Annual report pursuant to Section 13 and 15(d)

Long-Term Debt and Other Financings - Silicon Valley Bank Loan Agreement - Additional Information (Details)

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Long-Term Debt and Other Financings - Silicon Valley Bank Loan Agreement - Additional Information (Details) - Loan and Security Agreement [Member] - Silicon Valley Bank [Member] - USD ($)
12 Months Ended
May 07, 2018
Dec. 31, 2018
Warrants for Common Stock [Member]    
Debt Instrument [Line Items]    
Earlier effecitve date of term loan Mar. 31, 2019  
Aggregate number of shares of common stock called by warrants 6,332  
Exercise price of per share $ 23.69  
Exercisable period of warrants 10 years  
Fair value of warrant $ 100,000  
Term Loan [Member]    
Debt Instrument [Line Items]    
Maximum borrowing capacity under loan agreement 20,000,000  
Increase borrowing capacity under loan agreement $ 40,000,000  
Earlier effecitve date of term loan Mar. 31, 2019  
Effective date of term loan extended Mar. 31, 2020  
Gross cash proceeds received from milestone and licensing payments $ 20,000,000  
Basis spread on variable rate 4.75%  
Variable rate basis The interest-only period will be followed by equal monthly payments of principal and interest over 24 months. Each Term Loan Advance will mature at the earlier of (i) the 23 months following the applicable term loan amortization date for each such Term Loan Advance (ii) March 1, 2023, or (iii) 30 days prior to the earliest maturity of any portion of the Company’s loan with Novartis (the “Loan Maturity Date”). After repayment, no Term Loan Advance (or any portion thereof) may be reborrowed.  
Period of monthly payments of principal and interest 24 months  
Repayment of term loan $ 0  
Loan borrowed $ 0  
Percentage of final payment fee of Loan 8.50%  
Percentage of prepayment fee 3.00%  
Additional interest rate of outstanding payments due 4.00%  
Debt issuance costs $ 200,000  
Unamortized amount of deferred charges   $ 300,000
Non-cash interest expense resulting from amortization of discount and accretion of final payment   100,000
Term Loan [Member] | Agenus [Member]    
Debt Instrument [Line Items]    
Loan borrowed   7,500,000
Outstanding principal balance   $ 7,300,000
Term Loan [Member] | First Anniversary [Member]    
Debt Instrument [Line Items]    
Percentage of prepayment fee 2.00%  
Term Loan [Member] | Second Anniversary [Member]    
Debt Instrument [Line Items]    
Percentage of prepayment fee 1.00%  
Term Loan [Member] | Prime Rate [Member]    
Debt Instrument [Line Items]    
Basis spread on variable rate 0.25%  
Novartis [Member]    
Debt Instrument [Line Items]    
Maturity date Mar. 01, 2023  
Days of interest, period 30 days  
Earliest maturity of loan 30 days