Consolidated Statements Of Equity And Perpetual Preferred Units (USD $)	Total	Common Shares Of Beneficial Interest	Additional Paid-In Capital	Distributions In Excess Of Net Income	Notes Receivable Secured By Common Shares [Member]	Treasury Shares, At Cost	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Perpetual Preferred Units
Equity, Beginning Balance at Dec. 31, 2009	$ 1,609,013,000	$ 770,000	$ 2,525,656,000	$ (492,571,000)	$ (101,000)	$ (462,188,000)	$ (41,155,000)	$ 78,602,000
Perpetual Preferred Units, Beginning Balance at Dec. 31, 2009	97,925,000
Net income	24,142,000			23,216,000				926,000	7,000,000
Other comprehensive income	7,697,000						7,697,000
Common shares issued	231,651,000	49,000	231,602,000
Net share awards	11,613,000	4,000	11,609,000
Employee share purchase plan	1,165,000		232,000			933,000
Repayment Of Employee Notes Receivable Net	101,000				101,000
Common share options exercised	2,997,000		2,997,000
Conversions and redemptions of operating partnership units	(25,000)	3,000	3,525,000					(3,553,000)
Cash distributions declared to perpetual preferred units									(7,000,000)
Cash distributions declared to equity holders	(131,008,000)			(125,962,000)				(5,046,000)
Redemption of perpetual preferred units	0
Other	27,000	(2,000)	4,000					25,000
Equity, Ending Balance at Dec. 31, 2010	1,757,373,000	824,000	2,775,625,000	(595,317,000)	0	(461,255,000)	(33,458,000)	70,954,000
Perpetual Preferred Units, Ending Balance at Dec. 31, 2010	97,925,000
Net income	52,961,000			49,379,000				3,582,000	7,000,000
Other comprehensive income	32,775,000						32,775,000
Common shares issued	106,571,000	18,000	106,553,000
Net share awards	13,407,000	3,000	12,592,000			812,000
Employee share purchase plan	1,780,000		446,000			1,334,000
Common share options exercised	12,322,000		5,216,000			7,106,000
Conversions and redemptions of operating partnership units		1,000	591,000					(592,000)
Cash distributions declared to perpetual preferred units									(7,000,000)
Cash distributions declared to equity holders	(149,421,000)			(144,528,000)				(4,893,000)
Redemption of perpetual preferred units	0
Other		(1,000)	1,000
Equity, Ending Balance at Dec. 31, 2011	1,827,768,000	845,000	2,901,024,000	(690,466,000)	0	(452,003,000)	(683,000)	69,051,000
Perpetual Preferred Units, Ending Balance at Dec. 31, 2011	97,925,000								97,925,000
Net income	291,049,000			283,390,000				7,659,000	2,851,000
Other comprehensive income	(379,000)						(379,000)
Common shares issued	693,355,000	112,000	693,243,000
Net share awards	15,146,000		1,008,000			14,138,000
Employee share purchase plan	1,334,000		617,000			717,000
Common share options exercised	13,966,000		2,173,000			11,793,000
Conversions and redemptions of operating partnership units	(149,000)	6,000	8,988,000					(9,143,000)
Cash distributions declared to perpetual preferred units									(776,000)
Cash distributions declared to equity holders	(198,900,000)			(191,875,000)				(7,025,000)
Redemption of perpetual preferred units	(100,000,000)								(100,000,000)
Purchase of non-controlling interests	(16,482,000)		(19,549,000)					3,067,000
Other		(1,000)	1,000
Equity, Ending 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
Perpetual Preferred Units, Ending Balance at Dec. 31, 2012	$ 0