Segment Information (Details 2) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Information
Rental income	$ 238,790	$ 193,059	$ 662,596	$ 572,205
Operating expenses	(100,912)	(83,023)	(275,760)	(240,280)
Property net operating income (NOI)	137,878	110,036	386,836	331,925
Reconciliation of NOI to net income
Property NOI	137,878	110,036	386,836	331,925
Depreciation and amortization	(56,389)	(42,794)	(159,072)	(130,560)
General and administrative	(11,450)	(9,704)	(33,559)	(28,081)
Loss on asset impairment				(21,491)
Acquisition related costs	(4,805)	(1,559)	(9,722)	(2,965)
Operating income	65,234	55,979	184,483	148,828
Interest and other income	369	571	1,428	2,134
Interest expense	(49,423)	(44,192)	(145,037)	(133,716)
Gain (loss) on early extinguishment of debt	310	(796)	310	(796)
Equity in earnings of investees	2,768	1,999	8,390	6,643
Gain on issuance of shares by an equity investee	11,177	18,390	11,177	34,808
Income (loss) from continuing operations before income tax expense	30,435	31,951	60,751	57,901
Income tax (expense) benefit	(307)	34	(743)	(329)
Income (loss) from continuing operations	30,128	31,985	60,008	57,572
Income from discontinued operations	653	6,673	2,777	16,877
Loss on asset impairment from discontinued operations	(9,247)		(9,247)
Gain on sale of properties from discontinued operations	7,001	4,568	41,573	4,568
Income before gain on sale of properties	28,535	42,978	95,111	78,769
Gain on sale of properties		22,832		34,336
Net income	28,535	65,810	95,111	113,105
Loss on early extinguishment of debt from discontinued operations		$ (248)		$ (248)