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	Sep. 30, 2013		Jun. 30, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	$ 4,950,605			$ 4,648,452
Financing Receivable, Individually Evaluated for Impairment	85,143			98,837
Financing Receivable, Gross	5,035,748	[1]		4,747,289	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	10,876			10,231
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,566			6,659
Financing Receivable, Allowance for Credit Losses	13,442		13,478	16,890		17,786	18,140	17,516
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	2,508,919			2,147,274
Financing Receivable, Individually Evaluated for Impairment	23,004			24,075
Financing Receivable, Gross	2,531,923	[1]		2,171,349	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,699			1,882
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	481			707
Financing Receivable, Allowance for Credit Losses	2,180		2,405	2,589		3,976	4,281	4,133
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	870,362			844,927
Financing Receivable, Individually Evaluated for Impairment	35,251			37,605
Financing Receivable, Gross	905,613	[1]		882,532	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	533			801
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,530			1,515
Financing Receivable, Allowance for Credit Losses	2,063		2,168	2,316		2,323	2,522	3,099
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,225,307			1,271,033
Financing Receivable, Individually Evaluated for Impairment	14,282			16,708
Financing Receivable, Gross	1,239,589	[1]		1,287,741	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,011			1,179
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	184			355
Financing Receivable, Allowance for Credit Losses	1,195		1,279	1,534		1,342	1,471	1,697
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	156,964			186,769
Financing Receivable, Individually Evaluated for Impairment	12,491			15,096
Financing Receivable, Gross	169,455	[1]		201,865	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	69			103
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	369			681
Financing Receivable, Allowance for Credit Losses	438		425	784		676	557	477
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	179,627			187,449
Financing Receivable, Individually Evaluated for Impairment	0			4,337
Financing Receivable, Gross	179,627	[1]		191,786	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7,560			6,261
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0			3,400
Financing Receivable, Allowance for Credit Losses	7,560		7,196	9,661		9,463	9,302	8,106
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	9,426			11,000
Financing Receivable, Individually Evaluated for Impairment	115			1,016
Financing Receivable, Gross	9,541	[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	2			1
Financing Receivable, Allowance for Credit Losses	6		5	6		6	7	4
On-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,875,975			1,599,579
Financing Receivable, Individually Evaluated for Impairment	74,728			80,272
Financing Receivable, Gross	1,950,703	[1]		1,679,851	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,564			4,802
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,305			6,549
Financing Receivable, Allowance for Credit Losses	6,869			11,351
On-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,231,014			977,564
Financing Receivable, Individually Evaluated for Impairment	21,013			22,002
Financing Receivable, Gross	1,252,027	[1]		999,566	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,302			1,406
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	379			684
Financing Receivable, Allowance for Credit Losses	1,681			2,090
On-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	281,773			260,047
Financing Receivable, Individually Evaluated for Impairment	32,149			29,647
Financing Receivable, Gross	313,922	[1]		289,694	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	330			586
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,483			1,465
Financing Receivable, Allowance for Credit Losses	1,813			2,051
On-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	280,286			268,869
Financing Receivable, Individually Evaluated for Impairment	11,060			11,511
Financing Receivable, Gross	291,346	[1]		280,380	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	338			499
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	119			335
Financing Receivable, Allowance for Credit Losses	457			834
On-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	42,653			50,287
Financing Receivable, Individually Evaluated for Impairment	10,391			12,660
Financing Receivable, Gross	53,044	[1]		62,947	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	25			46
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	324			665
Financing Receivable, Allowance for Credit Losses	349			711
On-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	39,690			42,812
Financing Receivable, Individually Evaluated for Impairment	0			4,337
Financing Receivable, Gross	39,690	[1]		47,149	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,569			2,265
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0			3,400
Financing Receivable, Allowance for Credit Losses	2,569			5,665
On-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	559			0
Financing Receivable, Individually Evaluated for Impairment	115			115
Financing Receivable, Gross	674	[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	3,074,630			3,048,873
Financing Receivable, Individually Evaluated for Impairment	10,415			18,565
Financing Receivable, Gross	3,085,045	[1]		3,067,438	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	6,312			5,429
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	261			110
Financing Receivable, Allowance for Credit Losses	6,573			5,539
Off-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,277,905			1,169,710
Financing Receivable, Individually Evaluated for Impairment	1,991			2,073
Financing Receivable, Gross	1,279,896	[1]		1,171,783	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	397			476
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	102			23
Financing Receivable, Allowance for Credit Losses	499			499
Off-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	588,589			584,880
Financing Receivable, Individually Evaluated for Impairment	3,102			7,958
Financing Receivable, Gross	591,691	[1]		592,838	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	203			215
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	47			50
Financing Receivable, Allowance for Credit Losses	250			265
Off-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	945,021			1,002,164
Financing Receivable, Individually Evaluated for Impairment	3,222			5,197
Financing Receivable, Gross	948,243	[1]		1,007,361	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	673			680
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	65			20
Financing Receivable, Allowance for Credit Losses	738			700
Off-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	114,311			136,482
Financing Receivable, Individually Evaluated for Impairment	2,100			2,436
Financing Receivable, Gross	116,411	[1]		138,918	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	44			57
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	45			16
Financing Receivable, Allowance for Credit Losses	89			73
Off-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	139,937			144,637
Financing Receivable, Individually Evaluated for Impairment	0			0
Financing Receivable, Gross	139,937	[1]		144,637	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,991			3,996
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0			0
Financing Receivable, Allowance for Credit Losses	4,991			3,996
Off-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	8,867			11,000
Financing Receivable, Individually Evaluated for Impairment	0			901
Financing Receivable, Gross	8,867	[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	2			1
Financing Receivable, Allowance for Credit Losses	$ 6			$ 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.