Guarantees - Changes in Reserve for Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance			$ 3,277
Release of losses	$ (222)	$ (400)	(1,166)	$ (7)
Ending balance	2,111		2,111
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	1,366	2,020	2,097	2,164
Release of losses	(172)	(370)	(903)	(366)
Charge-offs	0	0	0	0
Ending balance	1,194	1,650	1,194	1,650
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	1,366	2,020	2,097	2,016
Rural Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	967	1,400	1,180	0
Release of losses	(50)	(30)	(263)	359
Charge-offs	0	0	0	0
Ending balance	917	1,370	917	1,370
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	$ 967	$ 1,400	$ 1,180	$ 1,011