Guarantees - Off-Balance Sheet Guaranteed Securities (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 475,772	$ 504,105
Farm & Ranch
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	97,302	107,322
USDA Guarantees
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	370,903	389,216
Institutional Credit
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 7,567	$ 7,567