Guarantees and Commitments - Reserve For Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Reserve for losses	$ 2,000		$ 3,277
Farm & Ranch
Guarantor Obligations [Line Items]
Reserve for losses	1,103	$ 1,194	2,097	$ 2,278	$ 1,650	$ 2,164
Rural Utilities
Guarantor Obligations [Line Items]
Reserve for losses	897	$ 917	1,180	$ 1,290	$ 1,370	$ 0
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Guarantor Obligations [Line Items]
Reserve for losses	1,103		2,097
LTSPCs | Rural Utilities
Guarantor Obligations [Line Items]
Reserve for losses	$ 897		$ 1,180