Loans and Allowance for Losses and Concentrations of Credit Risk Allowance for Credit Losses Roll Forward (Details) (USD $)	3 Months Ended							12 Months Ended			15 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Dec. 31, 2009
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Loan and Lease Losses, Real Estate	$ 11,351,000				$ 10,161,000			$ 11,351,000	$ 10,161,000
Reserve for losses	5,539,000				7,355,000			5,539,000	7,355,000
Financing Receivable, Allowance for Credit Losses	16,890,000				17,516,000			16,890,000	17,516,000	20,115,000		14,187,000
Provision for Loan Losses Expensed	4,354,000	137,000	(1,220,000)	420,000	(482,000)	160,000	1,281,000	3,691,000	610,000	1,893,000	(349,000)
(Release of)/provision for losses								(1,816,000)	(2,957,000)	2,417,000
Allowance for Loan and Lease Losses, Adjustments, Net									1,800,000	2,000,000
Total provision for/(release of) losses								1,875,000	(2,347,000)	4,310,000
Financing Receivable, Allowance for Credit Losses, Write-downs								(2,501,000)	(252,000)	(605,000)
Financing Receivable, Allowance for Credit Losses, Recovery										(2,223,000)
Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Loan and Lease Losses, Real Estate	11,351,000				10,161,000			11,351,000	10,161,000	9,803,000		6,292,000
Provision for Loan Losses Expensed								3,691,000	610,000	1,893,000
Allowance for Loan and Lease Losses, Write-offs								(2,501,000)	(252,000)	(605,000)
Financing Receivable, Allowance for Credit Losses, Recovery										(2,223,000)
Long-Term Standby Purchase Commitments and Farmer Mac Guaranteed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reserve for losses	5,539,000				7,355,000			5,539,000	7,355,000	10,312,000		7,895,000
(Release of)/provision for losses								(1,816,000)	(2,957,000)	2,417,000
Other Credit Losses, Write-Offs								0	0	0
Financing Receivable, Allowance for Credit Losses, Recovery										0
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	9,661,000				8,106,000			9,661,000	8,106,000	9,797,000
Total provision for/(release of) losses								1,555,000	(1,691,000)
Financing Receivable, Allowance for Credit Losses, Write-downs								0	0
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	2,589,000				4,133,000			2,589,000	4,133,000	3,572,000
Total provision for/(release of) losses								509,000	737,000
Financing Receivable, Allowance for Credit Losses, Write-downs								(2,053,000)	(176,000)
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	2,316,000				3,099,000			2,316,000	3,099,000	3,537,000
Total provision for/(release of) losses								(408,000)	(431,000)
Financing Receivable, Allowance for Credit Losses, Write-downs								(375,000)	(7,000)
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	1,534,000				1,697,000			1,534,000	1,697,000	2,749,000
Total provision for/(release of) losses								(163,000)	(988,000)
Financing Receivable, Allowance for Credit Losses, Write-downs								0	(64,000)
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	784,000				477,000			784,000	477,000	445,000
Total provision for/(release of) losses								380,000	37,000
Financing Receivable, Allowance for Credit Losses, Write-downs								(73,000)	(5,000)
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	6,000				4,000			6,000	4,000	15,000
Total provision for/(release of) losses								2,000	(11,000)
Financing Receivable, Allowance for Credit Losses, Write-downs								$ 0	$ 0