Loans and Allowance for Loan Losses - Schedule of Troubled Debt Restructuring (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012 Contract
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number	8
Balance	$ 1,558
Commercial [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number	1
Balance	30
Agricultural [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number	0
Balance	0
Real Estate [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number	6
Balance	1,509
Consumer [Member]
Troubled Debt Restructured Loan Modifications by Class [Line Items]
Number	1
Balance	$ 19