Condensed Consolidated Statements Of Equity - USD ($) $ in Thousands	Total	Common shares of beneficial interest	Additional paid-in capital	Distributions in excess of net income	Treasury shares, at cost	Accumulated other comprehensive loss	Non-controlling interests
Beginning balance at Dec. 31, 2015	$ 2,892,896	$ 976	$ 3,662,864	$ (458,577)	$ (386,793)	$ (1,913)	$ 76,339
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	796,146			778,930			17,216
Other comprehensive income	97					97
Common Shares Issued	0
Net share awards	18,912		9,175		9,737
Employee share purchase plan	1,298		757		541
Common share options exercised	3,921		1,003		2,918
Change in classification of deferred compensation plan	(10,110)		(10,110)
Change in redemption value of non-qualified share awards	(8,154)			(8,154)
Diversification of share awards within deferred compensation plan	25,406		11,913	13,493
Conversions of operating partnership units	(80)		217				(297)
Cash distributions declared to equity holders	(599,293)			(587,016)			(12,277)
Other	(11)	2	(13)
Ending balance at Sep. 30, 2016	3,121,028	978	3,675,806	(261,324)	(373,597)	(1,816)	80,981
Beginning balance at Dec. 31, 2015	2,892,896	976	3,662,864	(458,577)	(386,793)	(1,913)	76,339
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Diversification of share awards within deferred compensation plan	25,400
Ending balance at Dec. 31, 2016	3,095,553	978	3,678,277	(289,180)	(373,339)	(1,863)	80,680
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	111,778			108,433			3,345
Other comprehensive income	1,856					1,856
Common Shares Issued	445,038	48	444,990
Net share awards	18,985		10,844		8,141
Employee share purchase plan	1,183		721		462
Common share options exercised	77		77
Change in classification of deferred compensation plan	(10,690)		(10,690)
Change in redemption value of non-qualified share awards	(8,469)			(8,469)
Diversification of share awards within deferred compensation plan	23,181		10,121	13,060
Conversions of operating partnership units	0		117				(117)
Cash distributions declared to equity holders	(211,666)			(207,428)			(4,238)
Other	(249)	2	(251)
Ending balance at Sep. 30, 2017	$ 3,466,577	$ 1,028	$ 4,134,206	$ (383,584)	$ (364,736)	$ (7)	$ 79,670