Investments in Partially Owned Entities (Alexander's Inc.) (Details) $ / shares in Units, ft² in Thousands, $ in Thousands		4 Months Ended	12 Months Ended
	May 03, 2024 USD ($) ft²	Apr. 30, 2024	Dec. 31, 2024 USD ($) $ / shares $ / ft² shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2024 USD ($)	Sep. 29, 2024 USD ($)
Schedule of Equity Method Investments [Line Items]
Tenant and other receivables			$ 58,853	$ 69,543
Loans payable			5,676,014	5,688,020
Mortgages Payable
Schedule of Equity Method Investments [Line Items]
Loans payable			$ 5,676,014	5,688,020
Alexander's
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage			32.40%
Alexander's | Mortgage, 731 Lexington Avenue | Mortgages Payable
Schedule of Equity Method Investments [Line Items]
Loans payable						$ 400,000	$ 490,000
Stated rate (as a percent)						5.04%
Alexander's | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Ownership common shares, investee (in shares) | shares			1,654,068
Equity method ownership percentage			32.40%
Tenant and other receivables			$ 1,159	715
Closing share price (in dollars per share) | $ / shares			$ 200.06
Equity method investment fair value			$ 330,913
Excess of investee's fair value over carrying amount			262,421
Excess of investee's carrying amount over equity in net assets			29,272
Management fee income			$ 2,800
Development fee (as a percent)			6.00%
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 [Line Items]
Square footage of real estate property (in sqft) | ft²	947
Lease term	11 years
Lease commissions override	$ 5,500
Alexander's | Equity Method Investee | Fee and other income
Schedule of Equity Method Investments [Line Items]
Fee income recognized by equity method investees for building maintenance services			$ 4,611	$ 4,629	$ 4,601
Alexander's | Equity Method Investee | Rego Park 2 Property
Schedule of Equity Method Investments [Line Items]
Property management fee agreement percentage of income (as a percent)			2.00%
Alexander's | Equity Method Investee | 731 Lexington Avenue
Schedule of Equity Method Investments [Line Items]
Property management fee agreement price per square foot | $ / ft²			0.50
Alexander's | Equity Method Investee | Common Area 731 Lexington Avenue
Schedule of Equity Method Investments [Line Items]
Management fee income			$ 376
Property management fee agreement escalation percentage (as a percent)			3.00%