Non-Accrual Loan, Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 23,828	$ 23,410
Commercial | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	2,686	2,450
Commercial | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	5,532	5,989
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,712	1,315
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	10,765	10,791
Consumer loans | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,795	1,656
Consumer loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	62	96
Consumer loans | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	27	37
Consumer loans | Boat/RV
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 1,249	$ 1,076