Investments in Partially Owned Entities (Summary of Income (Loss) ) (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 04, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Non-cash impairment loss		$ (7,880)	$ (236,286)	$ (26,705)
Net gains on sale of real estate		0	0	2,571,099
Our share of net income (loss)		$ 130,517	(329,112)	78,865
Fifth Avenue and Times Square JV
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage		51.50%
Equity in net income (loss)		$ 47,144	21,063	31,130
Return on preferred equity, net of our share of the expense		37,416	37,357	27,586
Non-cash impairment loss		0	(413,349)	0
Our share of net income (loss)		84,560	(354,929)	58,716
Decrease in depreciation and amortization expense		17,448
Fifth Avenue and Times Square JV | 1540 Broadway
Schedule of Equity Method Investments [Line Items]
Rent reduction		$ 13,971	13,971
Write off of rent receivable			3,125
Alexanders Inc
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage		32.40%
Equity in net income (loss)		$ 20,116	13,326	19,204
Net gains on sale of real estate	$ 2,956	14,576	0	0
Management, leasing and development fees		5,429	5,309	4,575
Our share of net income (loss)		40,121	18,635	23,779
Write off of rent receivable			4,846
Partially Owned Office Buildings
Schedule of Equity Method Investments [Line Items]
Our share of net income (loss)		12,057	12,742	(3,443)
Other investments
Schedule of Equity Method Investments [Line Items]
Our share of net income (loss)		$ (6,221)	$ (5,560)	$ (187)