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, 2012	$ 1,310,593	$ 9,997	$ 648	$ 1,875,525	$ (586,970)	$ (12,388)	$ 23,781
Beginning balance (in shares) at Dec. 31, 2012		399,896	64,815,446
Net income, excluding $1,425 attributable to redeemable noncontrolling interests	73,214				72,127		1,087
Other Comprehensive Income - change in value of interest rate swaps	10,020					10,020
Dividends declared to common shareholders	(95,455)				(95,455)
Dividends declared to preferred shareholders	(271)				(271)
Distributions declared to noncontrolling interests	(962)						(962)
Common shares issued (in shares)			734,636
Common shares issued	81,997		8	81,989
Exercise of stock options (in shares)			16,304
Exercise of stock options	1,005		0	1,005
Shares issued under dividend reinvestment plan (in shares)			10,207
Shares issued under dividend reinvestment plan	1,112			1,112
Share-based compensation expense, net of shares withheld for employee taxes (in shares)			88,165
Share-based compensation expense, net of shares withheld for employee taxes	3,925		1	3,924
Conversion and redemption of OP units (in shares)			22,476
Conversion and redemption of OP units	(1,391)			(555)			(836)
Ending balance at Jun. 30, 2013	$ 1,383,787	$ 9,997	$ 657	$ 1,963,000	$ (610,569)	$ (2,368)	$ 23,070
Ending balance (in shares) at Jun. 30, 2013		399,896	65,687,234