Stock Option Activity (Detail) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares outstanding, beginning balance	268,007
Stock options, Exercised, Number of Shares	(22,119)
Stock option, Canceled, forfeited or expired, Shares	(2,002)
Number of Shares outstanding, ending balance	243,886	268,007
Exerciseable options at December 31, 2012	243,886
Outstanding options, Weighted average exercise price, beginning balance	$ 19.00
Stock option, Exercised, Weighted average exercise price	$ 7.05
Stock option, Canceled, forfeited or expired, Weighted average exercise price	$ 19.11
Outstanding options, Weighted average exercise price, ending balance	$ 20.08	$ 19.00
Exercisable options, Weighted average exercise price	$ 20.08
Outstanding options, Weighted average contractual life	1 year 7 months 28 days	2 years 5 months 27 days
Exercisable options, Weighted average contractual life	1 year 7 months 28 days

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ References

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

+ References

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

For presentations that combine terminations, 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 or that expired.

+ References

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

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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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- Definition

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

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