Segment Information (Summary of net income and EBITDA reconciliation by segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Information
Net income	$ 105,338	$ 147,484	$ 105,620	$ 221,331
(Income) loss from partially owned entities	(8,757)	(46,021)	1,147	(47,379)
Loss (income) from real estate fund investments	28,976	(4,391)	37,783	(4,659)
Interest and other investment income, net	(30,892)	(8,541)	(6,508)	(15,236)
Net gains on disposition of wholly owned and partially owned assets	(23,559)	0	(23,559)	(501)
Income from discontinued operations	(683)	(18,111)	(320)	(33,429)
NOI attributable to noncontrolling interests in consolidated subsidiaries	(17,160)	(16,269)	(34,472)	(32,607)
Depreciation and amortization expense	111,846	105,123	220,532	210,251
General and administrative expense	34,427	35,405	76,960	81,580
Transaction related costs and other	1,017	260	14,173	1,012
NOI from partially owned entities	65,752	67,016	133,265	133,113
Interest and debt expense	87,657	84,789	175,823	167,513
Income tax expense (benefit)	467	(610)	3,021	2,303
NOI at share	354,429	346,134	703,465	683,292
Non-cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other	(12,481)	(22,475)	(30,429)	(42,956)
NOI at share - cash basis	341,948	323,659	673,036	640,336
Real estate fund investments
Segment Information
Loss (income) from real estate fund investments	$ 28,976	$ (4,391)	$ 37,783	$ (4,659)