Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Additional Information (Detail)

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Stockholders' Equity - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Sep. 30, 2018
Feb. 01, 2018
Jul. 24, 2017
Feb. 07, 2017
Aug. 07, 2015
Feb. 28, 2019
Sep. 30, 2013
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2013
Dec. 28, 2018
Class of Stock [Line Items]                        
Preferred stock, shares authorized               10,000,000 10,000,000      
Common stock, shares authorized               100,000,000 100,000,000      
Common stock, shares issued   13,340,000 14,950,000 5,181,348       59,456,493 44,408,796      
Common stock offering price   $ 10.80 $ 6.50 $ 1.93                
Net proceeds from public offering   $ 135,500,000 $ 91,100,000 $ 9,200,000                
Registration filed on Form S-3   $ 200,000,000                   $ 200,000,000
Change in fair value of warrant liability               $ 3,710,000 $ 5,773,000 $ (75,000)    
Warrants exercised               443,505 40,250      
Cash proceeds from exercise of warrants               $ 2,550,000 $ 231,000      
Common stock warrants exercised in cashless transactions               938,300 166,193      
Net shares issued through cashless warrant exercises               513,340 58,957      
Number of unexercised warrants expired 79,150                      
Gain on extinguishment of warrant liability $ 400,000             $ 422,000        
Number of warrants outstanding               0        
Warrants, Exercise price of $5.75 per share [Member]                        
Class of Stock [Line Items]                        
Issued warrants to purchase common stock                     1,741,788  
Exercise price of common stock                     $ 5.75  
Warrant term                     5 years  
Warrants, Exercise Price of $5.00 Per Share [Member]                        
Class of Stock [Line Items]                        
Issued warrants to purchase common stock             121,739          
Exercise price of common stock             $ 5.00          
Warrant term             7 years          
Warrants, Exercise Price of $2.84 Per Share [Member]                        
Class of Stock [Line Items]                        
Common stock, shares issued         114,436              
Exercise price of common stock         $ 2.84              
Warrant term         10 years              
Subsequent Event [Member]                        
Class of Stock [Line Items]                        
Terminated amount of shelf registration statement           $ 200,000