Fair Value Measurements (Details Textual) (USD $)	12 Months Ended					12 Months Ended
	Dec. 31, 2012 Property	Dec. 31, 2011 Property	Dec. 31, 2013	Dec. 31, 2013 Cash Flow Hedging [Member]	Dec. 31, 2012 Cash Flow Hedging [Member]	Dec. 31, 2013 Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Face Value			$ 100,900,000
Excepted remaining term of available-for-sale debt securities			7 years 5 months
Amortized cost of the investment in securities	56,300,000		59,800,000
Interest Rate Swap Notional Amount				50,700,000	51,000,000
Weighted Average Remaining Term of interest Rate Swaps						7 years 0 months
Period for reclassification of earnings			12 months
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net						(1,700,000)
Weighted average fixed receive rate under total rate of return swaps						3.43%
Number of properties impaired	9	19
Carrying amount of real estate (held for use or held for sale) prior to recognition of impairment losses	81,800,000	108,200,000
Fair value measurement, impairment losses on real estate	65,800,000	92,300,000
Impairment losses on real estate	16,000,000	15,900,000
Unlevered FCF rate of return	7.39%	7.87%
Estimated fair value of consolidated debt	5,100,000,000		4,500,000,000
Carrying amount of consolidated debt (including amounts reported in liabilities related to assets for sale)	$ 4,700,000,000		$ 4,400,000,000