Summary of Significant Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	$ 5,390,977	$ 4,004,968
Long-term Debt	19,098,648	16,243,697
Farm & Ranch
Variable Interest Entity [Line Items]
Borrower remittances	15,600	11,900
USDA Guarantees
Variable Interest Entity [Line Items]
Unamortized premiums and discounts	200	200
On-Balance Sheet: | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	1,600,917	1,517,101
Long-term Debt	1,616,504	1,528,957
Off-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Maximum exposure to loss	496,538	503,546
Farmer Mac Guaranteed Securities: | On-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	32,041	27,627
Maximum exposure to loss	31,887	27,383
Debt Securities
Variable Interest Entity [Line Items]
Unamortized premiums and discounts	(1,382)	3,489
Debt Securities | On-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	1,117,203	1,000,942
Maximum exposure to loss	1,120,765	1,003,968
Operating Segments | On-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	1,600,917	1,517,101
Long-term Debt	1,616,504	1,528,957
Operating Segments | On-Balance Sheet: | USDA Guarantees | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	0	0
Long-term Debt	0	0
Operating Segments | Off-Balance Sheet: | Farm & Ranch | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Maximum exposure to loss	107,322	135,862
Operating Segments | Off-Balance Sheet: | USDA Guarantees | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Maximum exposure to loss	389,216	367,684
Operating Segments | Farmer Mac Guaranteed Securities: | On-Balance Sheet: | Farm & Ranch | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	0	0
Maximum exposure to loss	0	0
Operating Segments | Farmer Mac Guaranteed Securities: | On-Balance Sheet: | USDA Guarantees | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	32,041	27,627
Maximum exposure to loss	31,887	27,383
Operating Segments | Debt Securities | On-Balance Sheet: | Farm & Ranch | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	0	0
Maximum exposure to loss	0	0
Operating Segments | Debt Securities | On-Balance Sheet: | USDA Guarantees | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	0	0
Maximum exposure to loss	0	0
Corporate | On-Balance Sheet: | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	0	0
Long-term Debt	0	0
Corporate | Off-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Maximum exposure to loss	0	0
Corporate | Farmer Mac Guaranteed Securities: | On-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	0	0
Maximum exposure to loss	0	0
Corporate | Debt Securities | On-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	1,117,203	1,000,942
Maximum exposure to loss	$ 1,120,765	$ 1,003,968