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Real Estate Acquired and Sold - Additional Information (Detail) (USD $)
 12 Months Ended 1 Months Ended 3 Months Ended 1 Months Ended
Dec. 31, 2014
property
Apr. 30, 2014
sqft
Mar. 31, 2015
Jan. 31, 2014
Dec. 31, 2014
Aug. 31, 2014
Mar. 31, 2014
Business Acquisition [Line Items]              
Aggregate cost $ 68,000,000us-gaap_BusinessCombinationConsiderationTransferred1            
Property acquisition costs 900,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts       900,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts    
Number of properties purchased 5bfs_BusinessCombinationNumberofAcquisitions       5bfs_BusinessCombinationNumberofAcquisitions    
Olney Center              
Business Acquisition [Line Items]              
Name of property   Olney Center          
Location of property   Olney, Maryland          
Proceeds from sale of real estate   11,000,000us-gaap_ProceedsFromSaleOfRealEstate
/ bfs_BusinessDispositionAxis
= bfs_OlneyMember		 11,000,000us-gaap_ProceedsFromSaleOfRealEstate
/ bfs_BusinessDispositionAxis
= bfs_OlneyMember		        
Area of real estate property (in sq ft)   53,765us-gaap_AreaOfRealEstateProperty
/ bfs_BusinessDispositionAxis
= bfs_OlneyMember		          
Lease term   P20Y          
Sale leaseback, option to purchase the property   14,600,000bfs_SaleLeasebackTransactionRepurchaseOptionAmount
/ bfs_BusinessDispositionAxis
= bfs_OlneyMember		 14,600,000bfs_SaleLeasebackTransactionRepurchaseOptionAmount
/ bfs_BusinessDispositionAxis
= bfs_OlneyMember		        
Sales price of property     11,000,000us-gaap_SaleLeasebackTransactionHistoricalCost
/ bfs_BusinessDispositionAxis
= bfs_OlneyMember		        
Annual increase in rental payments, percentage     1.50%bfs_SaleLeasebackTransactionAnnualIncreaseinRentalPaymentsPercentage
/ bfs_BusinessDispositionAxis
= bfs_OlneyMember		        
Giant Center              
Business Acquisition [Line Items]              
Name of property   Giant Center          
Location of property   Milford Mill, Maryland          
Proceeds from sale of real estate   7,500,000us-gaap_ProceedsFromSaleOfRealEstate
/ bfs_BusinessDispositionAxis
= bfs_GiantCenterMember		          
Area of real estate property (in sq ft)   70,040us-gaap_AreaOfRealEstateProperty
/ bfs_BusinessDispositionAxis
= bfs_GiantCenterMember		          
Gain on sale of real estate   6,100,000us-gaap_GainsLossesOnSalesOfInvestmentRealEstate
/ bfs_BusinessDispositionAxis
= bfs_GiantCenterMember		          
Assets held-for-sale             500,000us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation
/ bfs_BusinessDispositionAxis
= bfs_GiantCenterMember
Liabilities of assets held-for-sale             100,000us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation
/ bfs_BusinessDispositionAxis
= bfs_GiantCenterMember
1580 Rockville Pike              
Business Acquisition [Line Items]              
Aggregate cost       8,000,000us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= bfs_OneFiveEightZeroRockvillePikeMember		      
Name of property       1580 Rockville Pike      
Property acquisition costs       163,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= bfs_OneFiveEightZeroRockvillePikeMember		      
1582 Rockville Pike              
Business Acquisition [Line Items]              
Aggregate cost   11,000,000us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= bfs_OneFiveEightTwoRockvillePikeMember		          
Name of property   1582 Rockville Pike          
Property acquisition costs   200,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= bfs_OneFiveEightTwoRockvillePikeMember		          
Location of property   Rockville, Maryland          
1584 Rockville Pike              
Business Acquisition [Line Items]              
Aggregate cost         6,200,000us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= bfs_OneFiveEightFourRockvillePikeMember		    
Name of property         1584 Rockville Pike    
Property acquisition costs 200,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= bfs_OneFiveEightFourRockvillePikeMember		       200,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= bfs_OneFiveEightFourRockvillePikeMember		    
750 N. Glebe Road              
Business Acquisition [Line Items]              
Aggregate cost           40,000,000us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= bfs_SevenFiftyNGlebeRoadMember		  
Name of property           750 N. Glebe Road  
Property acquisition costs   355,000us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= bfs_SevenFiftyNGlebeRoadMember		          
730 N. Glebe Road              
Business Acquisition [Line Items]              
Aggregate cost         2,800,000us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= bfs_SevenThirtyNGlebeRoadMember		    
Name of property         730 N. Glebe Road    
Property acquisition costs $ 40,400us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= bfs_SevenThirtyNGlebeRoadMember		       $ 40,400us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= bfs_SevenThirtyNGlebeRoadMember