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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 6 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average grant-date fair value $ 46.50 $ 30.12 $ 41.60 $ 28.26
Valuation assumptions:        
Risk-free interest rate 1.11% 1.63% 1.32% 1.59%
Expected option life (years) 4 years 1 month 21 days 4 years 1 month 17 days 4 years 1 month 17 days 4 years 1 month 21 days
Expected volatility 49.00% 48.30% 49.60% 49.70%