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		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 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	$ 37,687		$ 37,687		$ 41,737
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Other-than-Temporary Impairment Charges, During the Period	0	367	447	382
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses, Decreases	57	46	946	979
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net	33,481		33,481		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	0	432	37	2,962
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, Acquired During Period, Contractually Required Payments Receivable at Acquisition, During the Period	678	7,373	6,907	11,230
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, Balance During Period	629	7,174	6,704	11,031
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	$ 629	$ 6,742	$ 6,667	$ 8,069