Allowance for Losses and Concentration of Credit Risk - Credit Loss and Deliquencies On Guarantees (Details) (USD $)	9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Certain Loans Acquired in Transfer Acquired During Period [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 108,504,000				$ 88,026,000
Net Credit (Recoveries)/Losses	199,000		334,000
Eligible Loans [Member]
Certain Loans Acquired in Transfer Acquired During Period [Line Items]
Net Credit (Recoveries)/Losses	199,000		334,000
LTSPCs
Certain Loans Acquired in Transfer Acquired During Period [Line Items]
Net Credit (Recoveries)/Losses	0		0
90-day delinquencies [Member]
Certain Loans Acquired in Transfer Acquired During Period [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	40,797,000	[1]	44,848,000	[1]	40,622,000	[1]
90-day delinquencies [Member] | Eligible Loans [Member]
Certain Loans Acquired in Transfer Acquired During Period [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	29,120,000	[1]	35,860,000	[1]	33,243,000	[1]
Subject to removal-of-account provisions	2,600,000	[1]	6,200,000	[1]	5,600,000	[1]
90-day delinquencies [Member] | LTSPCs
Certain Loans Acquired in Transfer Acquired During Period [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 11,677,000	[1]	$ 8,988,000	[1]	$ 7,379,000	[1]

[1] Includes loans and loans underlying Farmer Mac I Guaranteed Securities and LTSPCs that are 90 days or more past due, in foreclosure, restructured after delinquency, and in bankruptcy, excluding loans performing under either their original loan terms or a court-approved bankruptcy plan.