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, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	$ 5,258,513		$ 5,334,737
Financing Receivable, Individually Evaluated for Impairment	88,735		82,437
Financing Receivable, Gross	5,347,248	[1],[2]	5,417,174	[1],[2]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	6,476		7,490
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,955		2,637
Financing Receivable, Allowance for Credit Losses	9,431		10,127		13,979	13,334
Crops [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	2,907,812		2,926,501
Financing Receivable, Individually Evaluated for Impairment	21,164		14,765
Financing Receivable, Gross	2,928,976	[1]	2,941,266	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,000		2,122
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	640		397
Financing Receivable, Allowance for Credit Losses	2,640		2,519		2,278	2,124
Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	867,884		881,052
Financing Receivable, Individually Evaluated for Impairment	41,204		39,143
Financing Receivable, Gross	909,088	[1]	920,195	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	675		644
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,609		1,515
Financing Receivable, Allowance for Credit Losses	2,284		2,159		2,131	2,186
Livestock [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	1,206,945		1,245,335
Financing Receivable, Individually Evaluated for Impairment	14,789		15,283
Financing Receivable, Gross	1,221,734	[1]	1,260,618	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	994		1,062
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	349		361
Financing Receivable, Allowance for Credit Losses	1,343		1,423		1,387	1,271
Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	157,839		160,708
Financing Receivable, Individually Evaluated for Impairment	11,578		13,246
Financing Receivable, Gross	169,417	[1]	173,954	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	102		103
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	357		364
Financing Receivable, Allowance for Credit Losses	459		467		464	454
Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	110,367		114,360
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	110,367	[1]	114,360	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,698		3,552
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	2,698		3,552		7,715	7,292
Other Commodity [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	7,666		6,781
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	7,666	[1]	6,781	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7		7
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	7		7		4	7
On-balance sheet [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	2,497,509		2,473,780
Financing Receivable, Individually Evaluated for Impairment	73,403		66,442
Financing Receivable, Gross	2,570,912	[1]	2,540,222	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,284		3,531
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,656		2,333
Financing Receivable, Allowance for Credit Losses	5,940		5,864
On-balance sheet [Member] | Crops [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	1,642,496		1,621,360
Financing Receivable, Individually Evaluated for Impairment	18,706		12,307
Financing Receivable, Gross	1,661,202	[1]	1,633,667	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,726		1,824
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	517		283
Financing Receivable, Allowance for Credit Losses	2,243		2,107
On-balance sheet [Member] | Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	367,380		359,517
Financing Receivable, Individually Evaluated for Impairment	38,030		35,904
Financing Receivable, Gross	405,410	[1]	395,421	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	520		495
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,502		1,410
Financing Receivable, Allowance for Credit Losses	2,022		1,905
On-balance sheet [Member] | Livestock [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	402,478		406,049
Financing Receivable, Individually Evaluated for Impairment	6,178		6,571
Financing Receivable, Gross	408,656	[1]	412,620	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	654		658
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	317		328
Financing Receivable, Allowance for Credit Losses	971		986
On-balance sheet [Member] | Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	57,995		57,851
Financing Receivable, Individually Evaluated for Impairment	10,489		11,660
Financing Receivable, Gross	68,484	[1]	69,511	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	49		51
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	320		312
Financing Receivable, Allowance for Credit Losses	369		363
On-balance sheet [Member] | Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	25,800		29,003
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	25,800	[1]	29,003	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	335		503
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	335		503
On-balance sheet [Member] | Other Commodity [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	1,360		0
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	1,360	[1]	0	[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	2,761,004		2,860,957
Financing Receivable, Individually Evaluated for Impairment	15,332		15,995
Financing Receivable, Gross	2,776,336	[1]	2,876,952	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3,192		3,959
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	299		304
Financing Receivable, Allowance for Credit Losses	3,491		4,263
Off-balance sheet [Member] | Crops [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	1,265,316		1,305,141
Financing Receivable, Individually Evaluated for Impairment	2,458		2,458
Financing Receivable, Gross	1,267,774	[1]	1,307,599	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	274		298
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	123		114
Financing Receivable, Allowance for Credit Losses	397		412
Off-balance sheet [Member] | Permanent Plantings [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	500,504		521,535
Financing Receivable, Individually Evaluated for Impairment	3,174		3,239
Financing Receivable, Gross	503,678	[1]	524,774	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	155		149
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	107		105
Financing Receivable, Allowance for Credit Losses	262		254
Off-balance sheet [Member] | Livestock [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	804,467		839,286
Financing Receivable, Individually Evaluated for Impairment	8,611		8,712
Financing Receivable, Gross	813,078	[1]	847,998	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	340		404
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	32		33
Financing Receivable, Allowance for Credit Losses	372		437
Off-balance sheet [Member] | Part-Time Farm [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	99,844		102,857
Financing Receivable, Individually Evaluated for Impairment	1,089		1,586
Financing Receivable, Gross	100,933	[1]	104,443	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	53		52
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	37		52
Financing Receivable, Allowance for Credit Losses	90		104
Off-balance sheet [Member] | Agriculture Storage and Processing [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	84,567		85,357
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	84,567	[1]	85,357	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	2,363		3,049
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses	2,363		3,049
Off-balance sheet [Member] | Other Commodity [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Financing Receivable, Collectively Evaluated for Impairment	6,306		6,781
Financing Receivable, Individually Evaluated for Impairment	0		0
Financing Receivable, Gross	6,306	[1]	6,781	[1]
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7		7
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
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).