Segment Information (Details 2) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Segment Information
Rental income	$ 222,181	$ 195,817	$ 436,697	$ 390,896
Operating expenses	(90,161)	(81,352)	(180,568)	(162,822)
Property net operating income (NOI)	132,020	114,465	256,129	228,074
Reconciliation of NOI to net income
Property NOI	132,020	114,465	256,129	228,074
Depreciation and amortization	(51,973)	(45,233)	(105,814)	(90,673)
General and administrative	(11,618)	(9,554)	(22,569)	(18,804)
Loss on asset impairment		(21,491)		(21,491)
Acquisition related costs	(2,415)	(1,103)	(5,060)	(1,413)
Operating income	66,014	37,084	122,686	95,693
Interest and other income	392	447	1,062	1,565
Interest expense	(48,200)	(44,659)	(95,614)	(89,524)
Equity in earnings of investees	2,910	2,305	5,622	4,644
Gain on issuance of shares by an equity investee				16,418
Income (loss) from continuing operations before income tax expense	21,116	(4,823)	33,756	28,796
Income tax expense	(90)	(181)	(436)	(363)
Income (loss) from continuing operations	21,026	(5,004)	33,320	28,433
(Loss) income from discontinued operations	(1,062)	3,498	(1,316)	7,358
Gain on sale of properties from discontinued operations			34,572
Income (loss) before gain on sale of properties	19,964	(1,506)	66,576	35,791
Gain (loss) on sale of properties		11,504		11,504
Net income	$ 19,964	$ 9,998	$ 66,576	$ 47,295