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Related Party Transactions - Narrative (Details) | 12 Months Ended
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Dec. 31, 2023 USD ($) $ / ft² | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Related Party Transaction [Line Items] |  |  |
Related party transaction, amounts of transaction | $ 10,729,000 | $ 10,093,000 | $ 11,331,000
Leasing Fees |  |  |
Related Party Transaction [Line Items] |  |  |
Related party transaction, amounts of transaction | 1,213,000 | 1,378,000 | $ 1,800,000
Vornado |  |  |
Related Party Transaction [Line Items] |  |  |
Other liabilities | 715,000 | 801,000 |
Vornado | Management and Development Agreement |  |  |
Related Party Transaction [Line Items] |  |  |
Annual management fee | $ 2,800,000 |  |
Vornado | 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 |  |
Vornado | Percentage of gross revenue | Rego Park II | Retail Site |  |  |
Related Party Transaction [Line Items] |  |  |
Property management fee, percent fee | 2.00% |  |
Vornado | Base management fee | 731 Lexington Avenue | Common Area |  |  |
Related Party Transaction [Line Items] |  |  |
Related party transaction, amounts of transaction | $ 365,000 |  |
Vornado | Escalating annualized management fee | 731 Lexington Avenue | Common Area |  |  |
Related Party Transaction [Line Items] |  |  |
Property management fee, percent fee | 3.00% |  |
Vornado | Development fee | 731 Lexington Avenue |  |  |
Related Party Transaction [Line Items] |  |  |
Property management fee, percent fee | 6.00% |  |
Vornado | 3% of rent for the first ten years |  |  |
Related Party Transaction [Line Items] |  |  |
Service fees, rate | 3.00% |  |
Vornado | 2% of rent for the eleventh through the twentieth year |  |  |
Related Party Transaction [Line Items] |  |  |
Service fees, rate | 2.00% |  |
Vornado | 1% of rent for the twenty-first through thirtieth year |  |  |
Related Party Transaction [Line Items] |  |  |
Service fees, rate | 1.00% |  |
Vornado | 1% increase in fee if third party is used |  |  |
Related Party Transaction [Line Items] |  |  |
Service fees, rate | 1.00% |  |
Vornado | 3% of gross proceeds used for commission for sales less than $50,000,000 |  |  |
Related Party Transaction [Line Items] |  |  |
Related party transaction, rate | 3.00% |  |
Asset sale commission threshold | $ 50,000,000 |  |
Vornado | 1% of gross proceeds used for commission for sales greater than $50,000,000 |  |  |
Related Party Transaction [Line Items] |  |  |
Related party transaction, rate | 1.00% |  |
Asset sale commission threshold | $ 50,000,000 |  |
Vornado | Management Property Management Cleaning Engineering and Security Fees |  |  |
Related Party Transaction [Line Items] |  |  |
Other liabilities | 646,000 | 742,000 |
Vornado | Leasing Fees |  |  |
Related Party Transaction [Line Items] |  |  |
Other liabilities | $ 69,000 | $ 59,000 |
Vornado | Alexander's Inc. | Vornado |  |  |
Related Party Transaction [Line Items] |  |  |
Parent ownership | 32.40% |  |
Director | Alexander's Inc. | Mr. Roth, Interstate, David Mandelbaum and Russell B, Wight, Jr. |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership percentage by noncontrolling owners | 26.00% |  |
Indirectly through Vornado | Alexander's Inc. | Directors indirect through Vornado |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership percentage by noncontrolling owners | 2.30% |  |

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