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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
Jun. 30, 2020
Jun. 30, 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 $ 75.75 $ 96.30
Valuation assumptions:    
Risk-free interest rate 0.31% 2.03%
Expected option life (years) 4 years 2 months 19 days 4 years 1 month 20 days
Expected volatility 42.80% 42.30%