Allowance for Losses and Concentration of Credit Risk - Concentration of Risk (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Concentration Risk [Line Items]
Financing receivable, loans	$ 4,402,957	[1]	$ 4,349,163	[1]
Commodity and Collateral Type Risk
Concentration Risk [Line Items]
Financing receivable, loans	4,402,957		4,349,163
Geographic Concentration Risk
Concentration Risk [Line Items]
Financing receivable, loans	4,402,957	[2]	4,349,163	[2]
Original Loan To Value Risk
Concentration Risk [Line Items]
Financing receivable, loans	4,402,957		4,349,163
Crops
Concentration Risk [Line Items]
Financing receivable, loans	1,957,295	[1]	1,864,959	[1]
Crops | Commodity and Collateral Type Risk
Concentration Risk [Line Items]
Financing receivable, loans	1,957,295		1,864,959
Permanent Plantings
Concentration Risk [Line Items]
Financing receivable, loans	833,455	[1]	824,345	[1]
Permanent Plantings | Commodity and Collateral Type Risk
Concentration Risk [Line Items]
Financing receivable, loans	833,455		824,345
Livestock
Concentration Risk [Line Items]
Financing receivable, loans	1,186,477	[1]	1,224,111	[1]
Livestock | Commodity and Collateral Type Risk
Concentration Risk [Line Items]
Financing receivable, loans	1,186,477		1,224,111
Part-Time Farm
Concentration Risk [Line Items]
Financing receivable, loans	214,566	[1]	245,120	[1]
Part-Time Farm | Commodity and Collateral Type Risk
Concentration Risk [Line Items]
Financing receivable, loans	214,566		245,120
Ag Storage and Processing (including ethanol facilities)
Concentration Risk [Line Items]
Financing receivable, loans	198,106	[1]	173,692	[1]
Ag Storage and Processing (including ethanol facilities) | Commodity and Collateral Type Risk
Concentration Risk [Line Items]
Financing receivable, loans	198,106		173,692
Other
Concentration Risk [Line Items]
Financing receivable, loans	13,058	[1]	16,936	[1]
Other | Commodity and Collateral Type Risk
Concentration Risk [Line Items]
Financing receivable, loans	13,058		16,936
Northwest | Geographic Concentration Risk
Concentration Risk [Line Items]
Financing receivable, loans	785,454	[2]	761,078	[2]
Southwest | Geographic Concentration Risk
Concentration Risk [Line Items]
Financing receivable, loans	1,555,368	[2]	1,597,369	[2]
Mid-North | Geographic Concentration Risk
Concentration Risk [Line Items]
Financing receivable, loans	897,453	[2]	857,659	[2]
Mid-South | Geographic Concentration Risk
Concentration Risk [Line Items]
Financing receivable, loans	512,628	[2]	484,176	[2]
Northeast | Geographic Concentration Risk
Concentration Risk [Line Items]
Financing receivable, loans	273,420	[2]	294,854	[2]
Southeast | Geographic Concentration Risk
Concentration Risk [Line Items]
Financing receivable, loans	378,634	[2]	354,027	[2]
Original Loan-To-Value Ratio, 0.00% to 40.00% | Original Loan To Value Risk
Concentration Risk [Line Items]
Financing receivable, loans	1,119,814		1,104,617
Loan-To-Value Ratio Range, Lower Range Limit	0.00%
Loan-To-Value Ratio Range, Upper Range Limit	40.00%
Original Loan-To-Value Ratio, 40.01% to 50.00% | Original Loan To Value Risk
Concentration Risk [Line Items]
Financing receivable, loans	802,204		769,618
Loan-To-Value Ratio Range, Lower Range Limit	40.01%
Loan-To-Value Ratio Range, Upper Range Limit	50.00%
Original Loan-To-Value Ratio, 50.01% to 60.00% | Original Loan To Value Risk
Concentration Risk [Line Items]
Financing receivable, loans	1,216,706		1,225,939
Loan-To-Value Ratio Range, Lower Range Limit	50.01%
Loan-To-Value Ratio Range, Upper Range Limit	60.00%
Original Loan-To-Value Ratio, 60.01% to 70.00% | Original Loan To Value Risk
Concentration Risk [Line Items]
Financing receivable, loans	1,097,884		1,062,061
Loan-To-Value Ratio Range, Lower Range Limit	60.01%
Loan-To-Value Ratio Range, Upper Range Limit	70.00%
Original Loan-To-Value Ratio, 70.01% to 80.00% | Original Loan To Value Risk
Concentration Risk [Line Items]
Financing receivable, loans	126,297		135,985
Loan-To-Value Ratio Range, Lower Range Limit	70.01%
Loan-To-Value Ratio Range, Upper Range Limit	80.00%
Original Loan-To-Value Ratio, 80.01% to 90.00% | Original Loan To Value Risk
Concentration Risk [Line Items]
Financing receivable, loans	$ 40,052		$ 50,943
Loan-To-Value Ratio Range, Lower Range Limit	80.01%
Loan-To-Value Ratio Range, Upper Range Limit	90.00%

[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] Geographic regions: Northwest (AK, ID, MT, ND, NE, OR, SD, WA, WY); Southwest (AZ, CA, CO, HI, NM, NV, UT); Mid-North (IA, IL, IN, MI, MN, MO, WI); Mid-South (KS, OK, TX); Northeast (CT, DE, KY, MA, MD, ME, NC, NH, NJ, NY, OH, PA, RI, TN, VA, VT, WV); Southeast (AL, AR, FL, GA, LA, MS, SC).