Schedule III - Real Estate and Accumulated Depreciation (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Balance at January 1	$ 340,073,911	$ 339,492,832	$ 320,444,168
Construction and acquisition cost	97,418,031	31,219,239	39,107,853
Impairment charge	0	(13,500,000)	(8,140,000)
Disposition of real estate	(38,680,112)	(17,138,160)	(11,919,189)
Balance at December 31	$ 398,811,830	$ 340,073,911	$ 339,492,832