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Organization (Details) ft² in Thousands, $ in Thousands |  | 12 Months Ended |
--- | --- | --- | ---
Jun. 30, 2018 USD ($) ft² | Dec. 31, 2018 USD ($) ft² a property aptunits segment condomium_unit | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Apr. 04, 2017 ft²
Operating Properties |  |  |  |  |
Number of properties | property |  | 7 |  |  |
Property rentals | $ |  | $ 152,795 | $ 152,857 | $ 151,444 |
Number of segments | segment |  | 1 |  |  |
Rego Park I | Sears |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  |  |  |  | 195
Property rentals | $ |  | $ 10,300 |  |  |
Rego Park II | Kohl's |  |  |  |  |
Operating Properties |  |  |  |  |
Lease expiration date |  | Jan. 01, 2031 |  |  |
Rego Park II | Anchor |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 609 |  |  |
Rego Park II | Tenant Occupant | Anchor | Toys R Us/ Babies R Us |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) | 47 |  |  |  |
Property rentals | $ | $ 2,600 |  |  |  |
Rego Park II | Retail space | Toys R Us/ Babies R Us |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 47 |  |  |
Percentage of affiliate owned |  | 33.33% |  |  |
Operating property | 731 Lexington Avenue |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 1,311 |  |  |
Operating property | 731 Lexington Avenue | Office space |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 889 |  |  |
Operating property | 731 Lexington Avenue | Retail space |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 174 |  |  |
Operating property | 731 Lexington Avenue | Retail space | Tenant Occupant | Home Depot |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 83 |  |  |
Operating property | 731 Lexington Avenue | Retail space | Tenant Occupant | Container Store |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 34 |  |  |
Operating property | 731 Lexington Avenue | Retail space | Tenant Occupant | Hennes Mauritz |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 27 |  |  |
Operating property | 731 Lexington Avenue | Residence space |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 248 |  |  |
Number of property units | condomium_unit |  | 105 |  |  |
Operating property | Rego Park I |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 343 |  |  |
Operating property | Rego Park I | Tenant Occupant | Anchor | Sears |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 195 |  |  |
Operating property | Rego Park I | Tenant Occupant | Anchor | Burlington Coat Factory |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 50 |  |  |
Operating property | Rego Park I | Tenant Occupant | Anchor | Bed Bath and Beyond |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 46 |  |  |
Operating property | Rego Park I | Tenant Occupant | Anchor | Marshalls |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 36 |  |  |
Operating property | Rego Park II | Tenant Occupant | Anchor | Costco |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 145 |  |  |
Operating property | Rego Park II | Tenant Occupant | Anchor | Century 21 |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 135 |  |  |
Operating property | Rego Park II | Tenant Occupant | Anchor | Kohl's |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 133 |  |  |
Operating property | Alexander apartment tower |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 255 |  |  |
Number of property units | aptunits |  | 312 |  |  |
Operating property | Paramus | Tenant Occupant | Ikea |  |  |  |  |
Operating Properties |  |  |  |  |
Area of land | a |  | 30.3 |  |  |
Operating property | Flushing property |  |  |  |  |
Operating Properties |  |  |  |  |
Area of property (in square feet) |  | 167 |  |  |
Properties to be developed | Rego Park III |  |  |  |  |
Operating Properties |  |  |  |  |
Area of land |  | 140 |  |  |

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