Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Information
Rental income	$ 201,741		$ 226,802	$ 699,207	$ 662,587
Operating expenses	(94,632)		(92,005)	(287,650)	(265,227)
NOI	107,109		134,797	411,557	397,360
Reconciliation of NOI to net income
NOI	107,109		134,797	411,557	397,360
Depreciation and amortization	(52,150)		(52,353)	(169,930)	(154,623)
General and administrative	(25,069)		(12,565)	(61,445)	(34,190)
Acquisition related costs	436		(1,066)	(337)	(5,002)
Operating income	30,326		68,813	179,845	203,545
Interest and other income	227		399	931	1,020
Interest expense	(39,359)		(50,736)	(134,824)	(148,924)
Loss on early extinguishment of debt		(60,027)	(220)	(60,027)	(287)
Equity in earnings of investees	10,492		2,868	14,913	8,655
Gain on sale of equity investment				66,293
Income from continuing operations before income tax expense	1,686		21,124	67,131	64,009
Income tax expense	(785)		(1,322)	(2,527)	(1,906)
Income from continuing operations	901		19,802	64,604	62,103
(Loss) income from discontinued operations	(28)		774	4,390	4,891
Loss on asset impairment from discontinued operations	(217,080)			(225,615)
Loss on early extinguishment of debt from discontinued operations					(1,608)
Net gain on sale of properties from discontinued operations			1,689	3,359	2,039
(Loss) income before gain on sale of properties	(216,207)		22,265	(153,262)	67,425
Gain on sale of properties				1,596
Net (loss) income	$ (216,207)		$ 22,265	$ (151,666)	$ 67,425