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Stock Option Plan - Additional Information (Detail) (USD $) | 12 Months Ended | 0 Months Ended |  |
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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) | $ 47.03 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice | $ 44.42 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice | $ 39.29 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice |  |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant | $ 9,596,150 bfs_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 |  |  |  |  |  |  |  |  |  |  |  |  |  | 400,000 us-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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 us-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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 us-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) |  |  |  | $ 33.22 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyZeroFiveMember |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant |  |  |  | 484,500 bfs_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 |  |  |  | 12 bfs_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 |  |  |  | 413,400 bfs_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 |  |  |  | 12 bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyZeroFiveMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |  |  |  |  |  |  |  |  |  |
Fair value stock option grant |  |  |  | 71,100 bfs_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) |  |  |  | 162,500 us-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) |  |  |  | 35,500 us-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) |  |  |  | 127,000 us-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) |  |  |  |  | $ 40.35 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyZeroSixMember |  |  |  |  |  |  |  |  |  |
Fair value stock option grant |  |  |  |  | 143,400 bfs_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 |  |  |  |  | 12 bfs_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) |  |  |  |  | 30,000 us-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) |  |  |  |  |  | $ 54.17 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyZeroSevenMember |  |  |  |  |  |  |  |  |
Fair value stock option grant |  |  |  |  |  | 1,500,000 bfs_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 |  |  |  |  |  | 13 bfs_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 |  |  |  |  |  | 1,300,000 bfs_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 |  |  |  |  |  | 12 bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyZeroSevenMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |  |  |  |  |  |  |  |
Fair value stock option grant |  |  |  |  |  | 285,300 bfs_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) |  |  |  |  |  | 165,000 us-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) |  |  |  |  |  | 27,560 us-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) |  |  |  |  |  | 137,440 us-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) |  |  |  |  |  |  | $ 50.15 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyZeroEightMember |  |  |  |  |  |  |  |
Fair value stock option grant |  |  |  |  |  |  | 254,700 bfs_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 |  |  |  |  |  |  | 12 bfs_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) |  |  |  |  |  |  | 30,000 us-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) |  |  |  |  |  |  |  | $ 32.68 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyZeroNineMember |  |  |  |  |  |  |
Fair value stock option grant |  |  |  |  |  |  |  | 222,950 bfs_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 |  |  |  |  |  |  |  | 13 bfs_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) |  |  |  |  |  |  |  | 32,500 us-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) |  |  |  |  |  |  |  |  | $ 38.76 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyTenMember |  |  |  |  |  |
Fair value stock option grant |  |  |  |  |  |  |  |  | 287,950 bfs_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 |  |  |  |  |  |  |  |  | 13 bfs_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) |  |  |  |  |  |  |  |  | 32,500 us-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) |  |  |  |  |  |  |  |  |  | $ 41.82 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyElevenMember |  |  |  |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  | 1,600,000 bfs_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 |  |  |  |  |  |  |  |  |  | 15 bfs_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 |  |  |  |  |  |  |  |  |  | 1,300,000 bfs_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 |  |  |  |  |  |  |  |  |  | 13 bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyElevenMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |  |  |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  | 297,375 bfs_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) |  |  |  |  |  |  |  |  |  | 195,000 us-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) |  |  |  |  |  |  |  |  |  | 65,300 us-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) |  |  |  |  |  |  |  |  |  | 129,700 us-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) |  |  |  |  |  |  |  |  |  |  | $ 39.29 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyTwelveMember |  |  |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  |  | 1,700,000 bfs_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 |  |  |  |  |  |  |  |  |  |  | 15 bfs_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 |  |  |  |  |  |  |  |  |  |  | 1,400,000 bfs_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 |  |  |  |  |  |  |  |  |  |  | 14 bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyTwelveMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |  |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  |  | 257,250 bfs_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) |  |  |  |  |  |  |  |  |  |  | 277,500 us-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) |  |  |  |  |  |  |  |  |  |  | 26,157 us-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) |  |  |  |  |  |  |  |  |  |  | 251,343 us-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 |  |  |  |  |  |  |  |  |  |  |  | 15 bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards / us-gaap_PlanNameAxis = bfs_StockOptionPlan2013Member |  |  |
Plan expiration date |  |  |  |  |  |  |  |  |  |  |  | May 09, 2023 |  |  |
Exercise price of options (in usd per share) |  |  |  |  |  |  |  |  |  |  |  | $ 44.42 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlan2013Member |  |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  |  |  | 1,500,000 bfs_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 |  |  |  |  |  |  |  |  |  |  |  | 1,300,000 bfs_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 |  |  |  |  |  |  |  |  |  |  |  | 14 bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards / us-gaap_PlanNameAxis = bfs_StockOptionPlan2013Member / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  |  |  | 300,000 bfs_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) |  |  |  |  |  |  |  |  |  |  |  | 237,500 us-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) |  |  |  |  |  |  |  |  |  |  |  | 35,592 us-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) |  |  |  |  |  |  |  |  |  |  |  | 201,908 us-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) |  |  |  |  |  |  |  |  |  |  |  |  | 47.03 us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyFourteenMember |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  |  |  |  | 1,300,000 bfs_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 |  |  |  |  |  |  |  |  |  |  |  |  | 18 bfs_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 |  |  |  |  |  |  |  |  |  |  |  |  | 1,200,000 bfs_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 |  |  |  |  |  |  |  |  |  |  |  |  | 12 bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEmployeesGrantedAwards / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyFourteenMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember |  |
Fair value stock option grant |  |  |  |  |  |  |  |  |  |  |  |  | 109,500 bfs_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) |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 us-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) |  |  |  |  |  |  |  |  |  |  |  |  | 29,300 us-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) |  |  |  |  |  |  |  |  |  |  |  |  | 170,700 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = bfs_NonqualifiedStockOptionsMember / us-gaap_PlanNameAxis = bfs_StockOptionPlanTwentyFourteenMember |  |

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