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Stock Option Plan - Additional Information (Detail) (USD $)
 12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
May 06, 2005
May 01, 2006
Apr. 27, 2007
Apr. 25, 2008
Apr. 24, 2009
May 07, 2010
May 13, 2011
May 04, 2012
May 10, 2013
May 09, 2014
Dec. 31, 1993
Dec. 31, 2004
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Exercise price of options (in usd per share) $ 47.03us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice $ 44.42us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice $ 39.29us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice                        
Fair value stock option grant $ 9,596,150bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue                            
the 1993 Plan | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Authorized shares for a grant                           400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanNineteenNinetyThreeMember		  
Amended 2004 Plan | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Authorized shares for a grant                             2,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_AmendedStockOptionPlanTwentyZeroFourMember
Amended 2004 Plan | Stock Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Authorized shares for a grant                             200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_AmendedStockOptionPlanTwentyZeroFourMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
2005 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date       May 05, 2015                      
Exercise price of options (in usd per share)       $ 33.22us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember		                      
Fair value stock option grant       484,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember		                      
2005 Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options       12bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		                      
Options vested (in percent)       25.00%bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedPercentage
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		                      
Fair value stock option grant       413,400bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		                      
2005 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options       12bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                      
Fair value stock option grant       71,100bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                      
2005 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)       162,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember		                      
2005 Options | Stock Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Option vesting period       4 years                      
2005 Options | Incentive Stock Option                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)       35,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_IncentiveStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember		                      
2005 Options | Nonqualified Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)       127,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_NonqualifiedStockOptionsMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroFiveMember		                      
2006 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date         Apr. 30, 2016                    
Exercise price of options (in usd per share)         $ 40.35us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSixMember		                    
Fair value stock option grant         143,400bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSixMember		                    
2006 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options         12bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                    
2006 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)         30,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSixMember		                    
2007 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date           Apr. 26, 2017                  
Exercise price of options (in usd per share)           $ 54.17us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember		                  
Fair value stock option grant           1,500,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember		                  
2007 Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options           13bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		                  
Options vested (in percent)           25.00%bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedPercentage
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		                  
Fair value stock option grant           1,300,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		                  
2007 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options           12bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                  
Fair value stock option grant           285,300bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                  
2007 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)           165,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember		                  
2007 Options | Stock Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Option vesting period           4 years                  
2007 Options | Incentive Stock Option                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)           27,560us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_IncentiveStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember		                  
2007 Options | Nonqualified Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)           137,440us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_NonqualifiedStockOptionsMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroSevenMember		                  
2008 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date             Apr. 24, 2018                
Exercise price of options (in usd per share)             $ 50.15us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroEightMember		                
Fair value stock option grant             254,700bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroEightMember		                
2008 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options             12bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                
2008 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)             30,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroEightMember		                
2009 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date               Apr. 23, 2019              
Exercise price of options (in usd per share)               $ 32.68us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroNineMember		              
Fair value stock option grant               222,950bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroNineMember		              
2009 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options               13bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		              
2009 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)               32,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyZeroNineMember		              
2010 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date                 May 06, 2020            
Exercise price of options (in usd per share)                 $ 38.76us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTenMember		            
Fair value stock option grant                 287,950bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTenMember		            
2010 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                 13bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		            
2010 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                 32,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTenMember		            
2011 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date                   May 12, 2021          
Exercise price of options (in usd per share)                   $ 41.82us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember		          
Fair value stock option grant                   1,600,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember		          
2011 Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                   15bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		          
Options vested (in percent)                   25.00%bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedPercentage
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		          
Fair value stock option grant                   1,300,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		          
2011 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                   13bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		          
Fair value stock option grant                   297,375bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		          
2011 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                   195,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember		          
2011 Options | Stock Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Option vesting period                   4 years          
2011 Options | Incentive Stock Option                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                   65,300us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_IncentiveStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember		          
2011 Options | Nonqualified Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                   129,700us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_NonqualifiedStockOptionsMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyElevenMember		          
2012 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date                     May 03, 2022        
Exercise price of options (in usd per share)                     $ 39.29us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember		        
Fair value stock option grant                     1,700,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember		        
2012 Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                     15bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		        
Options vested (in percent)                     25.00%bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedPercentage
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		        
Fair value stock option grant                     1,400,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		        
2012 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                     14bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		        
Fair value stock option grant                     257,250bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		        
2012 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                     277,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember		        
2012 Options | Incentive Stock Option                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                     26,157us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_IncentiveStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember		        
2012 Options | Nonqualified Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                     251,343us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_NonqualifiedStockOptionsMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyTwelveMember		        
2013 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                       15bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member		      
Plan expiration date                       May 09, 2023      
Exercise price of options (in usd per share)                       $ 44.42us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member		      
Fair value stock option grant                       1,500,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member		      
2013 Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options vested (in percent)                       25.00%bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedPercentage
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		      
Fair value stock option grant                       1,300,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		      
2013 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                       14bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		      
Fair value stock option grant                       300,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		      
2013 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                       237,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member		      
2013 Options | Stock Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Option vesting period                     4 years 4 years 4 years    
2013 Options | Incentive Stock Option                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                       35,592us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_IncentiveStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member		      
2013 Options | Nonqualified Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                       201,908us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_NonqualifiedStockOptionsMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlan2013Member		      
2014 Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Plan expiration date                         May 08, 2024    
Exercise price of options (in usd per share)                         47.03us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember		    
Fair value stock option grant                         1,300,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember		    
2014 Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                         18bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Options vested (in percent)                         25.00%bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedPercentage
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Fair value stock option grant                         1,200,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
2014 Options | Director                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Number of individuals granted options                         12bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Fair value stock option grant                         109,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
2014 Options | Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                         200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember		    
2014 Options | Stock Options | Officer                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Option vesting period                     4 years        
2014 Options | Incentive Stock Option                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                         29,300us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_IncentiveStockOptionMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember		    
2014 Options | Nonqualified Stock Options                              
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]                              
Options granted to purchase stocks (in shares)                         170,700us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= bfs_NonqualifiedStockOptionsMember
/ us-gaap_PlanNameAxis
= bfs_StockOptionPlanTwentyFourteenMember