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Organization - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Apr. 10, 2019
Mar. 22, 2019
Feb. 01, 2019
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Line Items]              
Entity incorporation date       Jul. 05, 2016      
Net proceeds received from offering         $ 46,816,000 $ 49,747,000 $ 90,908,000
Accumulated deficit       $ 161,170,000   154,132,000 71,393,000
Cash, cash equivalents and marketable securities             91,500,000
Initial Public Offering              
Organization Consolidation And Presentation Of Financial Statements [Line Items]              
Number of common stock shares sold 487,934 7,200,000          
Issuance price per shares $ 6.95 $ 6.95          
Net proceeds received from offering $ 3,200,000 $ 46,600,000          
Underwriting discounts and commissions and other offering expenses $ 200,000 $ 3,500,000          
Net proceeds received from offering         $ 46,585,000 49,747,000 $ 89,370,000
Initial Public Offering | Maximum              
Organization Consolidation And Presentation Of Financial Statements [Line Items]              
Option to purchase of common stock at public offering price   1,080,000          
At-the-Market Offering              
Organization Consolidation And Presentation Of Financial Statements [Line Items]              
Net proceeds received from offering           $ 6,716,000  
At-the-Market Offering | Controlled Equity Offering Sales Agreement | SVB Leerink LLC and Cantor Fitzgerald and Co              
Organization Consolidation And Presentation Of Financial Statements [Line Items]              
Number of common stock shares sold           688,000  
Issuance price per shares           $ 10.18  
Maximum aggregate value of common stock available for offering At-the-Market price     $ 50,000,000        
Sales commission percentage payable to sales agents in cash     3.00%        
Net proceeds received from offering           $ 6,700,000  
Issuance costs           75,000  
Common stock remained available for offering           $ 43,000,000