Quarterly report pursuant to Section 13 or 15(d)

Investment Securities - Additional Information (Detail)

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Investment Securities - Additional Information (Detail) (USD $)
3 Months Ended 12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]      
Investment securities, contractual maturity 2042    
Net realized gain (loss) on redemption of investment securities $ 9,000 $ 1,000  
Net unrealized gain (loss) included in comprehensive income (577,000) 674,000  
Recognized in earnings resulting from the redemption of investment securities 34,000 4,000  
Investment securities available-for- sale, carrying values $ 16,500,000   $ 18,200,000