Loans - Schedule of Financing Receivables Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Total
Total	$ 7,796,712		$ 7,796,712		$ 7,261,933
Farm & Ranch
Year One
Total	1,128,706		1,128,706		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	1,970,079		1,970,079		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	764,412		764,412		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	454,171		454,171		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	418,099		418,099		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	1,334,124		1,334,124		1,140,603
Current period charge-offs	0	394	0	394
Current period recoveries	0	0	0	0
Current period Farm & Ranch net charge-offs	0	394	0	394
Revolving Loans - Amortized Cost Basis
Total	531,614		531,614		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	6,601,205		6,601,205		6,176,438
Current period charge-offs	0	394	0	394
Financing Receivable, Allowance for Credit Loss, Recovery	0	0	0	0
Current period Farm & Ranch net charge-offs	0	394	0	394
Rural Utilities
Year One
Total	21,022		21,022		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	658,542		658,542		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	792,333		792,333		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	8,180		8,180		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	89,488		89,488		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	648,818		648,818		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	28,185		28,185		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	2,246,568		2,246,568		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	1,085,630		1,085,630		1,947,618
Year Two
Total	1,873,579		1,873,579		774,315
Year Three
Total	704,749		704,749		484,345
Year Four
Total	409,047		409,047		500,768
Year Five
Total	364,489		364,489		465,277
Prior
Total	1,232,910		1,232,910		1,068,693
Revolving Loans - Amortized Cost Basis
Total	511,353		511,353		535,742
Total
Total	6,181,757		6,181,757		5,776,758
Acceptable | Rural Utilities
Year One
Total	21,022		21,022		667,489
Year Two
Total	635,342		635,342		809,921
Year Three
Total	792,333		792,333		8,260
Year Four
Total	8,180		8,180		89,842
Year Five
Total	89,488		89,488		31,275
Prior
Total	648,818		648,818		641,145
Revolving Loans - Amortized Cost Basis
Total	28,185		28,185		12,480
Total
Total	2,223,368		2,223,368		2,260,412
Special mention | Farm & Ranch
Year One
Total	43,076		43,076		70,171
Year Two
Total	92,886		92,886		79,744
Year Three
Total	33,544		33,544		18,317
Year Four
Total	14,643		14,643		8,530
Year Five
Total	3,809		3,809		13,111
Prior
Total	16,706		16,706		21,328
Revolving Loans - Amortized Cost Basis
Total	8,826		8,826		7,656
Total
Total	213,490		213,490		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	0		0		3,400
Year Two
Total	3,614		3,614		5,821
Year Three
Total	26,119		26,119		21,879
Year Four
Total	30,481		30,481		52,709
Year Five
Total	49,801		49,801		37,173
Prior
Total	84,508		84,508		50,582
Revolving Loans - Amortized Cost Basis
Total	11,435		11,435		9,259
Total
Total	205,958		205,958		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