Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding Options at Beginning of Year	1,160,091	1,042,925	958,136
Number of Shares, Granted	187,121	187,375	125,734
Number of Shares, Exercised	(623,617)	(62,326)	(38,748)
Number of Shares, Cancelled	(15,094)	(7,883)	(2,197)
Number of Shares, Outstanding Options at End of Year	708,501	1,160,091	1,042,925
Number of Shares, Options Exercisable at End of Year	416,817	868,081	761,564
Weighted-Average Exercise Price, Outstanding Options at Beginning of Year	$ 80.36	$ 76.88	$ 72.52
Weighted-Average Exercise Price, Granted	61.92	91.58	103.53
Weighted-Average Exercise Price, Exercised	70.57	88.28	54.27
Weighted-Average Exercise Price, Cancelled	92.51	102.69	100.88
Weighted-Average Exercise Price, Outstanding Options at End of Year	83.85	80.36	76.88
Weighted-Average Fair Value of Options Granted during the Year	$ 22.68	$ 27.35	$ 33.11