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, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income	$ 962,501	$ 1,009,708	$ 685,192
Net (income) loss attributable to Noncontrolling Interests – Partially Owned Properties	$ (14,855)	$ (3,297)	$ (2,718)
Dilutive Securities Options	1,080	2,965	2,774
Denominator for net income per share – diluted	385,874	386,333	383,695
Net income per Unit – basic	$ 2.45	$ 2.61	$ 1.78
Net income per Unit – diluted	$ 2.45	$ 2.60	$ 1.77
ERPOP [Member]
Net income	$ 962,501	$ 1,009,708	$ 685,192
Net (income) loss attributable to Noncontrolling Interests – Partially Owned Properties	(14,855)	(3,297)	(2,718)
Allocation to Preference Units	(3,090)	(3,090)	(3,090)
Numerator for net income per Unit – basic and diluted	$ 944,556	$ 1,003,321	$ 679,384
Denominator for net income per Unit – basic	384,794	383,368	380,921
Dilutive Securities Options	1,080	2,965	2,774
Denominator for net income per share – diluted	385,874	386,333	383,695
Net income per Unit – basic	$ 2.45	$ 2.61	$ 1.78
Net income per Unit – diluted	$ 2.45	$ 2.60	$ 1.77