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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) - Stock Options - $ / shares
3 Months Ended 9 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average grant-date fair value $ 74.61 $ 117.50 $ 93.68 $ 142.08
Valuation assumptions:        
Risk-free interest rate 1.68% 2.81% 1.99% 2.93%
Expected option life (years) 4 years 1 month 6 days 4 years 14 days 4 years 1 month 20 days 4 years 14 days
Expected volatility 42.36% 45.20% 42.34% 42.80%