Summary of Stock Option Activity (Detail) (USD $)	3 Months Ended
Mar. 31, 2013
Stock Options
Stock Options, Beginning balance	1,691,357
Stock Options, Granted	125,325
Stock Options, Exercised	(351,216)
Stock Options, Cancelled	(250)
Stock Options, Ending balance	1,465,216
Stock Options, Exercisable	491,674
Weighted- Average Exercise Price
Weighted-Average Exercise Price, Beginning balance	$ 11.11
Weighted-Average Exercise Price, Granted	$ 47.08
Weighted-Average Exercise Price, Exercised	$ 4.60
Weighted-Average Exercise Price, Cancelled	$ 30.58
Weighted-Average Exercise Price, Ending balance	$ 15.74
Weighted-Average Exercise Price, Exercisable	$ 7.07

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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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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