Segment Information (Reconciliation of Net Income to NOI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting [Abstract]
Net income (loss)	$ 3,334,262	$ 422,603	$ 264,128
Depreciation and amortization expense	419,107	446,570	429,389
General and administrative expense	169,920	141,871	150,782
Transaction related costs, impairment losses and other	106,538	31,320	1,776
Income from partially owned entities	(78,865)	(9,149)	(15,200)
Loss (income) from real estate fund investments	104,082	89,231	(3,240)
Interest and other investment income, net	(21,819)	(17,057)	(30,861)
Interest and debt expense	286,623	347,949	345,654
Net gain on transfer to Fifth Avenue and Times Square JV	(2,571,099)	0	0
Purchase price fair value adjustment	0	(44,060)	0
Net gains on disposition of wholly owned and partially owned assets	(845,499)	(246,031)	(501)
Income tax expense	103,439	37,633	42,375
Loss (income) from discontinued operations	30	(638)	13,228
NOI from partially owned entities	322,390	253,564	269,164
NOI attributable to noncontrolling interests in consolidated subsidiaries	(69,332)	(71,186)	(65,311)
NOI at share	1,259,777	1,382,620	1,401,383
Non-cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other	(6,060)	(44,704)	(86,842)
NOI at share - cash basis	$ 1,253,717	$ 1,337,916	$ 1,314,541