Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Information
Rental income	$ 172,040	$ 211,300
Tenant reimbursements and other income	45,220	51,312
Operating expenses	(101,731)	(104,130)
NOI	115,529	158,482
Reconciliation of NOI to net income
NOI	115,529	158,482
Depreciation and amortization	(51,649)	(62,570)
General and administrative	(24,848)	(16,663)
Reversal of loss on asset impairment	4,761
Acquisition related costs	(5)	(628)
Operating income	43,788	78,621
Interest and other income	384	455
Interest expense	(37,935)	(51,896)
Loss on early extinguishment of debt		(60,027)
Gain on sale of equity investment		66,293
Gain on issuance of shares by an equity investee	109
Income from continuing operations before income tax expense and equity in earnings of investees	6,346	33,446
Income tax expense	(555)	(988)
Equity in earnings of investees	10,934	4,262
Income from continuing operations	16,725	36,720
Income (loss) from discontinued operations	4,011	(6)
Loss on asset impairment from discontinued operations	(288)	(3,946)
Gain on sale of properties from discontinued operations		1,260
Income before gain on sale of properties	20,448	34,028
Gain on sale of properties		1,596
Net income	$ 20,448	$ 35,624