Guarantees - Unpaid Principal Balances by Delinquency Status (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Financing receivable, not past due	$ 7,826,189
Financing receivables, past due	11,051	$ 57,700
Loans held for investment, at amortized cost	6,825,061	5,390,977
30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	3,513
60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	637
90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	6,901
Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	5,716,834
Financing receivables, past due	11,051
Loans held for investment, at amortized cost	5,857,324
Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	3,513
Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	637
Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	6,901	$ 57,719
Farm & Ranch | 90 Days and Greater | Payment Deferral, CARES Act
Guarantor Obligations [Line Items]
Financing receivables, past due	105,300
Rural  Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,109,355
Financing receivables, past due	0
Loans held for investment, at amortized cost	2,109,355
Rural  Utilities | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
Rural  Utilities | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
Rural  Utilities | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	0
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,352,454
Financing receivables, past due	39,571
Loans held for investment, at amortized cost	2,392,025
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | Payment Deferral, CARES Act
Guarantor Obligations [Line Items]
Financing receivable, not past due	185,400
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	2,934
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	22,690
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	13,947
LTSPCs | Rural  Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	575,954
Financing receivables, past due	0
Loans held for investment, at amortized cost	575,954
LTSPCs | Rural  Utilities | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
LTSPCs | Rural  Utilities | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
LTSPCs | Rural  Utilities | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	$ 0