Investments in Partially Owned Entities (Schedule of Income (Loss) ) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Equity in net income	$ 141,310	$ 112,464	$ 38,689
Return on preferred equity, net of our share of the expense	114,754	142,880	172,873
Net gain on sale	0	0	(45,007)
Our share of net income (loss)	$ 141,310	112,464	38,689
Fifth Avenue and Times Square JV
Schedule of Equity Method Investments [Line Items]
Interest	51.50%
Equity in net income	$ 14,716	43,451	35,209
Return on preferred equity, net of our share of the expense	27,528	40,668	37,416
Net gain on sale	76,162	0	0
Our share of net income (loss)	$ 118,406	84,119	72,625
Alexander's
Schedule of Equity Method Investments [Line Items]
Interest	32.40%
Equity in net income	$ 8,915	13,813	15,441
Management, leasing and development fees	5,717	5,263	5,238
Net gain on sale of land	0	0	16,396
Our share of net income (loss)	14,632	19,076	37,075
Partially owned office buildings
Schedule of Equity Method Investments [Line Items]
Our share of net income (loss)	(2,705)	(839)	(73,589)
Other equity method investments
Schedule of Equity Method Investments [Line Items]
Our share of net income (loss)	$ 10,977	$ 10,108	$ 2,578