Loans - Changes in the Allowance for Losses (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance			$ 10,454,000
(Release of)/provision for losses	$ 451,000	$ 578,000	3,889,000	$ 314,000
Provision for/(release of) losses			3,882,000	27,000
Ending balance	14,939,000		$ 14,939,000		$ 10,454,000
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	7,353,000		$ 10,454,000
Beginning balance		6,753,000		7,017,000	7,017,000
(Release of)/provision for losses	(920,000)		(112,000)
Provision for/(release of) losses		578,000		314,000
Charge-offs	(394,000)	(67,000)	(394,000)	(67,000)
Ending balance	6,039,000		6,039,000		$ 10,454,000
Ending balance		7,264,000		7,264,000
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0		(3,909,000)
Beginning balance		0		0	$ 0
Ending balance					(3,909,000)
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	7,353,000		6,545,000
Beginning balance		6,753,000		7,017,000	7,017,000
Ending balance					6,545,000
Farm & Ranch | Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
(Release of)/provision for losses			1,800,000
Rural  Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	7,503,000		0
Beginning balance		0		0	0
(Release of)/provision for losses	1,397,000		3,522,000
Provision for/(release of) losses		0		0
Charge-offs	0	0	0	0
Ending balance	8,900,000		8,900,000		$ 0
Ending balance		0		0
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member
Rural  Utilities | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0		5,378,000
Beginning balance		0		0	$ 0
Ending balance					5,378,000
Rural  Utilities | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 7,503,000		5,378,000
Beginning balance		$ 0		$ 0	0
Ending balance					$ 5,378,000
Rural  Utilities | Collateral Pledged
Financing Receivable, Allowance for Credit Losses [Roll Forward]
(Release of)/provision for losses			$ 0