Investments in Partially Owned Entities (Summary of Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule Of Equity Method Investments
Carrying amount of investments in partially owned entities	$ 3,355,401	$ 3,491,107
Other liabilities
Schedule Of Equity Method Investments
Carrying amount of investments in partially owned entities	$ (76,994)	(68,420)
7 West 34th Street
Schedule Of Equity Method Investments
Equity method ownership percentage	53.00%
7 West 34th Street | Other liabilities
Schedule Of Equity Method Investments
Carrying amount of investments in partially owned entities	$ (58,214)	(55,340)
85 Tenth Avenue
Schedule Of Equity Method Investments
Equity method ownership percentage	49.90%
85 Tenth Avenue | Other liabilities
Schedule Of Equity Method Investments
Carrying amount of investments in partially owned entities	$ (18,780)	(13,080)
Fifth Avenue and Times Square JV
Schedule Of Equity Method Investments
Equity method ownership percentage	51.50%
Carrying amount of investments in partially owned entities	$ 2,776,891	2,798,413
Partially Owned Office Buildings
Schedule Of Equity Method Investments
Carrying amount of investments in partially owned entities	$ 361,463	473,285
Alexanders Inc
Schedule Of Equity Method Investments
Equity method ownership percentage	32.40%
Carrying amount of investments in partially owned entities	$ 83,892	82,902
Other investments
Schedule Of Equity Method Investments
Carrying amount of investments in partially owned entities	$ 133,155	$ 136,507