Guarantees and Commitments - Changes in Reserve for Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance			$ 3,277
(Release of)/provision for losses	$ (111)	$ 547	(1,277)	$ 540
Ending balance	2,000		2,000
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	1,194	1,650	2,097	2,164
(Release of)/provision for losses	(91)	628	(994)	262
Charge-offs	0	0	0	0
Ending balance	1,103	2,278	1,103	2,278
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	0	0	(148)
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	1,194	1,650	2,097	2,016
Rural Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	917	1,370	1,180	0
(Release of)/provision for losses	(20)	(80)	(283)	279
Charge-offs	0	0	0	0
Ending balance	897	1,290	897	1,290
Rural Utilities | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	0	0	1,011
Rural Utilities | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 917	$ 1,370	$ 1,180	$ 1,011