Condensed Consolidated Statements Of Equity (USD $)	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, 2012	$ 2,626,708,000	$ 962,000	$ 3,587,505,000	$ (598,951,000)	$ (425,355,000)	$ (1,062,000)	$ 63,609,000
Net income	211,172,000			206,368,000			4,804,000
Other comprehensive income (loss)	41,000					41,000
Common shares issued	40,098,000	6,000	40,092,000
Net share awards	13,606,000	(1,000)	987,000		12,620,000
Employee share purchase plan	906,000		437,000		469,000
Common share options exercised	2,697,000		740,000		1,957,000
Change in classification of deferred compensation plan	(34,517,000)		(34,517,000)
Change in redemption value of non-qualified share awards	(12,928,000)			(12,928,000)
Diversification of share awards within deferred compensation plan	353,000		221,000	132,000
Conversions of operating partnership units	0		71,000				(71,000)
Cash distributions declared to equity holders	(170,146,000)			(166,556,000)			(3,590,000)
Ending balance at Sep. 30, 2013	2,677,990,000	967,000	3,595,536,000	(571,935,000)	(410,309,000)	(1,021,000)	64,752,000
Beginning balance at Dec. 31, 2013	2,760,181,000	967,000	3,596,069,000	(494,167,000)	(410,227,000)	(1,106,000)	68,645,000
Net income	116,690,000			113,591,000			3,099,000
Other comprehensive income (loss)	(368,000)					(368,000)
Common shares issued	50,535,000	7,000	50,528,000
Net share awards	14,773,000		3,538,000		11,235,000
Employee share purchase plan	1,932,000		870,000		1,062,000
Common share options exercised	769,000	1,000	335,000		433,000
Change in classification of deferred compensation plan	(4,916,000)		(4,916,000)
Change in redemption value of non-qualified share awards	(12,936,000)			(12,936,000)
Diversification of share awards within deferred compensation plan	4,669,000		3,273,000	1,396,000
Conversions of operating partnership units			52,000				(52,000)
Cash distributions declared to equity holders	(179,784,000)			(176,026,000)			(3,758,000)
Other	0	(1,000)	1,000
Ending balance at Sep. 30, 2014	$ 2,751,545,000	$ 974,000	$ 3,649,750,000	$ (568,142,000)	$ (397,497,000)	$ (1,474,000)	$ 67,934,000