Guarantees and Commitments - Off-Balance Sheet Guaranteed Securities (Details) - Unconsolidated VIE - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 324,654	$ 383,022
Farm & Ranch
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	60,349	79,312
USDA Guarantees
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	259,893	299,298
AgVantage Securities
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 4,412	$ 4,412