Accounting Policies - Supplemental Cash Flows (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Jan. 02, 2013
Supplemental Cash and Non-cash Transactions [Line Items]
Interest	$ 33,068,000	$ 34,082,000
Loans acquired and securitized as Farmer Mac Guaranteed Securities	25,042,000	3,380,000
Real Estate, Acquisitions Through Foreclosures	1,034,000	0
Purchases of Investment Securities Traded, Not Yet Settled	325,000,000	0
Consolidation of guaranteed securities from off-balance sheet to Loans Held for Investment and Debt Securities of consolidated trusts held by third parties	25,042,000	3,380,000
Transfer of Loans Held-for-sale to Portfolio Loans	673,991,000	0
Increase (Decrease) in Loans Held-for-sale			(5,900,000)
Transfer of Loans Held-for-sale to Loans Held-for Investment, unamortized discount				$ (5,900,000)
Maximum [Member]
Supplemental Cash and Non-cash Transactions [Line Items]
Cash Equivalent Maturity Period	3 months