Related Party Transactions - Zions (Details) - Zions First National Bank [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Related Party's percent of Farmer Mac Total Outstanding Book of Business	5.30%	5.70%
Related Party Transaction, Expenses from Transactions with Related Party	$ 9,900	$ 9,300	$ 8,400
Medium-term Notes [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	0	0	5,000
Sale of Farmer Mac Guaranteed Securities [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 273,586	$ 255,338	$ 147,234
Farm & Ranch [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's Percent of Total Program Loans	15.90%	23.90%	22.30%
Related Party Transaction, Related Party's percent of total Program	11.20%	15.20%	14.60%
USDA Guarantee [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Related Party's percent of total Program	3.40%	3.60%	12.40%
Mortgages [Member] | Farm & Ranch [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 153,140	$ 178,890	$ 155,808
USDA Securities [Member] | USDA Guarantee [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	16,600	13,718	42,637
On-balance sheet [Member] | Farmer Mac Guaranteed Securities [Member] | Institutional Credit [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	$ 0	$ 0	$ 50,237
Common Class A, Voting [Member]
Related Party Transaction [Line Items]
Common Stock Ownership Percentage by a Related Party	31.20%