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, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value	$ 48.15	$ 34.05	$ 42.21	$ 28.91
Valuation assumptions:
Risk-free interest rate	1.37%	1.50%	1.32%	1.60%
Expected option life (years)	4 years 2 months 1 day	4 years 1 month 24 days	4 years 1 month 21 days	4 years 1 month 21 days
Expected volatility	48.50%	49.60%	49.50%	49.70%