Disclosure - Stock Based Compensation and Stock Options - Outstanding Options (Detail) - USD ($)	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options outstanding, beginning balance	1,163,179	1,115,984
Granted, Number of Options	39,700	37,550
Exercised, Number of Options	(35,837)	(25,993)
Cancelled - forfeited, Number of Options	0
Cancelled - expired, Number of Options	0
Options outstanding, ending balance	1,167,042	1,118,530
Options vested and expected to vest, Number of Options	1,038,437
Ending exercisable, Number of Options	563,591
Options outstanding, beginning Average Price	$ 27.65	$ 24.80
Granted, Weighted Average Exercise Price per Share	34.67	44.86
Exercised, Weighted Average Exercise Price per Share	19.16	17.99
Cancelled - forfeited, Weighted Average Exercise Price per Share	0
Cancelled - expired, Weighted Average Exercise Price per Share	0
Option outstanding, Granted, Weighted Average Exercise per Share, ending balance	28.15	$ 25.60
Options vested and expected to vest, Weighted Average Exercise Price per Share	27.29
Ending exercisable, Weighted Average Exercise Price per Share	$ 22.12
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 3 months 22 days
Options vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 2 months 23 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 8 months 9 days
Option outstanding, Aggregate Intrinsic Value	$ 7,718,352
Options vested and expected to vest, Aggregate Intrinsic Value	7,526,529
Ending exercisable, Aggregate Intrinsic Value	$ 6,136,513