Stock Option Plan - Additional Information (Detail) (USD $)	9 Months Ended
Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options granted	$ 122,635
Directors Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	13,500
Option exercise price	$ 18.76
Option exercise price, start date	Oct. 26, 2012
Option exercise price, end date	Apr. 25, 2022
Cost of options granted	$ 119,834
Stock option expense recognition per month	19,972
Stock option expense, requisite service period	6 months
Stock option, deferred tax	44,698
Deferred tax amortization per month	$ 7,450
Deferred tax, requisite service period	6 months
Intrinsic value of options granted	$ 42,900
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options granted	$ 79,735

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- Definition

Share Based Compensation Arrangement by Share Based Payment Award, Award Exercise Period, Range End

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from compensation and benefits costs.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Aggregate unrecognized cost of option awards made to employees under a stock option plan or plans, that have yet to vest.

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

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- Definition

The grant-date intrinsic value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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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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