Guarantees - Changes in Reserve for Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 3,277
(Release of)/provision for losses	(944)	$ 393
Ending balance	2,333
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	2,097	2,164
(Release of)/provision for losses	(731)	4
Charge-offs	0	0
Ending balance	1,366	2,020
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	(148)
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	2,097	2,016
Rural Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	1,180	0
(Release of)/provision for losses	(213)	389
Charge-offs	0	0
Ending balance	967	1,400
Rural Utilities | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	1,011
Rural Utilities | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 1,180	$ 1,011