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Organization, Properties, Basis of Presentation, Financial Instruments and Recent Accounting Standards (Details) | Sep. 30, 2012 entity note item sqft property | Sep. 30, 2011 property sqft
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Organization |  |
Number of promissory notes secured by mortgages on real estate owned by Sponsored REITs | 8 |
Number of corporations organized to operate as real estate investment trusts (REITs) | 16 |
Number of properties held for sale | 1 |
Number of REITs in which the entity holds non-controlling preferred stock interest | 3 |
Commercial real estate: |  |
Number of properties | 37 | 35
Rentable square feet | 7,439,195 | 6,929,891
Mortgage loan |  |
Organization |  |
Number of promissory notes secured by mortgages on real estate owned by Sponsored REITs | 1 |
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% |

X
- Definition Represents the number of promissory notes secured by mortgages on real estate owned by Sponsored REITs. + References No definition available. + Details
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X
- Definition Represents the number of real estate properties held for sale as of the balance sheet date. + References No definition available. + Details
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X
- Definition Represents the number of entities in which the reporting entity has a non-controlling common stock interest. + References No definition available. + Details
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- Definition Represents the number of entities in which the reporting entity has a non-controlling preferred stock interest. + References No definition available. + Details
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- Details
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- Definition Represents the ownership interest percentage of the parent in consolidated entities. + References No definition available. + Details
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- Definition Area of a real estate property. + References No definition available. + Details
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- Definition The number of real estate properties owned as of the balance sheet date. + References No definition available. + Details
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- Details
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