Loans and Allowance for Losses and Concentrations of Credit Risk - Impaired Financing Receivables (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	$ 23,397			$ 23,397			$ 27,468
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	23,352			23,352			27,534
Impaired Financing Receivable, with Related Allowance, Recorded Investment	124,170	[1]		124,170	[1]		79,931	[2]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	123,966			123,966			80,205
Impaired Financing Receivable, Recorded Investment	147,567			147,567			107,399
Impaired Financing Receivable, Unpaid Principal Balance	147,318			147,318			107,739
Impaired Financing Receivable, Related Allowance	2,937			2,937			2,292
Financing Receivable, Recorded Investment, Nonaccrual Status	63,044	[3]		63,044	[3]		32,142	[4]
Impaired Financing Receivable, Average Recorded Investment	134,503		$ 76,304	123,262		$ 80,596
Impaired Financing Receivable, Interest Income, Cash Basis Method	419		437	1,474		1,377
Crops [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	11,909			11,909			20,761
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	11,885			11,885			20,816
Impaired Financing Receivable, with Related Allowance, Recorded Investment	65,391	[1]		65,391	[1]		32,326	[2]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	65,284			65,284			32,381
Impaired Financing Receivable, Recorded Investment	77,300			77,300			53,087
Impaired Financing Receivable, Unpaid Principal Balance	77,169			77,169			53,197
Impaired Financing Receivable, Related Allowance	1,422			1,422			945
Financing Receivable, Recorded Investment, Nonaccrual Status	29,535	[3]		29,535	[3]		13,405	[4]
Impaired Financing Receivable, Average Recorded Investment	72,180		33,032	65,244		28,293
Impaired Financing Receivable, Interest Income, Cash Basis Method	101		46	563		108
Permanent Plantings [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,963			4,963			3,683
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	4,953			4,953			3,688
Impaired Financing Receivable, with Related Allowance, Recorded Investment	38,565	[1]		38,565	[1]		26,748	[2]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	38,497			38,497			26,817
Impaired Financing Receivable, Recorded Investment	43,528			43,528			30,431
Impaired Financing Receivable, Unpaid Principal Balance	43,450			43,450			30,505
Impaired Financing Receivable, Related Allowance	1,068			1,068			790
Financing Receivable, Recorded Investment, Nonaccrual Status	25,653	[3]		25,653	[3]		10,785	[4]
Impaired Financing Receivable, Average Recorded Investment	38,396		22,980	35,101		25,277
Impaired Financing Receivable, Interest Income, Cash Basis Method	244		236	464		789
Livestock [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,942			3,942			1,054
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	3,935			3,935			1,055
Impaired Financing Receivable, with Related Allowance, Recorded Investment	14,048	[1]		14,048	[1]		14,322	[2]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	14,029			14,029			14,457
Impaired Financing Receivable, Recorded Investment	17,990			17,990			15,376
Impaired Financing Receivable, Unpaid Principal Balance	17,964			17,964			15,512
Impaired Financing Receivable, Related Allowance	309			309			399
Financing Receivable, Recorded Investment, Nonaccrual Status	2,819	[3]		2,819	[3]		2,696	[4]
Impaired Financing Receivable, Average Recorded Investment	15,582		12,120	14,620		13,704
Impaired Financing Receivable, Interest Income, Cash Basis Method	13		81	212		229
Part-Time Farm [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,939			1,939			1,970
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,936			1,936			1,975
Impaired Financing Receivable, with Related Allowance, Recorded Investment	6,088	[1]		6,088	[1]		6,535	[2]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	6,078			6,078			6,550
Impaired Financing Receivable, Recorded Investment	8,027			8,027			8,505
Impaired Financing Receivable, Unpaid Principal Balance	8,014			8,014			8,525
Impaired Financing Receivable, Related Allowance	136			136			158
Financing Receivable, Recorded Investment, Nonaccrual Status	5,037	[3]		5,037	[3]		5,256	[4]
Impaired Financing Receivable, Average Recorded Investment	7,944		8,172	8,096		8,654
Impaired Financing Receivable, Interest Income, Cash Basis Method	61		74	235		251
Agriculture Storage and Processing [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0			0			0
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	0			0			0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	[1]		0	[1]		0	[2]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0			0			0
Impaired Financing Receivable, Recorded Investment	0			0			0
Impaired Financing Receivable, Unpaid Principal Balance	0			0			0
Impaired Financing Receivable, Related Allowance	0			0			0
Financing Receivable, Recorded Investment, Nonaccrual Status	0	[3]		0	[3]		0	[4]
Impaired Financing Receivable, Average Recorded Investment	0		0	0		4,668
Impaired Financing Receivable, Interest Income, Cash Basis Method	0		0	0		0
Other Commodity [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	644			644			0
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	643			643			0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	78	[1]		78	[1]		0	[2]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	78			78			0
Impaired Financing Receivable, Recorded Investment	722			722			0
Impaired Financing Receivable, Unpaid Principal Balance	721			721			0
Impaired Financing Receivable, Related Allowance	2			2			0
Financing Receivable, Recorded Investment, Nonaccrual Status	0	[3]		0	[3]		0	[4]
Impaired Financing Receivable, Average Recorded Investment	401		0	201		0
Impaired Financing Receivable, Interest Income, Cash Basis Method	0		$ 0	0		$ 0
Collateral Dependent Not Individually Analyzed [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	123,300			123,300			76,500
Impaired Financing Receivable, Related Allowance	$ 2,700			$ 2,700			$ 1,600
Impaired Financing Receivable, Impairment analysis performed percent	84.00%			84.00%			71.00%
Less than 90 days past due [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 0	[3]		$ 0	[3]		$ 12,400	[4]

[1] Impairment analysis was performed in the aggregate in consideration of similar risk characteristics of the assets and historical statistics on $123.3 million (84 percent) of impaired loans as of September 30, 2017, which resulted in a specific allowance of $2.7 million.

[2] Impairment analysis was performed in the aggregate in consideration of similar risk characteristics of the assets and historical statistics on $76.5 million (71 percent) of impaired loans as of December 31, 2016, which resulted in a specific allowance of $1.6 million.

[3] Includes no loans that are less than 90 days delinquent but which have not met Farmer Mac's performance criteria for returning to accrual status.

[4] Includes $12.4 million of loans that are less than 90 days delinquent but which have not met Farmer Mac's performance criteria for returning to accrual status.