Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Sep. 30, 2012
Options
Beginning Balance	4,268
Granted	319
Exercised	(289)
Cancelled and expired	(56)
Ending Balance	4,242
Exercisable at September 30, 2012	3,199
Options vested and expected to vest at September 30, 2012	4,001
Weighted-Average Exercise Price
Beginning Balance	$ 10.42
Granted	$ 22.43
Exercised	$ 8.63
Cancelled and expired	$ 9.93
Ending Balance	$ 11.43
Exercisable at September 30, 2012	$ 10.76
Options vested and expected to vest at September 30, 2012	$ 11.42
Weighted-Average Remaining Contractual Term (years)
Beginning Balance	6 years 11 days
Ending Balance	5 years 9 months 11 days
Exercisable at September 30, 2012	5 years 7 days
Options vested and expected to vest at September 30, 2012	5 years 7 months 28 days
Aggregate Intrinsic Value
Outstanding at September 30, 2012	$ 41,046
Exercisable at September 30, 2012	32,714
Options vested and expected to vest at September 30, 2012	$ 38,723