Summary of Weighted Average Grant-Date Fair Values And Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Valuation assumptions:
Risk-free interest rate			0.20%
Expected volatility			35.50%
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value	$ 100.51	$ 70.40	$ 76.10	$ 95.62
Valuation assumptions:
Risk-free interest rate	0.30%	1.54%	0.31%	2.02%
Expected option life (years)	4 years 2 months 1 day	4 years 1 month 17 days	4 years 2 months 19 days	4 years 1 month 20 days
Expected volatility	43.50%	44.20%	42.82%	42.30%