Loans and Allowance for Losses and Concentrations of Credit Risk Certain Loans Acquired in Transfer (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance	$ 34,166		$ 41,737
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Other-than-Temporary Impairment Charges, During the Period	386	15
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses, Decreases	50	40
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	29,870		33,798
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	0
Long-Term Standby Purchase Commitments [Member] | Farm & Ranch Guaranteed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Number Defaulted		1
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Contractually Required Payments Receivable at Acquisition, During the Period	143	732
Long-Term Standby Purchase Commitments and Farmer Mac Guaranteed Securities [Member] | Farm & Ranch 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	729
Farmer Mac Guaranteed Securities [Member] | Farm & Ranch Guaranteed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Balance During Period	$ 103	$ 729