Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	$ 1,517,101	$ 1,399,827
Debt securities of consolidated trusts held by third parties	1,528,957	1,404,945
On-balance sheet [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	1,517,101	1,399,827
Debt securities of consolidated trusts held by third parties		1,404,945
On-balance sheet [Member] | Farm & Ranch [Member]
Variable Interest Entity [Line Items]
Debt securities of consolidated trusts held by third parties	1,528,957
On-balance sheet [Member] | USDA Guarantees [Member]
Variable Interest Entity [Line Items]
Debt securities of consolidated trusts held by third parties	0	0
On-balance sheet [Member] | Rural Utilities [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost		0
Debt securities of consolidated trusts held by third parties	0
On-balance sheet [Member] | Institutional Credit [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	0
Debt securities of consolidated trusts held by third parties		0
On-balance sheet [Member] | Corporate Segment [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	0
Debt securities of consolidated trusts held by third parties	0
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	503,546
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	135,862	333,511
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	367,684	254,217
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
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
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	27,627
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	27,383
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	0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	0
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	27,627	30,300
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	27,383	29,980
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	0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	0
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
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0
Investment Securities [Member]
Variable Interest Entity [Line Items]
Unamortized Premium/(Discount)	(3,489)	2,365
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	1,000,942
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	1,003,968	783,916
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, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	0
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
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	0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0
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
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0
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	$ 1,000,942	$ 783,964