Business Segment Reporting - Core Earnings - Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	$ 44,661	$ 40,112		$ 134,321	$ 123,765
Less: reconciling adjustments	0	0		0	0
Net effective spread	0	0		0	0
Guarantee and commitment fees	3,159	3,349		9,495	10,265
Other income/(expense)	(228)	(6,781)		(388)	2,725
Non-interest income/(loss)	2,931	(3,432)		9,107	12,990
Release of/(provision for) losses	(653)	(760)		(4,542)	(1,074)
(Provision for)/release of reserve for losses	(547)	137		(540)	424
Other non-interest expense	(14,560)	(13,595)		(44,882)	(38,695)
Non-interest expense	(15,107)	(13,458)		(45,422)	(38,271)
Core earnings before income taxes	31,832	22,462		93,464	97,410
Income tax (expense)/benefit	(6,340)	(4,629)		(19,516)	(20,362)
Core earnings before preferred stock dividends	25,492	17,833		73,948	77,048
Preferred stock dividends	(5,166)	(3,427)		(12,536)	(10,508)
Loss on retirement of preferred stock	(1,667)	0	$ (1,956)	(1,667)	(1,956)
Segment core earnings/(losses)	18,659	14,406		59,745	64,584
Total assets at carrying value	23,998,837	21,315,234		23,998,837	21,315,234	$ 21,709,374
Total on- and off-balance sheet program assets at principal balance	21,989,288	20,932,359		21,989,288	20,932,359
Corporate
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	1,941	2,821		5,025	8,607
Less: reconciling adjustments	431	(164)		74	(900)
Net effective spread	2,372	2,657		5,099	7,707
Guarantee and commitment fees	0	0		0	0
Other income/(expense)	(125)	(110)		(413)	494
Non-interest income/(loss)	(125)	(110)		(413)	494
Release of/(provision for) losses	1	0		(28)	0
(Provision for)/release of reserve for losses	0	0		0	0
Other non-interest expense	(3,938)	(3,837)		(12,171)	(10,903)
Non-interest expense	(3,938)	(3,837)		(12,171)	(10,903)
Core earnings before income taxes	(1,690)	(1,290)		(7,513)	(2,702)
Income tax (expense)/benefit	701	360		1,689	663
Core earnings before preferred stock dividends	(989)	(930)		(5,824)	(2,039)
Preferred stock dividends	(5,166)	(3,427)		(12,536)	(10,508)
Loss on retirement of preferred stock	0				0
Segment core earnings/(losses)	(6,155)	(4,357)		(18,360)	(12,547)
Total assets at carrying value	4,576,909	3,797,690		4,576,909	3,797,690
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	(7,141)	(2,349)		(8,113)	1,148
Net effective spread	(7,141)	(2,349)		(8,113)	1,148
Guarantee and commitment fees	(1,500)	(1,859)		(5,003)	(5,638)
Other income/(expense)	(681)	(7,170)		(3,048)	1,050
Non-interest income/(loss)	(2,181)	(9,029)		(8,051)	(4,588)
Release of/(provision for) losses	0	0		0	0
(Provision for)/release of 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	(9,322)	(11,378)		(16,164)	(3,440)
Income tax (expense)/benefit	1,957	2,389		3,395	722
Core earnings before preferred stock dividends	(7,365)	(8,989)		(12,769)	(2,718)
Preferred stock dividends	0	0		0	0
Loss on retirement of preferred stock	(1,667)				(1,956)
Segment core earnings/(losses)	(9,032)	(8,989)		(14,436)	(4,674)
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]
Release of/(provision for) losses	300	(760)		412	(1,074)
(Provision for)/release of reserve for losses	(628)	137		(262)	424
Farm & Ranch | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	18,093	15,345		53,768	46,424
Less: reconciling adjustments	(68)	(2,164)		(4,072)	(7,171)
Net effective spread	18,025	13,181		49,696	39,253
Guarantee and commitment fees	4,111	4,523		12,822	13,861
Other income/(expense)	443	390		2,197	1,058
Non-interest income/(loss)	4,554	4,913		15,019	14,919
Release of/(provision for) losses	300	(760)		412	(1,074)
(Provision for)/release of reserve for losses	(628)	137		(262)	424
Other non-interest expense	(5,381)	(5,062)		(16,632)	(14,448)
Non-interest expense	(6,009)	(4,925)		(16,894)	(14,024)
Core earnings before income taxes	16,870	12,409		48,233	39,074
Income tax (expense)/benefit	(3,543)	(2,606)		(10,129)	(8,206)
Core earnings before preferred stock dividends	13,327	9,803		38,104	30,868
Preferred stock dividends	0	0		0	0
Loss on retirement of preferred stock	0				0
Segment core earnings/(losses)	13,327	9,803		38,104	30,868
Total assets at carrying value	5,961,307	4,934,887		5,961,307	4,934,887
Total on- and off-balance sheet program assets at principal balance	8,249,349	7,393,728		8,249,349	7,393,728
USDA Guarantees | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	4,747	4,491		14,691	13,045
Less: reconciling adjustments	1,118	(177)		488	(670)
Net effective spread	5,865	4,314		15,179	12,375
Guarantee and commitment fees	213	250		658	712
Other income/(expense)	135	92		864	92
Non-interest income/(loss)	348	342		1,522	804
Release of/(provision for) losses	0	0		0	0
(Provision for)/release of reserve for losses	0	0		0	0
Other non-interest expense	(1,643)	(1,506)		(5,045)	(4,279)
Non-interest expense	(1,643)	(1,506)		(5,045)	(4,279)
Core earnings before income taxes	4,570	3,150		11,656	8,900
Income tax (expense)/benefit	(960)	(662)		(2,448)	(1,870)
Core earnings before preferred stock dividends	3,610	2,488		9,208	7,030
Preferred stock dividends	0	0		0	0
Loss on retirement of preferred stock	0				0
Segment core earnings/(losses)	3,610	2,488		9,208	7,030
Total assets at carrying value	2,487,687	2,238,558		2,487,687	2,238,558
Total on- and off-balance sheet program assets at principal balance	2,735,128	2,567,763		2,735,128	2,567,763
Rural  Utilities
Segment Reporting Information, Profit (Loss) [Abstract]
Release of/(provision for) losses	(1,182)	0		(4,704)	0
(Provision for)/release of reserve for losses	80	0		(279)	0
Rural  Utilities | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	5,709	2,602		12,778	6,264
Less: reconciling adjustments	1,230	1,900		4,597	5,467
Net effective spread	6,939	4,502		17,375	11,731
Guarantee and commitment fees	328	348		995	1,069
Other income/(expense)	0	17		12	31
Non-interest income/(loss)	328	365		1,007	1,100
Release of/(provision for) losses	(1,182)	0		(4,704)	0
(Provision for)/release of reserve for losses	81	0		(278)	0
Other non-interest expense	(1,438)	(913)		(4,428)	(2,595)
Non-interest expense	(1,357)	(913)		(4,706)	(2,595)
Core earnings before income taxes	4,728	3,954		8,972	10,236
Income tax (expense)/benefit	(993)	(830)		(1,884)	(2,149)
Core earnings before preferred stock dividends	3,735	3,124		7,088	8,087
Preferred stock dividends	0	0		0	0
Loss on retirement of preferred stock	0				0
Segment core earnings/(losses)	3,735	3,124		7,088	8,087
Total assets at carrying value	2,256,011	1,692,835		2,256,011	1,692,835
Total on- and off-balance sheet program assets at principal balance	2,685,309	2,232,602		2,685,309	2,232,602
Institutional Credit | Operating Segments
Segment Reporting Information, Profit (Loss) [Abstract]
Net interest income	14,171	14,853		48,059	49,425
Less: reconciling adjustments	4,430	2,954		7,026	2,126
Net effective spread	18,601	17,807		55,085	51,551
Guarantee and commitment fees	7	87		23	261
Other income/(expense)	0	0		0	0
Non-interest income/(loss)	7	87		23	261
Release of/(provision for) losses	228	0		(222)	0
(Provision for)/release of reserve for losses	0	0		0	0
Other non-interest expense	(2,160)	(2,277)		(6,606)	(6,470)
Non-interest expense	(2,160)	(2,277)		(6,606)	(6,470)
Core earnings before income taxes	16,676	15,617		48,280	45,342
Income tax (expense)/benefit	(3,502)	(3,280)		(10,139)	(9,522)
Core earnings before preferred stock dividends	13,174	12,337		38,141	35,820
Preferred stock dividends	0	0		0	0
Loss on retirement of preferred stock	0				0
Segment core earnings/(losses)	13,174	12,337		38,141	35,820
Total assets at carrying value	8,716,923	8,651,264		8,716,923	8,651,264
Total on- and off-balance sheet program assets at principal balance	$ 8,319,502	$ 8,738,266		$ 8,319,502	$ 8,738,266