Stock Option Activity (Detail) (USD $)	3 Months Ended
Mar. 31, 2013
Number of Shares
Options outstanding at beginning of period	134,644
Granted
Exercised
Cancelled
Options outstanding at end of period	134,644
Weighted Average Exercise Price
Options outstanding at beginning of period	$ 19.82
Granted
Exercised
Cancelled
Options outstanding at end of year	$ 19.82

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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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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

+ References

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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.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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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 that were terminated.

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Weighted average price at which grantees can acquire the shares reserved for issuance on stock options awarded.

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

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