Investments in Partially Owned Entities (Schedule of Investments) (Details) - USD ($) $ in Thousands		12 Months Ended
	Aug. 14, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities		$ 1,941,278	$ 2,691,478
Carrying amount of investments in partially owned entities		(90,924)	(89,530)
512 West 22nd Street | JV
Schedule of Equity Method Investments [Line Items]
Net gain on sale of land	$ 11,002	$ 11,002
Fifth Avenue and Times Square JV
Schedule of Equity Method Investments [Line Items]
Interest		51.50%
Carrying amount of investments in partially owned entities		$ 1,538,141	2,235,546
Partially owned office buildings/land
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities		$ 148,958	186,190
Alexander's
Schedule of Equity Method Investments [Line Items]
Interest		32.40%
Carrying amount of investments in partially owned entities		$ 47,276	68,492
Net gain on sale of land		0	0	$ 16,396
Other equity method investments
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities		$ 206,903	201,250
7 West 34th Street
Schedule of Equity Method Investments [Line Items]
Interest		53.00%
Carrying amount of investments in partially owned entities		$ (65,726)	(70,552)
85 Tenth Avenue
Schedule of Equity Method Investments [Line Items]
Interest		49.90%
Carrying amount of investments in partially owned entities		$ (25,198)	(18,978)
280 Park Avenue Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Net gain on early extinguishment of debt			$ 31,215