Guarantees - Changes in Reserve for Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance			$ 2,164
Provision for/(release of) losses	$ 547	$ (137)	540	$ (424)
Ending balance	3,568		3,568
Farm & Ranch
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	1,650	1,880	2,164	2,167
Provision for/(release of) losses	628	(137)	262	(424)
Ending balance	2,278	1,743	2,278	1,743
Farm & Ranch | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	0
Rural  Utilities
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	1,370	0	0	0
Provision for/(release of) losses	(80)	0	279	0
Ending balance	1,290	0	$ 1,290	$ 0
Rural  Utilities | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 0	$ 0