Quarterly report pursuant to Section 13 or 15(d)

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

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Long-Term Debt - Silicon Valley Bank Loan Agreement - Additional Information (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2019
Mar. 04, 2019
May 07, 2018
Jun. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Debt Instrument [Line Items]            
Current portion of long-term debt $ 2,675,000     $ 2,675,000 $ 2,675,000 $ 789,000 [1]
Long-term debt $ 23,348,000     23,348,000 23,348,000 21,690,000 [1]
Loan and Security Agreement [Member] | Silicon Valley Bank [Member] | Warrants for Common Stock [Member]            
Debt Instrument [Line Items]            
Aggregate number of shares of common stock called by warrants   4,845 6,332      
Exercise price of per share   $ 14.71 $ 23.69      
Fair value of warrant   $ 100,000 $ 100,000      
Exercisable period of warrants 10 years          
Loan and Security Agreement [Member] | Term Loan [Member] | Silicon Valley Bank [Member]            
Debt Instrument [Line Items]            
Maximum borrowing capacity under loan agreement     20,000,000      
Increase borrowing capacity under loan agreement     $ 40,000,000      
End of the draw period of the term loan     Mar. 31, 2019      
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      
Extended end of the draw period of the term loan   Mar. 31, 2020        
Loan and Security Agreement [Member] | Term Loan [Member] | Silicon Valley Bank [Member] | Agenus [Member]            
Debt Instrument [Line Items]            
Carrying value of debt $ 10,500,000     10,500,000 10,500,000 7,300,000
Current portion of long-term debt 2,700,000     2,700,000 2,700,000 800,000
Long-term debt 7,800,000     7,800,000 7,800,000 $ 6,500,000
Loan and Security Agreement [Member] | Term Loan [Member] | Silicon Valley Bank [Member] | First Anniversary [Member]            
Debt Instrument [Line Items]            
Percentage of prepayment fee     2.00%      
Loan and Security Agreement [Member] | Term Loan [Member] | Silicon Valley Bank [Member] | Second Anniversary [Member]            
Debt Instrument [Line Items]            
Percentage of prepayment fee     1.00%      
Loan and Security Agreement [Member] | Term Loan [Member] | Prime Rate [Member] | Silicon Valley Bank [Member]            
Debt Instrument [Line Items]            
Basis spread on variable rate     0.25%      
Loan and Security Agreement [Member] | Novartis [Member] | Silicon Valley Bank [Member]            
Debt Instrument [Line Items]            
Maturity date     Mar. 01, 2023      
Days of interest, period     30 days      
Earliest maturity of loan     30 days      
Loan and Security Agreement [Member] | First Term Loan [Member] | Silicon Valley Bank [Member] | Agenus [Member]            
Debt Instrument [Line Items]            
Loan borrowed 7,500,000     7,500,000 7,500,000  
Discount against debt 300,000     300,000 300,000  
Non-cash interest expense resulting from amortization of discount and accretion of final payment       100,000 200,000  
Loan and Security Agreement [Member] | Second Term Loan [Member] | Silicon Valley Bank [Member] | Aronora [Member]            
Debt Instrument [Line Items]            
Loan borrowed 3,000,000     3,000,000 3,000,000  
Discount against debt $ 45,000     $ 45,000 $ 45,000  
[1] The condensed consolidated balance sheet as of December 31, 2018 has been derived from the audited consolidated financial statements as of that date included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018.