Summary of Significant Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	$ 6,469,997	$ 5,390,977
Notes payable	21,421,550	19,098,648
Farm & Ranch
Variable Interest Entity [Line Items]
Loans held for investment, at amortized cost	5,617,512
Borrower remittances	40,900	15,600
USDA Guarantees
Variable Interest Entity [Line Items]
Unamortized premiums and discounts	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	1,436,090	1,600,917
Notes payable	1,476,964	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	420,534	496,538
Farmer Mac Guaranteed Securities
Variable Interest Entity [Line Items]
Available-for-sale, at fair value	7,898,387	7,143,025
Farmer Mac Guaranteed Securities | On-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Available-for-sale, at fair value	32,615	32,041
Maximum exposure to loss	32,537	31,887
Debt Securities
Variable Interest Entity [Line Items]
Available-for-sale, at fair value	3,467,378	2,959,843
Unamortized premiums and discounts	(5,792)	(1,382)
Debt Securities | On-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Available-for-sale, at fair value	1,651,031	1,117,203
Maximum exposure to loss	1,648,328	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	1,436,090	1,600,917
Notes payable	1,476,964	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
Notes payable	0	0
Operating Segments | Off-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss	90,225	107,322
Operating Segments | Off-Balance Sheet: | USDA Guarantees | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum exposure to loss	330,309	389,216
Operating Segments | Farmer Mac Guaranteed Securities | On-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Available-for-sale, at fair 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]
Available-for-sale, at fair value	32,615	32,041
Maximum exposure to loss	32,537	31,887
Operating Segments | Debt Securities | On-Balance Sheet: | Farm & Ranch | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Available-for-sale, at fair value	0	0
Maximum exposure to loss	0	0
Operating Segments | Debt Securities | On-Balance Sheet: | USDA Guarantees | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Available-for-sale, at fair 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
Notes payable	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]
Available-for-sale, at fair value	0	0
Maximum exposure to loss	0	0
Corporate | Debt Securities | On-Balance Sheet: | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Available-for-sale, at fair value	1,651,031	1,117,203
Maximum exposure to loss	$ 1,648,328	$ 1,120,765