Loans and Allowance for Losses and Concentrations of Credit Risk - Loan (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment, at amortized cost		$ 3,148,742	$ 2,833,461
Allowance for Loan and Lease Losses, Real Estate		4,775	5,864
Total loans, net of allowance		3,756,534	3,520,075
Unsecuritized [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance	[1]	3,148,203	2,837,080
Unamortized premiums, discounts and other cost basis adjustments		539	(3,619)
Loans held for investment, at amortized cost		3,148,742	2,833,461
Allowance for Loan and Lease Losses, Real Estate		4,158	5,324
Total loans, net of allowance		3,144,584	2,828,137
Unsecuritized [Member] | Farm & Ranch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance		2,166,125	2,118,867
Unsecuritized [Member] | Rural Utilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance		982,078	718,213
In Consolidated Trusts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance	[1]	612,567	688,751
Unamortized premiums, discounts and other cost basis adjustments		0	3,727
Loans held for investment, at amortized cost		612,567	692,478
Allowance for Loan and Lease Losses, Real Estate		617	540
Total loans, net of allowance		611,950	691,938
In Consolidated Trusts | Farm & Ranch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance		612,567	421,355
In Consolidated Trusts | Rural Utilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance		0	267,396
Loans Collateralized by Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance	[1]	3,760,770	3,525,831
Unamortized premiums, discounts and other cost basis adjustments		539	108
Loans held for investment, at amortized cost		3,761,309	3,525,939
Allowance for Loan and Lease Losses, Real Estate		4,775	5,864
Total loans, net of allowance		3,756,534	3,520,075
Loans Collateralized by Real Estate [Member] | Farm & Ranch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance		2,778,692	2,540,222
Loans Collateralized by Real Estate [Member] | Rural Utilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Lease Receivable Unpaid Principal Balance		$ 982,078	$ 985,609

[1] Unpaid principal balance is the basis of presentation in disclosures of outstanding balances for Farmer Mac's lines of business.