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Investment Securities - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Investment [Line Items]    
Number of investment positions in continuous loss position 23  
Government and Agencies Debt Securities
   
Investment [Line Items]    
Number of investment positions in continuous loss position 22  
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]    
Gross losses on sales of available for sale securities $ 18,000  
Collateralized Mortgage Obligations Issued By Private Enterprise | Securities Downgraded To Substandard
   
Investment [Line Items]    
Recognized other than temporary impairment loss   36,000
Agency mortgage-backed securities
   
Investment [Line Items]    
Gross gains on sales of available for sale securities 35,000 16,000
Agency CMO
   
Investment [Line Items]    
Gross gains on sales of available for sale securities 2,000  
Agency Collateralized Mortgage Obligations
   
Investment [Line Items]    
Gross losses on sales of available for sale securities 8,000  
Municipal Obligations
   
Investment [Line Items]    
Gross losses on sales of available for sale securities   $ 24,000