Segment Information - Schedule of Reconciliation of NOI to Net Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting [Abstract]
Rental income	$ 163,697	$ 172,407	$ 331,669	$ 344,447
Tenant reimbursements and other income	39,997	42,787	85,080	88,007
Operating expenses	(89,686)	(92,701)	(187,557)	(194,432)
NOI	114,008	122,493	229,192	238,022
Depreciation and amortization	(53,637)	(59,831)	(116,336)	(111,480)
General and administrative	(10,911)	(24,097)	(27,469)	(48,945)
Loss on asset impairment	(15,258)	(22,683)	(17,162)	(17,922)
Acquisition related costs	0	0	0	(5)
Operating income	34,202	15,882	68,225	59,670
Interest and other income	728	281	4,176	665
Interest expense	(27,973)	(37,899)	(57,815)	(75,834)
Gain on early extinguishment of debt	10,426	0	9,998	0
Loss on sale of equity investment	0	(33)	0	(33)
Gain on issuance of shares by an equity investee	0	16,911	0	17,020
Foreign currency exchange gain	856	0	856	0
(Loss) gain on sale of properties	(2,708)	0	3,160	0
Income (loss) from continuing operations before income taxes and equity in earnings of investees	15,531	(4,858)	28,600	1,488
Income tax expense	(2,915)	(908)	(2,354)	(1,463)
Equity in earnings of investees	0	12,454	0	23,388
Income from continuing operations	12,616	6,688	26,246	23,413
Income from discontinued operations	0	4,114	0	8,125
Loss on asset impairment from discontinued operations	0	(2,072)	0	(2,360)
Loss on early extinguishment of debt from discontinued operations	0	(3,345)	0	(3,345)
Net income	$ 12,616	$ 5,385	$ 26,246	$ 25,833