Investments in Partially Owned Entities (Alexander's Inc.) (Details) $ / shares in Units, ft² in Thousands, $ in Thousands			9 Months Ended
	May 03, 2024 USD ($) ft²	May 01, 2024	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 29, 2024 USD ($)	Dec. 31, 2023 USD ($)
Schedule Of Equity Method Investments
Loans payable			$ 5,675,054		$ 5,688,020
Alexander's | Equity Method Investee
Schedule Of Equity Method Investments
Percentage of third-party lease commission		33.00%
Mortgages Payable:
Schedule Of Equity Method Investments
Loans payable			$ 5,675,054		$ 5,688,020
Alexander's
Schedule Of Equity Method Investments
Equity method ownership percentage			32.40%
Alexander's | Mortgage, 731 Lexington Avenue | Mortgages Payable:
Schedule Of Equity Method Investments
Stated rate (in percent)			5.04%
Loans payable			$ 400,000	$ 490,000
Alexander's | Equity Method Investee
Schedule Of Equity Method Investments
Ownership common shares, investee (in shares) | shares			1,654,068
Equity method ownership percentage			32.40%
Closing share price (in dollars per share) | $ / shares			$ 242.36
Equity method investment fair value			$ 400,880
Excess of investee's fair value over carrying amount			327,997
Excess of investee's carrying amount over equity in net assets			$ 29,297
Lease fee percentage of rent one to ten years			3.00%
Lease fee percentage of rent eleven to twenty years			2.00%
Lease fee percentage of rent twenty first to thirty years			1.00%
Percentage increase lease fee if broker used			1.00%
Alexander's | Equity Method Investee | Bloomberg L.P
Schedule Of Equity Method Investments
Square footage of real estate property (in sqft) | ft²	947
Lease, term	11 years
Lease commission override	$ 5,500