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Fair Value Measurements - Schedule of Fair Value of Unobservable Input Related To Options to Acquire Under Sumitomo Transaction Agreement (Detail)
12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Measurement Input, Expected Term [Member] | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Time to expiration (in years) 3 years 7 months 2 days 5 months 26 days
Measurement Input, Expected Term [Member] | Maximum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Time to expiration (in years) 3 years 7 months 2 days 4 years 7 months 2 days
Risk-free rate | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment 0.0052 0.0015
Risk-free rate | Maximum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment 0.0052 0.0035
Measurement Input, Option Volatility [Member] | Minimum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment 0.890 0.910
Measurement Input, Option Volatility [Member] | Maximum    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment 0.950 1.100