Summary of Stock Option Activity (Detail) (USD $)	3 Months Ended
Mar. 31, 2013
Stock Option Shares
Outstanding Beginning of year	2,522,522
Granted	242,320
Exercised	(64,390)
Canceled	(5,774)
Outstanding at end of year	2,694,678
Vested and expected to vest	2,502,875
Exercisable at end of year	656,805
Weighted Average Exercise Price
Outstanding at Beginning of year	$ 11.76
Granted	$ 28.76
Exercised	$ 8.97
Canceled	$ 14.83
Outstanding at end of year	$ 13.35
Vested and expected to vest	$ 13.24
Exercisable at end of year	$ 12.36
Weighted Average Remaining Contractual Life (Years)
Outstanding at end of year	8 years 3 months 18 days
Vested and expected to vest	8 years 3 months 18 days
Exercisable at end of year	6 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at end of year	$ 63,877,000
Vested and expected to vest	59,634,000
Exercisable at end of year	$ 16,428,000

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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