Summary of Significant Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	$ 1,526,718	$ 1,517,101
Debt securities of consolidated trusts held by third parties	1,532,401	1,528,957
Farm & Ranch [Member]
Variable Interest Entity [Line Items]
Borrower remittances	5,700	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	1,526,718	1,517,101
Debt securities of consolidated trusts held by third parties	1,532,401	1,528,957
Off-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	519,358	503,546
Farmer Mac Guaranteed Securities [Member] \| On-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Carrying value	32,816	27,627
Maximum exposure to loss	32,645	27,383
Investment Securities [Member]
Variable Interest Entity [Line Items]
Unamortized premiums and discounts	2,396	3,489
Investment Securities [Member] \| On-balance sheet [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Carrying value	1,111,712	1,000,942
Maximum exposure to loss	1,114,220	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	1,526,718	1,517,101
Debt securities of consolidated trusts held by third parties	1,532,401	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]
Maximum exposure to loss	115,306	135,862
Operating Segments [Member] \| Off-balance sheet [Member] \| USDA Guarantees [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	404,052	367,684
Operating Segments [Member] \| Off-balance sheet [Member] \| Rural Utilities [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
Maximum exposure to loss	0	0
Operating Segments [Member] \| Off-balance sheet [Member] \| Institutional Credit [Member] \| Unconsolidated VIEs [Member]
Variable Interest Entity [Line Items]
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]
Carrying value	0	0
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]
Carrying value	32,816	27,627
Maximum exposure to loss	32,645	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]
Carrying value	0	0
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]
Carrying value	0	0
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]
Carrying value	0	0
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]
Carrying value	0	0
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]
Carrying value	0	0
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]
Carrying value	0	0
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]
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]
Carrying value	0	0
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]
Carrying value	1,111,712	1,000,942
Maximum exposure to loss	$ 1,114,220	$ 1,003,968

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

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