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	Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	$ 4,824,305			$ 4,648,452
Financing Receivable, Individually Evaluated for Impairment	93,184			98,837
Financing Receivable, Gross	4,917,489	[1]		4,747,289	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	10,988			10,231
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,490			6,659
Financing Receivable, Allowance for Credit Losses	13,478		14,252	16,890		18,140	17,966	17,516
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	2,370,842			2,147,274
Financing Receivable, Individually Evaluated for Impairment	29,387			24,075
Financing Receivable, Gross	2,400,229	[1]		2,171,349	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,885			1,882
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	520			707
Financing Receivable, Allowance for Credit Losses	2,405		2,617	2,589		4,281	4,266	4,133
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	849,578			844,927
Financing Receivable, Individually Evaluated for Impairment	36,756			37,605
Financing Receivable, Gross	886,334	[1]		882,532	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	700			801
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,468			1,515
Financing Receivable, Allowance for Credit Losses	2,168		2,326	2,316		2,688	3,482	3,365
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,224,844			1,271,033
Financing Receivable, Individually Evaluated for Impairment	15,766			16,708
Financing Receivable, Gross	1,240,610	[1]		1,287,741	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,117			1,179
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	162			355
Financing Receivable, Allowance for Credit Losses	1,279		1,587	1,534		463	636	685
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	167,101			186,769
Financing Receivable, Individually Evaluated for Impairment	11,160			15,096
Financing Receivable, Gross	178,261	[1]		201,865	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	87			103
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	338			681
Financing Receivable, Allowance for Credit Losses	425		733	784		1,399	1,475	1,223
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	201,180			187,449
Financing Receivable, Individually Evaluated for Impairment	0			4,337
Financing Receivable, Gross	201,180	[1]		191,786	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7,196			6,261
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0			3,400
Financing Receivable, Allowance for Credit Losses	7,196		6,971	9,661		9,302	8,100	8,106
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	10,760			11,000
Financing Receivable, Individually Evaluated for Impairment	115			1,016
Financing Receivable, Gross	10,875	[1]		12,016	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3			5
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2			1
Financing Receivable, Allowance for Credit Losses	5		18	6		7	7	4
On-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,800,508			1,599,579
Financing Receivable, Individually Evaluated for Impairment	76,450			80,272
Financing Receivable, Gross	1,876,958	[1]		1,679,851	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	5,059			4,802
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,309			6,549
Financing Receivable, Allowance for Credit Losses	7,368			11,351
On-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,155,620			977,564
Financing Receivable, Individually Evaluated for Impairment	22,979			22,002
Financing Receivable, Gross	1,178,599	[1]		999,566	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,506			1,406
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	427			684
Financing Receivable, Allowance for Credit Losses	1,933			2,090
On-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	280,110			260,047
Financing Receivable, Individually Evaluated for Impairment	33,647			29,647
Financing Receivable, Gross	313,757	[1]		289,694	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	485			586
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,467			1,465
Financing Receivable, Allowance for Credit Losses	1,952			2,051
On-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	275,527			268,869
Financing Receivable, Individually Evaluated for Impairment	10,116			11,511
Financing Receivable, Gross	285,643	[1]		280,380	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	474			499
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	102			335
Financing Receivable, Allowance for Credit Losses	576			834
On-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	46,808			50,287
Financing Receivable, Individually Evaluated for Impairment	9,593			12,660
Financing Receivable, Gross	56,401	[1]		62,947	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	46			46
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	313			665
Financing Receivable, Allowance for Credit Losses	359			711
On-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	40,797			42,812
Financing Receivable, Individually Evaluated for Impairment	0			4,337
Financing Receivable, Gross	40,797	[1]		47,149	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,548			2,265
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0			3,400
Financing Receivable, Allowance for Credit Losses	2,548			5,665
On-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,646			0
Financing Receivable, Individually Evaluated for Impairment	115			115
Financing Receivable, Gross	1,761	[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	3,023,797			3,048,873
Financing Receivable, Individually Evaluated for Impairment	16,734			18,565
Financing Receivable, Gross	3,040,531	[1]		3,067,438	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	5,929			5,429
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	181			110
Financing Receivable, Allowance for Credit Losses	6,110			5,539
Off-balance sheet [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	1,215,222			1,169,710
Financing Receivable, Individually Evaluated for Impairment	6,408			2,073
Financing Receivable, Gross	1,221,630	[1]		1,171,783	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	379			476
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	93			23
Financing Receivable, Allowance for Credit Losses	472			499
Off-balance sheet [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	569,468			584,880
Financing Receivable, Individually Evaluated for Impairment	3,109			7,958
Financing Receivable, Gross	572,577	[1]		592,838	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	215			215
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1			50
Financing Receivable, Allowance for Credit Losses	216			265
Off-balance sheet [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	949,317			1,002,164
Financing Receivable, Individually Evaluated for Impairment	5,650			5,197
Financing Receivable, Gross	954,967	[1]		1,007,361	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	643			680
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	60			20
Financing Receivable, Allowance for Credit Losses	703			700
Off-balance sheet [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	120,293			136,482
Financing Receivable, Individually Evaluated for Impairment	1,567			2,436
Financing Receivable, Gross	121,860	[1]		138,918	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	41			57
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	25			16
Financing Receivable, Allowance for Credit Losses	66			73
Off-balance sheet [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	160,383			144,637
Financing Receivable, Individually Evaluated for Impairment	0			0
Financing Receivable, Gross	160,383	[1]		144,637	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	4,648			3,996
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0			0
Financing Receivable, Allowance for Credit Losses	4,648			3,996
Off-balance sheet [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	9,114			11,000
Financing Receivable, Individually Evaluated for Impairment	0			901
Financing Receivable, Gross	9,114	[1]		11,901	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3			5
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2			1
Financing Receivable, Allowance for Credit Losses	$ 5			$ 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.