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Summary of Weighted Average Grant-Date Fair Values And Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail) - Employee Stock Option - $ / shares
12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Mar. 31, 2018
Valuation assumptions:      
Weighted average grant-date fair value $ 93.05 $ 141.47 $ 52.34
Risk-free interest rate 1.97% 2.91% 1.87%
Expected option life (years) 4 years 1 month 20 days 4 years 14 days 4 years 25 days
Expected volatility 42.30% 42.80% 43.50%