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, 2008	$ 1,084,569	$ 9,997	$ 590	$ 1,478,785	$ (426,574)	$ 0	$ 21,771
Beginning balance (in shares) at Dec. 31, 2008		399,896	58,985,678
Net income/Comprehensive income	100,654				98,304		2,350
Dividends declared to common shareholders	(157,638)				(157,638)
Dividends declared to preferred shareholders	(541)				(541)
Distributions declared to noncontrolling interests	(2,603)						(2,603)
Common shares issued (in shares)			1,995,563
Common shares issued	110,016		20	109,996
Exercise of stock options (in shares)			126,500
Exercise of stock options	2,758		1	2,757
Shares issued under dividend reinvestment plan (in shares)	50,888		50,888
Shares issued under dividend reinvestment plan	2,728			2,728
Share-based compensation expense, net (in shares)			83,421
Share-based compensation expense, net	7,139		1	7,138
Conversion and redemption of OP units	(86)			(31)			(55)
Adjustment to redeemable noncontrolling interests	4,742			4,742
Ending balance at Dec. 31, 2009	1,151,738	9,997	612	1,606,115	(486,449)	0	21,463
Ending balance (in shares) at Dec. 31, 2009		399,896	61,242,050
Net income/Comprehensive income	125,251				122,790		2,461
Dividends declared to common shareholders	(163,382)				(163,382)
Dividends declared to preferred shareholders	(541)				(541)
Distributions declared to noncontrolling interests	(2,223)						(2,223)
Common shares issued (in shares)			190
Common shares issued	14		0	14
Exercise of stock options (in shares)			107,493
Exercise of stock options	4,052		1	4,051
Shares issued under dividend reinvestment plan (in shares)	34,401		34,401
Shares issued under dividend reinvestment plan	2,544			2,544
Share-based compensation expense, net (in shares)			135,338
Share-based compensation expense, net	6,487		2	6,485
Conversion and redemption of OP units (in shares)			6,946
Conversion and redemption of OP units	(137)			532			(669)
Adjustment to redeemable noncontrolling interests	(8,035)			(8,035)
Ending balance at Dec. 31, 2010	1,115,768	9,997	615	1,611,706	(527,582)	0	21,032
Ending balance (in shares) at Dec. 31, 2010		399,896	61,526,418
Net income/Comprehensive income	146,120				143,917		2,203
Change in valuation on interest rate swaps	(3,940)					(3,940)
Total comprehensive income	142,180
Dividends declared to common shareholders	(171,335)				(171,335)
Dividends declared to preferred shareholders	(541)				(541)
Distributions declared to noncontrolling interests	(2,320)						(2,320)
Common shares issued (in shares)			1,662,230
Common shares issued	139,298		17	139,281
Exercise of stock options (in shares)	237,271		237,271
Exercise of stock options	15,190		3	15,187
Shares issued under dividend reinvestment plan (in shares)	28,823		28,823
Shares issued under dividend reinvestment plan	2,374			2,374
Share-based compensation expense, net (in shares)			89,408
Share-based compensation expense, net	8,247		1	8,246
Conversion and redemption of OP units	(151)			(96)			(55)
Purchase of noncontrolling interest	(2,538)			(2,331)			(207)
Deconsolidation of VIE	(420)						(420)
Contributions from noncontrolling interests	4,279						4,279
Adjustment to redeemable noncontrolling interests	(9,427)			(9,427)			0
Ending balance at Dec. 31, 2011	$ 1,240,604	$ 9,997	$ 636	$ 1,764,940	$ (555,541)	$ (3,940)	$ 24,512
Ending balance (in shares) at Dec. 31, 2011		399,896	63,544,150