Stock-Based Compensation - Summary of Stock Incentive Plans (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Options:
Outstanding at beginning of year, Shares	712,578	335,730	416,886
Granted, Shares	43,686	522,357	88,307
Exercised, Shares	(90,505)	(118,438)	(71,055)
Forfeited, Shares		(13,081)
Expired, Shares	(4,414)	(13,990)	(98,408)
Outstanding at end of year, Shares	661,345	712,578	335,730
Exercisable at end of year, Shares	84,964	103,549	178,432
Weighted-average fair value of awards granted, Shares	$ 17.35	$ 13.94	$ 12.50
Outstanding at beginning of year, Weighted-Average Exercise Price	$ 47.42	$ 42.14	$ 43.52
Granted, Weighted-Average Exercise Price	$ 71.47	$ 49.09	$ 39.66
Exercised, Weighted-Average Exercise Price	$ 47.52	$ 39.39	$ 30.78
Forfeited, Weighted-Average Exercise Price		$ 47.50
Expired, Weighted-Average Exercise Price	$ 23.55	$ 49.08	$ 53.99
Outstanding at end of year, Weighted-Average Exercise Price	$ 49.15	$ 47.42	$ 42.14
Exercisable at end of year, Weighted-Average Exercise Price	$ 43.30	$ 46.02	$ 45.28

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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-Name Accounting Standards Codification

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

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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

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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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