Stock-Based Compensation Plans - Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance	1,220,449	1,429,822	2,927,737
Number of Shares, Granted	382	51,597	13,292
Number of Shares, Canceled	(41,071)	(4,348)
Number of Shares, Exercised	(165,340)	(256,622)	(1,511,207)
Number of Shares, Ending Balance	1,014,420	1,220,449	1,429,822
Number of Shares, Exercisable	928,813
Weighted Average Exercise Price, Beginning Balance	$ 15.01	$ 13.62	$ 9.42
Weighted Average Exercise Price, Granted	$ 63.07	$ 41.75	$ 32.45
Weighted Average Exercise Price, Canceled		$ 33.84
Weighted Average Exercise Price, Exercised	$ 15.85	$ 12.33	$ 5.64
Weighted Average Exercise Price, Ending Balance	$ 13.81	$ 15.01	$ 13.62
Weighted Average Exercise Price, Exercisable	$ 13.05
Remaining contractual term, Outstanding at December 31, 2013	3 years 1 month 6 days
Remaining contractual term, Exercisable at December 31, 2014	2 years 10 months 24 days
Intrinsic Value, Exercised	$ 7,518
Intrinsic Value, Ending Balance	58,731
Intrinsic Value, Exercisable	$ 54,482

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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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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