Equity - Offering (Details) (Farmer Mac II LLC [Member], USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended				12 Months Ended
	Jan. 25, 2010 Private Offering	Jan. 25, 2010 GSE Preferred Stock	Jan. 25, 2010 GSE Preferred Stock Private Offering	Sep. 30, 2012 GSE Preferred Stock Private Offering	Dec. 31, 2012 Issuance To But Excluding March 30, 2015 GSE Preferred Stock	Dec. 31, 2012 March 30, 2015 To But Excluding March 30, 2020 GSE Preferred Stock	Dec. 31, 2012 March 30, 2020 and Thereafter GSE Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Consideration received on private offering	$ 250.0
Number of shares issued in private offering			250,000
Preferred Stock, Liquidation Preference Per Share				$ 1,000
Preferred stock dividend rate					8.875%	10.875%
Preferred stock variable dividend rate							8.211%
Sale of Stock, issuance costs incurred		$ 8.1