Summary of Significant Accounting Policies - Consolidation of Variable Interest Entities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	$ 7,758,286	$ 7,261,933
Debt securities of consolidated trusts held by third parties	22,350,985	21,795,677
Farmer Mac Guaranteed Securities
Variable Interest Entity [Line Items]
Fair Value	6,138,759	6,947,701
Investment securities:
Variable Interest Entity [Line Items]
Fair Value	3,696,204	3,853,692
Unamortized Premium/(Discount)	0	0
On-Balance Sheet: \| Consolidated VIE
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	977,372	1,287,045
Debt securities of consolidated trusts held by third parties	990,961	1,323,786
On-Balance Sheet: \| Farmer Mac Guaranteed Securities \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	28,265	34,537
Maximum exposure to loss	28,227	34,456
On-Balance Sheet: \| Investment securities: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	2,030,155	1,918,672
Maximum exposure to loss	2,019,108	1,909,535
Off-Balance Sheet: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Maximum exposure to loss	320,242	378,610
Farm & Ranch
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	6,777,749	6,176,438
Borrower remittances	13,600	36,700
USDA Guarantees
Variable Interest Entity [Line Items]
Unamortized Premium/(Discount)		100
Operating Segments \| Farm & Ranch \| On-Balance Sheet: \| Consolidated VIE
Variable Interest Entity [Line Items]
Loans held for investment in consolidated trusts, at amortized cost	977,372	1,287,045
Debt securities of consolidated trusts held by third parties	990,961	1,323,786
Operating Segments \| Farm & Ranch \| On-Balance Sheet: \| Farmer Mac Guaranteed Securities \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	0	0
Maximum exposure to loss	0	0
Operating Segments \| Farm & Ranch \| On-Balance Sheet: \| Investment securities: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	0	0
Maximum exposure to loss	0	0
Operating Segments \| Farm & Ranch \| Off-Balance Sheet: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Maximum exposure to loss	60,349	79,312
Operating Segments \| USDA Guarantees \| On-Balance Sheet: \| Consolidated VIE
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 \| USDA Guarantees \| On-Balance Sheet: \| Farmer Mac Guaranteed Securities \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	28,265	34,537
Maximum exposure to loss	28,227	34,456
Operating Segments \| USDA Guarantees \| On-Balance Sheet: \| Investment securities: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	0	0
Maximum exposure to loss	0	0
Operating Segments \| USDA Guarantees \| Off-Balance Sheet: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Maximum exposure to loss	259,893	299,298
Corporate \| On-Balance Sheet: \| Consolidated VIE
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 \| On-Balance Sheet: \| Farmer Mac Guaranteed Securities \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	0	0
Maximum exposure to loss	0	0
Corporate \| On-Balance Sheet: \| Investment securities: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Fair Value	2,030,155	1,918,672
Maximum exposure to loss	2,019,108	1,909,535
Corporate \| Off-Balance Sheet: \| Unconsolidated VIE
Variable Interest Entity [Line Items]
Maximum exposure to loss	$ 0	$ 0

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

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