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, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	$ 5,334,737		$ 5,068,039
Financing Receivable, Individually Evaluated for Impairment	82,437		95,041
Financing Receivable, Gross	5,417,174	[1],[2]	5,163,080	[1],[2]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7,490		10,638
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,637		2,696
Financing Receivable, Allowance for Credit Losses	10,127		13,334		16,890	17,516
Crops [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	2,926,501		2,643,748
Financing Receivable, Individually Evaluated for Impairment	14,765		23,109
Financing Receivable, Gross	2,941,266	[1]	2,666,857	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,122		1,718
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	397		406
Financing Receivable, Allowance for Credit Losses	2,519		2,124		2,589
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	881,052		862,969
Financing Receivable, Individually Evaluated for Impairment	39,143		44,855
Financing Receivable, Gross	920,195	[1]	907,824	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	644		484
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,515		1,702
Financing Receivable, Allowance for Credit Losses	2,159		2,186		2,316
Livestock [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	1,245,335		1,232,062
Financing Receivable, Individually Evaluated for Impairment	15,283		14,043
Financing Receivable, Gross	1,260,618	[1]	1,246,105	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,062		1,078
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	361		193
Financing Receivable, Allowance for Credit Losses	1,423		1,271		1,534
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	160,708		149,824
Financing Receivable, Individually Evaluated for Impairment	13,246		12,919
Financing Receivable, Gross	173,954	[1]	162,743	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	103		62
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	364		392
Financing Receivable, Allowance for Credit Losses	467		454		784
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	114,360		170,918
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	114,360	[1]	170,918	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,552		7,292
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	3,552		7,292		9,661
Other Commodity [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	6,781		8,518
Financing Receivable, Individually Evaluated for Impairment	0		115
Financing Receivable, Gross	6,781	[1]	8,633	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7		4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		3
Financing Receivable, Allowance for Credit Losses	7		7		6
On-balance sheet [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	2,473,780		2,051,498
Financing Receivable, Individually Evaluated for Impairment	66,442		83,969
Financing Receivable, Gross	2,540,222	[1]	2,135,467	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,531		4,392
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,333		2,474
Financing Receivable, Allowance for Credit Losses	5,864		6,866
On-balance sheet [Member] | Crops [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	1,621,360		1,363,861
Financing Receivable, Individually Evaluated for Impairment	12,307		21,147
Financing Receivable, Gross	1,633,667	[1]	1,385,008	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,824		1,321
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	283		362
Financing Receivable, Allowance for Credit Losses	2,107		1,683
On-balance sheet [Member] | Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	359,517		295,037
Financing Receivable, Individually Evaluated for Impairment	35,904		41,441
Financing Receivable, Gross	395,421	[1]	336,478	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	495		325
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,410		1,641
Financing Receivable, Allowance for Credit Losses	1,905		1,966
On-balance sheet [Member] | Livestock [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	406,049		319,665
Financing Receivable, Individually Evaluated for Impairment	6,571		10,844
Financing Receivable, Gross	412,620	[1]	330,509	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	658		436
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	328		140
Financing Receivable, Allowance for Credit Losses	986		576
On-balance sheet [Member] | Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	57,851		39,940
Financing Receivable, Individually Evaluated for Impairment	11,660		10,422
Financing Receivable, Gross	69,511	[1]	50,362	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	51		20
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	312		331
Financing Receivable, Allowance for Credit Losses	363		351
On-balance sheet [Member] | Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	29,003		32,636
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	29,003	[1]	32,636	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	503		2,290
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	503		2,290
On-balance sheet [Member] | Other Commodity [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	0		359
Financing Receivable, Individually Evaluated for Impairment	0		115
Financing Receivable, Gross	0	[1]	474	[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]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	2,860,957		3,016,541
Financing Receivable, Individually Evaluated for Impairment	15,995		11,072
Financing Receivable, Gross	2,876,952	[1]	3,027,613	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,959		6,246
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	304		222
Financing Receivable, Allowance for Credit Losses	4,263		6,468
Off-balance sheet [Member] | Crops [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	1,305,141		1,279,887
Financing Receivable, Individually Evaluated for Impairment	2,458		1,962
Financing Receivable, Gross	1,307,599	[1]	1,281,849	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	298		397
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	114		44
Financing Receivable, Allowance for Credit Losses	412		441
Off-balance sheet [Member] | Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	521,535		567,932
Financing Receivable, Individually Evaluated for Impairment	3,239		3,414
Financing Receivable, Gross	524,774	[1]	571,346	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	149		159
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	105		61
Financing Receivable, Allowance for Credit Losses	254		220
Off-balance sheet [Member] | Livestock [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	839,286		912,397
Financing Receivable, Individually Evaluated for Impairment	8,712		3,199
Financing Receivable, Gross	847,998	[1]	915,596	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	404		642
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	33		53
Financing Receivable, Allowance for Credit Losses	437		695
Off-balance sheet [Member] | Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	102,857		109,884
Financing Receivable, Individually Evaluated for Impairment	1,586		2,497
Financing Receivable, Gross	104,443	[1]	112,381	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	52		42
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	52		61
Financing Receivable, Allowance for Credit Losses	104		103
Off-balance sheet [Member] | Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	85,357		138,282
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	85,357	[1]	138,282	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,049		5,002
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	3,049		5,002
Off-balance sheet [Member] | Other Commodity [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	6,781		8,159
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	6,781	[1]	8,159	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7		4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		3
Financing Receivable, Allowance for Credit Losses	$ 7		$ 7

[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.

[2] Geographic regions: Northwest (AK, ID, MT, OR, WA, WY); Southwest (AZ, CA, CO, HI, NM, NV, UT); Mid-North (IA, IL, IN, MI, MN, NE, ND, SD, WI); Mid-South (AR, KS, LA, MO, OK, TX); Northeast (CT, DE, KY, MA, MD, ME, NH, NJ, NY, OH, PA, RI, VA, VT, WV); Southeast (AL, FL, GA, MS, NC, SC, TN).