Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income from continuing operations	$ 205,375	$ 231,252	$ 693,948	$ 430,142
Allocation to Noncontrolling Interests – Operating Partnership, net	(7,775)	(8,740)	(26,178)	(16,216)
Net (income) attributable to Noncontrolling Interests – Partially Owned Properties	(986)	(708)	(2,473)	(1,800)
Preferred distributions	(833)	(1,037)	(2,557)	(3,109)
Premium on redemption of Preferred Shares	0	0	(2,789)	0
Income from continuing operations available to Common Shares, net of Noncontrolling Interests	195,781	220,767	659,951	409,017
Discontinued operations, net of Noncontrolling Interests	78	(60)	337	1,443
Numerator for net income per share – basic	195,859	220,707	660,288	410,460
Income from continuing operations available to Common Shares	203,556	229,507	686,129	425,233
Discontinued operations, net	81	(62)	350	1,500
Numerator for net income per share – diluted	$ 203,637	$ 229,445	$ 686,479	$ 426,733
Denominator for net income per share – basic	363,579	361,409	363,386	360,900
Effect of dilutive securities - OP Units	13,568	13,707	13,584	13,726
Effect of dilutive securities - Long-term compensation shares/units	3,516	2,838	3,453	2,602
Denominator for net income per share – diluted	380,663	377,954	380,423	377,228
Net income per share – basic	$ 0.54	$ 0.61	$ 1.82	$ 1.14
Net income per share – diluted	0.53	0.61	1.80	1.13
Income from continuing operations available to Common Shares	0.54	0.61	1.82	1.13
Net income per share - basic - Discontinued operations, net of Noncontrolling Interests	0.00	0.00	0.00	0.01
Income from continuing operations available to Common Shares	0.53	0.61	1.80	1.13
Net income per share - diluted - discontinued operations, net	$ 0.00	$ 0.00	$ 0.00	$ 0.00
ERPOP [Member]
Income from continuing operations	$ 205,375	$ 231,252	$ 693,948	$ 430,142
Net (income) attributable to Noncontrolling Interests – Partially Owned Properties	(986)	(708)	(2,473)	(1,800)
Allocation to Preference Units	(833)	(1,037)	(2,557)	(3,109)
Premium on redemption of Preferred Shares	0	0	(2,789)	0
Discontinued operations, net	$ 81	$ (62)	$ 350	$ 1,500
Effect of dilutive securities - Long-term compensation shares/units	3,516	2,838	3,453	2,602
Denominator for net income per share – diluted	380,663	377,954	380,423	377,228
Net income per share – basic	$ 0.54	$ 0.61	$ 1.82	$ 1.14
Net income per share – diluted	0.53	0.61	1.80	1.13
Income from continuing operations available to Common Shares	0.54	0.61	1.82	1.13
Income from continuing operations available to Common Shares	$ 0.53	$ 0.61	$ 1.80	$ 1.13
Income from continuing operations available to Units	$ 203,556	$ 229,507	$ 686,129	$ 425,233
Numerator for net income per Unit – basic and diluted	$ 203,637	$ 229,445	$ 686,479	$ 426,733
Denominator for net income per Unit – basic	377,147	375,116	376,970	374,626
Net income per Unit - basic - Discontinued operations, net	$ 0.00	$ 0.00	$ 0.00	$ 0.01
Net income per Unit - diluted - Discontinued operations, net	$ 0.00	$ 0.00	$ 0.00	$ 0.00