Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options Outstanding at Beginning of Period	129,109
Number of Options Granted	0
Number of Options Exercised	48,089
Number of Options Forfeited	0
Number of Options Expired	(1,103)
Number of Options Outstanding & Exercisable at End of Period	79,917
Weighted Average Price of Options Outstanding at Beginning of Period	$ 17.06
Weighted Average Price of Options Granted	$ 0
Weighted Average Price of Options Exercised	$ 17.65
Weighted Average Price of Options Forfeited	$ 0
Weighted Average Price of Options Expired	$ 14.92
Weighted Average Price of Options Outstanding & Exercisable at End of Period	$ 16.73
Weighted Average Life of Options (in years) Outstanding & Exercisable at End of Period	3 years 11 months 9 days
Aggregate Intrinsic Value Outstanding at Beginning of Period	$ 0
Aggregate Intrinsic Value Outstanding & Exercisable at End of Period	$ 399

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

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options outstanding.

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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.

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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 remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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 of the plan that expired.

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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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