Stock Options and Stock-Based Compensation - Outstanding Options (Detail) (USD $)	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options outstanding, beginning balance	1,115,984	1,100,952	1,502,046
Granted, Number of Options	241,625	441,550	246,200
Exercised, Number of Options	(111,758)	(310,729)	(348,090)
Cancelled - forfeited, Number of Options	(44,854)
Cancelled - expired, Number of Options	(37,818)
Options outstanding, ending balance	1,163,179	1,115,984	1,100,952
Options vested and expected to vest, Number of Options	1,046,818
Ending exercisable, Number of Options	559,168
Options outstanding, Weighted Average Exercise per Share, beginning balance	$ 24.80	$ 18.66
Granted, Weighted Average Exercise Price per Share	$ 37.64	$ 33.06	$ 23.04
Exercised, Weighted Average Exercise Price per Share	$ 17.27	$ 15.31	$ 12.80
Cancelled - forfeited, Weighted Average Exercise Price per Share	$ 37.78
Cancelled - expired, Weighted Average Exercise Price per Share	$ 26.20
Option outstanding, Granted, Weighted Average Exercise per Share, ending balance	$ 27.65	$ 24.80	$ 18.66
Options vested and expected to vest, Weighted Average Exercise Price per Share	$ 26.70
Ending exercisable, Weighted Average Exercise Price per Share	$ 21.20
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 5 months 1 day
Options vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 3 months 29 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 9 months 11 days
Option outstanding, Aggregate Intrinsic Value	$ 9,894,029
Options vested and expected to vest, Aggregate Intrinsic Value	9,750,025
Ending exercisable, Aggregate Intrinsic Value	$ 7,636,110