SCHEDULE III 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
Changes in total real estate assets
Balance, beginning of year	$ 5,042,324	$ 4,377,730	$ 3,915,979
New property acquisitions	297,650	511,308	346,770
Additions	226,348	160,109	146,645
Disposals associated with deconsolidation of the VIE (1)			(27,464)
Disposals and retirements	(111,096)	(6,823)	(4,200)
Balance, end of year	5,455,226	5,042,324	4,377,730
Changes in accumulated depreciation
Balance, beginning of year	983,759	841,801	733,142
Depreciation	166,339	143,093	126,249
Disposals associated with deconsolidation of the VIE			(13,627)
Disposals and retirements	(41,258)	(1,135)	(3,963)
Balance, end of year	$ 1,108,840	$ 983,759	$ 841,801
Land improvements | Minimum
Estimated useful lives
Estimated useful lives of assets	3 years
Land improvements | Maximum
Estimated useful lives
Estimated useful lives of assets	20 years
Buildings and improvements | Minimum
Estimated useful lives
Estimated useful lives of assets	3 years
Buildings and improvements | Maximum
Estimated useful lives
Estimated useful lives of assets	40 years
Furniture, fixtures and equipment | Minimum
Estimated useful lives
Estimated useful lives of assets	5 years
Furniture, fixtures and equipment | Maximum
Estimated useful lives
Estimated useful lives of assets	10 years
Computer software
Estimated useful lives
Estimated useful lives of assets	5 years