
Maturity date Sep. 01, 2018        
Variable rate basis     The Hercules Term Loan has a variable interest rate that is the greater of either (i) 9.40% plus the prime rate as reported from time to time in The Wall Street Journal minus 7.25%, or (ii) 9.40%.    
Period of principal and interest amortized 30 months        
Amortization of interest payments period end date Jun. 01, 2016        
Period of interest 1 month        
Prepayment fee within twelve months of maturity 3.00%        
Prepayment fee after twelve months but before twenty four months of maturity 2.00%        
Prepayment fee after twenty four months of maturity 1.00%        
Additional interest rate in case of default 5.00%        
Debt issuance costs $ 500,000        
Final payment fee $ 1,200,000        
Amortization of debt discount     $ 200,000 $ 49,000  
Aggregate number of unregistered shares of common stock called by warrants (in shares) 181,268        
Exercise price of warrants (in dollars per share) $ 3.31        
Estimated fair value of warrants $ 500,000        
Exercisable period of warrants 5 years        
Warrants expiration period 2020-02        
Outstanding principal balance     20,000,000   20,000,000
Carrying value of the loan     $ 19,800,000   $ 19,700,000
Minimum [Member] | Hercules Loan [Member]          
Debt Instrument [Line Items]          
Percentage bearing variable rate     9.40%    
Prime Rate [Member] | Hercules Loan [Member]          
Debt Instrument [Line Items]          
Basis spread, addition     9.40%    
Basis spread, subtraction     7.25%