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Net Loss per Share - Additional Information (Detail) - $ / shares
1 Months Ended 9 Months Ended
Jun. 30, 2019
Sep. 30, 2019
Sep. 30, 2018
Common Stock      
Number of shares sold 6,340,771 6,340,771 9,179,500
Pre-Funded Warrants      
Warrants to purchase shares of common stock 2,548,117    
Warrants exercise price per share $ 9.00    
Warrants exercise price per share paid at closing of offering $ 8.99