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Summary of Outstanding Warrants Issued by Company (Detail) - $ / shares
12 Months Ended
Dec. 31, 2019
Feb. 08, 2017
Class Of Warrant Or Right [Line Items]    
Number of Shares Issuable Upon Exercise 620,000  
EWB Warrant    
Class Of Warrant Or Right [Line Items]    
Number of Shares Issuable Upon Exercise 40,000  
Weighted Average Exercise Price $ 3.64 $ 3.64
Issue Date Feb. 08, 2017  
Expiration Date Feb. 08, 2022  
VLL7 and VLL8 Warrants    
Class Of Warrant Or Right [Line Items]    
Number of Shares Issuable Upon Exercise 580,000  
Weighted Average Exercise Price $ 2.00  
Issue Date Feb. 08, 2017  
Expiration Date Feb. 08, 2022