SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in total cost of properties
Balance at beginning of year	$ 7,090,078	$ 6,825,627	$ 6,352,288
Acquisitions and capital expenditures	665,300	277,432	496,573
Dispositions	(71,319)	(12,981)	(15,288)
Loss on asset impairment			(7,946)
Balance at close of year	7,684,059	7,090,078	6,825,627
Change in accumulated depreciation
Balance at beginning of year	1,727,032	1,513,482	1,324,728
Depreciation expense	238,941	222,249	204,042
Dispositions	(27,150)	(8,699)	(15,288)
Balance at close of year	1,938,823	$ 1,727,032	$ 1,513,482
Tax basis for federal income tax purpose	$ 7,954,248