Related Party Transactions - Additional Information (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) $ / ft²	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 3,116,000		$ 2,116,000	$ 8,356,000	$ 7,653,000
Amounts due to Vornado	1,500,000			1,500,000		$ 801,000
Management And Development Agreement, Base Management Fee | 731 Lexington Avenue | Common Area
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction				$ 365,000
Leasing and Other Agreements, Percentage of Gross Proceeds Used for Commission for Sales Less Than Fifty Million
Related Party Transaction [Line Items]
Related party transaction, rate				3.00%
Asset sale commission threshold				$ 50,000,000
Leasing and Other Agreements, Percentage of Gross Proceeds Used For Commission for Sales Greater Than Fifty Million
Related Party Transaction [Line Items]
Related party transaction, rate				1.00%
Asset sale commission threshold				$ 50,000,000
Leasing fees
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	974,000		$ 58,000	1,144,000	$ 1,376,000
Related Party | Rego Park III Land Parcel
Related Party Transaction [Line Items]
Payments for commissions		$ 711,000
Related Party | Management and Development Agreement
Related Party Transaction [Line Items]
Annual management fee				$ 2,800,000
Related Party | Management and Development Agreement | 731 Lexington Avenue | Office and Retail Space
Related Party Transaction [Line Items]
Property management fee agreement, price per square foot | $ / ft²				0.50
Related Party | Management and Development Agreement, Percentage of Gross Revenue | Rego Park II | Retail Space
Related Party Transaction [Line Items]
Property management fee agreement percentage of gross revenue				2.00%
Related Party | Management and Development Agreement, Annualized Management Fee | 731 Lexington Avenue | Common Area
Related Party Transaction [Line Items]
Property management fee agreement percentage of gross revenue				3.00%
Related Party | Management and Development Agreement, Development Fee
Related Party Transaction [Line Items]
Property management fee agreement percentage of gross revenue				6.00%
Related Party | Leasing and Other Agreements, Percentage of Rent for First Ten Years
Related Party Transaction [Line Items]
Service fees, rate				3.00%
Related Party | Leasing and Other Agreements, Percentage of Rent for Eleventh Through Twentieth Year
Related Party Transaction [Line Items]
Service fees, rate				2.00%
Related Party | Leasing and Other Agreements, Percentage of Rent for the Twenty-First Through the Thirtieth Year
Related Party Transaction [Line Items]
Service fees, rate				1.00%
Related Party | Leasing and Other Agreements, Percentage Increase in Fee if Third Party is Used
Related Party Transaction [Line Items]
Service fees, rate				1.00%
Related Party | Leasing fees
Related Party Transaction [Line Items]
Amounts due to Vornado	974,000			$ 974,000		59,000
Related Party | Management, property management, cleaning, engineering and security fees
Related Party Transaction [Line Items]
Amounts due to Vornado	$ 526,000			$ 526,000		$ 742,000
Vornado | Alexander's Inc. | Related Party
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners	32.40%			32.40%