Investments in Tax-Exempt Bonds Certain Terms of Tax-Exempt Mortgage Revenue Bonds (Details) (USD $)				6 Months Ended	12 Months Ended																																		12 Months Ended														12 Months Ended					12 Months Ended				12 Months Ended
	Feb. 28, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2012 Arbors at Hickory Ridge [Member]	Dec. 31, 2012 Arbors at Hickory Ridge [Member]	Dec. 31, 2012 Ashley Square [Member]		Dec. 31, 2011 Ashley Square [Member]		Dec. 31, 2012 Autumn Pines [Member]		Dec. 31, 2011 Autumn Pines [Member]		Dec. 31, 2012 Bella Vista [Member]		Dec. 31, 2011 Bella Vista [Member]		Dec. 31, 2012 Bridle Ridge [Member]		Dec. 31, 2011 Bridle Ridge [Member]		Dec. 31, 2012 Brookstone [Member]		Dec. 31, 2011 Brookstone [Member]		Dec. 31, 2012 Cross Creek [Member]		Dec. 31, 2011 Cross Creek [Member]		Dec. 31, 2012 GMF-Madison Tower [Member]	Dec. 31, 2011 GMF-Madison Tower [Member]		Dec. 31, 2012 GMF-Warren/Tulane [Member]	Dec. 31, 2011 GMF-Warren/Tulane [Member]		Dec. 31, 2012 Iona Lakes [Member]	Dec. 31, 2011 Iona Lakes [Member]	Feb. 28, 2013 Iona Lakes [Member]	Dec. 31, 2012 Runnymede [Member]		Dec. 31, 2011 Runnymede [Member]		Dec. 31, 2012 Southpark [Member]		Dec. 31, 2011 Southpark [Member]		Dec. 31, 2012 Vantage at Judson [Member]	Dec. 31, 2012 Lost Creek [Member]		Dec. 31, 2011 Lost Creek [Member]		Jun. 30, 2010 Lost Creek [Member]	Dec. 31, 2012 Woodlynn Village [Member]		Dec. 31, 2011 Woodlynn Village [Member]		Feb. 28, 2013 Series A [Member]	Dec. 31, 2012 Series A [Member] Woodland Park [Member]	Dec. 31, 2011 Series A [Member] Woodland Park [Member]	Feb. 28, 2013 Series B [Member]	Dec. 31, 2012 Series B [Member] Vantage at Judson [Member]	Dec. 31, 2012 Series B [Member] Woodland Park [Member]	Dec. 31, 2011 Series B [Member] Woodland Park [Member]
Available-for-sale Security, Maturity Date at a point in time				Apr. 01, 2026	Dec. 01, 2049	Dec. 01, 2025	[1]	Dec. 01, 2025	[1]	Oct. 01, 2046	[2]	Oct. 01, 2046	[2]	Apr. 01, 2046	[1]	Apr. 01, 2046	[1]	Jan. 01, 2043	[1]	Jan. 01, 2043	[1]	May 01, 2040	[1]	May 01, 2040	[1]	Mar. 01, 2049	[1]	Mar. 01, 2049	[1]	Dec. 01, 2019	Dec. 01, 2046	[2]	Dec. 01, 2015	Dec. 01, 2046	[2]	Apr. 01, 2030	Apr. 01, 2030		Oct. 01, 2042	[1]	Oct. 01, 2042	[1]	Dec. 01, 2049	[1]	Dec. 01, 2049	[1]	Feb. 01, 2053	Jun. 01, 2041	[1]	Jun. 01, 2041	[1]		Nov. 01, 2042	[1]	Nov. 01, 2042	[1]		Nov. 01, 2047	Nov. 01, 2047			Nov. 01, 2047	Nov. 01, 2047
Debt Instrument, Interest Rate, Stated Percentage	9.00%			7.98%	6.25%	6.25%	[1]	6.25%	[1]	5.80%	[2]	5.80%	[2]	6.15%	[1]	6.15%	[1]	6.00%	[1]	6.00%	[1]	5.45%	[1]	5.45%	[1]	6.15%	[1]	6.15%	[1]	0.00%	6.75%	[2]	0.00%	6.75%	[2]	6.90%	6.90%	5.00%	6.00%	[1]	6.00%	[1]	6.13%	[1]	6.13%	[1]	9.00%	6.25%	[1]	6.25%	[1]		6.00%	[1]	6.00%	[1]	6.00%	6.00%	6.00%	9.00%	0.00%	8.00%	8.00%
Available-for-sale Securities, at Par Value		$ 146,806,203	$ 145,907,502	$ 10,000,000	$ 11,450,000	$ 5,260,000	[1]	$ 5,308,000	[1]	$ 13,220,000	[2]	$ 13,325,000	[2]	$ 6,600,000	[1]	$ 6,650,000	[1]	$ 7,765,000	[1]	$ 7,815,000	[1]	$ 9,416,794	[1]	$ 9,490,809	[1]	$ 8,568,409	[1]	$ 8,634,693	[1]		$ 3,810,000	[2]		$ 11,815,000	[2]	$ 15,535,000	$ 15,720,000		$ 10,605,000	[1]	$ 10,685,000	[1]	$ 13,900,000	[1]	$ 14,000,000	[1]	$ 6,049,000	$ 18,315,000	[1]	$ 18,500,000	[1]	$ 18,500,000	$ 4,460,000	[1]	$ 4,492,000	[1]		$ 15,013,000	$ 15,013,000		$ 26,687,000	$ 649,000	$ 649,000

[1] Bonds owned by ATAX TEBS I, LLC, Note 11

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