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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) - $ / shares
3 Months Ended 9 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Valuation assumptions:        
Risk-free interest rate     0.20%  
Expected volatility     35.50%  
Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average grant-date fair value $ 94.64 $ 74.61 $ 76.79 $ 93.68
Valuation assumptions:        
Risk-free interest rate 0.39% 1.68% 0.31% 1.99%
Expected option life (years) 4 years 2 months 1 day 4 years 1 month 6 days 4 years 2 months 19 days 4 years 1 month 20 days
Expected volatility 43.70% 42.36% 42.85% 42.34%