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]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interests [Member]
Beginning balance at Dec. 31, 2011	$ 1,240,604	$ 9,997	$ 636	$ 1,764,940	$ (555,541)	$ (3,940)	$ 24,512
Beginning balance (in shares) at Dec. 31, 2011		399,896	63,544,150
Net income, excluding $1,224 attributable to redeemable noncontrolling interests	76,494				75,589		905
Other Comprehensive Income	(6,435)					(6,435)
Dividends declared to common shareholders	(88,318)				(88,318)
Dividends declared to preferred shareholders	(271)				(271)
Distributions declared to noncontrolling interests	(1,010)						(1,010)
Common shares issued (in shares)			382,194
Common shares issued	37,056		4	37,052
Exercise of stock options (in shares)			43,870
Exercise of stock options	2,390		0	2,390
Shares issued under dividend reinvestment plan (in shares)			12,319
Shares issued under dividend reinvestment plan	1,129			1,129
Share-based compensation expense, net (in shares)			117,307
Share-based compensation expense, net	5,171		1	5,170
Conversion and redemption of OP units	(457)			(322)			(135)
Contributions from noncontrolling interests	105						105
Ending balance at Jun. 30, 2012	$ 1,266,458	$ 9,997	$ 641	$ 1,810,359	$ (568,541)	$ (10,375)	$ 24,377
Ending balance (in shares) at Jun. 30, 2012		399,896	64,099,840