Summary of Significant Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total	$ 7,261,933	$ 5,390,977
Debt securities of consolidated trusts held by third parties	21,795,677	19,091,215
Farm & Ranch
Variable Interest Entity [Line Items]
Total	6,176,438
Borrower remittances	36,700	15,600
USDA Guarantees
Variable Interest Entity [Line Items]
Unamortized Premium/(Discount)	(100)	(200)
On-Balance Sheet:
Variable Interest Entity [Line Items]
Total		5,276,557
On-Balance Sheet: | Consolidated VIEs:
Variable Interest Entity [Line Items]
Total	1,287,045	1,600,917
Debt securities of consolidated trusts held by third parties	1,323,786	1,616,504
On-Balance Sheet: | Farm & Ranch
Variable Interest Entity [Line Items]
Total		5,276,557
Off-balance sheet
Variable Interest Entity [Line Items]
Total		2,500,393
Off-balance sheet | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Maximum exposure to loss	378,610	496,538
Farmer Mac Guaranteed Securities
Variable Interest Entity [Line Items]
Carrying value	6,947,701	7,143,025
Farmer Mac Guaranteed Securities | On-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	34,537	32,041
Maximum exposure to loss	34,456	31,887
Investment securities:
Variable Interest Entity [Line Items]
Carrying value	3,853,692	2,959,843
Unamortized Premium/(Discount)	17,084	1,382
Investment securities: | On-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	1,918,672	1,117,203
Maximum exposure to loss	1,909,535	1,120,765
Operating Segments | On-Balance Sheet: | Farm & Ranch | Consolidated VIEs:
Variable Interest Entity [Line Items]
Total	1,287,045	1,600,917
Debt securities of consolidated trusts held by third parties	1,323,786	1,616,504
Operating Segments | On-Balance Sheet: | USDA Guarantees | Consolidated VIEs:
Variable Interest Entity [Line Items]
Total	0	0
Debt securities of consolidated trusts held by third parties	0	0
Operating Segments | Off-balance sheet | Farm & Ranch | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Maximum exposure to loss	79,312	107,322
Operating Segments | Off-balance sheet | USDA Guarantees | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Maximum exposure to loss	299,298	389,216
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	34,537	32,041
Maximum exposure to loss	34,456	31,887
Operating Segments | Investment 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 | Investment 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: | Consolidated VIEs:
Variable Interest Entity [Line Items]
Total	0	0
Debt securities of consolidated trusts held by third parties	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 | Investment securities: | On-Balance Sheet: | Unconsolidated VIEs:
Variable Interest Entity [Line Items]
Carrying value	1,918,672	1,117,203
Maximum exposure to loss	$ 1,909,535	$ 1,120,765