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Guarantees - Unpaid Principal Balances by Delinquency Status (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Financing receivable, not past due	$ 6,996,039
Financing receivables, past due	29,997
Recorded investment of loans on nonaccrual status	122,072	$ 87,781
Gross financing receivables	7,148,108
30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	4,821
60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	3,024
90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	22,152
Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	5,206,313
Financing receivables, past due	29,997
Recorded investment of loans on nonaccrual status	122,072
Gross financing receivables	5,358,382
Farm & Ranch \| 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	4,821
Farm & Ranch \| 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	3,024
Farm & Ranch \| 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	22,152
Rural Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	1,789,726
Financing receivables, past due	0
Recorded investment of loans on nonaccrual status	0
Gross financing receivables	1,789,726
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	2,434,531
Financing receivables, past due	18,681
Gross financing receivables	2,453,212
LTSPCs and Farmer Mac Guaranteed Securities \| Farm & Ranch \| 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	6,183
LTSPCs and Farmer Mac Guaranteed Securities \| Farm & Ranch \| 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	7,893
LTSPCs and Farmer Mac Guaranteed Securities \| Farm & Ranch \| 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	4,605
LTSPCs \| Rural Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	595,685
Financing receivables, past due	0
Gross financing receivables	595,685
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