Stock-Based Compensation and Stock Options - Stock Options (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance, Shares	1,063,254	1,151,722	1,064,439	1,143,928
Options granted, Shares	59,800	73,650	116,600	151,050
Options exercised, Shares	(66,870)	(145,911)	(121,108)	(211,832)
Options cancelled/forfeited, Shares	(2,877)	(10,958)	(6,624)	(14,643)
Options outstanding, ending balance, Shares	1,053,307	1,068,503	1,053,307	1,068,503
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 40.43	$ 33.24	$ 39.45	$ 32.02
Options granted, Weighted Average Exercise Price	57.35	48.35	53.48	47.11
Options exercised, Weighted Average Exercise Price	33.50	25.60	32.30	25.93
Options cancelled/forfeited, Weighted Average Exercise Price	40.45	38.39	45.32	39.28
Options outstanding, ending balance, Weighted Average Exercise Price	$ 41.81	$ 35.28	$ 41.81	$ 35.28