Investments in Partially Owned Entities (Alexander's Inc.) (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Dec. 05, 2025 USD ($)	Dec. 04, 2025 USD ($)	Dec. 31, 2025 USD ($) $ / shares $ / ft² shares	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 23, 2025 USD ($)
Schedule of Equity Method Investments [Line Items]
Tenant and other receivables			$ 77,137	$ 58,853
Repayments of long-term debt			$ 1,903,513	97,439	$ 148,000
Alexander's
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage			32.40%
Stated rate (as a percent)						7.00%
Alexander's | Senior A-Note
Schedule of Equity Method Investments [Line Items]
Stated rate (as a percent)						7.00%
Alexander's | Junior C-Note
Schedule of Equity Method Investments [Line Items]
Stated rate (as a percent)						4.55%
Alexander's | B-Note
Schedule of Equity Method Investments [Line Items]
Stated rate (as a percent)						13.50%
Alexander's | Mortgages Payable
Schedule of Equity Method Investments [Line Items]
Debt amount						$ 300,000
Alexander's | Mortgages Payable | Senior A-Note
Schedule of Equity Method Investments [Line Items]
Debt amount						132,500
Alexander's | Mortgages Payable | Junior C-Note
Schedule of Equity Method Investments [Line Items]
Debt amount						167,500
Alexander's | Mortgages Payable | B-Note
Schedule of Equity Method Investments [Line Items]
Debt amount						$ 65,000
Alexander's | Rego Park 2 Property
Schedule of Equity Method Investments [Line Items]
Basis spread on variable rate	2.00%
Debt amount	$ 175,000
Repayments of long-term debt	$ 23,544
Debt term	5 years
Alexander's | Rego Park 2 Property | Prior Alexander's Loan, Maturing in December 2025
Schedule of Equity Method Investments [Line Items]
Basis spread on variable rate		1.45%
Debt amount		$ 198,544
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			$ 134	1,159
Closing share price (in dollars per share) | $ / shares			$ 217.94
Equity method investment fair value			$ 360,488
Excess of investee's fair value over carrying amount			313,212
Excess of investee's carrying amount over equity in net assets			29,054
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%
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			$ 3,849	$ 4,611	$ 4,629
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			$ 387
Property management fee agreement escalation percentage (as a percent)			3.00%
Alexander's | Related Party
Schedule of Equity Method Investments [Line Items]
Percentage of lease fee, related party			33.33%