Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Sep. 30, 2013	Mar. 31, 2013
Options
Beginning Balance	4,228
Granted	299
Exercised	(596)
Cancelled and expired	(8)
Ending Balance	3,923	4,228
Exercisable at September 30, 2013	3,094
Options vested and expected to vest at September 30, 2013	3,825
Weighted-Average Exercise Price
Beginning Balance	$ 11.49
Granted	$ 23.10
Exercised	$ 8.81
Cancelled and expired	$ 10.24
Ending Balance	$ 12.78	$ 11.49
Exercisable at September 30, 2013	$ 11.12
Options vested and expected to vest at September 30, 2013	$ 12.71
Weighted-Average Remaining Contractual Term (years)
Outstanding	5 years 3 months 22 days	5 years 4 months 13 days
Exercisable at September 30, 2013	4 years 5 months 9 days
Options vested and expected to vest at September 30, 2013	5 years 2 months 27 days
Aggregate Intrinsic Value
Outstanding at September 30, 2013	$ 26,958
Exercisable at September 30, 2013	24,856
Options vested and expected to vest at September 30, 2013	$ 26,500