Loans and Allowance for Losses and Concentrations of Credit Risk Concentrations of Credit Risk (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	$ 4,747,289	[1]	$ 4,349,163	[1]
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	2,171,349	[1]	1,864,959	[1]
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	882,532	[1]	824,345	[1]
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	1,287,741	[1]	1,224,111	[1]
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	201,865	[1]	245,120	[1]
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	191,786	[1]	173,692	[1]
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	12,016	[1]	16,936	[1]
Commodity and Collateral Type Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	4,747,289		4,349,163
Commodity and Collateral Type Risk [Member] | Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	2,171,349		1,864,959
Commodity and Collateral Type Risk [Member] | Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	882,532		824,345
Commodity and Collateral Type Risk [Member] | Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	1,287,741		1,224,111
Commodity and Collateral Type Risk [Member] | Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	201,865		245,120
Commodity and Collateral Type Risk [Member] | Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	191,786		173,692
Commodity and Collateral Type Risk [Member] | Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	12,016		16,936
Geographic Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	4,747,289	[2]	4,349,163	[2]
Geographic Concentration Risk [Member] | Northwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	840,693	[2]	761,078	[2]
Geographic Concentration Risk [Member] | Southwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	1,781,822	[2]	1,597,369	[2]
Geographic Concentration Risk [Member] | Mid-North [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	989,903	[2]	857,659	[2]
Geographic Concentration Risk [Member] | Mid-South [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	504,914	[2]	484,176	[2]
Geographic Concentration Risk [Member] | Northeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	261,756	[2]	294,854	[2]
Geographic Concentration Risk [Member] | Southeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	368,201	[2]	354,027	[2]
Original Loan To Value Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	4,747,289		4,349,163
Original Loan To Value Risk [Member] | Financing Receivables, Original Loan-To-Value Ratio, Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivables, Loan-To-Value Ratio Range, Lower Range Limit	0.00%
Financing Receivables, Loan-To-Value Ratio Range, Upper Range Limit	40.00%
Financing Receivable, Gross	1,338,715		1,104,617
Original Loan To Value Risk [Member] | Financing Receivables, Original Loan-To-Value Ratio, Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivables, Loan-To-Value Ratio Range, Lower Range Limit	40.01%
Financing Receivables, Loan-To-Value Ratio Range, Upper Range Limit	50.00%
Financing Receivable, Gross	851,980		769,618
Original Loan To Value Risk [Member] | Financing Receivables, Original Loan-To-Value Ratio, Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivables, Loan-To-Value Ratio Range, Lower Range Limit	50.01%
Financing Receivables, Loan-To-Value Ratio Range, Upper Range Limit	60.00%
Financing Receivable, Gross	1,296,225		1,225,939
Original Loan To Value Risk [Member] | Financing Receivables, Original Loan-To-Value Ratio, Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivables, Loan-To-Value Ratio Range, Lower Range Limit	60.01%
Financing Receivables, Loan-To-Value Ratio Range, Upper Range Limit	70.00%
Financing Receivable, Gross	1,091,427		1,062,061
Original Loan To Value Risk [Member] | Financing Receivables, Original Loan-To-Value Ratio, Range Five [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivables, Loan-To-Value Ratio Range, Lower Range Limit	70.01%
Financing Receivables, Loan-To-Value Ratio Range, Upper Range Limit	80.00%
Financing Receivable, Gross	122,259		135,985
Original Loan To Value Risk [Member] | Financing Receivables, Original Loan-To-Value Ratio, Range Six [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivables, Loan-To-Value Ratio Range, Lower Range Limit	80.01%
Financing Receivables, Loan-To-Value Ratio Range, Upper Range Limit	90.00%
Financing Receivable, Gross	$ 46,683		$ 50,943

[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).