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SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION (Details) (USD $) | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 184,425,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand |  |  |
Initial cost of Buildings Improvements and Equipment | 1,487,981,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 118,185,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts |  |  |
Historical Cost of Land | 183,930,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand |  |  |
Historical Cost of Buildings Improvements and Equipment | 1,606,661,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments |  |  |
Total | 1,790,591,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments |  |  |
Accumulated Depreciation | 266,284,000 us-gaap_RealEstateAccumulatedDepreciation | 222,252,000 us-gaap_RealEstateAccumulatedDepreciation | 180,756,000 us-gaap_RealEstateAccumulatedDepreciation | 152,587,000 us-gaap_RealEstateAccumulatedDepreciation
Total Costs, Net of Accumulated Depreciation | 1,524,307,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet |  |  |
Encumbrances | 0 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances |  |  |
Aggregate cost for Federal Income Tax purposes | 1,966,780 us-gaap_RealEstateFederalIncomeTaxBasis |  |  |
Park Seneca, Charlotte, NC |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 1,815,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Initial cost of Buildings Improvements and Equipment | 7,917,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 1,025,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Historical Cost of Land | 1,812,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 8,945,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Total | 10,757,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Accumulated Depreciation | 3,793,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Total Costs, Net of Accumulated Depreciation | 6,964,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember |  |  |
Park Seneca, Charlotte, NC | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Park Seneca, Charlotte, NC | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Hillview Center, Milpitas, CA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,203,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 2,813,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 7,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Historical Cost of Land | 2,203,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 2,820,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Total | 5,023,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Accumulated Depreciation | 1,138,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 3,885,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember |  |  |
Hillview Center, Milpitas, CA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Hillview Center, Milpitas, CA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Forest Park, Charlotte, NC |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 1,559,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Initial cost of Buildings Improvements and Equipment | 5,672,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 170,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Historical Cost of Land | 1,559,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 5,842,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Total | 7,401,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Accumulated Depreciation | 1,843,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Total Costs, Net of Accumulated Depreciation | 5,558,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember |  |  |
Forest Park, Charlotte, NC | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Forest Park, Charlotte, NC | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Meadow Point, Chantilly, VA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,634,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 18,911,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 6,442,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Historical Cost of Land | 2,634,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 25,353,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Total | 27,987,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Accumulated Depreciation | 8,585,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 19,402,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember |  |  |
Meadow Point, Chantilly, VA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Meadow Point, Chantilly, VA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Timberlake, Chesterfield, MO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,984,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Initial cost of Buildings Improvements and Equipment | 38,661,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,165,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Historical Cost of Land | 2,984,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 41,826,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Total | 44,810,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Accumulated Depreciation | 13,814,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Total Costs, Net of Accumulated Depreciation | 30,996,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember |  |  |
Timberlake, Chesterfield, MO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Timberlake, Chesterfield, MO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Northwest Point, Elk Grove Village, IL |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,914,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Initial cost of Buildings Improvements and Equipment | 26,295,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 8,147,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Historical Cost of Land | 2,914,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 34,442,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Total | 37,356,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Accumulated Depreciation | 12,908,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Total Costs, Net of Accumulated Depreciation | 24,448,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember |  |  |
Northwest Point, Elk Grove Village, IL | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Northwest Point, Elk Grove Village, IL | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Timberlake East, Chesterfield, MO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,626,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Initial cost of Buildings Improvements and Equipment | 17,608,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 2,359,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Historical Cost of Land | 2,626,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 19,967,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Total | 22,593,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Accumulated Depreciation | 7,046,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Total Costs, Net of Accumulated Depreciation | 15,547,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember |  |  |
Timberlake East, Chesterfield, MO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Timberlake East, Chesterfield, MO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Park Ten, Houston, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 1,061,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 21,303,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,080,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Historical Cost of Land | 569,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 24,875,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Total | 25,444,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Accumulated Depreciation | 8,375,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 17,069,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember |  |  |
Park Ten, Houston, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Park Ten, Houston, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Federal Way, Federal Way, WA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,518,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 13,212,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,267,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Historical Cost of Land | 2,518,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 16,479,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Total | 18,997,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Accumulated Depreciation | 5,178,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 13,819,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember |  |  |
Federal Way, Federal Way, WA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Federal Way, Federal Way, WA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Addison, Addison, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 4,325,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 48,040,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 5,784,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Historical Cost of Land | 4,325,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 53,824,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Total | 58,149,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Accumulated Depreciation | 16,025,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 42,124,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember |  |  |
Addison, Addison, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Addison, Addison, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Collins, Richardson, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 4,000,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 42,598,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 6,768,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Historical Cost of Land | 4,000,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 49,366,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Total | 53,366,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Accumulated Depreciation | 13,194,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 40,172,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember |  |  |
Collins, Richardson, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Collins, Richardson, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Montague, San Jose, CA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 10,250,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 5,254,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,784,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Historical Cost of Land | 10,250,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 9,038,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Total | 19,288,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Accumulated Depreciation | 2,779,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 16,509,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember |  |  |
Montague, San Jose, CA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Montague, San Jose, CA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Greenwood, Englewood, CO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 3,100,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Initial cost of Buildings Improvements and Equipment | 30,201,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 8,399,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Historical Cost of Land | 3,100,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 38,600,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Total | 41,700,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Accumulated Depreciation | 9,128,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Total Costs, Net of Accumulated Depreciation | 32,572,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember |  |  |
Greenwood, Englewood, CO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Greenwood, Englewood, CO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
River Crossing, Indianapolis, IN |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 3,000,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
Initial cost of Buildings Improvements and Equipment | 36,926,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,195,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
Historical Cost of Land | 3,000,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 40,121,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
Total | 43,121,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
Accumulated Depreciation | 10,302,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
Total Costs, Net of Accumulated Depreciation | 32,819,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember |  |  |
River Crossing, Indianapolis, IN | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
River Crossing, Indianapolis, IN | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Willow Bend, Plano, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 3,800,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 14,842,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,513,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Historical Cost of Land | 3,800,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 18,355,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Total | 22,155,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Accumulated Depreciation | 4,632,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 17,523,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember |  |  |
Willow Bend, Plano, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Willow Bend, Plano, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Innsbrook, Glenn Allen, VA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 5,000,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 40,216,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 5,353,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Historical Cost of Land | 5,000,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 45,569,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Total | 50,569,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Accumulated Depreciation | 11,356,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 39,213,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember |  |  |
Innsbrook, Glenn Allen, VA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Innsbrook, Glenn Allen, VA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
380 Interlocken, Bloomfield, CO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 8,275,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
Initial cost of Buildings Improvements and Equipment | 34,462,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 6,913,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
Historical Cost of Land | 8,275,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 41,375,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
Total | 49,650,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
Accumulated Depreciation | 11,395,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
Total Costs, Net of Accumulated Depreciation | 38,255,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember |  |  |
380 Interlocken, Bloomfield, CO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
380 Interlocken, Bloomfield, CO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Blue Lagoon, Miami, FL |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 6,306,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Initial cost of Buildings Improvements and Equipment | 46,124,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 1,473,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Historical Cost of Land | 6,306,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 47,597,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Total | 53,903,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Accumulated Depreciation | 10,823,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Total Costs, Net of Accumulated Depreciation | 43,080,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember |  |  |
Blue Lagoon, Miami, FL | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Blue Lagoon, Miami, FL | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Eldridge Green, Houston, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 3,900,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 43,791,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,802,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Historical Cost of Land | 3,900,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 47,593,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Total | 51,493,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Accumulated Depreciation | 10,739,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 40,754,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember |  |  |
Eldridge Green, Houston, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Eldridge Green, Houston, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Liberty Plaza, Addison, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 4,374,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 21,146,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 5,488,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Historical Cost of Land | 4,374,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 26,634,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Total | 31,008,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Accumulated Depreciation | 7,547,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 23,461,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember |  |  |
Liberty Plaza, Addison, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Liberty Plaza, Addison, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
One Overton, Atlanta, GA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 3,900,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 77,229,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 7,440,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
Historical Cost of Land | 3,900,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 84,669,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
Total | 88,569,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
Accumulated Depreciation | 19,746,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 68,823,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember |  |  |
One Overton, Atlanta, GA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
One Overton, Atlanta, GA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
FSP 390 Interlocken, Broomfield, CO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 7,013,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
Initial cost of Buildings Improvements and Equipment | 37,751,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,605,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
Historical Cost of Land | 7,013,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 41,356,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
Total | 48,369,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
Accumulated Depreciation | 9,751,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
Total Costs, Net of Accumulated Depreciation | 38,618,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember |  |  |
FSP 390 Interlocken, Broomfield, CO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
FSP 390 Interlocken, Broomfield, CO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
East Baltimore, Baltimore, MD |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 4,600,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
Initial cost of Buildings Improvements and Equipment | 55,267,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,881,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
Historical Cost of Land | 4,600,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 59,148,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
Total | 63,748,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
Accumulated Depreciation | 11,644,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
Total Costs, Net of Accumulated Depreciation | 52,104,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember |  |  |
East Baltimore, Baltimore, MD | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
East Baltimore, Baltimore, MD | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Park Ten II, Houston, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 1,300,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 31,712,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 409,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Historical Cost of Land | 1,300,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 32,121,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Total | 33,421,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Accumulated Depreciation | 5,700,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 27,721,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember |  |  |
Park Ten II, Houston, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Park Ten II, Houston, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Lakeside Crossing, Maryland Heights, MO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 1,900,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Initial cost of Buildings Improvements and Equipment | 16,192,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 2,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Historical Cost of Land | 1,900,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 16,194,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Total | 18,094,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Accumulated Depreciation | 2,525,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Total Costs, Net of Accumulated Depreciation | 15,569,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember |  |  |
Lakeside Crossing, Maryland Heights, MO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Lakeside Crossing, Maryland Heights, MO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Dulles Virginia, Sterling, VA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 4,813,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 13,285,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 3,828,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Historical Cost of Land | 4,813,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 17,113,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Total | 21,926,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Accumulated Depreciation | 2,078,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 19,848,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember |  |  |
Dulles Virginia, Sterling, VA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Dulles Virginia, Sterling, VA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Stonecroft, Chantilly, VA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,102,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 18,003,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 0 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Historical Cost of Land | 2,102,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 18,003,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Total | 20,105,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Accumulated Depreciation | 2,540,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 17,565,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember |  |  |
Stonecroft, Chantilly, VA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Stonecroft, Chantilly, VA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Eden Bluff, Eden Prairie, MN |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 5,422,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Initial cost of Buildings Improvements and Equipment | 9,294,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 0 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Historical Cost of Land | 5,422,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 9,294,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Total | 14,716,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Accumulated Depreciation | 1,310,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Total Costs, Net of Accumulated Depreciation | 13,406,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember |  |  |
Eden Bluff, Eden Prairie, MN | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Eden Bluff, Eden Prairie, MN | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
121 South Eight Street, Minneapolis, MN |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 8,628,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
Initial cost of Buildings Improvements and Equipment | 15,214,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 8,575,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
Historical Cost of Land | 8,628,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 23,789,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
Total | 32,417,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
Accumulated Depreciation | 2,450,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
Total Costs, Net of Accumulated Depreciation | 29,967,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember |  |  |
121 South Eight Street, Minneapolis, MN | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
121 South Eight Street, Minneapolis, MN | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
909 Davis, Evanston, IL |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 4,912,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
Initial cost of Buildings Improvements and Equipment | 18,229,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 317,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
Historical Cost of Land | 4,912,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 18,546,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
Total | 23,458,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
Accumulated Depreciation | 1,611,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
Total Costs, Net of Accumulated Depreciation | 21,847,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember |  |  |
909 Davis, Evanston, IL | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
909 Davis, Evanston, IL | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Emperor Boulevard, Durham, NC |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,423,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Initial cost of Buildings Improvements and Equipment | 53,997,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 52,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Historical Cost of Land | 2,423,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 54,049,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Total | 56,472,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Accumulated Depreciation | 5,311,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Total Costs, Net of Accumulated Depreciation | 51,161,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember |  |  |
Emperor Boulevard, Durham, NC | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Emperor Boulevard, Durham, NC | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Legacy Tennyson Center, Plano, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 3,067,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 22,064,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 0 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Historical Cost of Land | 3,067,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 22,064,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Total | 25,131,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Accumulated Depreciation | 2,169,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 22,962,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember |  |  |
Legacy Tennyson Center, Plano, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Legacy Tennyson Center, Plano, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
One Legacy Circle, Plano, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,590,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 36,608,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 952,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
Historical Cost of Land | 2,590,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 37,560,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
Total | 40,150,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
Accumulated Depreciation | 3,857,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 36,293,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember |  |  |
One Legacy Circle, Plano, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
One Legacy Circle, Plano, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
One Ravinia Drive, Atlanta, GA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 2,686,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 35,125,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 2,742,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
Historical Cost of Land | 2,686,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 37,867,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
Total | 40,553,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
Accumulated Depreciation | 2,558,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 37,995,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember |  |  |
One Ravinia Drive, Atlanta, GA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
One Ravinia Drive, Atlanta, GA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
Westchase I & II, Houston, TX |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 8,491,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Initial cost of Buildings Improvements and Equipment | 121,508,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 1,930,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Historical Cost of Land | 8,491,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 123,438,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Total | 131,929,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Accumulated Depreciation | 6,956,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Total Costs, Net of Accumulated Depreciation | 124,973,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember |  |  |
Westchase I & II, Houston, TX | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
Westchase I & II, Houston, TX | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
1999 Broadway, CO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 16,334,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
Initial cost of Buildings Improvements and Equipment | 137,726,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 1,298,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
Historical Cost of Land | 16,334,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 139,024,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
Total | 155,358,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
Accumulated Depreciation | 5,664,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
Total Costs, Net of Accumulated Depreciation | 149,694,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember |  |  |
1999 Broadway, CO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
1999 Broadway, CO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
999 Peachtree, GA |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 10,187,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
Initial cost of Buildings Improvements and Equipment | 107,727,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 818,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
Historical Cost of Land | 10,187,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 108,545,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
Total | 118,732,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
Accumulated Depreciation | 4,168,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
Total Costs, Net of Accumulated Depreciation | 114,564,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember |  |  |
999 Peachtree, GA | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
999 Peachtree, GA | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |
1001 17th Street, CO |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Initial cost of Land | 17,413,000 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
Initial cost of Buildings Improvements and Equipment | 165,058,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
Costs Capitalized (Disposals) Subsequent to Acquisition | 202,000 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
Historical Cost of Land | 17,413,000 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
Historical Cost of Buildings Improvements and Equipment | 165,260,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
Total | 182,673,000 fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
Accumulated Depreciation | 5,646,000 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
Total Costs, Net of Accumulated Depreciation | 177,027,000 us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember |  |  |
1001 17th Street, CO | Minimum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 5 years |  |  |
1001 17th Street, CO | Maximum |  |  |  |
REAL ESTATE AND ACCUMULATED DEPRECIATION |  |  |  |
Depreciable Life Years | 39 years |  |  |

X
- Definition The carrying amount at which buildings improvements and equipments are carried at the end of the period. + References No definition available. + Details
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- Definition Gross amount at which land and buildings and improvements and equipments are carried at the end of the period for each property. + References No definition available. + Details
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- Definition Amount of accumulated depreciation pertaining to real estate investments for entities with a substantial portion of business acquiring and holding investment real estate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 970 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28.FN4) -URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04.(c) Schedule III) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5 + Details
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- Definition Amount of lien or mortgage outstanding on real estate investment properties for entities with a substantial portion of business acquiring and holding investment real estate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 970 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28) -URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04.(c) Schedule III) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5 + Details
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- Definition Amount of land for entities with a substantial portion of business acquiring and holding investment real estate. Excludes real estate not held as an investment or interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 970 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28) -URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04.(c) Schedule III) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5 + Details
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- Definition Amount of carrying costs of properties that were capitalized after acquisition, for example, but not limited to, real estate taxes and insurance for entities with a substantial portion of business acquiring and holding investment real estate. Excludes initial purchase price and improvements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 970 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28) -URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04.(c) Schedule III) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5 + Details
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