Equity Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended						3 Months Ended					12 Months Ended			0 Months Ended
	Mar. 31, 2013 class_of_stock	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Mar. 31, 2013 Common Class A [Member]	Mar. 31, 2013 Series A Preferred Stock [Member]	Jan. 17, 2013 Series A Preferred Stock [Member]	Dec. 31, 2012 Series A Preferred Stock [Member]	Mar. 31, 2013 Series C Preferred Stock	Dec. 31, 2012 Series C Preferred Stock	Dec. 31, 2012 Issuance To But Excluding January 1 following fifth year [Member] Series C Preferred Stock	Dec. 31, 2012 From January 1 following fifth year of issuance to but excluding January 1 following tenth year [Member] Series C Preferred Stock	Dec. 31, 2012 From January 1 following tenth year of issuance [Member] Series C Preferred Stock	Jan. 25, 2010 Farmer Mac II LLC [Member] Preferred Stock [Member]
Class of Stock [Line Items]
Number of Classes of Common Stock	3
Common Stock, Maximum Ownership Percentage by a Benefical Owner						33.00%
Common stock dividend, per share, cash paid	$ 0.12	$ 0.10	$ 0.10	$ 0.10	$ 0.10
Preferred Stock, shares issued							2,400,000	2,400,000	0	0	57,578
Preferred Stock, Dividend Rate, Percentage							5.875%
Payments of Stock Issuance Costs							$ 1.7								$ 8.1
Preferred Stock, Par or Stated Value Per Share							$ 25	$ 25	$ 0	$ 0	$ 1,000
Preferred Stock, Liquidation Preference Per Share								$ 25
Preferred Stock, shares outstanding							2,400,000		0	0	57,578
Preferred Stock, Dividend Rate, Per-Dollar-Amount												$ 0.050	$ 0.070	$ 0.090