Stock Options and Stock-Based Compensation - Stock Options (Detail) - $ / shares	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, beginning balance, Shares	1,064,439	1,143,928	1,115,465
Options granted, Shares	290,300	334,200	267,950
Options exercised, Shares	(250,604)	(314,846)	(115,592)
Options cancelled/forfeited, Shares	(45,724)	(98,843)	(123,895)
Options outstanding, ending balance, Shares	1,058,411	1,064,439	1,143,928
Options granted, weighted average exercise price	$ 57.27	$ 52.57	$ 37.13
Options exercised, weighted average exercise price	36.44	27.59	22.74
Options cancelled/forfeited, weighted average exercise price	36.71	35.59	36.90
Weighted average exercise price per share	$ 45.17	$ 39.45	$ 32.02
Options available for future grants	523,415	260,961	505,493
Exercisable options	440,386	445,387	585,424
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price range of outstanding options	$ 12.71	$ 12.71	$ 12.71
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price range of outstanding options	$ 62.31	$ 57.75	$ 45.73