Schedule III Real Estate Assets and Accumulated Depreciation Schedule III, Movement in Real Estate Assets and Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2008
Reconciliation of Carrying Amount of Real Estate Investments and Accumulated Depreciation [Roll Forward]
Balance, beginning of period	$ 7,767,819	$ 8,611,331		$ 8,600,875
Additions and improvements	217,161	201,359	170,696
Acquisitions of real estate assets	474,623	11,197	72,907
Disposals and deconsolidations	(108,554)	(999,685)	(183,762)
Transfers from real estate assets	808	(476)	(23,950)
Impairment of real estate assets	(50,844)	(55,907)	(25,435)
Balance, end of period	8,301,013	7,767,819	8,611,331	8,600,875
Accumulated depreciation, beginning of period	1,762,149	1,721,194		1,505,840
Depreciation expense	247,702	260,847	268,386
Accumulated depreciation on real estate assets sold, retired, or deconsolidated	(37,820)	(219,892)	(53,032)
Accumulated depreciation, end of period	$ 1,972,031	$ 1,762,149	$ 1,721,194	$ 1,505,840