Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Sep. 30, 2017		Dec. 31, 2016
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	$ 1,329,212		$ 1,132,966
Debt securities of consolidated trusts held by third parties	1,333,417		1,142,704
Farm & Ranch [Member]
Variable Interest Entity [Line Items]
Other Liabilities	4,200		9,700
USDA Guarantees [Member]
Variable Interest Entity [Line Items]
Unamortized Premium/(Discount)	300		400
Institutional Credit [Member]
Variable Interest Entity [Line Items]
Fair Value Adjustment			300
On-balance sheet [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	1,329,212		1,132,966
Debt securities of consolidated trusts held by third parties	1,333,417	[1]	1,142,704	[2]
On-balance sheet [Member] | Farm & Ranch [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	1,329,212		1,132,966
Debt securities of consolidated trusts held by third parties	1,333,417	[1]	1,142,704	[2]
On-balance sheet [Member] | USDA Guarantees [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	0		0
Debt securities of consolidated trusts held by third parties	0	[1]	0	[2]
On-balance sheet [Member] | Rural Utilities [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	0		0
Debt securities of consolidated trusts held by third parties	0	[1]	0	[2]
On-balance sheet [Member] | Institutional Credit [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	0		0
Debt securities of consolidated trusts held by third parties	0	[1]	0	[2]
On-balance sheet [Member] | Corporate Segment [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	0		0
Debt securities of consolidated trusts held by third parties	0	[1]	0	[2]
Off-balance sheet [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	581,625	[3],[4]	1,489,417	[5],[6]
Off-balance sheet [Member] | Farm & Ranch [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	354,823	[3],[4]	415,441	[5],[6]
Off-balance sheet [Member] | USDA Guarantees [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	226,802	[3],[4]	103,976	[5],[6]
Off-balance sheet [Member] | Rural Utilities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3],[4]	0	[5],[6]
Off-balance sheet [Member] | Institutional Credit [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3],[4]	970,000	[5],[6]
Off-balance sheet [Member] | Corporate Segment [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3],[4]	0	[5],[6]
Farmer Mac Guaranteed Securities: | On-balance sheet [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	31,003	[7]	66,389	[8]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	30,688	[3]	65,599	[5]
Farmer Mac Guaranteed Securities: | On-balance sheet [Member] | Farm & Ranch [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[7]	0	[8]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3]	0	[5]
Farmer Mac Guaranteed Securities: | On-balance sheet [Member] | USDA Guarantees [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	31,003	[7]	36,042	[8]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	30,688	[3]	35,599	[5]
Farmer Mac Guaranteed Securities: | On-balance sheet [Member] | Rural Utilities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[7]	0	[8]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3]	0	[5]
Farmer Mac Guaranteed Securities: | On-balance sheet [Member] | Institutional Credit [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[7]	30,347	[8]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3]	30,000	[5]
Farmer Mac Guaranteed Securities: | On-balance sheet [Member] | Corporate Segment [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[7]	0	[8]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3]	0	[5]
Investment Securities [Member]
Variable Interest Entity [Line Items]
Unamortized Premium/(Discount)	3,406		5,672
Investment Securities [Member] | On-balance sheet [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	783,665	[9]	827,874	[10]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	781,755	[3],[9]	825,909	[5],[10]
Investment Securities [Member] | On-balance sheet [Member] | Farm & Ranch [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[9]	0	[10]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3],[9]	0	[5],[10]
Investment Securities [Member] | On-balance sheet [Member] | USDA Guarantees [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[9]	0	[10]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3],[9]	0	[5],[10]
Investment Securities [Member] | On-balance sheet [Member] | Rural Utilities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[9]	0	[10]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3],[9]	0	[5],[10]
Investment Securities [Member] | On-balance sheet [Member] | Institutional Credit [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	[9]	0	[10]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	[3],[9]	0	[5],[10]
Investment Securities [Member] | On-balance sheet [Member] | Corporate Segment [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	783,665	[9]	827,874	[10]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 781,755	[3],[9]	$ 825,909	[5],[10]

[1] Includes borrower remittances of $4.2 million. The borrower remittances had not been passed through to third party investors as of September 30, 2017.

[2] Includes borrower remittances of $9.7 million, which have not been passed through to third party investors as of December 31, 2016.

[3] Farmer Mac uses unpaid principal balance and outstanding face amount of investment securities to represent maximum exposure to loss.

[4] The amount under the Farm & Ranch line of business relates to unconsolidated trusts where Farmer Mac determined it was not the primary beneficiary due to shared power with an unrelated party.

[5] Farmer Mac uses unpaid principal balance and the outstanding face amount of investment securities to represent maximum exposure to loss.

[6] The amount under the Farm & Ranch line of business relates to unconsolidated trusts where Farmer Mac determined it was not the primary beneficiary due to shared power with an unrelated party.

[7] Includes $0.3 million of unamortized premiums and discounts and fair value adjustments related to the USDA Guarantees line of business.

[8] Includes $0.4 million of unamortized premiums and discounts and fair value adjustments related to the USDA Guarantees line of business. Includes fair value adjustments related to the Institutional Credit line of business of $0.3 million.

[9] Includes auction-rate certificates, asset-backed securities, and government-sponsored enterprise ("GSE")-guaranteed mortgage-backed securities.

[10] Includes auction-rate certificates, asset-backed securities, and GSE-guaranteed mortgage-backed securities.