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Summary of Significant Accounting Policies - Construction in Progress (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Property, Plant and Equipment [Line Items]    
Construction in progress $ 39,301us-gaap_DevelopmentInProcess $ 30,261us-gaap_DevelopmentInProcess
Park Van Ness    
Property, Plant and Equipment [Line Items]    
Construction in progress 35,458us-gaap_DevelopmentInProcess
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= bfs_VanNessSquareMember
26,998us-gaap_DevelopmentInProcess
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= bfs_VanNessSquareMember
Other    
Property, Plant and Equipment [Line Items]    
Construction in progress $ 3,843us-gaap_DevelopmentInProcess
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= us-gaap_OtherPropertyMember
$ 3,263us-gaap_DevelopmentInProcess
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= us-gaap_OtherPropertyMember