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Properties Held for Sale and Property Dispositions (Details) $ in Thousands | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2019 USD ($) ft² | Nov. 30, 2019 USD ($) ft² | Aug. 31, 2019 USD ($) ft² | Nov. 30, 2018 USD ($) ft² a | Oct. 31, 2018 USD ($) ft² | Jul. 31, 2018 USD ($) ft² | Jun. 30, 2018 USD ($) ft² | May 31, 2018 USD ($) ft² | Feb. 28, 2018 | Jan. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) ft² | Nov. 30, 2017 | Oct. 31, 2017 USD ($) ft² | Sep. 30, 2017 | Jul. 31, 2017 USD ($) ft² | Apr. 30, 2017 USD ($) ft² | Dec. 31, 2019 USD ($) ft² | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) ft² | Sep. 30, 2019 USD ($) | Jan. 01, 2018 USD ($) ft²
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² | 27,607,971 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 27,607,971 |  |  |  |
Employee-related liabilities | $ 4,000 |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |  | $ 4,000 | $ 11,700 | $ 0 |  |
Purchase price and other fair value adjustments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 69,389 | $ 57,385 | $ 0 |  |
East 220 Street 42 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 815,000 |
Suburban |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² | 1,107,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,107,000 |  |  |  |
Gross asset valuation | $ 229,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 229,200 |  |  |  |
Gain on Sale | $ 1,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
1640 Flatbush Avenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² | 1,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,000 |  |  |  |
Gross asset valuation | $ 16,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 16,200 |  |  |  |
Gain on Sale | 5,500 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee-related liabilities | $ 2,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,000 |  |  |  |
562 Fifth Avenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² | 42,635 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 42,635 |  |  |  |
Gross asset valuation | $ 52,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 52,400 |  |  |  |
Gain on Sale | $ (26,600) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
1010 Washington Boulevard |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  | 143,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  | $ 23,100 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  | $ (7,100) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Spring Street 115 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  | 5,218 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  | $ 66,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  |  | 3,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase price and other fair value adjustments |  |  | $ 3,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage in disposed asset |  |  | 49.00% |  |  |  |  |  |  |  |  |  |  |  |  |  | 49.00% |  |  |  |
Deconsolidation of ownership interest percentage |  |  | 51.00% |  |  |  |  |  |  |  |  |  |  |  |  |  | 51.00% |  |  |  |
2 Herald Square |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  | 369,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  | $ 265,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage in disposed asset |  |  |  | 49.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
400 Summit Lake Drive |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | a |  |  |  | 39.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  | $ 3,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  |  |  | $ (36,200) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Upper East Side Assemblage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  | 70,142 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  |  | $ 143,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  |  |  |  | (6,300) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment charge |  |  |  |  | $ 5,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
1-6 International Drive |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  | 540,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  |  |  | $ 55,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  |  |  |  |  | $ (2,600) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
635 Madison Avenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  | 176,530 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  | $ 153,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  |  |  |  |  |  | $ (14,100) |  |  |  |  |  |  |  |  |  |  |  |  |  |
115-117 Stevens Avenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  | 178,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  |  | $ 12,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on Sale |  |  |  |  |  |  |  | $ (700) |  |  |  |  |  |  |  |  |  |  |  |  |
600 Lexington Avenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 303,515
Gross asset valuation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 305,000
Gain on Sale |  |  |  |  |  |  |  |  |  | $ 23,800 |  |  |  |  |  |  |  |  |  |  |
Employee-related liabilities |  |  |  |  |  |  |  |  |  | $ 1,300 |  |  |  |  |  |  |  |  |  |  |
1515 Broadway |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  | 1,750,000 |  |  |  |  |  |  |  | 1,750,000 |  |
Gross asset valuation |  |  |  |  |  |  |  |  |  |  | $ 1,950,000 |  |  |  |  |  |  |  | $ 1,950,000 |  |
Gain on Sale |  |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |
Joint venture ownership percentage sold |  |  |  |  |  |  |  |  | 12.87% |  |  | 30.13% |  |  |  |  |  |  |  |  |
125 Chubb Way |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  |  |  | 278,000 |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  |  |  |  |  |  |  | $ 29,500 |  |  |  |  |  |  |  |
Gain on Sale |  |  |  |  |  |  |  |  |  |  |  |  | $ (26,100) |  |  |  |  |  |  |  |
16 Court Street |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  |  |  | 317,600 |  |  |  |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  |  |  |  |  |  |  | $ 171,000 |  |  |  |  |  |  |  |
Gain on Sale |  |  |  |  |  |  |  |  |  |  |  |  | $ 64,900 |  |  |  |  |  |  |  |
Employee-related liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,500 |  |  |  |  |
680-750 Washington Boulevard |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 325,000 |  |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 97,000 |  |  |  |  |  |
Gain on Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (44,200) |  |  |  |  |  |
520 White Plains Road |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 180,000 |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 21,000 |  |  |  |  |
Gain on Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (14,600) |  |  |  |  |
102 Greene Street |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,200 |  |  |  |  |
Gross asset valuation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 43,500 |  |  |  |  |
Gain on Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,900 |  |  |  |  |
Employee-related liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 900 |  |  |  |  |
Ownership percentage in disposed asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00% |  |  |  |  |
Joint venture ownership percentage sold |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |
102 Greene Street |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment in joint venture, ownership percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |
Development Rights | Upper East Side Assemblage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property Dispositions and Assets Held for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unaudited Approximate Usable Square Feet | ft² |  |  |  |  | 31,076 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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