Loans - Changes in the Allowance for Losses (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 10,454,000
Provision for/(release of) losses	3,438,000	$ (264,000)
Provision for/(release of) losses	3,831,000	(393,000)
Ending balance	14,856,000
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		7,017,000
Beginning balance	10,454,000
Provision for/(release of) losses	808,000
Provision for/(release of) losses		(264,000)
Charge-offs	0	0
Ending balance		6,753,000
Ending balance	7,353,000
Farm & Ranch | Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for/(release of) losses	2,200,000
Rural  Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance		0
Beginning balance	0
Provision for/(release of) losses	2,125,000
Provision for/(release of) losses		0
Charge-offs	0	0
Ending balance		$ 0
Ending balance	7,503,000
Rural  Utilities | Collateral Pledged
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Provision for/(release of) losses	$ 0