Loans and Allowance for Losses and Concentrations of Credit Risk - Concentrations of Credit Risk (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[1],[2],[3]	$ 6,557,030	$ 6,139,304
Financing Receivables, Borrower Exposure, Range One [Member] [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross		2,297,648	2,195,103
Financing Receivables, Borrower Exposure, Range Two [Member] [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross		2,500,101	2,398,843
Financing Receivables, Borrower Exposure, Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross		815,411	782,171
Financing Receivables, Borrower Exposure, Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross		568,471	469,681
Financing Receivables, Borrower Exposure, Range Five [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross		375,399	293,506
Financing Receivables, Original Loan-To-Value Ratio, Range One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[2]	$ 1,274,050	1,220,432
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 Receivables, Original Loan-To-Value Ratio, Range Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[2]	$ 1,622,767	1,466,047
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 Receivables, Original Loan-To-Value Ratio, Range Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[2]	$ 2,268,852	2,078,099
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 Receivables, Original Loan-To-Value Ratio, Range Four [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[2]	$ 1,130,748	1,167,395
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 Receivables, Original Loan-To-Value Ratio, Range Five [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[2]	$ 233,963	191,664
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 Receivables, Original Loan-To-Value Ratio, Range Six [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[2]	$ 26,650	15,667
Financing Receivables, Loan-To-Value Ratio Range, Lower Range Limit		80.01%
Financing Receivables, Loan-To-Value Ratio Range, Upper Range Limit		90.00%
Northwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[3]	$ 723,616	657,403
Southwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[3]	1,917,692	1,791,745
Mid-North [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[3]	2,205,750	2,104,867
Mid-South [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[3]	899,293	837,121
Northeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[3]	290,655	229,679
Southeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[3]	520,024	518,489
Crops [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[1]	3,593,716	3,410,498
Permanent Plantings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[1]	1,184,221	1,037,440
Livestock [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[1]	1,309,743	1,305,844
Part-Time Farm [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[1]	407,708	324,074
Agriculture Storage and Processing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[1]	48,068	48,051
Other Commodity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Gross	[1]	$ 13,574	$ 13,397

[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] As of second quarter 2017, Farmer Mac revised its calculation of the original loan-to-value ratio of a loan to combine for any cross-collateralized loans: (i) the original loan principal balance amounts in the numerator and (ii) the original appraised property values in the denominator. In previous periods, the ratio was calculated on a loan-by-loan basis without considering the effects of any cross-collateralization. Prior period information has been reclassified to conform to the current period calculation and presentation.

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