Earnings 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	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 1,009,708	$ 685,192	$ 628,381
Partially Owned Properties	$ (3,297)	$ (2,718)	$ (2,323)
Dilutive Securities Options	2,965	2,774	2,809
Denominator for net income per share – diluted	386,333	383,695	382,678
Net income per Unit – basic	$ 2.61	$ 1.78	$ 1.64
Net income per Unit – diluted	$ 2.60	$ 1.77	$ 1.63
ERPOP [Member]
Net income	$ 1,009,708	$ 685,192	$ 628,381
Partially Owned Properties	(3,297)	(2,718)	(2,323)
Allocation to Preference Units	(3,090)	(3,090)	(3,091)
Numerator for net income per Unit – basic and diluted	$ 1,003,321	$ 679,384	$ 622,967
Denominator for net income per Unit – basic	383,368	380,921	379,869
Dilutive Securities Options	2,965	2,774	2,809
Denominator for net income per share – diluted	386,333	383,695	382,678
Net income per Unit – basic	$ 2.61	$ 1.78	$ 1.64
Net income per Unit – diluted	$ 2.60	$ 1.77	$ 1.63