Guarantees - Unpaid Principal Balances by Delinquency Status (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
Financing receivable, not past due	$ 8,401,520	$ 8,315,566
Financing receivables, past due	19,144	6,286
Total	7,341,912	7,261,933
30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	4,733	4,582
60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	261	632
90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	14,150	1,072
Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	6,154,416	6,055,154
Financing receivables, past due	19,144	6,286
Total	6,302,967	6,176,438
Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	4,733	4,582
Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	261	632
Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	14,150	1,072
Rural Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,247,104	2,260,412
Financing receivables, past due	0	0
Total	2,247,104	2,260,412
Rural Utilities | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0	0
Rural Utilities | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0	0
Rural Utilities | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	0	0
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch
Guarantor Obligations [Line Items]
Financing receivable, not past due	2,315,243	2,389,777
Financing receivables, past due	11,142	14,966
Total	2,326,385	2,404,743
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	3,901	2,189
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	332	1,344
LTSPCs and Farmer Mac Guaranteed Securities | Farm & Ranch | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	6,909	11,433
LTSPCs and Farmer Mac Guaranteed Securities | Rural Utilities
Guarantor Obligations [Line Items]
Total	557,333	556,425
LTSPCs | Rural Utilities
Guarantor Obligations [Line Items]
Financing receivable, not past due	557,333	556,425
Financing receivables, past due	0	0
Total	557,333	556,425
LTSPCs | Rural Utilities | 30-59 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0	0
LTSPCs | Rural Utilities | 60-89 Days
Guarantor Obligations [Line Items]
Financing receivables, past due	0	0
LTSPCs | Rural Utilities | 90 Days and Greater
Guarantor Obligations [Line Items]
Financing receivables, past due	$ 0	$ 0