REAL ESTATE AND ACCUMULATED DEPRECIATION (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Estimated useful lives
Aggregate cost of total real estate for federal income tax purposes	$ 21,271
Changes in total real estate assets
Balance, beginning of period	20,776,626	$ 19,268,099	$ 17,849,316
Acquisitions, construction costs and improvements	1,526,516	1,788,515	1,667,989
Dispositions, including impairment loss on planned dispositions	(367,206)	(279,988)	(249,206)
Balance, end of period	21,935,936	20,776,626	19,268,099
Changes in accumulated depreciation
Balance, beginning of period	3,743,632	3,325,790	2,913,576
Depreciation, including discontinued operations	584,150	531,434	477,923
Dispositions	(109,403)	(113,592)	(65,709)
Balance, end of period	$ 4,218,379	$ 3,743,632	$ 3,325,790
Building
Estimated useful lives
Estimated useful lives of assets (in years)	30 years
Improvements, upgrades and FF&E
Estimated useful lives
Estimated useful lives of assets (in years)	7 years