Investments in Partially Owned Entities (Summary of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities	$ 3,297,389	$ 3,491,107
Fifth Avenue and Times Square JV
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage	51.50%
Carrying amount of investments in partially owned entities	$ 2,770,633	2,798,413
Partially Owned Office Buildings
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities	$ 306,989	473,285
Alexanders Inc
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage	32.40%
Carrying amount of investments in partially owned entities	$ 91,405	82,902
Other investments
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities	$ 128,362	136,507
7 West 34th Street
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage	53.00%
85 Tenth Avenue
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage	49.90%
Other Liabilities
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities	$ (78,985)	(68,420)
Other Liabilities | 7 West 34th Street
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities	(60,918)	(55,340)
Other Liabilities | 85 Tenth Avenue
Schedule of Equity Method Investments [Line Items]
Carrying amount of investments in partially owned entities	$ (18,067)	$ (13,080)