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Related Party Transactions - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Sumitovant [Member]    
Related Party Transaction [Line Items]    
Cost incurred and recorded as offsets to general and administrative expenses $ 1.4 $ 0.2
Sumitomo [Member]    
Related Party Transaction [Line Items]    
Access fee paid pursuant to strategic cooperation agreement $ 1.0 $ 1.0