Guarantees - Reserve For Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Reserve for losses	$ 3,277		$ 2,164
Farm & Ranch
Guarantor Obligations [Line Items]
Reserve for losses	2,097	$ 2,016	2,164	$ 2,167	$ 2,070
Rural Utilities:
Guarantor Obligations [Line Items]
Reserve for losses	1,180	$ 1,011	0	$ 0	$ 0
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Guarantor Obligations [Line Items]
Reserve for losses	2,097		2,164
LTSPCs | Rural Utilities:
Guarantor Obligations [Line Items]
Reserve for losses	$ 1,180		$ 0