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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	184,425,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
Initial cost of Buildings Improvements and Equipment	1,487,981,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment
Costs Capitalized (Disposals) Subsequent to Acquisition	118,185,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts
Historical Cost of Land	183,930,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
Historical Cost of Buildings Improvements and Equipment	1,606,661,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments
Total	1,790,591,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments
Accumulated Depreciation	266,284,000us-gaap_RealEstateAccumulatedDepreciation	222,252,000us-gaap_RealEstateAccumulatedDepreciation	180,756,000us-gaap_RealEstateAccumulatedDepreciation	152,587,000us-gaap_RealEstateAccumulatedDepreciation
Total Costs, Net of Accumulated Depreciation	1,524,307,000us-gaap_SECScheduleIIIRealEstateInvestmentPropertyNet
Encumbrances	0us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
Aggregate cost for Federal Income Tax purposes	1,966,780us-gaap_RealEstateFederalIncomeTaxBasis
Park Seneca, Charlotte, NC
REAL ESTATE AND ACCUMULATED DEPRECIATION
Initial cost of Land	1,815,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember
Initial cost of Buildings Improvements and Equipment	7,917,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember
Costs Capitalized (Disposals) Subsequent to Acquisition	1,025,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember
Historical Cost of Land	1,812,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember
Historical Cost of Buildings Improvements and Equipment	8,945,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember
Total	10,757,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember
Accumulated Depreciation	3,793,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkSenecaCharlotteNCMember
Total Costs, Net of Accumulated Depreciation	6,964,000us-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	2,203,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember
Initial cost of Buildings Improvements and Equipment	2,813,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	7,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember
Historical Cost of Land	2,203,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember
Historical Cost of Buildings Improvements and Equipment	2,820,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember
Total	5,023,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember
Accumulated Depreciation	1,138,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_HillviewCenterMilpitasCAMember
Total Costs, Net of Accumulated Depreciation	3,885,000us-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	1,559,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember
Initial cost of Buildings Improvements and Equipment	5,672,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember
Costs Capitalized (Disposals) Subsequent to Acquisition	170,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember
Historical Cost of Land	1,559,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember
Historical Cost of Buildings Improvements and Equipment	5,842,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember
Total	7,401,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember
Accumulated Depreciation	1,843,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ForestParkCharlotteNCMember
Total Costs, Net of Accumulated Depreciation	5,558,000us-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	2,634,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember
Initial cost of Buildings Improvements and Equipment	18,911,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	6,442,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember
Historical Cost of Land	2,634,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember
Historical Cost of Buildings Improvements and Equipment	25,353,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember
Total	27,987,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember
Accumulated Depreciation	8,585,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MeadowPointChantillyVAMember
Total Costs, Net of Accumulated Depreciation	19,402,000us-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	2,984,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember
Initial cost of Buildings Improvements and Equipment	38,661,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,165,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember
Historical Cost of Land	2,984,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember
Historical Cost of Buildings Improvements and Equipment	41,826,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember
Total	44,810,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember
Accumulated Depreciation	13,814,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeChesterfieldMOMember
Total Costs, Net of Accumulated Depreciation	30,996,000us-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	2,914,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember
Initial cost of Buildings Improvements and Equipment	26,295,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember
Costs Capitalized (Disposals) Subsequent to Acquisition	8,147,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember
Historical Cost of Land	2,914,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember
Historical Cost of Buildings Improvements and Equipment	34,442,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember
Total	37,356,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember
Accumulated Depreciation	12,908,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_NorthwestPointElkGroveVillageILMember
Total Costs, Net of Accumulated Depreciation	24,448,000us-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	2,626,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember
Initial cost of Buildings Improvements and Equipment	17,608,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember
Costs Capitalized (Disposals) Subsequent to Acquisition	2,359,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember
Historical Cost of Land	2,626,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember
Historical Cost of Buildings Improvements and Equipment	19,967,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember
Total	22,593,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember
Accumulated Depreciation	7,046,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_TimberlakeEastChesterfieldMOMember
Total Costs, Net of Accumulated Depreciation	15,547,000us-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	1,061,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember
Initial cost of Buildings Improvements and Equipment	21,303,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,080,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember
Historical Cost of Land	569,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember
Historical Cost of Buildings Improvements and Equipment	24,875,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember
Total	25,444,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember
Accumulated Depreciation	8,375,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenHoustonTXMember
Total Costs, Net of Accumulated Depreciation	17,069,000us-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	2,518,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember
Initial cost of Buildings Improvements and Equipment	13,212,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,267,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember
Historical Cost of Land	2,518,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember
Historical Cost of Buildings Improvements and Equipment	16,479,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember
Total	18,997,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember
Accumulated Depreciation	5,178,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FederalWayFederalWayWAMember
Total Costs, Net of Accumulated Depreciation	13,819,000us-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	4,325,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember
Initial cost of Buildings Improvements and Equipment	48,040,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	5,784,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember
Historical Cost of Land	4,325,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember
Historical Cost of Buildings Improvements and Equipment	53,824,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember
Total	58,149,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember
Accumulated Depreciation	16,025,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_AddisonAddisonTXMember
Total Costs, Net of Accumulated Depreciation	42,124,000us-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	4,000,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember
Initial cost of Buildings Improvements and Equipment	42,598,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	6,768,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember
Historical Cost of Land	4,000,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember
Historical Cost of Buildings Improvements and Equipment	49,366,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember
Total	53,366,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember
Accumulated Depreciation	13,194,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_CollinsRichardsonTXMember
Total Costs, Net of Accumulated Depreciation	40,172,000us-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	10,250,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember
Initial cost of Buildings Improvements and Equipment	5,254,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,784,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember
Historical Cost of Land	10,250,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember
Historical Cost of Buildings Improvements and Equipment	9,038,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember
Total	19,288,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember
Accumulated Depreciation	2,779,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_MontagueSanJoseCAMember
Total Costs, Net of Accumulated Depreciation	16,509,000us-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	3,100,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember
Initial cost of Buildings Improvements and Equipment	30,201,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember
Costs Capitalized (Disposals) Subsequent to Acquisition	8,399,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember
Historical Cost of Land	3,100,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember
Historical Cost of Buildings Improvements and Equipment	38,600,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember
Total	41,700,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember
Accumulated Depreciation	9,128,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_GreenwoodEnglewoodCOMember
Total Costs, Net of Accumulated Depreciation	32,572,000us-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	3,000,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember
Initial cost of Buildings Improvements and Equipment	36,926,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,195,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember
Historical Cost of Land	3,000,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember
Historical Cost of Buildings Improvements and Equipment	40,121,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember
Total	43,121,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember
Accumulated Depreciation	10,302,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_RiverCrossingIndianapolisINMember
Total Costs, Net of Accumulated Depreciation	32,819,000us-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	3,800,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember
Initial cost of Buildings Improvements and Equipment	14,842,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,513,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember
Historical Cost of Land	3,800,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember
Historical Cost of Buildings Improvements and Equipment	18,355,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember
Total	22,155,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember
Accumulated Depreciation	4,632,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WillowBendPlanoTXMember
Total Costs, Net of Accumulated Depreciation	17,523,000us-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	5,000,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember
Initial cost of Buildings Improvements and Equipment	40,216,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	5,353,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember
Historical Cost of Land	5,000,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember
Historical Cost of Buildings Improvements and Equipment	45,569,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember
Total	50,569,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember
Accumulated Depreciation	11,356,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_InnsbrookGlennAllenVAMember
Total Costs, Net of Accumulated Depreciation	39,213,000us-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	8,275,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember
Initial cost of Buildings Improvements and Equipment	34,462,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember
Costs Capitalized (Disposals) Subsequent to Acquisition	6,913,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember
Historical Cost of Land	8,275,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember
Historical Cost of Buildings Improvements and Equipment	41,375,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember
Total	49,650,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember
Accumulated Depreciation	11,395,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Interlocken380BloomfieldCOMember
Total Costs, Net of Accumulated Depreciation	38,255,000us-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	6,306,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember
Initial cost of Buildings Improvements and Equipment	46,124,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember
Costs Capitalized (Disposals) Subsequent to Acquisition	1,473,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember
Historical Cost of Land	6,306,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember
Historical Cost of Buildings Improvements and Equipment	47,597,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember
Total	53,903,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember
Accumulated Depreciation	10,823,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_BlueLagoonMiamiFLMember
Total Costs, Net of Accumulated Depreciation	43,080,000us-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	3,900,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember
Initial cost of Buildings Improvements and Equipment	43,791,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,802,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember
Historical Cost of Land	3,900,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember
Historical Cost of Buildings Improvements and Equipment	47,593,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember
Total	51,493,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember
Accumulated Depreciation	10,739,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EldridgeGreenHoustonTXMember
Total Costs, Net of Accumulated Depreciation	40,754,000us-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	4,374,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember
Initial cost of Buildings Improvements and Equipment	21,146,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	5,488,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember
Historical Cost of Land	4,374,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember
Historical Cost of Buildings Improvements and Equipment	26,634,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember
Total	31,008,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember
Accumulated Depreciation	7,547,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LibertyPlazaAddisonTXMember
Total Costs, Net of Accumulated Depreciation	23,461,000us-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	3,900,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember
Initial cost of Buildings Improvements and Equipment	77,229,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	7,440,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember
Historical Cost of Land	3,900,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember
Historical Cost of Buildings Improvements and Equipment	84,669,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember
Total	88,569,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember
Accumulated Depreciation	19,746,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneOvertonAtlantaGAMember
Total Costs, Net of Accumulated Depreciation	68,823,000us-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	7,013,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember
Initial cost of Buildings Improvements and Equipment	37,751,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,605,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember
Historical Cost of Land	7,013,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember
Historical Cost of Buildings Improvements and Equipment	41,356,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember
Total	48,369,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember
Accumulated Depreciation	9,751,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_FSP390InterlockenBroomfieldCOMember
Total Costs, Net of Accumulated Depreciation	38,618,000us-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	4,600,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember
Initial cost of Buildings Improvements and Equipment	55,267,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,881,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember
Historical Cost of Land	4,600,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember
Historical Cost of Buildings Improvements and Equipment	59,148,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember
Total	63,748,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember
Accumulated Depreciation	11,644,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EastBaltimoreBaltimoreMDMember
Total Costs, Net of Accumulated Depreciation	52,104,000us-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	1,300,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember
Initial cost of Buildings Improvements and Equipment	31,712,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	409,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember
Historical Cost of Land	1,300,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember
Historical Cost of Buildings Improvements and Equipment	32,121,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember
Total	33,421,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember
Accumulated Depreciation	5,700,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_ParkTenIIHoustonTXMember
Total Costs, Net of Accumulated Depreciation	27,721,000us-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	1,900,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember
Initial cost of Buildings Improvements and Equipment	16,192,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember
Costs Capitalized (Disposals) Subsequent to Acquisition	2,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember
Historical Cost of Land	1,900,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember
Historical Cost of Buildings Improvements and Equipment	16,194,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember
Total	18,094,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember
Accumulated Depreciation	2,525,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LakesideCrossingMarylandHeightsMOMember
Total Costs, Net of Accumulated Depreciation	15,569,000us-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	4,813,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember
Initial cost of Buildings Improvements and Equipment	13,285,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	3,828,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember
Historical Cost of Land	4,813,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember
Historical Cost of Buildings Improvements and Equipment	17,113,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember
Total	21,926,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember
Accumulated Depreciation	2,078,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_DullesVirginiaSterlingVAMember
Total Costs, Net of Accumulated Depreciation	19,848,000us-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	2,102,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember
Initial cost of Buildings Improvements and Equipment	18,003,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	0us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember
Historical Cost of Land	2,102,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember
Historical Cost of Buildings Improvements and Equipment	18,003,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember
Total	20,105,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember
Accumulated Depreciation	2,540,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_StonecroftChantillyVAMember
Total Costs, Net of Accumulated Depreciation	17,565,000us-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	5,422,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember
Initial cost of Buildings Improvements and Equipment	9,294,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember
Costs Capitalized (Disposals) Subsequent to Acquisition	0us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember
Historical Cost of Land	5,422,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember
Historical Cost of Buildings Improvements and Equipment	9,294,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember
Total	14,716,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember
Accumulated Depreciation	1,310,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EdenBluffEdenPrairieMNMember
Total Costs, Net of Accumulated Depreciation	13,406,000us-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	8,628,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember
Initial cost of Buildings Improvements and Equipment	15,214,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember
Costs Capitalized (Disposals) Subsequent to Acquisition	8,575,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember
Historical Cost of Land	8,628,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember
Historical Cost of Buildings Improvements and Equipment	23,789,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember
Total	32,417,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember
Accumulated Depreciation	2,450,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_SouthEightStreet121MinneapolisMNMember
Total Costs, Net of Accumulated Depreciation	29,967,000us-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	4,912,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember
Initial cost of Buildings Improvements and Equipment	18,229,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember
Costs Capitalized (Disposals) Subsequent to Acquisition	317,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember
Historical Cost of Land	4,912,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember
Historical Cost of Buildings Improvements and Equipment	18,546,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember
Total	23,458,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember
Accumulated Depreciation	1,611,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Davis909EvanstonILMember
Total Costs, Net of Accumulated Depreciation	21,847,000us-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	2,423,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember
Initial cost of Buildings Improvements and Equipment	53,997,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember
Costs Capitalized (Disposals) Subsequent to Acquisition	52,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember
Historical Cost of Land	2,423,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember
Historical Cost of Buildings Improvements and Equipment	54,049,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember
Total	56,472,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember
Accumulated Depreciation	5,311,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_EmperorBoulevardDurhamNCMember
Total Costs, Net of Accumulated Depreciation	51,161,000us-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	3,067,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember
Initial cost of Buildings Improvements and Equipment	22,064,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	0us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember
Historical Cost of Land	3,067,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember
Historical Cost of Buildings Improvements and Equipment	22,064,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember
Total	25,131,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember
Accumulated Depreciation	2,169,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_LegacyTennysonCenterPlanoTXMember
Total Costs, Net of Accumulated Depreciation	22,962,000us-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	2,590,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember
Initial cost of Buildings Improvements and Equipment	36,608,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	952,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember
Historical Cost of Land	2,590,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember
Historical Cost of Buildings Improvements and Equipment	37,560,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember
Total	40,150,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember
Accumulated Depreciation	3,857,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneLegacyCirclePlanoTXMember
Total Costs, Net of Accumulated Depreciation	36,293,000us-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	2,686,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember
Initial cost of Buildings Improvements and Equipment	35,125,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember
Costs Capitalized (Disposals) Subsequent to Acquisition	2,742,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember
Historical Cost of Land	2,686,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember
Historical Cost of Buildings Improvements and Equipment	37,867,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember
Total	40,553,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember
Accumulated Depreciation	2,558,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_OneRaviniaDriveAtlantaGAMember
Total Costs, Net of Accumulated Depreciation	37,995,000us-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	8,491,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember
Initial cost of Buildings Improvements and Equipment	121,508,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationInitialCostOfBuildingsImprovementsAndEquipment / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember
Costs Capitalized (Disposals) Subsequent to Acquisition	1,930,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember
Historical Cost of Land	8,491,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember
Historical Cost of Buildings Improvements and Equipment	123,438,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember
Total	131,929,000fsp_SECScheduleIIIRealEstateAndAccumulatedDepreciationCarryingAmountOfLandAndBuildingsAndImprovementsAndEquipments / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember
Accumulated Depreciation	6,956,000us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_WestchaseIAndIIHoustonTXMember
Total Costs, Net of Accumulated Depreciation	124,973,000us-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
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Costs Capitalized (Disposals) Subsequent to Acquisition	1,298,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Broadway1999COMember
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1999 Broadway, CO | Minimum
REAL ESTATE AND ACCUMULATED DEPRECIATION
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1999 Broadway, CO | Maximum
REAL ESTATE AND ACCUMULATED DEPRECIATION
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999 Peachtree, GA
REAL ESTATE AND ACCUMULATED DEPRECIATION
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Costs Capitalized (Disposals) Subsequent to Acquisition	818,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Peachtree999GAMember
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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
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Costs Capitalized (Disposals) Subsequent to Acquisition	202,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionCarryingCosts / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember
Historical Cost of Land	17,413,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = fsp_Street17th1001COMember
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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

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