Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Number of options
Number of Options outstanding, Beginning Balance	633,663	860,779	2,431,233
Number of Options, Exercised		(227,116)	(1,415,391)
Number of Options, Canceled			(155,063)
Number of Options outstanding, Ending Balance		633,663	860,779	2,431,233
Number of Options, Exercised	(555,677)
Options expected to vest, Number of Options, Ending Balance	77,986
Options outstanding, Weighted Average Remaining Contract Term
Options exercised, Weighted Average Remaining Contract Term (Years)	0 years
Options exercisable, Weighted Average Remaining Contract Term (Years), Ending Balance	2 years 6 months	6 years 2 months 6 days	6 years 2 months 12 days	4 years
Weighted average exercise price
Options outstanding, Weighted Average Exercise Price, Beginning Balance	$ 20.85	$ 19.52	$ 17.69
Weighted Average Exercise Price, Exercised	$ 21.70	$ 15.82	$ 15.34
Weighted Average Exercise Price, Canceled			$ 29.32
Options outstanding, Weighted Average Exercise Price, Ending Balance	$ 14.76	$ 20.85	$ 19.52	$ 17.69
Aggregate intrinsic value
Options outstanding, Aggregate Intrinsic Value, Beginning Balance	$ 8,879	$ 17,129	$ 19,191
Aggregate Intrinsic Value, Exercised	8,860	3,691	18,482
Aggregate Intrinsic Value, Canceled			9
Options exercisable, Aggregate Intrinsic Value, Ending Balance	2,404
Options outstanding, Aggregate Intrinsic Value, Ending Balance		$ 8,879	$ 17,129	$ 19,191