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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
Jun. 30, 2018
Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted average grant-date fair value $ 142.51 $ 49.04
Valuation assumptions:    
Risk-free interest rate 2.93% 1.84%
Expected option life (years) 4 years 14 days 4 years 25 days
Expected volatility 42.60% 43.70%