REAL ESTATE AND ACCUMULATED DEPRECIATION (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Estimated useful lives
Aggregate cost of total real estate for federal income tax purposes	$ 9,901,570
Changes in total real estate assets
Balance, beginning of period	9,288,496	8,661,211	8,360,091
Acquisitions, construction costs and improvements	934,935	864,439	475,211
Dispositions, including impairment loss on planned dispositions	(152,089)	(237,154)	(174,091)
Balance, end of period	10,071,342	9,288,496	8,661,211
Changes in accumulated depreciation
Balance, beginning of period	1,863,466	1,705,567	1,526,604
Depreciation, including discontinued operations	260,094	250,269	232,942
Dispositions	(67,338)	(92,370)	(53,979)
Balance, end of period	$ 2,056,222	$ 1,863,466	$ 1,705,567
Building
Estimated useful lives
Estimated useful lives of assets	30 years
Improvements, upgrades and FF&E | Maximum
Estimated useful lives
Estimated useful lives of assets	7 years