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Related-Party Transactions - Additional Information (Detail) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended
Mar. 31, 2017
Apr. 30, 2018
Apr. 30, 2017
Related Party Transaction [Line Items]      
Percentage of entity's voting stock owned by related party   10.00%  
Other Entity [Member]      
Related Party Transaction [Line Items]      
Committed to make license payment through January 2020 $ 10.3    
Unpaid liabilities   $ 6.0  
Payment for license fees   0.8 $ 0.1
License amortization expenses included in research and development expense   $ 0.8 $ 0.8