Loans - Changes in the Allowance for Losses (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance			$ 13,832,000
Provision for/(release of) losses	$ 366,000	$ 653,000	518,000	$ 4,542,000
Ending balance	14,294,000		14,294,000
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	3,092,000	6,039,000	3,745,000	10,454,000
Provision for/(release of) losses	414,000	(300,000)	(239,000)	(412,000)
Charge-offs	0	0	0	(394,000)
Ending balance	3,506,000	5,739,000	3,506,000	5,739,000
Farm & Ranch | Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for/(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	3,092,000	6,039,000	3,745,000	6,545,000
Rural Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	10,908,000	8,900,000	10,087,000	0
Provision for/(release of) losses	(120,000)	1,182,000	701,000	4,704,000
Charge-offs	0	0	0	0
Ending balance	10,788,000	10,082,000	10,788,000	10,082,000
Rural Utilities | Collateral Pledged
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for/(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	$ 10,908,000	$ 8,900,000	$ 10,087,000	$ 5,378,000