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Financings - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Mar. 10, 2020
Feb. 05, 2020
Sep. 12, 2019
Jun. 30, 2019
Nov. 11, 2018
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Class of Stock [Line Items]                  
Sale of stock consideration received on transaction             $ 88,661,000 $ 2,971,000  
Common stock, par value             $ 0.001   $ 0.001
Gross proceeds received           $ 2,971,000 $ 13,015,000 $ 2,971,000  
Proceeds from private placement     $ 52,500,000            
At The Market Offering [Member]                  
Class of Stock [Line Items]                  
Stock issued during period             2,814,673 639,442  
Sale of stock consideration received on transaction             $ 13,000,000.0 $ 3,000,000.0  
Underwriting offering cost             $ 13,000,000.0    
Private Placement [Member]                  
Class of Stock [Line Items]                  
Class of warrant or right, number of securities called by warrants or rights     17,803,031       18,939,394    
Warrant Exercise Price per share     $ 3.01       $ 3.01    
Placement agent fees and other expenses     $ 1,100,000            
Private Placement [Member] | New Warrants [Member]                  
Class of Stock [Line Items]                  
Class of warrant or right, number of securities called by warrants or rights     17,803,031            
Warrant Exercise Price per share     $ 7.00            
Securities Purchase Agreement [Member]                  
Class of Stock [Line Items]                  
Stock issued during period         18,939,394        
Common stock, par value         $ 0.001        
par value per share         $ 2.64        
Gross proceeds received         $ 47.1   $ 47,100,000    
Underwriting Agreement [Member]                  
Class of Stock [Line Items]                  
Stock issued during period   27,826,086              
Issuance & sale of common stock in public offering price per share   $ 3.25              
Sale of stock consideration received on transaction   $ 84,800,000              
par value per share   $ 3.055              
Underwriting Agreement [Member] | Maximum                  
Class of Stock [Line Items]                  
Stock issued during period   4,173,912              
par value per share   $ 3.055              
Underwriting Agreement [Member] | Stock Option [Member]                  
Class of Stock [Line Items]                  
Stock issued during period 1,284,025                
Sale of stock consideration received on transaction $ 3,900,000                
Open Market Sale Agreement [Member] | At The Market Offering [Member]                  
Class of Stock [Line Items]                  
Sale of stock consideration received on transaction       $ 100,000,000.0