Business Segment Reporting - Core Earnings - Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	$ 48,348	$ 43,054	$ 89,660	$ 83,653
Less: reconciling adjustments	0	0	0	0
Net effective spread	0	0	0	0
Guarantee and commitment fees	3,140	3,403	6,336	6,916
Other income/(expense)	7,731	9,329	(160)	9,506
Non-interest income/(loss)	10,871	12,732	6,176	16,422
Provision for losses	(451)	(578)	(3,889)	(314)
Provision for reserve for losses	400	158	7	287
Other non-interest expense	(14,107)	(12,210)	(30,322)	(25,100)
Non-interest expense	(13,707)	(12,052)	(30,315)	(24,813)
Core earnings before income taxes	45,061	43,156	61,632	74,948
Income tax (expense)/benefit	(9,435)	(9,111)	(13,176)	(15,733)
Core earnings before preferred stock dividends	35,626	34,045	48,456	59,215
Preferred stock dividends	(3,939)	(3,785)	(7,370)	(7,081)
Loss on retirement of preferred stock	0	(1,956)	0	(1,956)
Segment core earnings/(losses)	31,687	28,304	41,086	50,178
Total assets at carrying value	23,932,656	20,738,160	23,932,656	20,738,160	$ 21,709,374
Total on- and off-balance sheet program assets at principal balance	22,042,108	20,746,735	22,042,108	20,746,735
Corporate
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	1,229	2,824	3,084	5,786
Less: reconciling adjustments	(480)	(268)	(357)	(736)
Net effective spread	749	2,556	2,727	5,050
Guarantee and commitment fees	0	0	0	0
Other income/(expense)	(159)	582	(288)	604
Non-interest income/(loss)	(159)	582	(288)	604
Provision for losses	(15)	0	(29)	0
Provision for reserve for losses	0	0	0	0
Other non-interest expense	(3,800)	(3,428)	(8,233)	(7,066)
Non-interest expense	(3,800)	(3,428)	(8,233)	(7,066)
Core earnings before income taxes	(3,225)	(290)	(5,823)	(1,412)
Income tax (expense)/benefit	705	13	988	303
Core earnings before preferred stock dividends	(2,520)	(277)	(4,835)	(1,109)
Preferred stock dividends	(3,939)	(3,785)	(7,370)	(7,081)
Loss on retirement of preferred stock		0		0
Segment core earnings/(losses)	(6,459)	(4,062)	(12,205)	(8,190)
Total assets at carrying value	4,446,504	3,452,842	4,446,504	3,452,842
Total on- and off-balance sheet program assets at principal balance	0	0	0	0
Reconciling Adjustments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	0	0	0	0
Less: reconciling adjustments	1,879	1,699	(972)	3,497
Net effective spread	1,879	1,699	(972)	3,497
Guarantee and commitment fees	(1,803)	(1,873)	(3,503)	(3,779)
Other income/(expense)	6,683	8,552	(2,367)	8,220
Non-interest income/(loss)	4,880	6,679	(5,870)	4,441
Provision for losses	0	0	0	0
Provision for reserve for losses	0	0	0	0
Other non-interest expense	0	0	0	0
Non-interest expense	0	0	0	0
Core earnings before income taxes	6,759	8,378	(6,842)	7,938
Income tax (expense)/benefit	(1,419)	(1,760)	1,438	(1,667)
Core earnings before preferred stock dividends	5,340	6,618	(5,404)	6,271
Preferred stock dividends	0	0	0	0
Loss on retirement of preferred stock		(1,956)		(1,956)
Segment core earnings/(losses)	5,340	4,662	(5,404)	4,315
Total assets at carrying value	0	0	0	0
Total on- and off-balance sheet program assets at principal balance	0	0	0	0
Farm & Ranch
Segment Reporting Information, Profit (Loss) [Abstract]
Provision for losses	920		112
Provision for reserve for losses	370	158	366	287
Farm & Ranch | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	19,310	15,797	35,675	31,079
Less: reconciling adjustments	(2,577)	(2,462)	(4,004)	(5,007)
Net effective spread	16,733	13,335	31,671	26,072
Guarantee and commitment fees	4,394	4,594	8,711	9,338
Other income/(expense)	585	188	1,754	668
Non-interest income/(loss)	4,979	4,782	10,465	10,006
Provision for losses	920	(578)	112	(314)
Provision for reserve for losses	370	158	366	287
Other non-interest expense	(5,254)	(4,587)	(11,251)	(9,386)
Non-interest expense	(4,884)	(4,429)	(10,885)	(9,099)
Core earnings before income taxes	17,748	13,110	31,363	26,665
Income tax (expense)/benefit	(3,727)	(2,753)	(6,586)	(5,600)
Core earnings before preferred stock dividends	14,021	10,357	24,777	21,065
Preferred stock dividends	0	0	0	0
Loss on retirement of preferred stock		0		0
Segment core earnings/(losses)	14,021	10,357	24,777	21,065
Total assets at carrying value	5,746,556	4,872,766	5,746,556	4,872,766
Total on- and off-balance sheet program assets at principal balance	8,017,850	7,291,352	8,017,850	7,291,352
USDA Guarantees | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	5,403	4,112	9,944	8,554
Less: reconciling adjustments	(714)	(15)	(630)	(493)
Net effective spread	4,689	4,097	9,314	8,061
Guarantee and commitment fees	210	238	445	462
Other income/(expense)	617	0	729	0
Non-interest income/(loss)	827	238	1,174	462
Provision for losses	0	0	0	0
Provision for reserve for losses	0	0	0	0
Other non-interest expense	(1,584)	(1,345)	(3,402)	(2,773)
Non-interest expense	(1,584)	(1,345)	(3,402)	(2,773)
Core earnings before income taxes	3,932	2,990	7,086	5,750
Income tax (expense)/benefit	(826)	(628)	(1,488)	(1,208)
Core earnings before preferred stock dividends	3,106	2,362	5,598	4,542
Preferred stock dividends	0	0	0	0
Loss on retirement of preferred stock		0		0
Segment core earnings/(losses)	3,106	2,362	5,598	4,542
Total assets at carrying value	2,408,713	2,198,514	2,408,713	2,198,514
Total on- and off-balance sheet program assets at principal balance	2,677,807	2,521,394	2,677,807	2,521,394
Rural  Utilities
Segment Reporting Information, Profit (Loss) [Abstract]
Provision for losses	(1,397)		(3,522)
Provision for reserve for losses	30	0	(359)	0
Rural  Utilities | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	2,322	3,936	7,069	3,662
Less: reconciling adjustments	3,194	60	3,367	3,567
Net effective spread	5,516	3,996	10,436	7,229
Guarantee and commitment fees	332	358	667	721
Other income/(expense)	5	7	12	14
Non-interest income/(loss)	337	365	679	735
Provision for losses	(1,397)	0	(3,522)	0
Provision for reserve for losses	30	0	(359)	0
Other non-interest expense	(1,386)	(816)	(2,990)	(1,682)
Non-interest expense	(1,356)	(816)	(3,349)	(1,682)
Core earnings before income taxes	3,100	3,545	4,244	6,282
Income tax (expense)/benefit	(651)	(744)	(891)	(1,319)
Core earnings before preferred stock dividends	2,449	2,801	3,353	4,963
Preferred stock dividends	0	0	0	0
Loss on retirement of preferred stock		0		0
Segment core earnings/(losses)	2,449	2,801	3,353	4,963
Total assets at carrying value	2,281,490	1,580,979	2,281,490	1,580,979
Total on- and off-balance sheet program assets at principal balance	2,691,621	2,155,671	2,691,621	2,155,671
Institutional Credit | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	20,084	16,385	33,888	34,572
Less: reconciling adjustments	(1,302)	986	2,596	(828)
Net effective spread	18,782	17,371	36,484	33,744
Guarantee and commitment fees	7	86	16	174
Other income/(expense)	0	0	0	0
Non-interest income/(loss)	7	86	16	174
Provision for losses	41	0	(450)	0
Provision for reserve for losses	0	0	0	0
Other non-interest expense	(2,083)	(2,034)	(4,446)	(4,193)
Non-interest expense	(2,083)	(2,034)	(4,446)	(4,193)
Core earnings before income taxes	16,747	15,423	31,604	29,725
Income tax (expense)/benefit	(3,517)	(3,239)	(6,637)	(6,242)
Core earnings before preferred stock dividends	13,230	12,184	24,967	23,483
Preferred stock dividends	0	0	0	0
Loss on retirement of preferred stock		0		0
Segment core earnings/(losses)	13,230	12,184	24,967	23,483
Total assets at carrying value	9,049,393	8,633,059	9,049,393	8,633,059
Total on- and off-balance sheet program assets at principal balance	$ 8,654,830	$ 8,778,318	$ 8,654,830	$ 8,778,318