Summary of Significant Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	$ 6,825,061	$ 5,390,977
Debt securities of consolidated trusts held by third parties	21,589,285	19,098,648
Farm & Ranch
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	5,857,324
Borrower remittances	16,000	15,600
USDA Guarantees
Variable Interest Entity [Line Items]
Unamortized Premium/(Discount)	(100)	(200)
On-Balance Sheet:
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost		5,276,557
On-Balance Sheet: | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	1,276,407	1,600,917
Debt securities of consolidated trusts held by third parties	1,292,416	1,616,504
On-Balance Sheet: | Farm & Ranch
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost		5,276,557
Off-Balance Sheet:
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost		2,500,393
Off-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss	396,449	496,538
Farmer Mac Guaranteed Securities
Variable Interest Entity [Line Items]
Carrying value	7,511,638	7,143,025
Farmer Mac Guaranteed Securities | On-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying value	36,505	32,041
Maximum exposure to loss	36,414	31,887
Investment securities
Variable Interest Entity [Line Items]
Carrying value	3,532,190	2,959,843
Unamortized Premium/(Discount)	9,439	1,382
Investment securities | On-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying value	1,835,688	1,117,203
Maximum exposure to loss	1,829,604	1,120,765
Operating Segments | On-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	1,276,407	1,600,917
Debt securities of consolidated trusts held by third parties	1,292,416	1,616,504
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
Debt securities of consolidated trusts held by third parties	0	0
Operating Segments | Off-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss	85,767	107,322
Operating Segments | Off-Balance Sheet: | USDA Guarantees | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss	310,682	389,216
Operating Segments | Farmer Mac Guaranteed Securities | On-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Not Primary Beneficiary
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 | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying value	36,505	32,041
Maximum exposure to loss	36,414	31,887
Operating Segments | Investment securities | On-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying value	0	0
Maximum exposure to loss	0	0
Operating Segments | Investment securities | On-Balance Sheet: | USDA Guarantees | Variable Interest Entity, Not Primary Beneficiary
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
Debt securities of consolidated trusts held by third parties	0	0
Corporate | Off-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss	0	0
Corporate | Farmer Mac Guaranteed Securities | On-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying value	0	0
Maximum exposure to loss	0	0
Corporate | Investment securities | On-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Carrying value	1,835,688	1,117,203
Maximum exposure to loss	$ 1,829,604	$ 1,120,765