Investments in Partially Owned Entities (Summary of Income (Loss)) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 04, 2021	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Schedule Of Equity Method Investments
Our share of net income (loss)		$ 25,720	$ 31,426	$ 59,434	$ 60,499
Fifth Avenue and Times Square JV
Schedule Of Equity Method Investments
Equity method ownership percentage		51.50%		51.50%
Equity in net income		$ 13,665	10,037	$ 29,974	19,643
Return on preferred equity, net of our share of the expense		9,329	9,329	18,555	18,555
Our share of net income (loss)		$ 22,994	19,366	$ 48,529	38,198
Alexanders Inc
Schedule Of Equity Method Investments
Equity method ownership percentage		32.40%		32.40%
Equity in net income		$ 4,824	8,325	$ 9,495	14,054
Management, leasing and development fees		1,162	1,962	2,182	2,537
Our share of net income (loss)		5,986	10,287	11,677	16,591
Proceeds from sale of land held-for-investment	$ 10,000
Net gain on sale of real estate	2,956
Proceeds from commissions received	$ 300
Partially owned office buildings/land
Schedule Of Equity Method Investments
Our share of net income (loss)		(3,584)	3,758	(1,107)	9,730
Other investments
Schedule Of Equity Method Investments
Our share of net income (loss)		$ 324	$ (1,985)	$ 335	$ (4,020)