Stock Options and Stock-Based Compensation - Stock Options (Detail) - $ / shares	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, beginning balance, Shares	1,143,928	1,115,465	1,163,179
Options granted, Shares	334,200	267,950	276,275
Options exercised, Shares	(314,846)	(115,592)	(200,753)
Options cancelled/forfeited, Shares	(98,843)	(123,895)	(123,236)
Options outstanding, ending balance, Shares	1,064,439	1,143,928	1,115,465
Options granted, weighted average exercise price	$ 52.57	$ 37.13	$ 35.51
Options exercised, weighted average exercise price	27.59	22.74	19.75
Options cancelled/forfeited, weighted average exercise price	35.59	36.90	33.44
Weighted average exercise price per share	$ 39.45	$ 32.02	$ 30.36
Options available for future grants	260,961	505,493	650,345
Exercisable options	445,387	585,424	529,691
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price range of outstanding options	$ 12.71	$ 12.71	$ 9.05
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price range of outstanding options	$ 57.75	$ 45.73	$ 45.55