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, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value	$ 70.14	$ 48.15	$ 51.20	$ 42.21
Valuation assumptions:
Risk-free interest rate	2.13%	1.37%	1.86%	1.32%
Expected option life (years)	4 years 29 days	4 years 2 months 1 day	4 years 25 days	4 years 1 month 20 days
Expected volatility	42.20%	48.50%	43.60%	49.50%