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Real Estate Acquired - Additional Information (Detail) (USD $) | 12 Months Ended | 1 Months Ended
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Dec. 31, 2014 property | Dec. 31, 2013 Property | Dec. 31, 2012 Property | Dec. 31, 2012 | Jan. 31, 2014 | Apr. 30, 2014 | Dec. 31, 2014 | Aug. 31, 2014 | Aug. 31, 2013 sqft | Dec. 31, 2013 sqft
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate cost | $ 68,000,000 us-gaap_BusinessCombinationConsiderationTransferred1 | $ 5,100,000 us-gaap_BusinessCombinationConsiderationTransferred1 | $ 34,100,000 us-gaap_BusinessCombinationConsiderationTransferred1 |  |  |  |  |  |  |
Property acquisition costs | 900,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts | 106,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts | 1,100,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts | 1,100,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts |  |  | 900,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts |  |  | 106,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
Number of properties acquired | 5 bfs_BusinessCombinationNumberofAcquisitions |  |  |  |  |  | 5 bfs_BusinessCombinationNumberofAcquisitions |  |  |
Number of properties acquired |  | 2 bfs_NumberOfPropertiesAcquired | 2 bfs_NumberOfPropertiesAcquired | 2 bfs_NumberOfPropertiesAcquired |  |  |  |  |  | 2 bfs_NumberOfPropertiesAcquired
Purchase price allocated to buildings | 4,873,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings | 2,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings | 3,800,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings | 3,800,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings |  |  | 4,873,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings |  |  | 2,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings
Purchase price allocated to land | 66,047,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand | 3,100,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand | 30,400,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand | 30,400,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand |  |  | 66,047,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand |  |  | 3,100,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand
Purchase price allocated to below market lease | 5,069,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease |  | 700,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease | 700,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease |  |  | 5,069,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease |  |  |
Business acquisition, intangible asset estimated useful life |  |  | 3 years 1 month 6 days |  |  |  |  |  |  |
Intangible liabilities gross carrying amount | 29,900,000 us-gaap_BelowMarketLeaseGross | 24,800,000 us-gaap_BelowMarketLeaseGross |  |  |  |  | 29,900,000 us-gaap_BelowMarketLeaseGross |  |  | 24,800,000 us-gaap_BelowMarketLeaseGross
Intangible liabilities, accumulated amortization | 11,900,000 us-gaap_BelowMarketLeaseAccumulatedAmortization | 10,000,000 us-gaap_BelowMarketLeaseAccumulatedAmortization |  |  |  |  | 11,900,000 us-gaap_BelowMarketLeaseAccumulatedAmortization |  |  | 10,000,000 us-gaap_BelowMarketLeaseAccumulatedAmortization
Accretion income, intangible liabilities | 1,900,000 us-gaap_AmortizationOfBelowMarketLease | 1,700,000 us-gaap_AmortizationOfBelowMarketLease | 1,600,000 us-gaap_AmortizationOfBelowMarketLease |  |  |  |  |  |  |
In-Place Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 2,099,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  | 500,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember | 500,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  | 2,099,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |
Above Market Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |
Intangible assets gross carrying amount | 1,000,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember | 1,000,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  | 1,000,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  | 1,000,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember
Intangible assets, accumulated amortization | 996,700 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember | 974,100 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  | 996,700 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  | 974,100 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember
Amortization expense of intangible assets | 23,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember | 45,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember | 60,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  |  |  |
Lease Acquisition Costs |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Intangible assets gross carrying amount | 24,000,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember | 21,900,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember |  |  |  |  | 24,000,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember |  |  | 21,900,000 us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember
Intangible assets, accumulated amortization | 18,000,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember | 16,700,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember |  |  |  |  | 18,000,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember |  |  | 16,700,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember
Amortization expense of intangible assets | 1,300,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember | 2,000,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember | 2,000,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = bfs_AcquisitionCostsMember |  |  |  |  |  |  |
1500 Rockville Pike |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  | Dec. 31, 2012 |  |  |  |  |  |
Aggregate cost |  |  |  | 22,400,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_FifteenHundredRockvillePikeMember |  |  |  |  |  |
Name of property |  |  |  | 1500 Rockville Pike |  |  |  |  |  |
Property acquisition costs |  |  | 600,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_FifteenHundredRockvillePikeMember | 600,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_FifteenHundredRockvillePikeMember |  |  |  |  |  |
1580 Rockville Pike |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  |  | Jan. 31, 2014 |  |  |  |  |
Aggregate cost |  |  |  |  | 8,000,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |  |  |
Name of property |  |  |  |  | 1580 Rockville Pike |  |  |  |  |
Property acquisition costs |  |  |  |  | 200,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |  |  |
Purchase price allocated to buildings | 2,200,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |  |  |  | 2,200,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |
Purchase price allocated to land | 9,600,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |  |  |  | 9,600,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |
Purchase price allocated to below market lease | 4,313,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |  |  |  | 4,313,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember |  |  |
1580 Rockville Pike | In-Place Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 513,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |  |  |  | 513,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |
1580 Rockville Pike | Above Market Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightZeroRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |
1582 Rockville Pike |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  |  |  | Apr. 30, 2014 |  |  |  |
Aggregate cost |  |  |  |  |  | 11,000,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |  |
Name of property |  |  |  |  |  | 1582 Rockville Pike |  |  |  |
Property acquisition costs |  |  |  |  |  | 200,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |  |
Purchase price allocated to buildings | 828,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |  |  |  | 828,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |
Purchase price allocated to land | 9,742,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |  |  |  | 9,742,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |
Purchase price allocated to below market lease | 419,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |  |  |  | 419,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember |  |  |
1582 Rockville Pike | In-Place Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 849,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |  |  |  | 849,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |
1582 Rockville Pike | Above Market Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightTwoRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |
1584 Rockville Pike |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  |  |  |  | Dec. 31, 2014 |  |  |
Aggregate cost |  |  |  |  |  |  | 6,200,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |
Name of property |  |  |  |  |  |  | 1584 Rockville Pike |  |  |
Property acquisition costs | 200,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |  |  |  | 200,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |
Purchase price allocated to buildings | 440,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |  |  |  | 440,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |
Purchase price allocated to land | 5,798,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |  |  |  | 5,798,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |
Purchase price allocated to below market lease | 337,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |  |  |  | 337,000 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember |  |  |
1584 Rockville Pike | In-Place Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 249,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |  |  |  | 249,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |
1584 Rockville Pike | Above Market Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_OneFiveEightFourRockvillePikeMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |
750 N. Glebe Road |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  |  |  |  |  | Aug. 31, 2014 |  |
Aggregate cost |  |  |  |  |  |  |  | 40,000,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |
Name of property |  |  |  |  |  |  |  | 750 N. Glebe Road |  |
Property acquisition costs |  |  |  |  |  |  |  | 400,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |
Purchase price allocated to buildings | 1,327,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |  |  |  |  | 1,327,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |  |
Purchase price allocated to land | 38,224,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |  |  |  |  | 38,224,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |  |
Purchase price allocated to below market lease | 0 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |  |  |  |  | 0 bfs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedBelowMarketLease / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember |  |  |
750 N. Glebe Road | In-Place Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 449,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |  |  |  | 449,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |
750 N. Glebe Road | Above Market Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenFiftyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |
730 N. Glebe Road |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  |  |  |  | Dec. 31, 2014 |  |  |
Aggregate cost |  |  |  |  |  |  | 2,800,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember |  |  |
Name of property |  |  |  |  |  |  | 730 N. Glebe Road |  |  |
Property acquisition costs | 40,400 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember |  |  |  |  |  | 40,400 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember |  |  |
Purchase price allocated to buildings | 78,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember |  |  |  |  |  | 78,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember |  |  |
Purchase price allocated to land | 2,683,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember |  |  |  |  |  | 2,683,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember |  |  |
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730 N. Glebe Road | In-Place Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 39,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |  |  |  | 39,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_LeasesAcquiredInPlaceMember |  |  |
730 N. Glebe Road | Above Market Leases |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Purchase price allocated to leases | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |  |  |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = bfs_SevenThirtyNGlebeRoadMember / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember |  |  |
5541 Nicholson Lane |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  | Dec. 31, 2012 |  |  |  |  |  |
Aggregate cost |  |  |  | 11,700,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_FiftyFiveFortyOneNicholsonLaneMember |  |  |  |  |  |
Name of property |  |  |  | 5541 Nicholson Lane |  |  |  |  |  |
Property acquisition costs |  |  | 500,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_FiftyFiveFortyOneNicholsonLaneMember | 500,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_FiftyFiveFortyOneNicholsonLaneMember |  |  |  |  |  |
Kentlands Pad |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  |  |  |  |  |  | Aug. 31, 2013 |
Aggregate cost |  |  |  |  |  |  |  |  | 4,300,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_KentlandsPadMember |
Property acquisition costs |  |  |  |  |  |  |  |  | 106,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = bfs_KentlandsPadMember |
Area of real estate property (in square feet) |  |  |  |  |  |  |  |  | 7,100 us-gaap_AreaOfRealEstateProperty / us-gaap_BusinessAcquisitionAxis = bfs_KentlandsPadMember |
Hunt Club Pad |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Year of acquisition |  |  |  |  |  |  |  |  |  | Dec. 31, 2013
Aggregate cost |  |  |  |  |  |  |  |  |  | $ 800,000 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = bfs_HuntClubPadMember
Area of real estate property (in square feet) |  | 5,500 us-gaap_AreaOfRealEstateProperty / us-gaap_BusinessAcquisitionAxis = bfs_HuntClubPadMember |  |  |  |  |  |  |  | 5,500 us-gaap_AreaOfRealEstateProperty / us-gaap_BusinessAcquisitionAxis = bfs_HuntClubPadMember

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