Business Segment Reporting - Core Earnings (Details) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2021 USD ($) segment	Sep. 30, 2021 segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment	7	5
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			$ 220,775	$ 190,588	$ 173,135
Less: reconciling adjustments			0	0	0
Net effective spread			0	0	0
Guarantee and commitment fees			12,669	12,549	13,666
Gain on sale of mortgage loans			6,539	0	0
Other income/(expense)			(1,141)	3,754	7,276
Total revenues			238,842	206,891	194,077
Release of/(provision for) losses			860	(7,805)	(3,504)
Release of/(provision for) reserve for losses			1,327	(250)	3
Operating expenses			(73,416)	(61,403)	(51,925)
Total non-interest expense			(72,089)	(61,653)	(51,922)
Core earnings before income taxes			167,613	137,433	138,651
Income tax (expense)/benefit			(35,353)	(28,785)	(29,105)
Core earnings before preferred stock dividends			132,260	108,648	109,546
Preferred stock dividends			(24,677)	(17,805)	(13,940)
Loss on retirement of preferred stock				(1,667)	(1,956)
Segment core earnings			107,583	89,176	93,650
Total Assets	$ 25,145,491		25,145,491	24,355,501	21,709,374
Total on- and off-balance sheet program assets at principal balance	23,614,463		23,614,463	21,924,095	21,117,942
Reconciling Adjustments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			0	0	0
Less: reconciling adjustments			107	(6,368)	4,527
Net effective spread			107	(6,368)	4,527
Guarantee and commitment fees			(4,864)	(6,601)	(7,669)
Gain on sale of mortgage loans			0
Other income/(expense)			(2,821)	604	5,501
Total revenues			(7,578)	(12,365)	2,359
Release of/(provision for) losses			0	0	0
Release of/(provision for) reserve for losses			0	0	0
Operating expenses			0	0	0
Total non-interest expense			0	0	0
Core earnings before income taxes			(7,578)	(12,365)	2,359
Income tax (expense)/benefit			1,591	2,596	(495)
Core earnings before preferred stock dividends			(5,987)	(9,769)	1,864
Preferred stock dividends			0	0	0
Loss on retirement of preferred stock				(1,667)	(1,956)
Segment core earnings			(5,987)	(11,436)	(92)
Total Assets	0		0	0	0
Total on- and off-balance sheet program assets at principal balance	0		0	0	0
Farm & Ranch | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			118,289	96,355	83,226
Less: reconciling adjustments			(4,753)	(6,197)	(7,095)
Net effective spread			113,536	90,158	76,131
Guarantee and commitment fees			16,178	17,800	19,551
Gain on sale of mortgage loans			6,539
Other income/(expense)			1,966	3,652	1,571
Total revenues			138,219	111,610	97,253
Release of/(provision for) losses			1,574	(2,941)	(3,165)
Release of/(provision for) reserve for losses			1,034	(80)	3
Operating expenses			0	0	0
Total non-interest expense			1,034	(80)	3
Core earnings before income taxes			140,827	108,589	94,091
Income tax (expense)/benefit			(29,574)	(22,802)	(19,759)
Core earnings before preferred stock dividends			111,253	85,787	74,332
Preferred stock dividends			0	0	0
Loss on retirement of preferred stock				0	0
Segment core earnings			111,253	85,787	74,332
Total Assets	13,112,193		13,112,193	12,373,781	11,889,538
Total on- and off-balance sheet program assets at principal balance	16,094,640		16,094,640	14,872,894	14,559,268
Corporate AgFinance | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			27,081	21,441	13,757
Less: reconciling adjustments			0	0	0
Net effective spread			27,081	21,441	13,757
Guarantee and commitment fees			48	5	0
Gain on sale of mortgage loans			0
Other income/(expense)			0	0	0
Total revenues			27,129	21,446	13,757
Release of/(provision for) losses			(210)	36	(339)
Release of/(provision for) reserve for losses			0	0	0
Operating expenses			0	0	0
Total non-interest expense			0	0	0
Core earnings before income taxes			26,919	21,482	13,418
Income tax (expense)/benefit			(5,653)	(4,511)	(2,818)
Core earnings before preferred stock dividends			21,266	16,971	10,600
Preferred stock dividends			0	0	0
Loss on retirement of preferred stock				0	0
Segment core earnings			21,266	16,971	10,600
Total Assets	1,507,848		1,507,848	1,663,581	1,338,114
Total on- and off-balance sheet program assets at principal balance	1,537,834		1,537,834	1,664,115	1,328,602
Rural  Utilities | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			8,224	7,083	5,242
Less: reconciling adjustments			(157)	(207)	(176)
Net effective spread			8,067	6,876	5,066
Guarantee and commitment fees			1,287	1,345	1,784
Gain on sale of mortgage loans			0
Other income/(expense)			5	32	37
Total revenues			9,359	8,253	6,887
Release of/(provision for) losses			(291)	(4,763)	0
Release of/(provision for) reserve for losses			293	(170)	0
Operating expenses			0	0	0
Total non-interest expense			293	(170)	0
Core earnings before income taxes			9,361	3,320	6,887
Income tax (expense)/benefit			(1,965)	(697)	(1,446)
Core earnings before preferred stock dividends			7,396	2,623	5,441
Preferred stock dividends			0	0	0
Loss on retirement of preferred stock				0	0
Segment core earnings			7,396	2,623	5,441
Total Assets	5,344,707		5,344,707	4,760,585	4,625,125
Total on- and off-balance sheet program assets at principal balance	5,895,226		5,895,226	5,314,051	5,220,270
Renewable Energy | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			1,219	303	22
Less: reconciling adjustments			0	0	0
Net effective spread			1,219	303	22
Guarantee and commitment fees			20	0	0
Gain on sale of mortgage loans			0
Other income/(expense)			0	0	0
Total revenues			1,239	303	22
Release of/(provision for) losses			(198)	(110)	0
Release of/(provision for) reserve for losses			0	0	0
Operating expenses			0	0	0
Total non-interest expense			0	0	0
Core earnings before income taxes			1,041	193	22
Income tax (expense)/benefit			(219)	(41)	(5)
Core earnings before preferred stock dividends			822	152	17
Preferred stock dividends			0	0	0
Loss on retirement of preferred stock				0	0
Segment core earnings			822	152	17
Total Assets	87,553		87,553	73,493	9,802
Total on- and off-balance sheet program assets at principal balance	86,763		86,763	73,035	9,802
Funding | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			65,405	66,446	70,500
Less: reconciling adjustments			4,803	12,772	2,744
Net effective spread			70,208	79,218	73,244
Guarantee and commitment fees			0	0	0
Gain on sale of mortgage loans			0
Other income/(expense)			0	0	0
Total revenues			70,208	79,218	73,244
Release of/(provision for) losses			0	0	0
Release of/(provision for) reserve for losses			0	0	0
Operating expenses			0	0	0
Total non-interest expense			0	0	0
Core earnings before income taxes			70,208	79,218	73,244
Income tax (expense)/benefit			(14,744)	(16,636)	(15,381)
Core earnings before preferred stock dividends			55,464	62,582	57,863
Preferred stock dividends			0	0	0
Loss on retirement of preferred stock				0	0
Segment core earnings			55,464	62,582	57,863
Total Assets	0		0	0	0
Total on- and off-balance sheet program assets at principal balance	0		0	0	0
Investments | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			557	(1,040)	388
Less: reconciling adjustments			0	0	0
Net effective spread			557	(1,040)	388
Guarantee and commitment fees			0	0	0
Gain on sale of mortgage loans			0
Other income/(expense)			0	0	0
Total revenues			557	(1,040)	388
Release of/(provision for) losses			(15)	(27)	0
Release of/(provision for) reserve for losses			0	0	0
Operating expenses			0	0	0
Total non-interest expense			0	0	0
Core earnings before income taxes			542	(1,067)	388
Income tax (expense)/benefit			(114)	224	(82)
Core earnings before preferred stock dividends			428	(843)	306
Preferred stock dividends			0	0	0
Loss on retirement of preferred stock				0	0
Segment core earnings			428	(843)	306
Total Assets	5,037,636		5,037,636	5,441,426	3,809,891
Total on- and off-balance sheet program assets at principal balance	0		0	0	0
Corporate | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income			0	0	0
Less: reconciling adjustments			0	0	0
Net effective spread			0	0	0
Guarantee and commitment fees			0	0	0
Gain on sale of mortgage loans			0
Other income/(expense)			(291)	(534)	167
Total revenues			(291)	(534)	167
Release of/(provision for) losses			0	0	0
Release of/(provision for) reserve for losses			0	0	0
Operating expenses			(73,416)	(61,403)	(51,925)
Total non-interest expense			(73,416)	(61,403)	(51,925)
Core earnings before income taxes			(73,707)	(61,937)	(51,758)
Income tax (expense)/benefit			15,325	13,082	10,881
Core earnings before preferred stock dividends			(58,382)	(48,855)	(40,877)
Preferred stock dividends			(24,677)	(17,805)	(13,940)
Loss on retirement of preferred stock				0	0
Segment core earnings			(83,059)	(66,660)	(54,817)
Total Assets	55,554		55,554	42,635	36,904
Total on- and off-balance sheet program assets at principal balance	$ 0		$ 0	$ 0	$ 0