Guarantees - Credit Quality Indicators (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
2020
Current period recoveries	$ 0
2019
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
2017
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
2016
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Prior
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Revolving Loans - Amortized Cost Basis
Financing Receivable, Revolving, Allowance for Credit Loss, Recovery	0
Total
Total	7,261,933	$ 5,390,977
Current period charge-offs	5,800
Total	7,261,933	5,390,977
Financing receivables, past due	6,286
Off-balance sheet
Total
Total		2,500,393
Total		2,500,393
Financing receivables, past due		3,235
Off-balance sheet | Crops
Total
Total		1,157,681
Total		1,157,681
Financing receivables, past due		1,493
Off-balance sheet | Permanent Plantings
Total
Total		514,105
Total		514,105
Financing receivables, past due		196
Off-balance sheet | Livestock
Total
Total		591,584
Total		591,584
Financing receivables, past due		1,066
Off-balance sheet | Part-time Farm
Total
Total		168,101
Total		168,101
Financing receivables, past due		480
Off-balance sheet | Ag. Storage and Processing
Total
Total		66,106
Total		66,106
Financing receivables, past due		0
Off-balance sheet | Other
Total
Total		2,816
Total		2,816
Financing receivables, past due		0
Rural Utilities:
2020
Total	667,489
Current period charge-offs	0
Current period Farm & Ranch net charge-offs	0
2019
Total	809,921
Current period charge-offs	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2018
Total	8,260
Current period charge-offs	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2017
Total	89,842
Current period charge-offs	0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2016
Total	31,275
Current period charge-offs	0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
Prior
Total	641,145
Current period charge-offs	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
Revolving Loans - Amortized Cost Basis
Total	12,480
Current period charge-offs	0
Financing Receivable, Revolving, Allowance for Credit Loss, Writeoff, After Recovery	0
Total
Total	2,260,412
Current period charge-offs	0
Financing Receivable, Allowance for Credit Loss, Recovery	0
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	0	0	$ 0
Total	2,260,412
Financing receivables, past due	0
Farm & Ranch
2020
Total	2,021,189
Current period charge-offs	0
Current period recoveries	0
Current period Farm & Ranch net charge-offs	0
2019
Total	859,880
Current period charge-offs	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2018
Total	524,541
Current period charge-offs	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2017
Total	562,007
Current period charge-offs	5,365
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	5,365
2016
Total	515,561
Current period charge-offs	0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
Prior
Total	1,140,603
Current period charge-offs	394
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	394
Revolving Loans - Amortized Cost Basis
Total	552,657
Current period charge-offs	0
Financing Receivable, Revolving, Allowance for Credit Loss, Recovery	0
Financing Receivable, Revolving, Allowance for Credit Loss, Writeoff, After Recovery	0
Total
Total	6,176,438
Current period charge-offs	5,759
Financing Receivable, Allowance for Credit Loss, Recovery	0
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	5,759	67	$ 17
Total	6,176,438
Financing receivables, past due	6,286
Acceptable | Off-balance sheet
Total
Total		2,269,005
Total		2,269,005
Acceptable | Off-balance sheet | Crops
Total
Total		1,033,002
Total		1,033,002
Acceptable | Off-balance sheet | Permanent Plantings
Total
Total		484,601
Total		484,601
Acceptable | Off-balance sheet | Livestock
Total
Total		521,341
Total		521,341
Acceptable | Off-balance sheet | Part-time Farm
Total
Total		161,361
Total		161,361
Acceptable | Off-balance sheet | Ag. Storage and Processing
Total
Total		66,106
Total		66,106
Acceptable | Off-balance sheet | Other
Total
Total		2,594
Total		2,594
Acceptable | Rural Utilities:
2020
Total	667,489
2019
Total	809,921
2018
Total	8,260
2017
Total	89,842
2016
Total	31,275
Prior
Total	641,145
Revolving Loans - Amortized Cost Basis
Total	12,480
Total
Total	2,260,412
Total	2,260,412
Acceptable | Farm & Ranch
2020
Total	1,947,618
2019
Total	774,315
2018
Total	484,345
2017
Total	500,768
2016
Total	465,277
Prior
Total	1,068,693
Revolving Loans - Amortized Cost Basis
Total	535,742
Total
Total	5,776,758
Total	5,776,758
Special mention | Off-balance sheet
Total
Total		128,511
Total		128,511
Special mention | Off-balance sheet | Crops
Total
Total		68,372
Total		68,372
Special mention | Off-balance sheet | Permanent Plantings
Total
Total		22,909
Total		22,909
Special mention | Off-balance sheet | Livestock
Total
Total		35,618
Total		35,618
Special mention | Off-balance sheet | Part-time Farm
Total
Total		1,612
Total		1,612
Special mention | Off-balance sheet | Ag. Storage and Processing
Total
Total		0
Total		0
Special mention | Off-balance sheet | Other
Total
Total		0
Total		0
Special mention | Rural Utilities:
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
2016
Total	0
Prior
Total	0
Revolving Loans - Amortized Cost Basis
Total	0
Total
Total	0
Total	0
Special mention | Farm & Ranch
2020
Total	70,171
2019
Total	79,744
2018
Total	18,317
2017
Total	8,530
2016
Total	13,111
Prior
Total	21,328
Revolving Loans - Amortized Cost Basis
Total	7,656
Total
Total	218,857
Total	218,857
Substandard | Off-balance sheet
Total
Total		102,877
Total		102,877
Substandard | Off-balance sheet | Crops
Total
Total		56,307
Total		56,307
Substandard | Off-balance sheet | Permanent Plantings
Total
Total		6,595
Total		6,595
Substandard | Off-balance sheet | Livestock
Total
Total		34,625
Total		34,625
Substandard | Off-balance sheet | Part-time Farm
Total
Total		5,128
Total		5,128
Substandard | Off-balance sheet | Ag. Storage and Processing
Total
Total		0
Total		0
Substandard | Off-balance sheet | Other
Total
Total		222
Total		$ 222
Substandard | Rural Utilities:
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
2016
Total	0
Prior
Total	0
Revolving Loans - Amortized Cost Basis
Total	0
Total
Total	0
Total	0
Substandard | Farm & Ranch
2020
Total	3,400
2019
Total	5,821
2018
Total	21,879
2017
Total	52,709
2016
Total	37,173
Prior
Total	50,582
Revolving Loans - Amortized Cost Basis
Total	9,259
Total
Total	180,823
Total	180,823
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
2020
Total	182,397
Current period charge-offs	0
Current period recoveries	0
Current period Farm & Ranch net charge-offs	0
2019
Total	225,612
Current period charge-offs	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2018
Total	198,061
Current period charge-offs	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Two Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2017
Total	257,223
Current period charge-offs	0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Three Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
2016
Total	234,781
Current period charge-offs	0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Four Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
Prior
Total	1,080,466
Current period charge-offs	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Recovery	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Allowance for Credit Loss, Writeoff, After Recovery	0
Revolving Loans - Amortized Cost Basis
Total	226,203
Current period charge-offs	0
Financing Receivable, Revolving, Allowance for Credit Loss, Recovery	0
Financing Receivable, Revolving, Allowance for Credit Loss, Writeoff, After Recovery	0
Total
Total	2,404,743
Current period charge-offs	0
Financing Receivable, Allowance for Credit Loss, Recovery	0
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	0
Total	2,404,743
Financing receivables, past due	14,966
LTSPCs and Farmer Mac Guaranteed Securities | Acceptable | Farm & Ranch
2020
Total	178,213
2019
Total	213,620
2018
Total	183,948
2017
Total	237,042
2016
Total	207,296
Prior
Total	969,860
Revolving Loans - Amortized Cost Basis
Total	211,620
Total
Total	2,201,599
Total	2,201,599
LTSPCs and Farmer Mac Guaranteed Securities | Special mention | Farm & Ranch
2020
Total	3,920
2019
Total	1,742
2018
Total	1,502
2017
Total	5,603
2016
Total	19,644
Prior
Total	50,004
Revolving Loans - Amortized Cost Basis
Total	10,058
Total
Total	92,473
Total	92,473
LTSPCs and Farmer Mac Guaranteed Securities | Substandard | Farm & Ranch
2020
Total	264
2019
Total	10,250
2018
Total	12,611
2017
Total	14,578
2016
Total	7,841
Prior
Total	60,602
Revolving Loans - Amortized Cost Basis
Total	4,525
Total
Total	110,671
Total	110,671
LTSPCs | Rural Utilities:
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
2016
Total	0
Prior
Total	549,405
Revolving Loans - Amortized Cost Basis
Total	7,020
Total
Total	556,425
Total	556,425
Financing receivables, past due	0
LTSPCs | Acceptable | Rural Utilities:
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
2016
Total	0
Prior
Total	549,405
Revolving Loans - Amortized Cost Basis
Total	7,020
Total
Total	556,425
Total	556,425
LTSPCs | Special mention | Rural Utilities:
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
2016
Total	0
Prior
Total	0
Revolving Loans - Amortized Cost Basis
Total	0
Total
Total	0
Total	0
LTSPCs | Substandard | Rural Utilities:
2020
Total	0
2019
Total	0
2018
Total	0
2017
Total	0
2016
Total	0
Prior
Total	0
Revolving Loans - Amortized Cost Basis
Total	0
Total
Total	0
Total	$ 0