Guarantees - Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
2020
Current period recoveries	$ 0		$ 0
2019
Current period recoveries	0		0
2017
Current period recoveries	0		0
2016
Current period recoveries	0		0
Prior
Current period recoveries	0		0
Revolving Loans - Amortized Cost Basis
Current period recoveries	0		0
Total
Loans held for investment, at amortized cost	6,825,061		6,825,061		$ 5,390,977
Current period charge-offs			100
Loans held for investment, at amortized cost	6,825,061		6,825,061		5,390,977
Financing receivables, past due	11,051		11,051		57,700
Off-Balance Sheet:
Total
Loans held for investment, at amortized cost					2,500,393
Loans held for investment, at amortized cost					2,500,393
Financing receivables, past due					3,235
Off-Balance Sheet: | Crops
Total
Loans held for investment, at amortized cost					1,157,681
Loans held for investment, at amortized cost					1,157,681
Financing receivables, past due					1,493
Off-Balance Sheet: | Permanent Plantings
Total
Loans held for investment, at amortized cost					514,105
Loans held for investment, at amortized cost					514,105
Financing receivables, past due					196
Off-Balance Sheet: | Livestock
Total
Loans held for investment, at amortized cost					591,584
Loans held for investment, at amortized cost					591,584
Financing receivables, past due					1,066
Off-Balance Sheet: | Part-time Farm
Total
Loans held for investment, at amortized cost					168,101
Loans held for investment, at amortized cost					168,101
Financing receivables, past due					480
Off-Balance Sheet: | Ag. Storage and Processing
Total
Loans held for investment, at amortized cost					66,106
Loans held for investment, at amortized cost					66,106
Financing receivables, past due					0
Off-Balance Sheet: | Other
Total
Loans held for investment, at amortized cost					2,816
Loans held for investment, at amortized cost					2,816
Financing receivables, past due					0
Rural  Utilities
2020
Total	502,873		502,873
Current period charge-offs	0		0
Current period net charge-offs	0		0
2019
Total	819,099		819,099
Current period charge-offs	0		0
Current period net charge-offs	0		0
2018
Total	8,260		8,260
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2017
Total	92,223		92,223
Current period charge-offs	0		0
Current period net charge-offs	0		0
2016
Total	31,275		31,275
Current period charge-offs	0		0
Current period net charge-offs	0		0
Prior
Total	642,755		642,755
Current period charge-offs	0		0
Current period net charge-offs	0		0
Revolving Loans - Amortized Cost Basis
Total	12,870		12,870
Current period charge-offs	0		0
Current period net charge-offs	0		0
Total
Loans held for investment, at amortized cost	2,109,355		2,109,355
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0	$ 0	0	$ 0
Loans held for investment, at amortized cost	2,109,355		2,109,355
Financing receivables, past due	0		0
Farm & Ranch
2020
Total	1,470,275		1,470,275
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2019
Total	895,361		895,361
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2018
Total	554,657		554,657
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2017
Total	619,269		619,269
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2016
Total	547,029		547,029
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Prior
Total	1,239,199		1,239,199
Current period charge-offs	0		394
Current period recoveries	0		0
Current period net charge-offs	0		394
Revolving Loans - Amortized Cost Basis
Total	531,534		531,534
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Total
Loans held for investment, at amortized cost	5,857,324		5,857,324
Current period charge-offs	0		394
Current period recoveries	0		0
Current period net charge-offs	0	$ 0	394	$ 67
Loans held for investment, at amortized cost	5,857,324		5,857,324
Financing receivables, past due	11,051		11,051
Acceptable | Off-Balance Sheet:
Total
Loans held for investment, at amortized cost					2,269,005
Loans held for investment, at amortized cost					2,269,005
Acceptable | Off-Balance Sheet: | Crops
Total
Loans held for investment, at amortized cost					1,033,002
Loans held for investment, at amortized cost					1,033,002
Acceptable | Off-Balance Sheet: | Permanent Plantings
Total
Loans held for investment, at amortized cost					484,601
Loans held for investment, at amortized cost					484,601
Acceptable | Off-Balance Sheet: | Livestock
Total
Loans held for investment, at amortized cost					521,341
Loans held for investment, at amortized cost					521,341
Acceptable | Off-Balance Sheet: | Part-time Farm
Total
Loans held for investment, at amortized cost					161,361
Loans held for investment, at amortized cost					161,361
Acceptable | Off-Balance Sheet: | Ag. Storage and Processing
Total
Loans held for investment, at amortized cost					66,106
Loans held for investment, at amortized cost					66,106
Acceptable | Off-Balance Sheet: | Other
Total
Loans held for investment, at amortized cost					2,594
Loans held for investment, at amortized cost					2,594
Acceptable | Rural  Utilities
2020
Total	502,873		502,873
2019
Total	819,099		819,099
2018
Total	8,260		8,260
2017
Total	92,223		92,223
2016
Total	31,275		31,275
Prior
Total	638,281		638,281
Revolving Loans - Amortized Cost Basis
Total	12,870		12,870
Total
Loans held for investment, at amortized cost	2,104,881		2,104,881
Loans held for investment, at amortized cost	2,104,881		2,104,881
Acceptable | Farm & Ranch
2020
Total	1,423,112		1,423,112
2019
Total	765,367		765,367
2018
Total	507,218		507,218
2017
Total	557,095		557,095
2016
Total	499,642		499,642
Prior
Total	1,157,633		1,157,633
Revolving Loans - Amortized Cost Basis
Total	472,209		472,209
Total
Loans held for investment, at amortized cost	5,382,276		5,382,276
Loans held for investment, at amortized cost	5,382,276		5,382,276
Special mention | Off-Balance Sheet:
Total
Loans held for investment, at amortized cost					128,511
Loans held for investment, at amortized cost					128,511
Special mention | Off-Balance Sheet: | Crops
Total
Loans held for investment, at amortized cost					68,372
Loans held for investment, at amortized cost					68,372
Special mention | Off-Balance Sheet: | Permanent Plantings
Total
Loans held for investment, at amortized cost					22,909
Loans held for investment, at amortized cost					22,909
Special mention | Off-Balance Sheet: | Livestock
Total
Loans held for investment, at amortized cost					35,618
Loans held for investment, at amortized cost					35,618
Special mention | Off-Balance Sheet: | Part-time Farm
Total
Loans held for investment, at amortized cost					1,612
Loans held for investment, at amortized cost					1,612
Special mention | Off-Balance Sheet: | Ag. Storage and Processing
Total
Loans held for investment, at amortized cost					0
Loans held for investment, at amortized cost					0
Special mention | Off-Balance Sheet: | Other
Total
Loans held for investment, at amortized cost					0
Loans held for investment, at amortized cost					0
Special mention | Rural  Utilities
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
2016
Total	0		0
Prior
Total	0		0
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Loans held for investment, at amortized cost	0		0
Loans held for investment, at amortized cost	0		0
Special mention | Farm & Ranch
2020
Total	39,607		39,607
2019
Total	124,068		124,068
2018
Total	27,757		27,757
2017
Total	4,633		4,633
2016
Total	10,897		10,897
Prior
Total	22,236		22,236
Revolving Loans - Amortized Cost Basis
Total	50,395		50,395
Total
Loans held for investment, at amortized cost	279,593		279,593
Loans held for investment, at amortized cost	279,593		279,593
Substandard | Off-Balance Sheet:
Total
Loans held for investment, at amortized cost					102,877
Loans held for investment, at amortized cost					102,877
Substandard | Off-Balance Sheet: | Crops
Total
Loans held for investment, at amortized cost					56,307
Loans held for investment, at amortized cost					56,307
Substandard | Off-Balance Sheet: | Permanent Plantings
Total
Loans held for investment, at amortized cost					6,595
Loans held for investment, at amortized cost					6,595
Substandard | Off-Balance Sheet: | Livestock
Total
Loans held for investment, at amortized cost					34,625
Loans held for investment, at amortized cost					34,625
Substandard | Off-Balance Sheet: | Part-time Farm
Total
Loans held for investment, at amortized cost					5,128
Loans held for investment, at amortized cost					5,128
Substandard | Off-Balance Sheet: | Ag. Storage and Processing
Total
Loans held for investment, at amortized cost					0
Loans held for investment, at amortized cost					0
Substandard | Off-Balance Sheet: | Other
Total
Loans held for investment, at amortized cost					222
Loans held for investment, at amortized cost					$ 222
Substandard | Rural  Utilities
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
2016
Total	0		0
Prior
Total	4,474		4,474
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Loans held for investment, at amortized cost	4,474		4,474
Loans held for investment, at amortized cost	4,474		4,474
Substandard | Farm & Ranch
2020
Total	7,556		7,556
2019
Total	5,926		5,926
2018
Total	19,682		19,682
2017
Total	57,541		57,541
2016
Total	36,490		36,490
Prior
Total	59,330		59,330
Revolving Loans - Amortized Cost Basis
Total	8,930		8,930
Total
Loans held for investment, at amortized cost	195,455		195,455
Loans held for investment, at amortized cost	195,455		195,455
LTSPCs | Rural  Utilities
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
2016
Total	0		0
Prior
Total	569,324		569,324
Revolving Loans - Amortized Cost Basis
Total	6,630		6,630
Total
Loans held for investment, at amortized cost	575,954		575,954
Loans held for investment, at amortized cost	575,954		575,954
Financing receivables, past due	0		0
LTSPCs | Acceptable | Rural  Utilities
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
2016
Total	0		0
Prior
Total	569,324		569,324
Revolving Loans - Amortized Cost Basis
Total	6,630		6,630
Total
Loans held for investment, at amortized cost	575,954		575,954
Loans held for investment, at amortized cost	575,954		575,954
LTSPCs | Special mention | Rural  Utilities
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
2016
Total	0		0
Prior
Total	0		0
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Loans held for investment, at amortized cost	0		0
Loans held for investment, at amortized cost	0		0
LTSPCs | Substandard | Rural  Utilities
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
2016
Total	0		0
Prior
Total	0		0
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Loans held for investment, at amortized cost	0		0
Loans held for investment, at amortized cost	0		0
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
2020
Total	118,380		118,380
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2019
Total	219,765		219,765
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2018
Total	198,606		198,606
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2017
Total	284,304		284,304
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2016
Total	246,012		246,012
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Prior
Total	1,136,686		1,136,686
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Revolving Loans - Amortized Cost Basis
Total	188,272		188,272
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Total
Loans held for investment, at amortized cost	2,392,025		2,392,025
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Loans held for investment, at amortized cost	2,392,025		2,392,025
Financing receivables, past due	39,571		39,571
LTSPCs and Farmer Mac Guaranteed Securities | Acceptable | Farm & Ranch
2020
Total	118,116		118,116
2019
Total	207,202		207,202
2018
Total	184,421		184,421
2017
Total	245,490		245,490
2016
Total	216,983		216,983
Prior
Total	1,021,400		1,021,400
Revolving Loans - Amortized Cost Basis
Total	173,617		173,617
Total
Loans held for investment, at amortized cost	2,167,229		2,167,229
Loans held for investment, at amortized cost	2,167,229		2,167,229
LTSPCs and Farmer Mac Guaranteed Securities | Special mention | Farm & Ranch
2020
Total	0		0
2019
Total	1,742		1,742
2018
Total	1,509		1,509
2017
Total	23,200		23,200
2016
Total	14,628		14,628
Prior
Total	47,948		47,948
Revolving Loans - Amortized Cost Basis
Total	10,040		10,040
Total
Loans held for investment, at amortized cost	99,067		99,067
Loans held for investment, at amortized cost	99,067		99,067
LTSPCs and Farmer Mac Guaranteed Securities | Substandard | Farm & Ranch
2020
Total	264		264
2019
Total	10,821		10,821
2018
Total	12,676		12,676
2017
Total	15,614		15,614
2016
Total	14,401		14,401
Prior
Total	67,338		67,338
Revolving Loans - Amortized Cost Basis
Total	4,615		4,615
Total
Loans held for investment, at amortized cost	125,729		125,729
Loans held for investment, at amortized cost	$ 125,729		$ 125,729