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 9 Months Ended 12 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Dec. 31, 2011
Fair value of reclassified securities $ 52,600   $ 52,600    
Amortized cost of reclassified securities 50,600   50,600   59,742,000
Equity security other than temporary impairment charge 176,000   292,000    
Investment equity security at carrying value 218,000   218,000    
Net unrealized gain (loss) included in comprehensive income 3,800,000 584,000 3,100,000 6,900,000  
Net realized gain (loss) on sales of investment securities 10,000 1,704,000 1,392,000 1,634,000  
Recognized in earnings resulting from the sale of investment securities 4,000 1,600,000 1,700,000 249,000,000,000  
Net unrealized gains on newly reclassified 2,000,000        
Net unrealized gains on newly reclassified Securities     2,000,000    
Investment securities available for sale, carrying values     $ 19,400,000   $ 45,800,000
Municipal Bonds - Taxable [Member]
          
Reclassified municipal bonds 95.00%   95.00%