Loans - Schedule of Financing Receivables Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Total
Total	$ 7,758,286		$ 7,758,286		$ 7,261,933
Farm & Ranch
Year One
Total	1,654,597		1,654,597		2,021,189
Current period charge-offs	0	$ 0	0	$ 0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Two
Total	1,892,856		1,892,856		859,880
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Three
Total	723,427		723,427		524,541
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Four
Total	423,585		423,585		562,007
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Five
Total	375,483		375,483		515,561
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Prior
Total	1,154,262		1,154,262		1,140,603
Current period charge-offs	0	0	0	394
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	394
Revolving Loans - Amortized Cost Basis
Total	553,539		553,539		552,657
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Total
Total	6,777,749		6,777,749		6,176,438
Current period charge-offs	0	0	0	394
Financing Receivable, Allowance for Credit Loss, Recovery	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	394
Rural Utilities
Year One
Total	60,793		60,793		667,489
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Two
Total	642,972		642,972		809,921
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Three
Total	784,153		784,153		8,260
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Four
Total	8,100		8,100		89,842
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Year Five
Total	89,263		89,263		31,275
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Prior
Total	628,903		628,903		641,145
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Revolving Loans - Amortized Cost Basis
Total	28,988		28,988		12,480
Current period charge-offs	0	0	0	0
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	0	0	0
Total
Total	2,243,172		2,243,172		2,260,412
Current period charge-offs	0	0	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0	0	0
Current period Farm & Ranch net charge-offs	0	$ 0	0	$ 0
Acceptable | Farm & Ranch
Year One
Total	1,570,766		1,570,766		1,947,618
Year Two
Total	1,798,703		1,798,703		774,315
Year Three
Total	660,485		660,485		484,345
Year Four
Total	382,027		382,027		500,768
Year Five
Total	318,043		318,043		465,277
Prior
Total	1,054,024		1,054,024		1,068,693
Revolving Loans - Amortized Cost Basis
Total	531,063		531,063		535,742
Total
Total	6,315,111		6,315,111		5,776,758
Acceptable | Rural Utilities
Year One
Total	60,793		60,793		667,489
Year Two
Total	619,772		619,772		809,921
Year Three
Total	784,153		784,153		8,260
Year Four
Total	8,100		8,100		89,842
Year Five
Total	89,263		89,263		31,275
Prior
Total	628,903		628,903		641,145
Revolving Loans - Amortized Cost Basis
Total	28,988		28,988		12,480
Total
Total	2,219,972		2,219,972		2,260,412
Special mention | Farm & Ranch
Year One
Total	83,224		83,224		70,171
Year Two
Total	88,848		88,848		79,744
Year Three
Total	36,050		36,050		18,317
Year Four
Total	13,828		13,828		8,530
Year Five
Total	6,962		6,962		13,111
Prior
Total	18,998		18,998		21,328
Revolving Loans - Amortized Cost Basis
Total	10,531		10,531		7,656
Total
Total	258,441		258,441		218,857
Special mention | Rural Utilities
Year One
Total	0		0		0
Year Two
Total	0		0		0
Year Three
Total	0		0		0
Year Four
Total	0		0		0
Year Five
Total	0		0		0
Prior
Total	0		0		0
Revolving Loans - Amortized Cost Basis
Total	0		0		0
Total
Total	0		0		0
Substandard | Farm & Ranch
Year One
Total	607		607		3,400
Year Two
Total	5,305		5,305		5,821
Year Three
Total	26,892		26,892		21,879
Year Four
Total	27,730		27,730		52,709
Year Five
Total	50,478		50,478		37,173
Prior
Total	81,240		81,240		50,582
Revolving Loans - Amortized Cost Basis
Total	11,945		11,945		9,259
Total
Total	204,197		204,197		180,823
Substandard | Rural Utilities
Year One
Total	0		0		0
Year Two
Total	23,200		23,200		0
Year Three
Total	0		0		0
Year Four
Total	0		0		0
Year Five
Total	0		0		0
Prior
Total	0		0		0
Revolving Loans - Amortized Cost Basis
Total	0		0		0
Total
Total	$ 23,200		$ 23,200		$ 0