Stock-Based Compensation - Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of shares, Beginning Balance	190,160
Number of shares, Granted	0
Number of shares, Exercised	(27,336)
Number of shares, Forfeited	0
Number of shares, Ending Balance	162,824
Vested and exercisable at December 31, 2014	162,824
Weighted Average Exercise Price, Beginning Balance	$ 20.11
Weighted Average Exercise Price, Granted	$ 0
Weighted Average Exercise Price, Exercised	$ 27.97
Weighted Average Exercise Price, Forfeited	$ 0
Weighted Average Exercise Price, Ending Balance	$ 18.79
Vested and exercisable at December 31, 2014	$ 18.79

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Weighted average price of options that were either forfeited or expired.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(3)-(4)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(3)

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

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No definition available.

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

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-Name Accounting Standards Codification

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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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The number of exercisable share options (fully vested and expected to vest) that may be converted as of the balance sheet date.

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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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No definition available.

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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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