Stock Based Compensation and Stock Options - Outstanding Options (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options outstanding, beginning balance	1,167,042	1,118,530	1,163,179	1,115,984
Granted, Number of Options	47,300	48,650	87,000	86,050
Exercised, Number of Options	(59,804)	(30,957)	(95,641)	(56,950)
Cancelled - forfeited, Number of Options	(18,952)
Cancelled - expired, Number of Options	0
Options outstanding, ending balance	1,135,586	1,136,073	1,135,586	1,136,073
Options vested and expected to vest, Number of Options	1,028,863		1,028,863
Ending exercisable, Number of Options	563,790		563,790
Options outstanding, beginning Average Price	$ 28.15	$ 25.60	$ 27.65	$ 24.80
Granted, Weighted Average Exercise Price per Share	33.15	40.57	33.85	42.43
Exercised, Weighted Average Exercise Price per Share	16.91	18.75	17.75	18.41
Cancelled - forfeited, Weighted Average Exercise Price per Share	36.25
Cancelled - expired, Weighted Average Exercise Price per Share	0
Option outstanding, Weighted Average Exercise per Share, ending balance	28.81	$ 26.42	28.81	$ 26.42
Options vested and expected to vest, Weighted Average Exercise Price per Share	28.08		28.08
Ending exercisable, Weighted Average Exercise Price per Share	$ 23.48		$ 23.48
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 3 months 11 days
Options vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 2 months 12 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 9 months 11 days
Option outstanding, Aggregate Intrinsic Value	$ 6,975,029		$ 6,975,029
Options vested and expected to vest, Aggregate Intrinsic Value	6,911,556		6,911,556
Ending exercisable, Aggregate Intrinsic Value	$ 5,708,498		$ 5,708,498