Guarantees and Long-Term Standby Purchase Commitments - Off-Balance Sheet Guaranteed Securities (Details) - Unconsolidated VIEs [Member] - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	$ 828,999	$ 813,444
Farm & Ranch [Member]
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	121,064	135,862
USDA Guarantees [Member]
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	398,710	367,684
Institutional Credit [Member]
Guarantor Obligations [Line Items]
Total off-balance sheet Farmer Mac Guaranteed Securities	9,225	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