Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2013
Options
Beginning Balance	4,268
Granted	367
Exercised	(337)
Cancelled and expired	(70)
Ending Balance	4,228
Exercisable at end of year	3,241
Options vested and expected to vest at end of year	4,002
Weighted-Average Exercise Price
Beginning Balance	$ 10.42
Granted	$ 21.44
Exercised	$ 8.68
Cancelled and expired	$ 10.67
Ending Balance	$ 11.49
Exercisable at end of year	$ 10.80
Options vested and expected to vest at end of year	$ 11.47
Weighted-Average Remaining Contractual Term (years)
Beginning Balance	6 years 11 days
Ending Balance	5 years 4 months 13 days
Exercisable at end of year	4 years 7 months 13 days
Options vested and expected to vest at end of year	5 years 3 months
Aggregate Intrinsic Value
Outstanding at end of year	$ 31,627
Exercisable at end of year	25,538
Options vested and expected to vest at end of year	$ 29,914