Guarantees - Unpaid Principal Balances by Delinquency Status (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Financing receivable, not past due	$ 7,578,530
Financing receivables, past due	23,420
Loans held for investment, at amortized cost	6,469,997	$ 5,390,977
30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	7,892
60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	15,528
Rural  Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,101,568
Financing receivables, past due	0
Loans held for investment, at amortized cost	2,101,568
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
Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	5,476,962
Financing receivables, past due	23,420
Loans held for investment, at amortized cost	5,617,512
Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	7,892
Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0
Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	15,528
Farm & Ranch | 90 Days and Greater | Payment Deferral, CARES Act
Guarantor Obligations [Line Items]
Financing receivables, past due	82,200
LTSPCs | Rural  Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	590,053
Financing receivables, past due	0
Loans held for investment, at amortized cost	590,053
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
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,374,988
Financing receivables, past due	25,350
Loans held for investment, at amortized cost	2,400,338
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | Payment Deferral, CARES Act
Guarantor Obligations [Line Items]
Financing receivable, not past due	109,500
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	9,947
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	12,587
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	$ 2,816