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	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	$ 4,648,452		$ 4,261,137
Financing Receivable, Individually Evaluated for Impairment	98,837		88,026
Financing Receivable, Gross	4,747,289	[1]	4,349,163	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	10,231		10,220
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	6,659		7,296
Financing Receivable, Allowance for Credit Losses	16,890		17,516		20,115	14,187
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	2,147,274		1,835,439
Financing Receivable, Individually Evaluated for Impairment	24,075		29,520
Financing Receivable, Gross	2,171,349	[1]	1,864,959	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,882		1,723
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	707		2,410
Financing Receivable, Allowance for Credit Losses	2,589		4,133		3,572
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	844,927		796,100
Financing Receivable, Individually Evaluated for Impairment	37,605		28,245
Financing Receivable, Gross	882,532	[1]	824,345	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	801		775
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,515		2,324
Financing Receivable, Allowance for Credit Losses	2,316		3,099		3,537
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,271,033		1,213,227
Financing Receivable, Individually Evaluated for Impairment	16,708		10,884
Financing Receivable, Gross	1,287,741	[1]	1,224,111	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,179		1,290
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	355		407
Financing Receivable, Allowance for Credit Losses	1,534		1,697		2,749
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	186,769		232,607
Financing Receivable, Individually Evaluated for Impairment	15,096		12,513
Financing Receivable, Gross	201,865	[1]	245,120	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	103		172
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	681		305
Financing Receivable, Allowance for Credit Losses	784		477		445
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	187,449		167,850
Financing Receivable, Individually Evaluated for Impairment	4,337		5,842
Financing Receivable, Gross	191,786	[1]	173,692	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	6,261		6,256
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3,400		1,850
Financing Receivable, Allowance for Credit Losses	9,661		8,106		9,797
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	11,000		15,914
Financing Receivable, Individually Evaluated for Impairment	1,016		1,022
Financing Receivable, Gross	12,016	[1]	16,936	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	5		4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1		0
Financing Receivable, Allowance for Credit Losses	6		4		15
On-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,599,579		1,897,773
Financing Receivable, Individually Evaluated for Impairment	80,272		53,468
Financing Receivable, Gross	1,679,851	[1]	1,951,241	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,802		5,115
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	6,549		5,046
Financing Receivable, Allowance for Credit Losses	11,351		10,161
On-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	977,564		902,236
Financing Receivable, Individually Evaluated for Impairment	22,002		13,437
Financing Receivable, Gross	999,566	[1]	915,673	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,406		1,278
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	684		2,118
Financing Receivable, Allowance for Credit Losses	2,090		3,396
On-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	260,047		454,341
Financing Receivable, Individually Evaluated for Impairment	29,647		24,350
Financing Receivable, Gross	289,694	[1]	478,691	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	586		630
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,465		2,318
Financing Receivable, Allowance for Credit Losses	2,051		2,948
On-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	268,869		410,635
Financing Receivable, Individually Evaluated for Impairment	11,511		6,513
Financing Receivable, Gross	280,380	[1]	417,148	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	499		724
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	335		397
Financing Receivable, Allowance for Credit Losses	834		1,121
On-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	50,287		72,557
Financing Receivable, Individually Evaluated for Impairment	12,660		9,168
Financing Receivable, Gross	62,947	[1]	81,725	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	46		90
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	665		213
Financing Receivable, Allowance for Credit Losses	711		303
On-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	42,812		56,282
Financing Receivable, Individually Evaluated for Impairment	4,337		0
Financing Receivable, Gross	47,149	[1]	56,282	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,265		2,393
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3,400		0
Financing Receivable, Allowance for Credit Losses	5,665		2,393
On-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	0		1,722
Financing Receivable, Individually Evaluated for Impairment	115		0
Financing Receivable, Gross	115	[1]	1,722	[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	3,048,873		2,363,364
Financing Receivable, Individually Evaluated for Impairment	18,565		34,558
Financing Receivable, Gross	3,067,438	[1]	2,397,922	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	5,429		5,105
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	110		2,250
Financing Receivable, Allowance for Credit Losses	5,539		7,355
Off-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,169,710		933,203
Financing Receivable, Individually Evaluated for Impairment	2,073		16,083
Financing Receivable, Gross	1,171,783	[1]	949,286	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	476		445
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	23		292
Financing Receivable, Allowance for Credit Losses	499		737
Off-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	584,880		341,759
Financing Receivable, Individually Evaluated for Impairment	7,958		3,895
Financing Receivable, Gross	592,838	[1]	345,654	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	215		145
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	50		6
Financing Receivable, Allowance for Credit Losses	265		151
Off-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,002,164		802,592
Financing Receivable, Individually Evaluated for Impairment	5,197		4,371
Financing Receivable, Gross	1,007,361	[1]	806,963	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	680		566
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	20		10
Financing Receivable, Allowance for Credit Losses	700		576
Off-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	136,482		160,050
Financing Receivable, Individually Evaluated for Impairment	2,436		3,345
Financing Receivable, Gross	138,918	[1]	163,395	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	57		82
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	16		92
Financing Receivable, Allowance for Credit Losses	73		174
Off-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	144,637		111,568
Financing Receivable, Individually Evaluated for Impairment	0		5,842
Financing Receivable, Gross	144,637	[1]	117,410	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,996		3,863
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		1,850
Financing Receivable, Allowance for Credit Losses	3,996		5,713
Off-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	11,000		14,192
Financing Receivable, Individually Evaluated for Impairment	901		1,022
Financing Receivable, Gross	11,901	[1]	15,214	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	5		4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1		0
Financing Receivable, Allowance for Credit Losses	$ 6		$ 4

[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.