Summary of Stock Option Activity (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013
Stock Option Shares
Outstanding Beginning of year	2,522,522
Granted	1,754,170
Exercised	(119,547)
Canceled	(180,956)
Outstanding at end of year	3,976,189
Vested and expected to vest	3,639,329
Exercisable at end of year	714,247
Weighted Average Exercise Price
Outstanding at Beginning of year	$ 11.76
Granted	$ 34.10
Exercised	$ 8.35
Canceled	$ 9.60
Outstanding at end of year	$ 21.82
Vested and expected to vest	$ 21.27
Exercisable at end of year	$ 11.81
Weighted Average Remaining Contractual Life (Years)
Outstanding at end of year	8 years 10 months 28 days
Vested and expected to vest	8 years 10 months 2 days
Exercisable at end of year	6 years 9 months 26 days
Aggregate Intrinsic Value
Outstanding at end of year	$ 64,737,000
Vested and expected to vest	61,269,000
Exercisable at end of year	$ 18,963,000