Loans and Allowance for Losses and Concentrations of Credit Risk - Allowance for Credit Losses Roll Forward (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	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Loan and Lease Losses, Real Estate	$ 6,869		$ 6,869			$ 11,351
Reserve for losses	6,573		6,573			5,539
Financing Receivable, Allowance for Credit Losses	13,442	17,786	13,442	17,786	13,478	16,890	18,140	17,516
Provision for Loan Losses Expensed	(499)	137	(598)	(663)
Provision for losses	463	(43)	1,034	1,381
Total provision for/(release of) losses	(36)	94	436	718
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(448)	(3,884)	(448)
Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Loan and Lease Losses, Real Estate	6,869	9,050	6,869	9,050	7,368	11,351	9,361	10,161
Provision for Loan Losses Expensed	(499)	137	(598)	(663)
Allowance for Loan and Lease Losses, Write-offs	0	(448)	(3,884)	(448)
Long-Term Standby Purchase Commitments and Farmer Mac Guaranteed Securities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reserve for losses	6,573	8,736	6,573	8,736	6,110	5,539	8,779	7,355
Provision for losses	463	(43)	1,034	1,381
Other Credit Losses, Write-Offs	0	0	0	0
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	7,560	9,463	7,560	9,463	7,196	9,661	9,302	8,106
Total provision for/(release of) losses	364	161	1,524	1,357
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	(3,625)	0
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	2,180	3,976	2,180	3,976	2,405	2,589	4,281	4,133
Total provision for/(release of) losses	(225)	(305)	(409)	(157)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	2,063	2,323	2,063	2,323	2,168	2,316	2,522	3,099
Total provision for/(release of) losses	(105)	176	(64)	(401)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(375)	(189)	(375)
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	1,195	1,342	1,195	1,342	1,279	1,534	1,471	1,697
Total provision for/(release of) losses	(84)	(129)	(339)	(355)
Financing Receivable, Allowance for Credit Losses, Write-downs	0	0	0	0
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	438	676	438	676	425	784	557	477
Total provision for/(release of) losses	13	192	(276)	272
Financing Receivable, Allowance for Credit Losses, Write-downs	0	(73)	(70)	(73)
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Losses	6	6	6	6	5	6	7	4
Total provision for/(release of) losses	1	(1)	0	2
Financing Receivable, Allowance for Credit Losses, Write-downs	$ 0	$ 0	$ 0	$ 0