Quarterly report pursuant to Section 13 or 15(d)

Investment Securities Continuous Unrealized Loss Position (Detail)

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Investment Securities Continuous Unrealized Loss Position (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Gain (Loss) on Investments [Line Items]    
Less Than Twelve Months Gross Unrealized Losses $ (6) $ (94)
Less Than Twelve Months Fair Value 1,421 19,633
Twelve Months or More Gross Unrealized Losses (3) 0
Twelve Months or More Fair Value 333 0
Total Gross Unrealized Losses (9) (94)
Total Fair Value 1,754 19,633
U S Treasury And Government [Member]
    
Gain (Loss) on Investments [Line Items]    
Less Than Twelve Months Gross Unrealized Losses 0 (59)
Less Than Twelve Months Fair Value 0 15,074
Twelve Months or More Gross Unrealized Losses 0 0
Twelve Months or More Fair Value 0 0
Total Gross Unrealized Losses 0 (59)
Total Fair Value 0 15,074
Mortgage Backed Securities [Member]
    
Gain (Loss) on Investments [Line Items]    
Less Than Twelve Months Gross Unrealized Losses 0 0
Less Than Twelve Months Fair Value 0 0
Twelve Months or More Gross Unrealized Losses 0 0
Twelve Months or More Fair Value 0 0
Total Gross Unrealized Losses 0 0
Total Fair Value 0 0
U S States And Political Subdivisions [Member]
    
Gain (Loss) on Investments [Line Items]    
Less Than Twelve Months Gross Unrealized Losses (6) (35)
Less Than Twelve Months Fair Value 1,421 4,559
Twelve Months or More Gross Unrealized Losses (3) 0
Twelve Months or More Fair Value 333 0
Total Gross Unrealized Losses (9) (35)
Total Fair Value 1,754 4,559
Corporate Debt Securities [Member]
    
Gain (Loss) on Investments [Line Items]    
Less Than Twelve Months Gross Unrealized Losses 0 0
Less Than Twelve Months Fair Value 0 0
Twelve Months or More Gross Unrealized Losses 0 0
Twelve Months or More Fair Value 0 0
Total Gross Unrealized Losses 0 0
Total Fair Value $ 0 $ 0