Loans and Allowance for Losses and Concentrations of Credit Risk Allowance for Losses by Impairment Method and Commodity (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	$ 4,657,488		$ 4,648,452
Financing Receivable, Individually Evaluated for Impairment	125,121		98,837
Financing Receivable, Gross	4,782,609	[1]	4,747,289	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	10,791		10,231
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3,461		6,659
Financing Receivable, Allowance for Credit Losses	14,252		16,890		17,966	17,516
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	2,197,364		2,147,274
Financing Receivable, Individually Evaluated for Impairment	38,236		24,075
Financing Receivable, Gross	2,235,600	[1]	2,171,349	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,880		1,882
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	737		707
Financing Receivable, Allowance for Credit Losses	2,617		2,589		4,266	4,133
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	814,678		844,927
Financing Receivable, Individually Evaluated for Impairment	54,451		37,605
Financing Receivable, Gross	869,129	[1]	882,532	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	709		801
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,617		1,515
Financing Receivable, Allowance for Credit Losses	2,326		2,316		3,482	3,365
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,237,951		1,271,033
Financing Receivable, Individually Evaluated for Impairment	18,398		16,708
Financing Receivable, Gross	1,256,349	[1]	1,287,741	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,134		1,179
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	453		355
Financing Receivable, Allowance for Credit Losses	1,587		1,534		636	685
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	176,564		186,769
Financing Receivable, Individually Evaluated for Impairment	13,020		15,096
Financing Receivable, Gross	189,584	[1]	201,865	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	93		103
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	640		681
Financing Receivable, Allowance for Credit Losses	733		784		1,475	1,223
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	220,938		187,449
Financing Receivable, Individually Evaluated for Impairment	0		4,337
Financing Receivable, Gross	220,938	[1]	191,786	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	6,971		6,261
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		3,400
Financing Receivable, Allowance for Credit Losses	6,971		9,661		8,100	8,106
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	9,993		11,000
Financing Receivable, Individually Evaluated for Impairment	1,016		1,016
Financing Receivable, Gross	11,009	[1]	12,016	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4		5
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	14		1
Financing Receivable, Allowance for Credit Losses	18		6		7	4
On-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,601,096		1,599,579
Financing Receivable, Individually Evaluated for Impairment	103,448		80,272
Financing Receivable, Gross	1,704,544	[1]	1,679,851	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,788		4,802
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3,179		6,549
Financing Receivable, Allowance for Credit Losses	7,967		11,351
On-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	999,390		977,564
Financing Receivable, Individually Evaluated for Impairment	31,342		22,002
Financing Receivable, Gross	1,030,732	[1]	999,566	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,485		1,406
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	688		684
Financing Receivable, Allowance for Credit Losses	2,173		2,090
On-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	245,448		260,047
Financing Receivable, Individually Evaluated for Impairment	47,429		29,647
Financing Receivable, Gross	292,877	[1]	289,694	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	499		586
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,547		1,465
Financing Receivable, Allowance for Credit Losses	2,046		2,051
On-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	264,593		268,869
Financing Receivable, Individually Evaluated for Impairment	13,667		11,511
Financing Receivable, Gross	278,260	[1]	280,380	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	478		499
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	328		335
Financing Receivable, Allowance for Credit Losses	806		834
On-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	48,215		50,287
Financing Receivable, Individually Evaluated for Impairment	10,895		12,660
Financing Receivable, Gross	59,110	[1]	62,947	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	45		46
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	616		665
Financing Receivable, Allowance for Credit Losses	661		711
On-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	43,450		42,812
Financing Receivable, Individually Evaluated for Impairment	0		4,337
Financing Receivable, Gross	43,450	[1]	47,149	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,281		2,265
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		3,400
Financing Receivable, Allowance for Credit Losses	2,281		5,665
On-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	0		0
Financing Receivable, Individually Evaluated for Impairment	115		115
Financing Receivable, Gross	115	[1]	115	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	0		0
Off-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	3,056,392		3,048,873
Financing Receivable, Individually Evaluated for Impairment	21,673		18,565
Financing Receivable, Gross	3,078,065	[1]	3,067,438	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	6,003		5,429
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	282		110
Financing Receivable, Allowance for Credit Losses	6,285		5,539
Off-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,197,974		1,169,710
Financing Receivable, Individually Evaluated for Impairment	6,894		2,073
Financing Receivable, Gross	1,204,868	[1]	1,171,783	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	395		476
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	49		23
Financing Receivable, Allowance for Credit Losses	444		499
Off-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	569,230		584,880
Financing Receivable, Individually Evaluated for Impairment	7,022		7,958
Financing Receivable, Gross	576,252	[1]	592,838	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	210		215
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	70		50
Financing Receivable, Allowance for Credit Losses	280		265
Off-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	973,358		1,002,164
Financing Receivable, Individually Evaluated for Impairment	4,731		5,197
Financing Receivable, Gross	978,089	[1]	1,007,361	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	656		680
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	125		20
Financing Receivable, Allowance for Credit Losses	781		700
Off-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	128,349		136,482
Financing Receivable, Individually Evaluated for Impairment	2,125		2,436
Financing Receivable, Gross	130,474	[1]	138,918	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	48		57
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	24		16
Financing Receivable, Allowance for Credit Losses	72		73
Off-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	177,488		144,637
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	177,488	[1]	144,637	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,690		3,996
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	4,690		3,996
Off-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	9,993		11,000
Financing Receivable, Individually Evaluated for Impairment	901		901
Financing Receivable, Gross	10,894	[1]	11,901	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4		5
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	14		1
Financing Receivable, Allowance for Credit Losses	$ 18		$ 6

[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.