Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Jun. 30, 2012
Options
Beginning Balance	4,268
Granted	303
Exercised	(161)
Cancelled and expired	(31)
Ending Balance	4,379
Exercisable at June 30, 2012	3,327
Options vested and expected to vest at June 30, 2012	4,133
Weighted-Average Exercise Price
Beginning Balance	$ 10.42
Granted	$ 22.44
Exercised	$ 7.62
Cancelled and expired	$ 9.21
Ending Balance	$ 11.34
Exercisable at June 30, 2012	$ 10.72
Options vested and expected to vest at June 30, 2012	$ 11.33
Weighted-Average Remaining Contractual Term (years)
Beginning Balance	6 years 11 days
Ending Balance	6 years 4 days
Exercisable at June 30, 2012	5 years 3 months 15 days
Options vested and expected to vest at June 30, 2012	5 years 10 months 21 days
Aggregate Intrinsic Value
Outstanding at June 30, 2012	$ 50,278
Exercisable at June 30, 2012	40,249
Options vested and expected to vest at June 30, 2012	$ 47,479