Loans - Allowance for Losses Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	$ 15,821		$ 15,821				$ 10,454
(Release of)/provision for losses	653	$ 760	4,542	$ 1,074
Current period charge-offs			100
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans						$ 2,656
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	5,739	8,024	5,739	8,024	$ 6,039		10,454	$ 7,264	$ 7,017
(Release of)/provision for losses	(300)	760	(412)	1,074
Current period charge-offs	0		394
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans					0	(3,909)	(3,909)	0	0
Rural  Utilities
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	10,082	0	10,082	0	8,900		0	0	0
(Release of)/provision for losses	1,182	$ 0	4,704	$ 0
Current period charge-offs	0		0
Rural  Utilities | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans					$ 0	$ 5,378	$ 5,378	$ 0	$ 0
Farm & Ranch and Rural Utilities
Financing Receivable, Allowance for Credit Losses [Line Items]
(Release of)/provision for losses	$ 900		$ 4,300