Allowance for Losses and Concentration of Credit Risk - Impairment Method (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011		Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Financing Receivable, Allowance for Credit Losses [Line Items]
Evaluated collectively for impairment	$ 4,304,457			$ 4,261,137
Evaluated individually for impairment	98,755			88,026
Total financing receivable	4,403,212	[1]		4,349,163	[1]
Allowance for Losses, evaluated collectively for impairment	10,024			10,220
Allowance for Losses, evaluated individually for impairment	8,116			7,296
Total allowance for losses	18,140		17,966	17,516		18,496	19,462	20,115
Crops
Financing Receivable, Allowance for Credit Losses [Line Items]
Evaluated collectively for impairment	1,912,073			1,835,439
Evaluated individually for impairment	29,002			29,520
Total financing receivable	1,941,075	[1]		1,864,959	[1]
Allowance for Losses, evaluated collectively for impairment	1,662			1,723
Allowance for Losses, evaluated individually for impairment	2,619			2,410
Total allowance for losses	4,281		4,266	4,133		3,715	3,922	3,572
Permanent Plantings
Financing Receivable, Allowance for Credit Losses [Line Items]
Evaluated collectively for impairment	792,842			796,100
Evaluated individually for impairment	30,557			28,245
Total financing receivable	823,399	[1]		824,345	[1]
Allowance for Losses, evaluated collectively for impairment	1,221			1,290
Allowance for Losses, evaluated individually for impairment	1,467			2,075
Total allowance for losses	2,688		3,482	3,365		3,803	3,802	3,537
Livestock
Financing Receivable, Allowance for Credit Losses [Line Items]
Evaluated collectively for impairment	1,201,256			1,213,227
Evaluated individually for impairment	17,465			10,884
Total financing receivable	1,218,721	[1]		1,224,111	[1]
Allowance for Losses, evaluated collectively for impairment	122			172
Allowance for Losses, evaluated individually for impairment	341			513
Total allowance for losses	463		636	685		1,774	1,850	2,749
Part-Time Farm
Financing Receivable, Allowance for Credit Losses [Line Items]
Evaluated collectively for impairment	208,088			232,607
Evaluated individually for impairment	16,377			12,513
Total financing receivable	224,465	[1]		245,120	[1]
Allowance for Losses, evaluated collectively for impairment	761			775
Allowance for Losses, evaluated individually for impairment	638			448
Total allowance for losses	1,399		1,475	1,223		1,095	1,053	445
Ag Storage and Processing (including ethanol facilities)
Financing Receivable, Allowance for Credit Losses [Line Items]
Evaluated collectively for impairment	177,018			167,850
Evaluated individually for impairment	4,337			5,842
Total financing receivable	181,355	[1]		173,692	[1]
Allowance for Losses, evaluated collectively for impairment	6,252			6,256
Allowance for Losses, evaluated individually for impairment	3,050			1,850
Total allowance for losses	9,302		8,100	8,106		8,100	8,823	9,797
Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Evaluated collectively for impairment	13,180			15,914
Evaluated individually for impairment	1,017			1,022
Total financing receivable	14,197	[1]		16,936	[1]
Allowance for Losses, evaluated collectively for impairment	6			4
Allowance for Losses, evaluated individually for impairment	1			0
Total allowance for losses	$ 7		$ 7	$ 4		$ 9	$ 12	$ 15

[1] Amounts represent unpaid principal balance of risk-rated loans, which is the basis Farmer Mac uses to analyze its portfolio, and recorded investment of past due loans.