Loans and Allowance for Losses and Concentrations of Credit Risk - Narrative (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Loan Losses Expensed	$ (499,000)		$ 137,000	$ (598,000)		$ (663,000)
Financing Receivable, Allowance for Credit Losses	13,442,000		17,786,000	13,442,000		17,786,000	13,478,000	16,890,000	18,140,000	17,516,000
Loans and Leases Receivable, Impaired, Loans Past Due Period, Minimum				90 days
Provision for Other Credit Losses	463,000		(43,000)	1,034,000		1,381,000
Financing Receivable, Allowance for Credit Losses, Write-downs	0		448,000	3,884,000		448,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,566,000			2,566,000				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	(499,000)		137,000	(598,000)		(663,000)
Allowance for Loan and Lease Losses, Write-offs	0		448,000	3,884,000		448,000
Long-Term Standby Purchase Commitments and Farmer Mac Guaranteed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Other Credit Losses	463,000		(43,000)	1,034,000		1,381,000
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	0		432,000	37,000		2,962,000
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	3			11
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Balance During Period	629,000		7,174,000	6,704,000		11,031,000
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			7			12
Financing Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment, During the Period	200,000		400,000	1,100,000		1,500,000
Financing Receivable, Modifications, Post-Modification Recorded Investment, During the Period	200,000		400,000	1,100,000		1,700,000
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	1			1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	200,000			200,000
Collateral Dependent Not Individually Analyzed [Member] | Financing Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Loan, Lease, and Other Losses	100,000	[1]		100,000	[1]
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	7,560,000		9,463,000	7,560,000		9,463,000	7,196,000	9,661,000	9,302,000	8,106,000
Financing Receivable, Allowance for Credit Losses, Write-downs	0		0	3,625,000		0
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 0			$ 0				$ 3,400,000

[1] Impairment analysis was performed in the aggregate in consideration of similar risk characteristics of the assets and historical statistics on $53.6 million (61 percent) of impaired loans as of September 30, 2013, which resulted in a specific reserve of $1.3 million.