Guarantees - Off-Balance Sheet Guaranteed Securities (Details) - Unconsolidated VIE - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 361,483	$ 383,022
Farm & Ranch
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	72,203	79,312
USDA Guarantees
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	284,868	299,298
AgVantage Securities
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 4,412	$ 4,412