Guarantees - Reserve For Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Reserve for losses	$ 2,333	$ 3,277
Farm & Ranch
Guarantor Obligations [Line Items]
Reserve for losses	1,366	2,097	$ 2,020	$ 2,164
Rural Utilities
Guarantor Obligations [Line Items]
Reserve for losses	967	1,180	$ 1,400	$ 0
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Guarantor Obligations [Line Items]
Reserve for losses	1,366	2,097
LTSPCs | Rural Utilities
Guarantor Obligations [Line Items]
Reserve for losses	$ 967	$ 1,180