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Organization, Properties, Basis of Presentation, Financial Instruments and Recent Accounting Standards (Details) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2023 ft² property | Sep. 30, 2022 ft² property
Properties |  |
Number of properties | 19 |
Number of owned and consolidated properties | 20 | 22
Rentable square feet | ft² | 6,206,460 | 6,433,954
Number of properties classified as assets held for sale | 3 |
FSP Investments LLC |  |
Organization |  |
Ownership interest (as a percent) | 100.00% |
FSP Property Management LLC |  |
Organization |  |
Ownership interest (as a percent) | 100.00% |
FSP Holdings LLC |  |
Organization |  |
Ownership interest (as a percent) | 100.00% |
FSP Protective TRS Corp. |  |
Organization |  |
Ownership interest (as a percent) | 100.00% |

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