Loans and Allowance - Summary of Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Loan	Dec. 31, 2011 Loan
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 15,194	$ 29,105
Post-Modification Recorded Balance	14,723	27,201
Number of Loans	50	103
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	1,562	4,023
Post-Modification Recorded Balance	1,547	4,033
Number of Loans	9	17
Construction
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	794	791
Post-Modification Recorded Balance	653	726
Number of Loans	2	5
Commercial and farm land
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	10,366	17,297
Post-Modification Recorded Balance	10,154	15,260
Number of Loans	14	19
Residential
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	2,302	6,892
Post-Modification Recorded Balance	2,172	7,076
Number of Loans	20	52
Consumer
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	170	90
Post-Modification Recorded Balance	197	94
Number of Loans	5	9
Other Loans
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance		12
Post-Modification Recorded Balance		$ 12
Number of Loans		1