Allowance for Losses and Concentration of Credit Risk - Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	$ 4,402,957	[1]	$ 4,349,163	[1]
90 days or more past due	40,797	[2]	40,622	[2]
Acceptable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	4,060,446	[1]	3,942,725	[1]
Other Assets Especially Mentioned (OAEM)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	146,895	[1],[3]	208,894	[1],[3]
Substandard
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	195,616	[1],[3]	197,544	[1],[3]
Crops
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	1,957,295	[1]	1,864,959	[1]
90 days or more past due	13,414	[2]	11,605	[2]
Crops | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	1,881,406	[1]	1,769,768	[1]
Crops | Other Assets Especially Mentioned (OAEM)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	34,118	[1],[3]	60,076	[1],[3]
Crops | Substandard
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	41,771	[1],[3]	35,115	[1],[3]
Permanent Plantings
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	833,455	[1]	824,345	[1]
90 days or more past due	11,861	[2]	19,227	[2]
Permanent Plantings | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	764,097	[1]	748,558	[1]
Permanent Plantings | Other Assets Especially Mentioned (OAEM)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	16,025	[1],[3]	20,442	[1],[3]
Permanent Plantings | Substandard
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	53,333	[1],[3]	55,345	[1],[3]
Livestock
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	1,186,477	[1]	1,224,111	[1]
90 days or more past due	4,899	[2]	2,475	[2]
Livestock | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	1,084,277	[1]	1,097,184	[1]
Livestock | Other Assets Especially Mentioned (OAEM)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	45,158	[1],[3]	74,959	[1],[3]
Livestock | Substandard
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	57,042	[1],[3]	51,968	[1],[3]
Part-Time Farm
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	214,566	[1]	245,120	[1]
90 days or more past due	6,125	[2]	7,315	[2]
Part-Time Farm | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	188,445	[1]	215,525	[1]
Part-Time Farm | Other Assets Especially Mentioned (OAEM)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	6,241	[1],[3]	7,103	[1],[3]
Part-Time Farm | Substandard
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	19,880	[1],[3]	22,492	[1],[3]
Ag Storage and Processing (including ethanol facilities)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	198,106	[1]	173,692	[1]
90 days or more past due	4,498	[2]	0	[2]
Ag Storage and Processing (including ethanol facilities) | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	130,902	[1]	96,532	[1]
Ag Storage and Processing (including ethanol facilities) | Other Assets Especially Mentioned (OAEM)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	44,754	[1],[3]	45,673	[1],[3]
Ag Storage and Processing (including ethanol facilities) | Substandard
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	22,450	[1],[3]	31,487	[1],[3]
Other
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	13,058	[1]	16,936	[1]
90 days or more past due	0	[2]	0	[2]
Other | Acceptable
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	11,319	[1]	15,158	[1]
Other | Other Assets Especially Mentioned (OAEM)
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	599	[1],[3]	641	[1],[3]
Other | Substandard
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, loans	$ 1,140	[1],[3]	$ 1,137	[1],[3]

[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] 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.

[3] Assets in the OAEM category generally have potential weaknesses due to performance issues but are currently considered to be adequately secured. Substandard assets have a well-defined weakness or weaknesses and there is a distinct possibility that some loss will be sustained if deficiencies are not corrected.