Segment Information (Summary of net income and EBITDA reconciliation by segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting [Abstract]
Net income (loss)	$ 68,736	$ 363,849	$ (253,119)	$ 3,173,586
Depreciation and amortization expense	107,013	96,437	292,611	326,181
General and administrative expense	32,407	33,237	120,255	130,129
Expense from transaction related costs and impairment losses and (gain from lease liability extinguishment), net	584	1,576	(68,566)	103,315
Loss (income) from partially owned entities	80,909	(25,946)	353,679	(56,139)
Loss (income) from real estate fund investments	13,823	(2,190)	225,328	13,780
Interest and other investment (income) loss, net	(1,729)	(3,045)	7,068	(15,930)
Interest and debt expense	57,371	61,448	174,618	226,940
Net gain on transfer to Fifth Avenue and Times Square JV	0	0	0	(2,571,099)
Net gains on disposition of wholly owned and partially owned assets	(214,578)	(309,657)	(338,862)	(641,664)
Income tax expense	23,781	23,885	38,431	80,542
Loss from discontinued operations	0	8	0	85
NOI from partially owned entities	78,175	86,024	229,543	236,400
NOI attributable to noncontrolling interests in consolidated subsidiaries	(25,959)	(18,096)	(56,900)	(51,915)
NOI at share	220,533	307,530	724,086	954,211
Non cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other	10,981	(4,037)	48,247	530
NOI at share - cash basis	$ 231,514	$ 303,493	$ 772,333	$ 954,741