Guarantees and Long-Term Standby Purchase Commitments - Off-Balance Sheet Guaranteed Securities (Details) - Unconsolidated VIEs [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 814,606	$ 813,444
Farm & Ranch [Member]
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	128,221	135,862
USDA Guarantees [Member]
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	376,487	367,684
Institutional Credit [Member]
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	9,898	9,898
Revolving Credit Facility [Member] | Institutional Credit [Member]
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 300,000	$ 300,000