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Long Term Lease Obligations - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Leases Disclosure [Line Items]      
Minimum rental obligations $ 176,000us-gaap_OperatingLeasesRentExpenseMinimumRentals $ 176,000us-gaap_OperatingLeasesRentExpenseMinimumRentals $ 176,000us-gaap_OperatingLeasesRentExpenseMinimumRentals
Lease extension period     5 years
Percentage of annual increase in base rent     3.00%bfs_OperatingLeasesAnnualIncreaseInRentExpense
Rent expense 840,800us-gaap_OperatingLeasesRentExpenseNet 850,600us-gaap_OperatingLeasesRentExpenseNet 850,000us-gaap_OperatingLeasesRentExpenseNet
90-year Ground Leasehold Interest      
Leases Disclosure [Line Items]      
Ground leasehold interest period 90 years    
Minimum annual lease rent over lease term 1bfs_AnnualRentalPaymentsOverLeaseTerm
/ bfs_CapitalizedCostByTypeAxis
= bfs_NinetyYearGroundLeaseMember		    
99-year Ground Lease      
Leases Disclosure [Line Items]      
Ground leasehold interest period 99 years    
Minimum annual lease rent over lease term $ 1bfs_AnnualRentalPaymentsOverLeaseTerm
/ bfs_CapitalizedCostByTypeAxis
= bfs_NinetyNineYearGroundLeaseMember		    
Percent of underlying land held under a 99-year ground lease 3.40%bfs_PercentageOfLeaseCommitment
/ bfs_CapitalizedCostByTypeAxis
= bfs_NinetyNineYearGroundLeaseMember		    
Flagship Center      
Leases Disclosure [Line Items]      
Number of developed parcels 2bfs_NumberofDevelopedParcels
/ bfs_RealEstatePropertyNameAxis
= bfs_FlagshipCenterMember		    
Minimum      
Leases Disclosure [Line Items]      
Lease expiration year 2058    
Maximum      
Leases Disclosure [Line Items]      
Lease expiration year 2068