Valuation Methodology and Unobservable Inputs for Level Three Assets Measured at Fair Value on Non Recurring Basis (Detail) (Company Determined Fair Value (Level 3), Fair Value, Measurements, Nonrecurring, USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Impaired Loans Partially Charged Off
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	4,299	[1]
Impaired Loans Partially Charged Off | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	10.00%	[1]
Impaired Loans Partially Charged Off | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	30.00%	[1]
Impaired Loans Specifically Reserved
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	4,601	[1]
Other real estate owned
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	596
Other real estate owned | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	10.00%
Estimated selling cost	6.00%
Other real estate owned | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Management adjustment of appraisal	30.00%
Estimated selling cost	10.00%

[1] Does not include impaired loans that are measured by the present value of expected future cash flows discounted at the loan's effective interest rate.