Annual report pursuant to Section 13 and 15(d)

Facility Loans - Additional Information (Detail)

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Facility Loans - Additional Information (Detail) - USD ($)
12 Months Ended
Jun. 04, 2018
Aug. 07, 2015
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Sep. 30, 2013
Debt Instrument [Line Items]            
Repayment of facility loan     $ 6,527,000 $ 3,137,000 $ 986,000  
Loss on extinguishment of debt     $ (407,000)      
Facility loan, less current portion       $ 2,990,000    
Warrants [Member]            
Debt Instrument [Line Items]            
Fair value of warrant liabilities           $ 300,000
2015 Term Loan Facility [Member]            
Debt Instrument [Line Items]            
Maximum borrowing capacity   $ 15,000,000        
Facility loan, fixed interest rate   8.77%        
Debt instrument payment terms     The Company was required to make 12 monthly interest only payments after the funding date followed by a repayment schedule equal to 36 equal monthly payments of interest and principal.      
Percentage of principal amount as final payment   6.50%        
Facility fee   1.00%        
Issued warrants to purchase common stock     114,436      
Exercise price of common stock     $ 2.84      
Warrant term     10 years      
Repayment of facility loan $ 4,200,000          
Facility loan, final fee 700,000          
Prepayment penalty 100,000          
Loss on extinguishment of debt $ (400,000)          
Facility loan, less current portion     $ 0      
2015 Term Loan Facility [Member] | First Tranche [Member]            
Debt Instrument [Line Items]            
Facility loan, drawn   $ 10,000,000        
2015 Term Loan Facility [Member] | Second Tranche [Member]            
Debt Instrument [Line Items]            
Facility loan available for draw down   5,000,000        
2013 Term Loan Facility [Member]            
Debt Instrument [Line Items]            
Retiring of existing debt   $ 4,100,000