Related Party Transactions - Zions (Details) - Zions First National Bank [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Related Party's percent of Farmer Mac Total Outstanding Book of Business	4.70%	5.00%
Related Party Transaction, Expenses from Transactions with Related Party	$ 11,600	$ 11,500	$ 9,900
Sale of Farmer Mac Guaranteed Securities [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 68,721	$ 128,924	$ 273,586
Common Class A [Member]
Related Party Transaction [Line Items]
Common Stock Ownership Percentage by a Related Party	31.20%
Farm & Ranch [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's Percent of Total Program Loans	11.90%	11.20%	15.90%
Related Party Transaction, Related Party's percent of total Program	8.20%	7.50%	11.20%
USDA Guarantee [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's percent of total Program	4.20%	3.80%	3.40%
Mortgages [Member] | Farm & Ranch [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 114,719	$ 126,449	$ 153,140
USDA Securities [Member] | USDA Guarantee [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 19,120	$ 20,368	$ 16,600