Stock Options and Stock-Based Compensation - Outstanding Options (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance, Shares	1,058,411	1,064,439	1,143,928
Granted, Number of Options	271,575	290,300	334,200
Exercised, Number of Options	(235,932)	(250,604)	(314,846)
Cancelled - forfeited, Number of Options	(60,466)
Cancelled - expired, Number of Options	(4,485)
Options outstanding, ending balance, Shares	1,029,103	1,058,411	1,064,439
Options vested and expected to vest, Number of Options	877,664
Ending exercisable, Number of Options	468,107
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 45.17	$ 39.45
Granted, Weighted Average Exercise Price per Share	79.49	57.27	$ 52.57
Exercised, Weighted Average Exercise Price per Share	38.34	36.44	27.59
Cancelled - forfeited, Weighted Average Exercise Price per Share	61.23
Cancelled - expired, Weighted Average Exercise Price per Share	41.63
Options outstanding, ending balance, Weighted Average Exercise Price	54.87	$ 45.17	$ 39.45
Options vested and expected to vest, Weighted Average Exercise Price per Share	48.41
Ending exercisable, Weighted Average Exercise Price per Share	$ 41.35
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 3 months 10 days
Options vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	2 years 10 months 28 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 5 months 1 day
Option outstanding, Aggregate Intrinsic Value	$ 7,345,665
Options vested and expected to vest, Aggregate Intrinsic Value	4,465,053
Ending exercisable, Aggregate Intrinsic Value	$ 6,589,011