Loans and Allowance for Losses and Concentrations of Credit Risk Allowance for Credit Losses Roll Forward (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]
Allowance for Loan and Lease Losses, Real Estate	$ 7,967,000		$ 11,351,000
Reserve for losses	6,285,000		5,539,000
Financing Receivable, Allowance for Credit Losses	14,252,000	17,966,000	16,890,000	17,516,000
Provision for Loan Losses Expensed	430,000	420,000
Provision for losses	746,000	30,000
Total provision for/(release of) losses	1,176,000	450,000
Financing Receivable, Allowance for Credit Losses, Write-downs	(3,814,000)	0
Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Loan and Lease Losses, Real Estate	7,967,000	10,581,000	11,351,000	10,161,000
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]
Reserve for losses	6,285,000	7,385,000	5,539,000	7,355,000
Provision for losses	746,000	30,000
Other Credit Losses, Write-Offs	0	0
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	6,971,000	8,100,000	9,661,000	8,106,000
Total provision for/(release of) losses	935,000	(6,000)
Financing Receivable, Allowance for Credit Losses, Write-downs	(3,625,000)	0
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	2,617,000	4,266,000	2,589,000	4,133,000
Total provision for/(release of) losses	28,000	133,000
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	2,326,000	3,482,000	2,316,000	3,365,000
Total provision for/(release of) losses	199,000	117,000
Financing Receivable, Allowance for Credit Losses, Write-downs	(189,000)	0
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	1,587,000	636,000	1,534,000	685,000
Total provision for/(release of) losses	53,000	(49,000)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	733,000	1,475,000	784,000	1,223,000
Total provision for/(release of) losses	(51,000)	252,000
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	18,000	7,000	6,000	4,000
Total provision for/(release of) losses	12,000	3,000
Financing Receivable, Allowance for Credit Losses, Write-downs	$ 0	$ 0