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Related Party Transactions - Additional Information (Detail) ft² in Thousands | 9 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 USD ($) $ / ft² | Dec. 31, 2018 USD ($) | Jun. 30, 2018 ft²
Rego Park II | Retail Space | Toys R Us |  |  |
Related Party Transaction [Line Items] |  |  |
Area of property (in sqft.) | ft² |  |  | 47
Annual revenue from leased property |  | $ 2,600,000 |
Vornado |  |  |
Related Party Transaction [Line Items] |  |  |
Management fee agreement value | $ 2,800,000 |  |
Vornado | Property management, cleaning, engineering and security fees | Rego Park II | Retail Space |  |  |
Related Party Transaction [Line Items] |  |  |
Property management fee agreement percentage of income | 2.00% |  |
Vornado | Property management, cleaning, engineering and security fees | 731 Lexington Avenue | Office and Retail Space |  |  |
Related Party Transaction [Line Items] |  |  |
Property management fee agreement, price per square foot | $ / ft² | 0.50 |  |
Vornado | Property management, cleaning, engineering and security fees | 731 Lexington Avenue | Common Area |  |  |
Related Party Transaction [Line Items] |  |  |
Property management fee agreement value | $ 324,000 |  |
Property management fee escalation percentage per annum | 3.00% |  |
Vornado | Development fees |  |  |
Related Party Transaction [Line Items] |  |  |
Development fee as percentage of development costs | 6.00% |  |
Amounts due from / (Amounts due to) related party | $ (68,000) | (146,000) |
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 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% |  |
Amounts due from / (Amounts due to) related party | $ (3,871,000) | (13,000) |
Vornado | Management, property management, cleaning, engineering and security fees |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts due from / (Amounts due to) related party | $ (699,000) | $ (549,000) |
Vornado | Alexander's Inc. | Vornado |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners | 32.40% |  |
Vornado | Toys R Us | Vornado |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling interest, ownership percentage by parent |  | 32.50% |

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