Segment Information (Summary of net income and EBITDA reconciliation by segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Information
Net income (loss)	$ 219,162	$ (10,754)	$ 324,782	$ 210,577
(Income) loss from partially owned entities	(7,206)	41,801	(6,059)	(5,578)
Loss from real estate fund investments	190	6,308	37,973	1,649
Interest and other investment income, net	(2,893)	(7,331)	(9,401)	(22,567)
Net gains on disposition of wholly owned and partially owned assets	(141,269)	0	(164,828)	(501)
Income (loss) from discontinued operations	(61)	47,930	(381)	14,501
NOI attributable to noncontrolling interests in consolidated subsidiaries	(16,943)	(16,171)	(51,415)	(48,778)
Depreciation and amortization expense	113,169	104,972	333,701	315,223
General and administrative expense	31,977	34,286	108,937	115,866
Transaction related costs and other	2,510	61	16,683	1,073
NOI from partially owned entities	60,094	66,876	193,359	199,989
Interest and debt expense	88,951	85,068	264,774	252,581
Income tax expense	1,943	1,188	4,964	3,491
NOI at share	349,624	354,234	1,053,089	1,037,526
Non-cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other	(8,743)	(22,307)	(39,172)	(65,263)
NOI at share - cash basis	340,881	331,927	1,013,917	972,263
Real estate fund investments
Segment Information
Loss from real estate fund investments	$ 190	$ 6,308	$ 37,973	$ 1,649