Loans - Schedule of Financing Receivables 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
Total	6,469,997		6,469,997		$ 5,390,977
90-Days Delinquencies	23,420		23,420
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
Total	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
90-Days Delinquencies	23,420		23,420
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
Total	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
90-Days Delinquencies	0		0
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
Total	5,087,596		5,087,596
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
Total	2,096,554		2,096,554
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
Total	320,226		320,226
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
Total	0		0
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
Total	209,690		209,690
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
Total	$ 5,014		$ 5,014
On-Balance Sheet:
Total
Total					5,276,557
90-Days Delinquencies					57,719
On-Balance Sheet: | Farm & Ranch
Total
Total					5,276,557
90-Days Delinquencies					57,719
On-Balance Sheet: | Acceptable | Farm & Ranch
Total
Total					4,790,636
On-Balance Sheet: | Special mention(1) | Farm & Ranch
Total
Total					278,843
On-Balance Sheet: | Substandard(2) | Farm & Ranch
Total
Total					207,078
On-Balance Sheet: | Crops
Total
Total					2,773,177
On-Balance Sheet: | Crops | Farm & Ranch
Total
Total					2,773,177
90-Days Delinquencies					21,167
On-Balance Sheet: | Crops | Acceptable | Farm & Ranch
Total
Total					2,556,956
On-Balance Sheet: | Crops | Special mention(1) | Farm & Ranch
Total
Total					107,406
On-Balance Sheet: | Crops | Substandard(2) | Farm & Ranch
Total
Total					108,815
On-Balance Sheet: | Permanent Plantings
Total
Total					1,213,156
On-Balance Sheet: | Permanent Plantings | Farm & Ranch
Total
Total					1,213,156
90-Days Delinquencies					15,828
On-Balance Sheet: | Permanent Plantings | Acceptable | Farm & Ranch
Total
Total					1,050,160
On-Balance Sheet: | Permanent Plantings | Special mention(1) | Farm & Ranch
Total
Total					111,739
On-Balance Sheet: | Permanent Plantings | Substandard(2) | Farm & Ranch
Total
Total					51,257
On-Balance Sheet: | Livestock
Total
Total					911,303
On-Balance Sheet: | Livestock | Farm & Ranch
Total
Total					911,303
90-Days Delinquencies					19,354
On-Balance Sheet: | Livestock | Acceptable | Farm & Ranch
Total
Total					825,234
On-Balance Sheet: | Livestock | Special mention(1) | Farm & Ranch
Total
Total					46,107
On-Balance Sheet: | Livestock | Substandard(2) | Farm & Ranch
Total
Total					39,962
On-Balance Sheet: | Part-time Farm
Total
Total					363,964
On-Balance Sheet: | Part-time Farm | Farm & Ranch
Total
Total					363,964
90-Days Delinquencies					1,370
On-Balance Sheet: | Part-time Farm | Acceptable | Farm & Ranch
Total
Total					343,329
On-Balance Sheet: | Part-time Farm | Special mention(1) | Farm & Ranch
Total
Total					13,591
On-Balance Sheet: | Part-time Farm | Substandard(2) | Farm & Ranch
Total
Total					7,044
On-Balance Sheet: | Ag. Storage and Processing
Total
Total					10,360
On-Balance Sheet: | Ag. Storage and Processing | Farm & Ranch
Total
Total					10,360
90-Days Delinquencies					0
On-Balance Sheet: | Ag. Storage and Processing | Acceptable | Farm & Ranch
Total
Total					10,360
On-Balance Sheet: | Ag. Storage and Processing | Special mention(1) | Farm & Ranch
Total
Total					0
On-Balance Sheet: | Ag. Storage and Processing | Substandard(2) | Farm & Ranch
Total
Total					0
On-Balance Sheet: | Other
Total
Total					4,597
On-Balance Sheet: | Other | Farm & Ranch
Total
Total					4,597
90-Days Delinquencies					0
On-Balance Sheet: | Other | Acceptable | Farm & Ranch
Total
Total					4,597
On-Balance Sheet: | Other | Special mention(1) | Farm & Ranch
Total
Total					0
On-Balance Sheet: | Other | Substandard(2) | Farm & Ranch
Total
Total					$ 0