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, 2014		Dec. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	$ 18,917,000	[1]	$ 28,296,000	[2]
Net credit losses (recoveries)	(6,000)		2,975,000		1,673,000
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Subject To Be Purchased	1,800,000	[3]	1,200,000	[3]
On-balance sheet [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	18,427,000	[1]	27,580,000	[2]
Net credit losses (recoveries)	(6,000)		2,975,000		1,673,000
Off-balance sheet [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	490,000	[1]	716,000	[2]
Net credit losses (recoveries)	$ 0		$ 0		$ 0

[1] Amounts represent unpaid principal balance of risk-rated loans, which is the basis Farmer Mac uses to analyze its portfolio, and recorded investment of past due loans.

[2] (1)Amounts represent unpaid principal balance of risk-rated loans, which is the basis Farmer Mac uses to analyze its portfolio, and recorded investment of past due loans.

[3] Includes loans and loans underlying off-balance sheet Farm & Ranch Guaranteed Securities and LTSPCs that are 90 days or more past due, in foreclosure, restructured after delinquency, or in bankruptcy, excluding loans performing under either their original loan terms or a court-approved bankruptcy plan.