Investments in Tax-Exempt Bonds Sale of TN Bonds (Details) (USD $)	12 Months Ended				3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended			6 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 28, 2013	Jun. 30, 2012 GMF-Madison Tower [Member]	Dec. 31, 2012 GMF-Madison Tower [Member]	Dec. 31, 2011 GMF-Madison Tower [Member]		Jun. 30, 2012 GMF-Warren/Tulane [Member]	Dec. 31, 2012 GMF-Warren/Tulane [Member]	Dec. 31, 2011 GMF-Warren/Tulane [Member]		Jun. 30, 2011 TN Bonds [Member]	Dec. 31, 2012 TN Bonds [Member]	Jun. 30, 2012 TN Bonds [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from the sale of bonds	$ 31,872,522	$ 0	$ 0		$ 4,100,000				$ 12,700,000
Undistributed Net Realized Gain (Loss) on Sale of Properties															668,000
Available-for-sale Security, Purchase Date													Jun. 01, 2011
Debt Instrument, Interest Rate, Stated Percentage				9.00%		0.00%	6.75%	[1]		0.00%	6.75%	[1]
Available-for-sale Security, Maturity Date at a point in time						Dec. 01, 2019	Dec. 01, 2046	[1]		Dec. 01, 2015	Dec. 01, 2046	[1]
Available-for-sale Securities, Debt Securities	$ 1,524,873	$ 774,946												$ 600,000

[1] Bond held by Duetsche Bank in a secured financing transaction, Note 11