Stock-based Compensation - Summary of Stock Option Activity (Detail) - 6 months ended Jun. 30, 2015 - $ / shares	Total
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of Shares, Beginning Balance	162,824
Number of Shares, Granted	0
Number of Shares, Exercised	(3,675)
Number of Shares, Forfeited	0
Number of Shares, Ending Balance	159,149
Weighted Average Exercise Price, Beginning Balance	$ 18.79
Weighted Average Exercise Price, Granted	0
Weighted Average Exercise Price, Exercised	16.87
Weighted Average Exercise Price, Forfeited	0
Weighted Average Exercise Price, Ending Balance	$ 18.83

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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)

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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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- Definition

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

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

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- Definition

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

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