Loans and Allowance - Subsequent Default (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Loan	Dec. 31, 2011 Loan
Financing Receivable, Impaired [Line Items]
Number of Loans	7	14
Recorded Balance	$ 620	$ 2,984
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Number of Loans	1	3
Recorded Balance	23	471
Commercial and farm land
Financing Receivable, Impaired [Line Items]
Number of Loans	2	3
Recorded Balance	212	1,951
Residential
Financing Receivable, Impaired [Line Items]
Number of Loans	4	7
Recorded Balance	385	557
Consumer
Financing Receivable, Impaired [Line Items]
Number of Loans		1
Recorded Balance		$ 5