Loans - Changes in the Allowance for Losses (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance			$ 13,832,000
Release of losses	$ (761,000)	$ 451,000	152,000	$ 3,889,000
Ending balance	14,000,000		14,000,000
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	3,718,000	7,353,000	3,745,000	10,454,000
Release of losses	(626,000)	(920,000)	(653,000)	(112,000)
Charge-offs	0	(394,000)	0	(394,000)
Ending balance	3,092,000	6,039,000	3,092,000	6,039,000
Farm & Ranch | Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Release of losses			0	1,800,000
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	0	0	(3,909,000)
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	3,718,000	7,353,000	3,745,000	6,545,000
Rural Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	11,089,000	7,503,000	10,087,000	0
Release of losses	(181,000)	1,397,000	821,000	3,522,000
Charge-offs	0	0	0	0
Ending balance	10,908,000	8,900,000	10,908,000	8,900,000
Rural Utilities | Collateral Pledged
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Release of losses			0	0
Rural Utilities | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	0	0	5,378,000
Rural Utilities | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 11,089,000	$ 7,503,000	$ 10,087,000	$ 5,378,000