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Organization, Properties, Basis of Presentation, Financial Instruments and Recent Accounting Standards- Management fees and interest income from loans (Details) - USD ($) | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Oct. 29, 2021 | Oct. 28, 2021
Sponsored REITs |  |  |  |  |  |
Asset management fees, low end of range (as a percent) |  |  | 1.00% |  |  |
Asset management fees, high end of range (as a percent) |  |  | 5.00% |  |  |
Notice period for cancellation of applicable contracts |  |  | 30 days |  |  |
Type of revenue |  |  | us-gaap:AssetManagement1Member | us-gaap:AssetManagement1Member |  |
Interest income and fees from the Sponsored REIT Loans | $ 0 | $ 0 | $ 0 | $ 0 |  |
Related party mortgage loan receivable |  |  |  |  | $ 24,000,000 | $ 21,000,000
Related party | FSP Monument Circle LLC |  |  |  |  |  |
Sponsored REITs |  |  |  |  |  |
Additional loan amount |  |  |  |  | $ 3,000,000 |

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