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Organization (Details) | Dec. 31, 2015 property entity item | Dec. 31, 2014 entity | Dec. 31, 2013 entity | Dec. 31, 2012 entity
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Organization |  |  |  |
Number of promissory notes secured by mortgages on real estate owned by Sponsored REITs | 6 |  |  |
Number of REITs in which the entity holds non-controlling common stock interest | entity | 9 |  |  |
Number of REITs in which the entity holds non-controlling preferred stock interest | entity | 2 |  |  |
Number of Sponsored REITs | entity | 9 | 10 | 14 | 15
Real estate |  |  |  |
Number of properties | property | 36 |  |  |
Mortgage loan secured by property |  |  |  |
Organization |  |  |  |
Number of promissory notes secured by mortgages on real estate owned by Sponsored REITs | 2 |  |  |
Secured construction loan |  |  |  |
Organization |  |  |  |
Number of promissory notes secured by mortgages on real estate owned by Sponsored REITs | 1 |  |  |
Secured revolving lines of credit |  |  |  |
Organization |  |  |  |
Number of promissory notes secured by mortgages on real estate owned by Sponsored REITs | 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% |  |  |

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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Period Type: | instant

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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Namespace Prefix: | fsp_
Data Type: | xbrli:integerItemType
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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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- Definition Number of sponsored real estate investment trusts in which the entity has an interest. + References No definition available. + 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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Data Type: | num:percentItemType
Balance Type: | na
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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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- References No definition available. + Details
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- Details
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Namespace Prefix: |
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- Details
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- Details
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- Details
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- Details
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- Details
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