Stock Options and Stock-Based Compensation - Outstanding Options (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance, Shares	1,029,103	1,058,411	1,064,439
Granted, Number of Options	234,175	271,575	290,300
Exercised, Number of Options	(278,094)	(235,932)	(250,604)
Cancelled - forfeited, Number of Options	(43,436)
Cancelled - expired, Number of Options	(4,590)
Options outstanding, ending balance, Shares	937,158	1,029,103	1,058,411
Options vested and expected to vest, Number of Options	772,156
Ending exercisable, Number of Options	421,964
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 54.87	$ 45.17
Granted, Weighted Average Exercise Price per Share	81.12	79.49	$ 57.27
Exercised, Weighted Average Exercise Price per Share	44.17	38.34	36.44
Cancelled - forfeited, Weighted Average Exercise Price per Share	62.99
Cancelled - expired, Weighted Average Exercise Price per Share	44.93
Options outstanding, ending balance, Weighted Average Exercise Price	64.28	$ 54.87	$ 45.17
Options vested and expected to vest, Weighted Average Exercise Price per Share	52.45
Ending exercisable, Weighted Average Exercise Price per Share	$ 50.95
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 4 months 2 days
Options vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 3 months 29 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 5 months 23 days
Option outstanding, Aggregate Intrinsic Value	$ 35,924,719
Options vested and expected to vest, Aggregate Intrinsic Value	33,914,366
Ending exercisable, Aggregate Intrinsic Value	$ 21,790,325