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Organization (Details)	Dec. 31, 2015 property entity item	Dec. 31, 2014 entity	Dec. 31, 2013 entity	Dec. 31, 2012 entity
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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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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X

- 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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X

- Definition

Number of sponsored real estate investment trusts in which the entity has an interest.

+ References

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+ Details

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- Definition

Represents the ownership interest percentage of the parent in consolidated entities.

+ References

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+ Details

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X

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

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- References

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- Details

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- Details

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- Details

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X

- Details

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