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Related Party Transactions - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($) $ / ft²	Jun. 30, 2025 USD ($)	Dec. 31, 2025 USD ($)
Related Party Transaction [Line Items]
Fees to related party	$ 5,638,000	$ 2,600,000	$ 7,712,000	$ 5,191,000
Development fees
Related Party Transaction [Line Items]
Fees to related party	79,000	207,000	144,000	626,000
Leasing fees
Related Party Transaction [Line Items]
Fees to related party	492,000	229,000	522,000	242,000
Property management, cleaning, engineering, parking and security fees
Related Party Transaction [Line Items]
Fees to related party	2,012,000	$ 1,464,000	3,291,000	$ 2,923,000
Related Party
Related Party Transaction [Line Items]
Management fee agreement value			2,800,000
Other liabilities	1,044,000		$ 1,044,000		$ 134,000
Related Party | Rego Park I property
Related Party Transaction [Line Items]
Payments for commissions	2,355,000
Related Party | Development fees
Related Party Transaction [Line Items]
Development fee as percentage of development costs			6.00%
Other liabilities	79,000		$ 79,000		34,000
Related Party | 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 of third-party lease commission			33.333%
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%
Other liabilities	492,000		$ 492,000		$ 100,000
Related Party | Property management, cleaning, engineering, parking and security fees
Related Party Transaction [Line Items]
Other liabilities	$ 473,000		$ 473,000
Related Party | Retail Space | Rego Park Shopping Center | Property management fees
Related Party Transaction [Line Items]
Property management fee, percent fee			2.00%
Related Party | Office and Retail Space | 731 Lexington Avenue | Property management fees
Related Party Transaction [Line Items]
Property management fee agreement, price per square foot | $ / ft²			0.50
Related Party | Common Area | 731 Lexington Avenue | Property management fees
Related Party Transaction [Line Items]
Property management fee escalation percentage per annum			3.00%
Related Party | Common Area | 731 Lexington Avenue | Management and development agreement, base management fee
Related Party Transaction [Line Items]
Fees to related party			$ 399,000
Vornado | Leasing fees
Related Party Transaction [Line Items]
Asset sale commission threshold			$ 50,000,000
Alexander's Inc. | Related Party | Vornado
Related Party Transaction [Line Items]
Subsidiary, ownership percentage, parent	32.40%		32.40%

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