Summary of Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Loan	Mar. 31, 2012 Loan
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 644	$ 2,236
Post-Modification Recorded Balance	565	2,097
Number of Loans	6	8
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	96	238
Post-Modification Recorded Balance	96	238
Number of Loans	3	2
Commercial and farm land
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	511	1,774
Post-Modification Recorded Balance	431	1,635
Number of Loans	2	2
Residential
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	37	224
Post-Modification Recorded Balance	$ 38	$ 224
Number of Loans	1	4