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Investment Securities - Additional Information (Detail) (USD $)
3 Months Ended
Mar. 31, 2013
Investment
Investment [Line Items]  
Number of investment positions in continuous loss position 32
Government and Agencies Debt Securities
 
Investment [Line Items]  
Number of investment positions in continuous loss position 31
Percentage amount by which investment positions in continuous loss position had depreciated from amortized cost basis 1.20%
Municipal Obligations
 
Investment [Line Items]  
Gross gains on sales of available for sale securities 21,000