Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments - Maximum Exposure (Details) (Variable Interest Entity, Not Primary Beneficiary, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Farmer Mac I Guaranteed Securities AgVantage [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 970,000	$ 970,000
Farmer Mac I Guaranteed Securities [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	911,370	621,871
Farmer Mac II Guaranteed Securities
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	29,658	42,088
Rural Utilities Farmer Mac Guaranteed Securities AgVantage [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	12,669	16,271
Farmer Mac Guaranteed Securities [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 1,923,697	$ 1,650,230