Consolidated Statement Of Shareholders' Equity (USD $) In Thousands, except Share data	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Dividends in Excess of Net Income [Member]	Noncontrolling Interests [Member]
Beginning balance at Dec. 31, 2010	$ 1,181,130	$ 9,997	$ 615	$ 1,666,803	$ (527,582)	$ 31,297
Beginning balance (in shares) at Dec. 31, 2010		399,896	61,526,418
Net income/Comprehensive income	117,157				112,996	4,161
Dividends declared to common shareholders	(127,488)				(127,488)
Dividends declared to preferred shareholders	(406)				(406)
Distributions declared to noncontrolling interests	(4,055)					(4,055)
Common shares issued (in shares)			1,662,185
Common shares issued	139,337		17	139,320
Exercise of stock options (in shares)			194,586
Exercise of stock options	12,679		2	12,677
Shares issued under dividend reinvestment plan (in shares)			21,680
Shares issued under dividend reinvestment plan	1,777			1,777
Share-based compensation expense, net (in shares)			89,408
Share-based compensation expense, net	6,105		1	6,104
Conversion and redemption of OP units	(151)			(96)		(55)
Purchase of noncontrolling interest	(2,538)			(2,331)		(207)
Deconsolidation of VIE	(420)					(420)
Ending balance at Sep. 30, 2011	$ 1,323,127	$ 9,997	$ 635	$ 1,824,254	$ (542,480)	$ 30,721
Ending balance (in shares) at Sep. 30, 2011		399,896	63,494,277