Guarantees - Credit Quality Indicators (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
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	6,469,997		6,469,997		$ 5,390,977
Loans held for investment, at amortized cost	6,469,997		6,469,997		5,390,977
Financing receivables, past due	23,420		23,420
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	470,419		470,419
Current period charge-offs	0		0
Current period net charge-offs	0		0
2019
Total	827,336		827,336
Current period charge-offs	0		0
Current period net charge-offs	0		0
2018
Total	8,337		8,337
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2017
Total	92,440		92,440
Current period charge-offs	0		0
Current period net charge-offs	0		0
2016
Total	31,829		31,829
Current period charge-offs	0		0
Current period net charge-offs	0		0
Prior
Total	663,841		663,841
Current period charge-offs	0		0
Current period net charge-offs	0		0
Revolving Loans - Amortized Cost Basis
Total	7,366		7,366
Current period charge-offs	0		0
Current period net charge-offs	0		0
Total
Loans held for investment, at amortized cost	2,101,568		2,101,568
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	2,101,568		2,101,568
Financing receivables, past due	0		0
Farm & Ranch
2020
Total	836,001		836,001
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2019
Total	946,683		946,683
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2018
Total	613,094		613,094
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2017
Total	686,574		686,574
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2016
Total	587,184		587,184
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Prior
Total	1,425,492		1,425,492
Current period charge-offs	394		394
Current period recoveries	0		0
Current period net charge-offs	394		394
Revolving Loans - Amortized Cost Basis
Total	522,484		522,484
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	5,617,512		5,617,512
Current period charge-offs	394		394
Current period recoveries	0		0
Current period net charge-offs	394	$ 67	394	$ 67
Loans held for investment, at amortized cost	5,617,512		5,617,512
Financing receivables, past due	23,420		23,420
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	470,419		470,419
2019
Total	827,336		827,336
2018
Total	8,337		8,337
2017
Total	92,440		92,440
2016
Total	31,829		31,829
Prior
Total	658,827		658,827
Revolving Loans - Amortized Cost Basis
Total	7,366		7,366
Total
Loans held for investment, at amortized cost	2,096,554		2,096,554
Loans held for investment, at amortized cost	2,096,554		2,096,554
Acceptable | Farm & Ranch
2020
Total	758,965		758,965
2019
Total	773,199		773,199
2018
Total	562,604		562,604
2017
Total	617,751		617,751
2016
Total	528,068		528,068
Prior
Total	1,345,384		1,345,384
Revolving Loans - Amortized Cost Basis
Total	501,625		501,625
Total
Loans held for investment, at amortized cost	5,087,596		5,087,596
Loans held for investment, at amortized cost	5,087,596		5,087,596
Special mention(1) | Off-Balance Sheet:
Total
Loans held for investment, at amortized cost					128,511
Loans held for investment, at amortized cost					128,511
Special mention(1) | 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(1) | 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(1) | 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(1) | 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(1) | 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(1) | Off-Balance Sheet: | Other
Total
Loans held for investment, at amortized cost					0
Loans held for investment, at amortized cost					0
Special mention(1) | 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(1) | Farm & Ranch
2020
Total	76,588		76,588
2019
Total	166,829		166,829
2018
Total	32,164		32,164
2017
Total	9,278		9,278
2016
Total	5,477		5,477
Prior
Total	19,630		19,630
Revolving Loans - Amortized Cost Basis
Total	10,260		10,260
Total
Loans held for investment, at amortized cost	320,226		320,226
Loans held for investment, at amortized cost	320,226		320,226
Substandard(2) | Off-Balance Sheet:
Total
Loans held for investment, at amortized cost					102,877
Loans held for investment, at amortized cost					102,877
Substandard(2) | Off-Balance Sheet: | Crops
Total
Loans held for investment, at amortized cost					56,307
Loans held for investment, at amortized cost					56,307
Substandard(2) | 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(2) | Off-Balance Sheet: | Livestock
Total
Loans held for investment, at amortized cost					34,625
Loans held for investment, at amortized cost					34,625
Substandard(2) | 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(2) | 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(2) | Off-Balance Sheet: | Other
Total
Loans held for investment, at amortized cost					222
Loans held for investment, at amortized cost					$ 222
Substandard(2) | Rural  Utilities
2020
Total	0		0
2019
Total	0		0
2018
Total	0		0
2017
Total	0		0
2016
Total	0		0
Prior
Total	5,014		5,014
Revolving Loans - Amortized Cost Basis
Total	0		0
Total
Loans held for investment, at amortized cost	5,014		5,014
Loans held for investment, at amortized cost	5,014		5,014
Substandard(2) | Farm & Ranch
2020
Total	448		448
2019
Total	6,655		6,655
2018
Total	18,326		18,326
2017
Total	59,545		59,545
2016
Total	53,639		53,639
Prior
Total	60,478		60,478
Revolving Loans - Amortized Cost Basis
Total	10,599		10,599
Total
Loans held for investment, at amortized cost	209,690		209,690
Loans held for investment, at amortized cost	209,690		209,690
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	577,920		577,920
Revolving Loans - Amortized Cost Basis
Total	12,133		12,133
Total
Loans held for investment, at amortized cost	590,053		590,053
Loans held for investment, at amortized cost	590,053		590,053
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	577,920		577,920
Revolving Loans - Amortized Cost Basis
Total	12,133		12,133
Total
Loans held for investment, at amortized cost	590,053		590,053
Loans held for investment, at amortized cost	590,053		590,053
LTSPCs | Special mention(1) | 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(2) | 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	71,855		71,855
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2019
Total	216,427		216,427
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2018
Total	189,604		189,604
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2017
Total	290,944		290,944
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
2016
Total	250,697		250,697
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Prior
Total	1,193,275		1,193,275
Current period charge-offs	0		0
Current period recoveries	0		0
Current period net charge-offs	0		0
Revolving Loans - Amortized Cost Basis
Total	187,536		187,536
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	2,400,338		2,400,338
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	2,400,338		2,400,338
Financing receivables, past due	25,350		25,350
LTSPCs and Farmer Mac Guaranteed Securities | Acceptable | Farm & Ranch
2020
Total	71,569		71,569
2019
Total	206,177		206,177
2018
Total	177,787		177,787
2017
Total	251,149		251,149
2016
Total	222,988		222,988
Prior
Total	1,072,259		1,072,259
Revolving Loans - Amortized Cost Basis
Total	172,509		172,509
Total
Loans held for investment, at amortized cost	2,174,438		2,174,438
Loans held for investment, at amortized cost	2,174,438		2,174,438
LTSPCs and Farmer Mac Guaranteed Securities | Special mention(1) | Farm & Ranch
2020
Total	0		0
2019
Total	10,250		10,250
2018
Total	7,835		7,835
2017
Total	24,518		24,518
2016
Total	16,090		16,090
Prior
Total	61,674		61,674
Revolving Loans - Amortized Cost Basis
Total	10,359		10,359
Total
Loans held for investment, at amortized cost	130,726		130,726
Loans held for investment, at amortized cost	130,726		130,726
LTSPCs and Farmer Mac Guaranteed Securities | Substandard(2) | Farm & Ranch
2020
Total	286		286
2019
Total	0		0
2018
Total	3,982		3,982
2017
Total	15,277		15,277
2016
Total	11,619		11,619
Prior
Total	59,342		59,342
Revolving Loans - Amortized Cost Basis
Total	4,668		4,668
Total
Loans held for investment, at amortized cost	95,174		95,174
Loans held for investment, at amortized cost	$ 95,174		$ 95,174