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Common Stock, Preferred Stock and Warrants - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 9 Months Ended
Nov. 03, 2017
Aug. 31, 2019
Sep. 30, 2019
Sep. 30, 2019
Aug. 12, 2019
Dec. 31, 2018
Class Of Stock [Line Items]            
Common stock, shares outstanding     83,865,119 83,865,119   62,862,000
Issuance of common stock and preferred stock (in shares)   18,525,000        
Common stock, par value   $ 0.001 $ 0.001 $ 0.001   $ 0.001
Preferred stock, par value     $ 0.001 $ 0.001   $ 0.001
Net cash proceeds received from issuance or sale of equity   $ 65,600,000        
Net cash proceeds received       $ 65,948,000    
Preferred stock deemed dividend     $ 3,267,000 3,267,000    
Increase in estimated fair value as loss on warrant liability       $ 234,000    
Common Stock            
Class Of Stock [Line Items]            
Issuance of common stock and preferred stock (in shares)     18,525,000 19,912,000    
Warrants            
Class Of Stock [Line Items]            
Fair value of derivative liability     $ 7,600,000 $ 7,600,000 $ 7,400,000  
Warrants | Other Income, Net            
Class Of Stock [Line Items]            
Increase in estimated fair value as loss on warrant liability     $ 200,000 $ 200,000    
Offering            
Class Of Stock [Line Items]            
Number of common stock allowed to purchase   250        
Combined price of common stock and warrant   $ 3.00        
Net cash proceeds received from issuance or sale of equity   $ 65,600,000        
Payment of issuance costs   $ 4,500,000        
2017 ATM Agreement            
Class Of Stock [Line Items]            
Issuance of common stock and preferred stock (in shares)       1,386,906    
Net cash proceeds received       $ 13,900,000    
Remaining proceeds from common stock, under sales agreement       $ 118,600,000    
Series B Convertible Preferred Stock            
Class Of Stock [Line Items]            
Issuance of common stock and preferred stock (in shares)   4,840        
Preferred stock, par value   $ 0.001        
Preferred stock, shares outstanding     4,840 4,840   0
Preferred stock deemed dividend       $ 3,300,000    
Series B Convertible Preferred Stock | Common Stock            
Class Of Stock [Line Items]            
Number of common stock allowed to purchase     1,000 1,000    
Series B Convertible Preferred Stock | Offering            
Class Of Stock [Line Items]            
Number of common stock allowed to purchase   250        
Combined price of preferred stock and warrant   $ 3,000        
Maximum | Warrants            
Class Of Stock [Line Items]            
Percentage of common stock to be held for exercise of warrants       19.99%    
Maximum | Offering            
Class Of Stock [Line Items]            
Warrant issued   5,841,250        
Maximum | 2017 ATM Agreement            
Class Of Stock [Line Items]            
Common stock sales agreement aggregate sales proceeds $ 150,000,000          
Commission on gross sales proceeds of common stock 3.00%          
Maximum | Series B Convertible Preferred Stock            
Class Of Stock [Line Items]            
Percentage of common stock to be held for conversion       19.99%    
Minimum | Warrants            
Class Of Stock [Line Items]            
Percentage of common stock to be held for exercise of warrants       4.99%    
Minimum | Series B Convertible Preferred Stock            
Class Of Stock [Line Items]            
Percentage of common stock to be held for conversion       4.99%