Loans and Allowance for Losses and Concentrations of Credit Risk Certain Loans Acquired Delinquencies and Net Credit Losses (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 98,837,000		$ 88,026,000
Net credit losses/(recoveries)	1,673,000		200,000		555,000
90-day delinquencies [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	33,263,000	[1]	40,622,000	[1]
90-day delinquencies [Member] | Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Subject To Be Purchased	4,600,000	[1]	5,600,000	[1]
On-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses/(recoveries)	1,673,000		200,000		555,000
On-balance sheet [Member] | Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses/(recoveries)	1,673,000		200,000		555,000
On-balance sheet [Member] | 90-day delinquencies [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	29,592,000	[1]	33,243,000	[1]
On-balance sheet [Member] | 90-day delinquencies [Member] | Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	29,592,000	[1]	33,243,000	[1]
Off-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses/(recoveries)	0		0		0
Off-balance sheet [Member] | Long-Term Standby Purchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses/(recoveries)	0		0		0
Off-balance sheet [Member] | 90-day delinquencies [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	3,671,000	[1]	7,379,000	[1]
Off-balance sheet [Member] | 90-day delinquencies [Member] | Long-Term Standby Purchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 3,671,000	[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.