Related Party Transactions - Schedule of Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Zions Bancorporation, National Association | Sales of Farmer Mac Guaranteed Securities
Related Party Transaction [Line Items]
Sales of Farmer Mac Guaranteed Securities	$ 41,247	$ 163,134	$ 68,721
Zions Bancorporation, National Association | USDA Guarantee | USDA Securities:
Related Party Transaction [Line Items]
Unpaid principal balance	10,764	8,875	19,120
Zions Bancorporation, National Association | Mortgages | Farm & Ranch
Related Party Transaction [Line Items]
Unpaid principal balance	177,143	129,040	114,719
CFC
Related Party Transaction [Line Items]
Unpaid principal balance	542,443	660,000	986,645
CFC | AgVantage Securities | Guarantee Obligations
Related Party Transaction [Line Items]
Unpaid principal balance	250,000	575,000	675,000
CFC | AgVantage Securities | Revolving Credit Facility | Off-balance sheet
Related Party Transaction [Line Items]
Unpaid principal balance	19,500	0	0
CFC | AgVantage Securities | US Government-sponsored Enterprises Debt Securities | Off-balance sheet
Related Party Transaction [Line Items]
Unpaid principal balance	0	0	300,000
CFC | Real Estate Loan
Related Party Transaction [Line Items]
Unpaid principal balance	$ 272,943	$ 85,000	$ 11,645