Related Party Transactions - Additional Information (Details)			3 Months Ended		9 Months Ended
	May 01, 2024	Apr. 30, 2024	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) $ / ft²	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Related Party Transaction [Line Items]
Fees to related party			$ 2,302,000	$ 2,580,000	$ 7,493,000	$ 12,510,000
Property Management Fees
Related Party Transaction [Line Items]
Fees to related party			1,117,000	1,688,000	4,040,000	4,537,000
Leasing fees
Related Party Transaction [Line Items]
Fees to related party			303,000	0	545,000	5,555,000
Development fees
Related Party Transaction [Line Items]
Fees to related party			182,000	$ 192,000	808,000	$ 318,000
Vornado
Related Party Transaction [Line Items]
Management fee agreement value					$ 2,800,000
Vornado | Property Management Fees | Rego Park II | Retail Space
Related Party Transaction [Line Items]
Property management fee, percent fee					2.00%
Vornado | Property Management Fees | 731 Lexington Avenue Retail | Office and Retail Space
Related Party Transaction [Line Items]
Property management fee agreement, price per square foot | $ / ft²					0.50
Vornado | Property Management Fees | 731 Lexington Avenue Retail | Common Area
Related Party Transaction [Line Items]
Property management fee escalation percentage per annum					3.00%
Vornado | Leasing fees
Related Party Transaction [Line Items]
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%
Percentage of third-party lease commission	33.00%
Percentage commissions on sale of assets under fifty million					3.00%
Asset sale commission threshold					$ 50,000,000
Percentage commissions on sale of assets over fifty million					1.00%
Vornado | Development fees
Related Party Transaction [Line Items]
Development fee as percentage of development costs					6.00%
Related Party
Related Party Transaction [Line Items]
Other Liabilities			499,000		$ 499,000		$ 1,159,000
Related Party | Management And Development Agreement, Base Management Fee | 731 Lexington Avenue Retail | Common Area
Related Party Transaction [Line Items]
Fees to related party					387,000
Related Party | Leasing fees
Related Party Transaction [Line Items]
Other Liabilities			182,000		182,000		171,000
Related Party | Development fees
Related Party Transaction [Line Items]
Other Liabilities			182,000		182,000		642,000
Related Party | Management, property management, cleaning, engineering and security fees
Related Party Transaction [Line Items]
Other Liabilities			$ 135,000		$ 135,000		$ 346,000
Alexander's Inc. | Vornado | Vornado
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners			32.40%		32.40%