Loans - Changes in the Allowance for Losses (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		$ 10,454,000
Increase (Decrease) in allowance for loan losses	$ 3,504,000	7,805,000	$ 3,504,000	$ 238,000
Ending balance	10,454,000	13,832,000	10,454,000
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		10,454,000	7,017,000	6,796,000
Increase (Decrease) in allowance for loan losses		2,959,000	3,504,000	238,000
Charge-offs		(5,759,000)	(67,000)	(17,000)
Ending balance	10,454,000	3,745,000	10,454,000	7,017,000
Farm & Ranch | Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Increase (Decrease) in allowance for loan losses		0
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		(3,909,000)
Ending balance	(3,909,000)		(3,909,000)
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		6,545,000
Ending balance	6,545,000		6,545,000
Rural Utilities:
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		0	0	0
Increase (Decrease) in allowance for loan losses		4,709,000	0	0
Charge-offs		0	0	0
Ending balance	0	10,087,000	0	$ 0
Rural Utilities: | Collateral Pledged
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Increase (Decrease) in allowance for loan losses		0
Rural Utilities: | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		5,378,000
Ending balance	5,378,000		5,378,000
Rural Utilities: | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		$ 5,378,000
Ending balance	$ 5,378,000		$ 5,378,000