Quantitative Information about Unobservable Inputs used in Recurring and Nonrecurring Level Three Fair Value Measurements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Pooled Trust Preferred Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 2,465	$ 2,475
Valuation Technique	Discounted cash flow	Discounted cash flow
Constant prepayment rate	2.00%	2.00%
Cumulative projected prepayments	40.00%	40.00%
Pooled Trust Preferred Securities | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	9.00%	9.00%
Probability of default	1.50%	1.50%
Projected cures given deferral	0.00%	0.00%
Loss severity	58.00%	58.00%
Pooled Trust Preferred Securities | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	17.00%	17.00%
Probability of default	2.20%	2.20%
Projected cures given deferral	15.00%	15.00%
Loss severity	79.40%	79.40%
Impaired loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,015	8,032
Valuation Technique	Third party valuations	Third party valuations
Impaired loans | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.00%	0.00%
Impaired loans | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	40.00%	40.00%
Foreclosed real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	246	355
Valuation Technique	Third party valuations	Third party valuations
Foreclosed real estate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount to reflect realizable value less estimated selling costs	0.00%	0.00%
Foreclosed real estate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount to reflect realizable value less estimated selling costs	25.00%	25.00%
Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		$ 1,731
Valuation Technique		Third party valuations
Discount rate		10.10%
Servicing fee		0.25%
Mortgage servicing rights | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate		100.00%
Mortgage servicing rights | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Constant prepayment rate		700.00%