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
	Mar. 31, 2018	Mar. 31, 2017
Net income	$ 220,548	$ 149,941
Partially Owned Properties	$ (680)	$ (788)
Dilutive Securities Options	2,355	2,776
Weighted average Common Shares outstanding	383,018	382,280
Net income available to Common Shares	$ 0.57	$ 0.39
Net income available to Common Shares	$ 0.57	$ 0.39
ERPOP [Member]
Net income	$ 220,548	$ 149,941
Partially Owned Properties	(680)	(788)
Allocation to Preference Units	(773)	(773)
Numerator for net income per Unit – basic and diluted	$ 219,095	$ 148,380
Denominator for net income per Unit – basic	380,663	379,504
Dilutive Securities Options	2,355	2,776
Weighted average Common Shares outstanding	383,018	382,280
Net income available to Common Shares	$ 0.57	$ 0.39
Net income available to Common Shares	$ 0.57	$ 0.39