Annual report pursuant to Section 13 and 15(d)

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

v3.19.1
Description of Business and Basis of Preparation - Additional Information (Detail) - USD ($)
12 Months Ended
Sep. 14, 2018
Mar. 08, 2018
Jun. 21, 2016
Dec. 31, 2018
Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]          
Shelf registration maximum equity offering price $ 175,000,000        
Aggregate amount receivable upon exercise of warrants 53,000,000        
Common stock issued, net of expenses (in shares)   17,751,500 9,375,000    
Common stock issued, net of expenses       $ 20,437,000 $ 9,954,000
Common Stock          
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]          
Common stock issued, net of expenses (in shares)       18,959,675 4,344,108
Common stock issued, net of expenses       $ 19,000 $ 5,000
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  
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    
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 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