Summary of Significant Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	$ 1,566,330	$ 1,517,101
Debt securities of consolidated trusts held by third parties	1,567,195	1,528,957
Farm & Ranch [Member]
Variable Interest Entity [Line Items]
Borrower remittances	900	11,900
USDA Guarantees [Member]
Variable Interest Entity [Line Items]
Unamortized premiums and discounts	200	200
On-balance sheet [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	1,566,330	1,517,101
Debt securities of consolidated trusts held by third parties	1,567,195	1,528,957
Off-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Maximum exposure to loss	504,708	503,546
Farmer Mac Guaranteed Securities [Member] \| On-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	27,031	27,627
Unconsolidated VIEs Maximum exposure to loss	26,794	27,383
Investment Securities [Member]
Variable Interest Entity [Line Items]
Unamortized premiums and discounts	4,280	3,489
Investment Securities [Member] \| On-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	1,026,064	1,000,942
Unconsolidated VIEs Maximum exposure to loss	1,030,108	1,003,968
Operating Segments [Member] \| On-balance sheet [Member] \| Farm & Ranch [Member]
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	1,566,330	1,517,101
Debt securities of consolidated trusts held by third parties	1,567,195	1,528,957
Operating Segments [Member] \| 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	0
Operating Segments [Member] \| 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	0
Operating Segments [Member] \| 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	0
Operating Segments [Member] \| Off-balance sheet [Member] \| Farm & Ranch [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Maximum exposure to loss	128,221	135,862
Operating Segments [Member] \| Off-balance sheet [Member] \| USDA Guarantees [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Maximum exposure to loss	376,487	367,684
Operating Segments [Member] \| Off-balance sheet [Member] \| Rural Utilities [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Off-balance sheet [Member] \| Institutional Credit [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Farmer Mac Guaranteed Securities [Member] \| On-balance sheet [Member] \| Farm & Ranch [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Farmer Mac Guaranteed Securities [Member] \| On-balance sheet [Member] \| USDA Guarantees [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	27,031	27,627
Unconsolidated VIEs Maximum exposure to loss	26,794	27,383
Operating Segments [Member] \| Farmer Mac Guaranteed Securities [Member] \| On-balance sheet [Member] \| Rural Utilities [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Farmer Mac Guaranteed Securities [Member] \| On-balance sheet [Member] \| Institutional Credit [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Investment Securities [Member] \| On-balance sheet [Member] \| Farm & Ranch [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Investment Securities [Member] \| On-balance sheet [Member] \| USDA Guarantees [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Investment Securities [Member] \| On-balance sheet [Member] \| Rural Utilities [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Operating Segments [Member] \| Investment Securities [Member] \| On-balance sheet [Member] \| Institutional Credit [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Corporate, Non-Segment [Member] \| On-balance sheet [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	0
Corporate, Non-Segment [Member] \| Off-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Maximum exposure to loss	0	0
Corporate, Non-Segment [Member] \| Farmer Mac Guaranteed Securities [Member] \| On-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	0	0
Unconsolidated VIEs Maximum exposure to loss	0	0
Corporate, Non-Segment [Member] \| Investment Securities [Member] \| On-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Unconsolidated VIEs Carrying value	1,026,064	1,000,942
Unconsolidated VIEs Maximum exposure to loss	$ 1,030,108	$ 1,003,968

Amount, after accumulated amortization, of debt discount (premium).

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