Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments Off-Balance Sheet Guaranteed Securities (Details) (Variable Interest Entity, Not Primary Beneficiary [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Farmer Mac I Guaranteed Securities AgVantage [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 970,000	$ 970,000
Farm & Ranch Guaranteed Securities [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	856,500	911,370
USDA Guarantees - Farmer Mac Guaranteed Securities [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	25,581	29,658
Rural Utilities Farmer Mac Guaranteed Securities AgVantage [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	12,669	12,669
Farmer Mac Guaranteed Securities [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 1,864,750	$ 1,923,697