Stock Options and Stock-Based Compensation - Outstanding Options (Detail) (USD $)	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Option outstanding, beginning balance	1,100,952	1,502,046	1,627,324
Granted, Number of Options	441,550	246,200	298,150
Exercised, Number of Options	(310,729)	(348,090)	(346,128)
Cancelled - forfeited, Number of Options	(50,374)
Cancelled - expired, Number of Options	(65,415)
Options outstanding, ending balance	1,115,984	1,100,952	1,502,046
Options vested and expected to vest, Number of Options	976,333
Ending exercisable, Number of Options	430,294
Option outstanding, Granted, Weighted Average Exercise Per Share, beginning balance	$ 18.66	$ 17.10
Granted, Weighted Average Exercise Price per Share	$ 33.06	$ 23.04	$ 25.22
Exercised, Weighted Average Exercise Price per Share	$ 15.31	$ 12.80	$ 12.50
Cancelled - forfeited, Weighted Average Exercise Price per Share	$ 25.56
Cancelled - expired, Weighted Average Exercise Price per Share	$ 21.61
Option outstanding, Granted, Weighted Average Exercise Per Share, ending balance	$ 24.80	$ 18.66	$ 17.10
Options vested and expected to vest, Weighted Average Exercise Price per Share	$ 23.64
Ending exercisable, Weighted Average Exercise Price per Share	$ 17.32
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 9 months
Options vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 7 months 28 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 11 months 12 days
Option outstanding, Aggregate Intrinsic Value	$ 27,852,690
Options vested and expected to vest, Aggregate Intrinsic Value	25,504,491
Ending exercisable, Aggregate Intrinsic Value	$ 13,960,617