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 $2,117 attributable to redeemable noncontrolling interests	135,888				134,225		1,663
Other Comprehensive Income - change in value of interest rate swaps	8,849					8,849
Dividends declared to common shareholders	(146,940)				(146,940)
Dividends declared to preferred shareholders	(406)				(406)
Distributions declared to noncontrolling interests	(1,529)						(1,529)
Common shares issued (in shares)			1,075,123
Common shares issued	116,797		11	116,786
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)			15,002
Shares issued under dividend reinvestment plan	1,610			1,610
Share-based compensation expense, net of shares withheld for employee taxes (in shares)			91,823
Share-based compensation expense, net of shares withheld for employee taxes	6,665		1	6,664
Conversion and redemption of OP units (in shares)			22,476
Conversion and redemption of OP units	(1,422)			(625)			(797)
Ending balance at Sep. 30, 2013	$ 1,431,110	$ 9,997	$ 660	$ 2,000,965	$ (600,091)	$ (3,539)	$ 23,118
Ending balance (in shares) at Sep. 30, 2013		399,896	66,036,174