Earning Per Share and Earnings Per Unit - Computation of Net Income per Share Basic and Net Income per Share Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 118,410	$ 204,160	$ 338,958	$ 354,101
Allocation to Noncontrolling Interests – Operating Partnership	(4,299)	(7,354)	(12,358)	(12,765)
Partially Owned Properties	(509)	(765)	(1,189)	(1,553)
Preferred distributions	(772)	(773)	(1,545)	(1,546)
Net income available to Common Shares	112,830	195,268	323,866	338,237
Numerator for net income per share – diluted	$ 117,129	$ 202,622	$ 336,224	$ 351,002
Weighted average Common Shares outstanding	367,930	366,820	367,865	366,713
Dilutive Op Units	12,865	12,913	12,864	12,906
Dilutive Securities Options	2,628	2,959	2,495	2,886
Weighted average Common Shares outstanding	383,423	382,692	383,224	382,505
Net income available to Common Shares	$ 0.31	$ 0.53	$ 0.88	$ 0.92
Net income available to Common Shares	$ 0.31	$ 0.53	$ 0.88	$ 0.92