Stockholders' Equity - Summary of Stock Option Activity (Detail) (Stock options [Member], USD $)	9 Months Ended
Sep. 30, 2013
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Outstanding at December 31, 2012	7,038,291
Number of Options, Granted	345,286
Number of Options, Exercised	(551,216)
Number of Options, Forfeited	(91,220)
Number of Options, Outstanding at September 30, 2013	6,741,141
Number of Options, Vested and exercisable at September 30, 2013	4,190,995
Weighted Average Exercise Price, Outstanding at December 31, 2012	$ 18.90
Weighted Average Exercise Price, Granted	$ 49.80
Weighted Average Exercise Price, Exercised	$ 11.72
Weighted Average Exercise Price, Forfeited	$ 24.98
Weighted Average Exercise Price, Outstanding at September 30, 2013	$ 20.99
Weighted Average Exercise Price, Vested and exercisable at September 30, 2013	$ 12.60
Weighted Average Remaining Contractual Term (in years), Outstanding at September 30, 2013	6 years 8 months 9 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at September 30, 2013	5 years 6 months 29 days
Aggregate Intrinsic Value, Outstanding at September 30, 2013	$ 262.5
Aggregate Intrinsic Value, Vested and exercisable at September 30, 2013	$ 198.4

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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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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Net number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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