Loans and Allowance for Loan Losses (TDRs) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2011 Loans	Dec. 31, 2012	Dec. 31, 2011 Loans	Dec. 31, 2010
Financing Receivable, Modifications [Line Items]
Number of loans	12		31
Pre-modification recorded investment	$ 5,085		$ 5,218
Post-modification recorded investment	5,085		4,249
Allowance For Unfunded Commitments [Roll Forward]
Balance, beginning of year		13	17	11
Adjustments		2	(4)	6
Balance, end of period	13	15	13	17
Troubled debt restructuring, reserve	930	763	930
Trouble debt restructuring, defaulted amount			52
Commercial
Financing Receivable, Modifications [Line Items]
Number of loans	3		6
Pre-modification recorded investment	1,938		558
Post-modification recorded investment	1,938		558
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of loans	3		2
Pre-modification recorded investment	2,558		382
Post-modification recorded investment	2,558		382
Land and land development loans
Financing Receivable, Modifications [Line Items]
Number of loans	2		10
Pre-modification recorded investment	73		3,159
Post-modification recorded investment	73		2,190
Agriculture
Financing Receivable, Modifications [Line Items]
Number of loans	2		1
Pre-modification recorded investment	291		58
Post-modification recorded investment	291		58
Residential real estate
Financing Receivable, Modifications [Line Items]
Number of loans	1		7
Pre-modification recorded investment	170		948
Post-modification recorded investment	170		948
Consumer
Financing Receivable, Modifications [Line Items]
Number of loans	1		5
Pre-modification recorded investment	55		113
Post-modification recorded investment	55		113
Adjusted Interest Rate Only
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	878		3,006
Adjusted Interest Rate Only | Commercial
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	75		558
Adjusted Interest Rate Only | Commercial real estate
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	214		382
Adjusted Interest Rate Only | Land and land development loans
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	73		1,041
Adjusted Interest Rate Only | Agriculture
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	291		0
Adjusted Interest Rate Only | Residential real estate
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	170		912
Adjusted Interest Rate Only | Residential construction
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	0		0
Adjusted Interest Rate Only | Consumer
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	55		113
Other Concessions
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	4,207		1,243
Other Concessions | Commercial
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	1,863		0
Other Concessions | Commercial real estate
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	2,344		0
Other Concessions | Land and land development loans
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	0		1,149
Other Concessions | Agriculture
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	0		58
Other Concessions | Residential real estate
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	0		36
Other Concessions | Residential construction
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	0		0
Other Concessions | Consumer
Financing Receivable, Modifications [Line Items]
Information as to how TDRs were modified during period	$ 0		$ 0