Fair Value Measurements (Details Textual) (USD $)	3 Months Ended
	Mar. 31, 2012 Property Y	Mar. 31, 2011 Property	Dec. 31, 2011
Fair Value Measurements (Textual) [Abstract]
Excepted remaining term of available-for-sale debt securities	9
Amortized cost of the investment in securities	$ 54,000,000		$ 53,200,000
Carrying amount of real estate (held for use or held for sale) prior to recognition of impairment losses	19,900,000		10,700,000
Estimated aggregate fair value of notes receivable	106,800,000		107,900,000
Carrying amounts of notes receivable	116,200,000		117,900,000
Estimated aggregate fair value of consolidated debt (including amounts reported in liabilities related to assets held for sale)	5,500,000,000		5,400,000,000
Carrying amount of consolidated debt (including amounts reported in liabilities related to assets for sale)	5,200,000,000		5,200,000,000
Face value of investment in debt securities classsified as available for sale	100,900,000
Fair value measurement, impairment losses on real estate	13,700,000	7,600,000
Total gain(loss), impairment losses on real estate	$ 6,200,000	$ 3,100,000
Number of properties impaired	3	3
Unlevered FCF rate of return	Less than 6.5%	Less than 4.6%