Annual report pursuant to Section 13 and 15(d)

Description of Business and Basis of Preparation - Additional Information (Detail)

v3.20.1
Description of Business and Basis of Preparation - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 12, 2019
Sep. 14, 2018
Mar. 08, 2018
Jun. 21, 2016
Dec. 31, 2019
Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Accumulated deficit $ (271,428,000)         $ (271,428,000) $ (217,718,000)
Cash and cash equivalents 41,920,000         41,920,000 11,439,000
Short-term investments 6,494,000         6,494,000 32,718,000
Shelf registration maximum equity offering price $ 127,500,000   $ 175,000,000        
Number of warrants issued to purchase common stock (in shares)     13,198,075        
Aggregate amount receivable upon exercise of warrants     $ 28,600,000        
Warrants, expiration date     Mar. 14, 2019        
Common stock issued, net of expenses (in shares)       17,751,500 9,375,000    
Common stock issued, net of expenses           $ 30,530,000 $ 20,437,000
Option to Purchase Common Stock              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Options expiration date   2020-01          
Option to Purchase Common Stock | Maximum              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of options not exercised   5,833,333          
Common Stock              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Common stock issued, net of expenses (in shares)           47,736,920 18,959,675
Common stock issued, net of expenses           $ 47,000 $ 19,000
Series 1 Warrant              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)             115,550
Warrants, expiration date       Mar. 14, 2019      
Sales Agreement | Common Stock              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Shelf registration maximum equity offering price     $ 25,000,000        
June 2016 Public Offering              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)     4,218,750        
Exercise price of warrants (in dollars per share)     $ 3.00   $ 3.00    
June 2016 Public Offering | Warrant liability | Maximum              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)         4,218,750    
March 2018 Public Offering              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)       21,301,800      
Common stock issued, net of expenses (in shares)       17,751,500      
Share price (in dollars per share)       $ 1.69      
Common stock issued, net of expenses       $ 27,900,000      
March 2018 Public Offering | Series 1 Warrant              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)     13,198,075        
Exercise price of warrants (in dollars per share)     $ 1.85 $ 1.85      
March 2018 Public Offering | Series 1 Warrant | Maximum              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)       13,313,625      
March 2018 Public Offering | Series 2 Warrant              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)     7,988,175        
Exercise price of warrants (in dollars per share)     $ 2.00 $ 2.00      
March 2018 Public Offering | Series 2 Warrant | Maximum              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)       7,988,175      
March 2018 Public Offering | Warrant liability | Maximum              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)       21,301,800      
December 2019 Public Offering              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)   38,888,889          
Exercise price of warrants (in dollars per share)   $ 1.10          
Warrants, expiration date   Jun. 12, 2023          
Common stock issued, net of expenses (in shares)   38,888,889          
Share price (in dollars per share)   $ 0.90          
Common stock issued, net of expenses   $ 32,500,000          
December 2019 Public Offering | Warrant liability | Maximum              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)   38,888,889          
Underwriters | Maximum              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Option to purchase shares of common stock   5,833,333          
Underwriters | Warrant liability              
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]              
Number of warrants issued to purchase common stock (in shares)   5,833,333          
Number of warrants exercised   5,833,333