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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, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted average grant-date fair value $ 49.04 $ 40.33
Valuation assumptions:    
Risk-free interest rate 1.84% 1.38%
Expected option life (years) 4 years 26 days 4 years 1 month 16 days
Expected volatility 43.70% 49.80%