Share-Based Compensation - Summary of Options Granted under All Plans (Detail) (Stock Option [Member], USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Stock Option [Member]
Number of Options
Outstanding, Beginning Balance	107,000
Granted	0
Exercised	(1,429)	(16,964)
Forfeited	0
Expired	0
Outstanding, Ending Balance	106,000
Exercisable, Ending Balance	86,000
Weighted Average Exercise Price
Outstanding, Beginning Balance	$ 48.32
Granted	$ 0
Exercised	$ 21.42
Forfeited	$ 0
Expired	$ 0
Outstanding, Ending Balance	$ 47.87
Exercisable, Ending Balance	$ 39.19
Weighted Average Remaining Contractual Life
Outstanding, Ending Balance	4 years 1 month 28 days
Exercisable, Ending Balance	3 years 3 months 15 days
Aggregate Intrinsic Value
Outstanding, Ending Balance	$ 4,284
Exercisable, Ending Balance	$ 4,203

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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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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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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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Gross 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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As of the balance sheet date, the weighted-average exercise price (at which grantees can acquire the shares reserved for issuance) for exercisable stock options that are fully vested or expected to vest.

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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 of the plan that expired.

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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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