Earning Per Share and Earnings Per Unit - Computation of Net Income per Unit Basic and Net Income per Unit Diluted for Operating Partnership (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 118,410	$ 204,160	$ 338,958	$ 354,101
Partially Owned Properties	$ (509)	$ (765)	$ (1,189)	$ (1,553)
Dilutive Securities Options	2,628	2,959	2,495	2,886
Weighted average Common Shares outstanding	383,423	382,692	383,224	382,505
Net income available to Common Shares	$ 0.31	$ 0.53	$ 0.88	$ 0.92
Net income available to Common Shares	$ 0.31	$ 0.53	$ 0.88	$ 0.92
ERPOP [Member]
Net income	$ 118,410	$ 204,160	$ 338,958	$ 354,101
Partially Owned Properties	(509)	(765)	(1,189)	(1,553)
Allocation to Preference Units	(772)	(773)	(1,545)	(1,546)
Numerator for net income per Unit – basic and diluted	$ 117,129	$ 202,622	$ 336,224	$ 351,002
Denominator for net income per Unit – basic	380,795	379,733	380,729	379,619
Dilutive Securities Options	2,628	2,959	2,495	2,886
Weighted average Common Shares outstanding	383,423	382,692	383,224	382,505
Net income available to Common Shares	$ 0.31	$ 0.53	$ 0.88	$ 0.92
Net income available to Common Shares	$ 0.31	$ 0.53	$ 0.88	$ 0.92