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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