Summary of Stock Option Activity (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Stock Option Shares
Outstanding Beginning of year	2,522,522
Granted	2,063,396
Exercised	(196,012)
Canceled	(239,072)
Outstanding at end of year	4,150,834
Vested and expected to vest	3,395,249
Exercisable at end of year	891,157
Weighted Average Exercise Price
Outstanding at Beginning of year	$ 11.76
Granted	$ 34.86
Exercised	$ 8.51
Canceled	$ 11.51
Outstanding at end of year	$ 23.37
Vested and expected to vest	$ 21.29
Exercisable at end of year	$ 11.60
Weighted Average Remaining Contractual Life (Years)
Outstanding at end of year	8 years 8 months 16 days
Vested and expected to vest	8 years 6 months 11 days
Exercisable at end of year	6 years 11 months 12 days
Aggregate Intrinsic Value
Outstanding at end of year	$ 99,056,000
Vested and expected to vest	88,063,000
Exercisable at end of year	$ 31,748,000