Stock-based Compensation - Summary of Stock Option Activity (Detail) (USD $)	3 Months Ended
Mar. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning Balance	220,349
Number of Shares, Exercised	(12,491)
Number of Shares, Forfeited
Number of Shares, Ending Balance	207,858
Weighted Average Exercise Price, Beginning Balance	$ 20.03
Weighted Average Exercise Price, Exercised	$ 10.08
Weighted Average Exercise Price, Forfeited
Weighted Average Exercise Price, Ending Balance	$ 20.63

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

+ References

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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

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- Definition

The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including 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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Number of share options (or share units) exercised during the current period.

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