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Real Estate (Narrative) (Details) - ft² | Feb. 25, 2021 | Feb. 01, 2021
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One Five Nine East 53rd Street |  |
Real Estate Properties [Line Items] |  |
Net Rentable Area (in sf) |  | 220,000
Construction in Progress | 180 CityPoint |  |
Real Estate Properties [Line Items] |  |
Net Rentable Area (in sf) | 329,000 |
Construction in Progress | 880 Winter Street [Member] |  |
Real Estate Properties [Line Items] |  |
Net Rentable Area (in sf) | 224,000 |
Construction in Progress | The Prudential Center Observatory |  |
Real Estate Properties [Line Items] |  |
Net Rentable Area (in sf) | 59,000 |

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