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v3.8.0.1

Significant Accounting Policies - Asset Held For Sale, Cash (Details) | 12 Months Ended
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Dec. 31, 2017
Discontinued Operations |
Time period within which sale or disposition of properties held for sale is probable | 1 year

X
- Definition Represents the maximum time period within which the sale or disposal of disposal group is expected. + References No definition available. + Details
Name: | fsp_DisposalGroupIncludingDiscontinuedOperationMaximumPeriodForDisposal
Namespace Prefix: | fsp_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_DiscontinuedOperationAdditionalDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration