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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 223,846	$ 144,196	$ 562,804	$ 498,297
Partially Owned Properties	$ (750)	$ (801)	$ (1,939)	$ (2,354)
Dilutive Securities Options	2,972	3,039	2,642	2,924
Weighted average Common Shares outstanding	383,884	382,945	383,433	382,640
Net income available to Common Shares	$ 0.58	$ 0.37	$ 1.46	$ 1.30
Net income available to Common Shares	$ 0.58	$ 0.37	$ 1.46	$ 1.29
ERPOP [Member]
Net income	$ 223,846	$ 144,196	$ 562,804	$ 498,297
Partially Owned Properties	(750)	(801)	(1,939)	(2,354)
Allocation to Preference Units	(773)	(772)	(2,318)	(2,318)
Numerator for net income per Unit – basic and diluted	$ 222,323	$ 142,623	$ 558,547	$ 493,625
Denominator for net income per Unit – basic	380,912	379,906	380,791	379,716
Dilutive Securities Options	2,972	3,039	2,642	2,924
Weighted average Common Shares outstanding	383,884	382,945	383,433	382,640
Net income available to Common Shares	$ 0.58	$ 0.37	$ 1.46	$ 1.30
Net income available to Common Shares	$ 0.58	$ 0.37	$ 1.46	$ 1.29