Segment Information (Summary of net income and EBITDA reconciliation by segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting [Abstract]
Net (loss) income	$ (217,352)	$ 2,596,693	$ (321,855)	$ 2,809,737
Depreciation and amortization expense	92,805	113,035	185,598	229,744
General and administrative expense	35,014	38,872	87,848	96,892
(Lease liability extinguishment gain) transaction related costs and impairment losses	(69,221)	101,590	(69,150)	101,739
Loss (income) from partially owned entities	291,873	(22,873)	272,770	(30,193)
Loss from real estate fund investments	28,042	15,803	211,505	15,970
Interest and other investment loss (income), net	2,893	(7,840)	8,797	(12,885)
Interest and debt expense	58,405	63,029	117,247	165,492
Net gain on transfer to Fifth Avenue and Times Square JV	0	(2,571,099)	0	(2,571,099)
Net gains on disposition of wholly owned and partially owned assets	(55,695)	(111,713)	(124,284)	(332,007)
Income tax expense	1,837	26,914	14,650	56,657
(Income) loss from discontinued operations	0	(60)	0	77
NOI from partially owned entities	69,487	82,974	151,368	150,376
NOI attributable to noncontrolling interests in consolidated subsidiaries	(15,448)	(16,416)	(30,941)	(33,819)
NOI at share	222,640	308,909	503,553	646,681
Non cash adjustments for straight-line rents, amortization of acquired below-market leases, net and other	34,190	9,748	37,266	4,567
NOI at share - cash basis	$ 256,830	$ 318,657	$ 540,819	$ 651,248