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Oxford Term Loans - Narrative (Details) - USD ($)
Mar. 15, 2019
Mar. 31, 2019
Term Loan Facility    
Debt Instrument [Line Items]    
Maximum borrowing capacity   $ 75,000,000
Interest rate on debt   11.60%
Percentage of final payment of full principal amount 5.50%  
Prepayment fee percentage, next twelve months 3.00%  
Prepayment fee percentage, year two 2.00%  
Prepayment fee percentage, thereafter 1.00%  
Debt discount   $ 1,100,000
Debt issuance costs   $ 2,200,000
Term Loan Facility | Applicable Rate    
Debt Instrument [Line Items]    
Default interest rate 5.00%  
Secured Debt    
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 100,000,000.0  
Interest rate on debt 9.50%  
Period of interest only payments 36 months  
Amortization period 23 months  
Additional period of agreement of interest payment 12 months  
Aggregate period 48 months  
Additional amortization period 11 months  
Secured Debt | London Interbank Offered Rate (LIBOR)    
Debt Instrument [Line Items]    
Basis spread on variable rate 7.00%  
Secured Debt | Term Loan Facility, Tranche One    
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 75,000,000.0  
Secured Debt | Term Loan Facility, Tranche Two    
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 25,000,000.0