Stock Based Compensation and Stock Options - Outstanding Options (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance	1,151,722	1,074,521	1,143,928	1,115,465
Granted, Number of Options	73,650	45,600	151,050	90,500
Exercised, Number of Options	(145,911)	(14,593)	(211,832)	(91,216)
Cancelled - forfeited, Number of Options	(10,866)
Cancelled - expired, Number of Options	(92)
Options outstanding, ending balance	1,068,503	1,102,919	1,068,503	1,102,919
Options vested and expected to vest, Number of Options	1,068,503		1,068,503
Ending exercisable, Number of Options	451,320		451,320
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 33.24	$ 31.56	$ 32.02	$ 28.81
Granted, Weighted Average Exercise Price per Share	48.35	43.32	47.11	44.52
Exercised, Weighted Average Exercise Price per Share	25.60	20.61	25.93	21.87
Cancelled - forfeited, Weighted Average Exercise Price per Share	38.63
Cancelled - expired, Weighted Average Exercise Price per Share	33.16
Options outstanding, ending balance, Weighted Average Exercise Price	35.28	$ 32.17	35.28	$ 32.17
Options vested and expected to vest, Weighted Average Exercise Price per Share	35.28		35.28
Ending exercisable, Weighted Average Exercise Price per Share	$ 30.42		$ 30.42
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 4 months 13 days
Options vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 4 months 13 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 5 months 23 days
Option outstanding, Aggregate Intrinsic Value					$ 20,430,746
Options vested and expected to vest, Aggregate Intrinsic Value					20,430,746
Ending exercisable, Aggregate Intrinsic Value					$ 10,821,153