Loans and Allowance for Losses and Concentrations of Credit Risk Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Loan Losses Expensed	$ 430,000	$ 420,000
Financing Receivable, Allowance for Credit Losses	14,252,000	17,966,000	16,890,000	17,516,000
Loans and Leases Receivable, Impaired, Loans Past Due Period, Minimum	90 days
Provision for Other Credit Losses	746,000	30,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3,461,000		6,659,000
Alternate minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Impaired, Loans Past Due Period, Minimum	120 days
Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Loan Losses Expensed	430,000	420,000
Allowance for Loan and Lease Losses, Write-offs	3,814,000	0
Long-Term Standby Purchase Commitments and Farmer Mac Guaranteed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Other Credit Losses	746,000	30,000
Long-Term Standby Purchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Balance During Period	37,000	0
Farm & Ranch Guaranteed Securities [Member] | Long-Term Standby Purchase Commitments and Farmer Mac Guaranteed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Number Defaulted	2
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Balance During Period	$ 140,000	$ 729,000
Farm & Ranch Guaranteed Securities [Member] | Long-Term Standby Purchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Number Defaulted		1