Quarterly report pursuant to Section 13 or 15(d)

Borrowing Arrangements - Additional Information - (Detail)

v3.8.0.1
Borrowing Arrangements - Additional Information - (Detail) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Feb. 27, 2018
Mar. 31, 2018
Apr. 30, 2016
Jun. 30, 2015
May 31, 2015
Mar. 31, 2017
Dec. 31, 2017
Apr. 30, 2015
Perceptive                
Debt Instrument [Line Items]                
Final fee due at the loan maturity date $ 3,400,000              
Debt instrument, annual interest rate   12.96%            
Term Loan Facility | Perceptive                
Debt Instrument [Line Items]                
Maximum borrowing capacity under loan $ 10,000,000              
Common stock exercise price $ 9.5792              
Increase in applicable margin percentage on event of default 4.00%              
Period for which interest only payments will be made 24 months              
Credit Facility, principal payments $ 200,000              
Credit Facility, maturity date Feb. 27, 2022              
Exit fee $ 100,000              
Number of shares issued for each warrant 190,000              
Warrant exercisable period 7 years              
LIBOR | Term Loan Facility | Perceptive                
Debt Instrument [Line Items]                
Debt instrument, basis spread on variable rate 11.00%              
SVB Growth Capital Loan                
Debt Instrument [Line Items]                
Maximum borrowing capacity under loan               $ 6,000,000
Number of warrants to purchase shares of common stock     17,310 14,254       48,874
Final fee due at the loan maturity date               $ 375,000
Amount drew down from bank     $ 3,000,000 $ 2,300,000 $ 800,000      
Common stock exercise price     $ 3.07 $ 3.07        
Aggregate amount drawn down from credit facility             $ 6,000,000  
Debt instrument, frequency of periodic payment             30  
Debt instrument first installment due date             Nov. 01, 2016  
Debt instrument maturity date             Apr. 30, 2019  
Debt instrument, annual interest rate             5.44%  
Debt instrument principal paid during period   $ 3,200,000       $ 600,000    
Final fee paid   375,000            
Debt instrument interest paid during period   42,000       $ 66,000    
Total debt   $ 0         $ 3,500,000  
SVB Growth Capital Loan | Prime Rate                
Debt Instrument [Line Items]                
Debt instrument, basis spread on variable rate             1.19%  
Term Loan Drawn on Effective Date of Credit Facility | Term Loan Facility | Perceptive                
Debt Instrument [Line Items]                
Proceeds from initial term loan on closing date of Credit Facility $ 5,000,000              
Additional Term Loan Drawn Six Months Following Effective Date of Credit Facility | Term Loan Facility | Perceptive                
Debt Instrument [Line Items]                
Remaining available amount from credit facility to be drawn six months following effective date of credit facility $ 5,000,000