Investment Securities - Additional Information (Detail) (USD $)	9 Months Ended
Sep. 30, 2012	Dec. 31, 2011
Investment [Line Items]
Number of investment positions in continuous loss position	23
Available-for-sale Securities, amortized cost	$ 120,679,000	$ 108,921,000
Available-for-sale Securities, fair value	123,375,000	111,440,000
Government and Agencies Debt Securities
Investment [Line Items]
Number of investment positions in continuous loss position	21
Percentage amount by which investment positions in continuous loss position had depreciated from amortized cost basis	0.70%
Collateralized Mortgage Obligations Issued By Private Enterprise
Investment [Line Items]
Percentage amount by which investment positions in continuous loss position had depreciated from amortized cost basis	12.20%
Available-for-sale Securities, amortized cost	666,000	896,000
Available-for-sale Securities, fair value	657,000	880,000
Collateralized Mortgage Obligations Issued By Private Enterprise \| Securities Downgraded To Substandard
Investment [Line Items]
Available-for-sale Securities, amortized cost	230,000
Available-for-sale Securities, fair value	$ 202,000

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.

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