Stock Options and Stock-Based Compensation - Stock Options (Detail) - $ / shares	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, beginning balance, Shares	1,058,411	1,064,439	1,143,928
Options granted, Shares	271,575	290,300	334,200
Options exercised, Shares	(235,932)	(250,604)	(314,846)
Options cancelled/forfeited, Shares	(64,951)	(45,724)	(98,843)
Options outstanding, ending balance, Shares	1,029,103	1,058,411	1,064,439
Options granted, weighted average exercise price	$ 79.49	$ 57.27	$ 52.57
Options exercised, weighted average exercise price	38.34	36.44	27.59
Options cancelled/forfeited, weighted average exercise price	59.87	36.71	35.59
Weighted average exercise price per share	$ 54.87	$ 45.17	$ 39.45
Options available for future grants	316,691	523,415	260,961
Exercisable options	468,107	440,386	445,387
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price range of outstanding options	$ 20.08	$ 12.71	$ 12.71
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price range of outstanding options	$ 88.22	$ 62.31	$ 57.75