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Stock Option Plan - Stock Options Issued (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total grant (in shares) 1,362,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross    
Vested (in shares) 716,250bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod    
Exercised (in shares) 301,792bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod    
Forfeited (in shares) 312,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod    
Exercisable at December 31 (in shares) 380,708us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber 413,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber 377,715us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
Remaining unexercised (in shares) 748,208bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber    
Exercise price (in usd per share) $ 37.71us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice $ 33.15us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice $ 31.03us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
Total value at grant date $ 9,596,150bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue    
Estimated forfeitures 1,823,557bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue    
Expensed in previous years 3,404,622bfs_AllocatedShareBasedCompensationExpenseInPreviousYears    
Future expense 1,891,071bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions    
Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 632,365us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember		    
Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 879,710us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember		    
Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 964,825us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember		    
Directors      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 112,900us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		 124,400us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		 110,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
Directors | 5/6/2005      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 06, 2005    
Total grant (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 22,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 7,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 7,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 33.22us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.198bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 10 years    
Assumed yield 6.91%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 4.28%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 71,100bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 71,100bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/6/2005 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/6/2005 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/6/2005 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/1/2006      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 01, 2006    
Total grant (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 10,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 2,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 17,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 17,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 40.35us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.206bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 9 years    
Assumed yield 5.93%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 5.11%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 143,400bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 143,400bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/1/2006 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/1/2006 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/1/2006 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayOneTwoThousandSixMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/27/2007      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date Apr. 27, 2007    
Total grant (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 0bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 7,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 22,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 22,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 54.17us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.225bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 8 years    
Assumed yield 4.39%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 4.65%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 285,300bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 285,300bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/27/2007 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/27/2007 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/27/2007 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/25/2008      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date Apr. 25, 2008    
Total grant (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 0bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 7,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 22,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 22,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 50.15us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.237bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 7 years    
Assumed yield 4.09%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 3.49%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 254,700bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 254,700bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/25/2008 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/25/2008 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/25/2008 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_AprilTwentyFiveTwoThousandEightMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/24/2009      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date Apr. 24, 2009    
Total grant (in shares) 32,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 32,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 20,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 12,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 12,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 32.68us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.344bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 6 years    
Assumed yield 4.54%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 2.19%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 222,950bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 222,950bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/24/2009 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/24/2009 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 4/24/2009 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_AprilFourTwoThousandNineMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/7/2010      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 07, 2010    
Total grant (in shares) 32,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 32,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 10,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 2,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 20,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 20,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 38.76us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.369bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 5 years    
Assumed yield 4.23%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 2.17%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 287,950bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 287,950bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/7/2010 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/7/2010 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/7/2010 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MaySevenTwoThousandTenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/13/2011      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 13, 2011    
Total grant (in shares) 32,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 32,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 10,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 2,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 20,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 20,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 41.82us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.358bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 5 years    
Assumed yield 4.16%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 1.86%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 297,375bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 297,375bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/13/2011 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/13/2011 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/13/2011 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/4/2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 04, 2012    
Total grant (in shares) 35,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 35,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 10,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 25,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 25,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 39.29us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.348bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 5 years    
Assumed yield 4.61%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 0.78%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 257,250bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 0bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/4/2012 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 257,250us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/4/2012 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/4/2012 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/10/2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 10, 2013    
Total grant (in shares) 35,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 35,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 7,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 27,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 27,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 44.42us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.333bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 5 years    
Assumed yield 4.53%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 0.82%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 278,250bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 0bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/10/2013 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/10/2013 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 278,250us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/10/2013 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/9/2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 09, 2014    
Total grant (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 0bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 30,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercise price (in usd per share) $ 47.03us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Volatility 0.173bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expected life (years) 5 years    
Assumed yield 4.48%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Risk-free rate 1.63%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 109,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 0bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/9/2014 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/9/2014 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | 5/9/2014 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 109,500us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | Subtotals      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total grant (in shares) 317,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Vested (in shares) 317,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercised (in shares) 90,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Forfeited (in shares) 22,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Exercisable at December 31 (in shares) 205,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Remaining unexercised (in shares) 205,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Total value at grant date 2,207,775bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Expensed in previous years 1,562,775bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | Subtotals | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 257,250us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | Subtotals | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 278,250us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Directors | Subtotals | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 109,500us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		    
Officers | 5/6/2005      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 06, 2005    
Total grant (in shares) 132,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Vested (in shares) 118,750bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercised (in shares) 115,750bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Forfeited (in shares) 13,750us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercisable at December 31 (in shares) 3,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Remaining unexercised (in shares) 3,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercise price (in usd per share) $ 33.22us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Volatility 0.207bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expected life (years) 8 years    
Assumed yield 6.37%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Risk-free rate 4.15%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Total value at grant date 413,400bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Estimated forfeitures 35,100bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expensed in previous years 378,300bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/6/2005 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MaySixTwoThousandFiveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 4/27/2007      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date Apr. 27, 2007    
Total grant (in shares) 135,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Vested (in shares) 67,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercised (in shares) 3,528bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Forfeited (in shares) 67,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercisable at December 31 (in shares) 63,972us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Remaining unexercised (in shares) 63,972bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercise price (in usd per share) $ 54.17us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Volatility 0.233bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expected life (years) 6 years 6 months    
Assumed yield 4.13%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Risk-free rate 4.61%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Total value at grant date 1,339,200bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Estimated forfeitures 62,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expensed in previous years 1,277,200bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Future expense 0bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Weighted average term of remaining future expense 2 years 8 months 3 days    
Officers | 4/27/2007 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 4/27/2007 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 4/27/2007 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_AprilTwentySevenTwoThousandSevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/13/2011      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 13, 2011    
Total grant (in shares) 162,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Vested (in shares) 105,625bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercised (in shares) 46,889bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Forfeited (in shares) 43,750us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercisable at December 31 (in shares) 47,486us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Remaining unexercised (in shares) 71,861bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercise price (in usd per share) $ 41.82us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Volatility 0.330bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expected life (years) 8 years    
Assumed yield 4.81%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Risk-free rate 2.75%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Total value at grant date 1,366,625bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Estimated forfeitures 387,550bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expensed in previous years 186,347bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Future expense 69,512bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/13/2011 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 270,391us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/13/2011 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 235,350us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/13/2011 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 217,475us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayThirteenTwoThousandElevenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/4/2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 04, 2012    
Total grant (in shares) 242,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Vested (in shares) 56,250bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercised (in shares) 30,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Forfeited (in shares) 135,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercisable at December 31 (in shares) 26,250us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Remaining unexercised (in shares) 77,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercise price (in usd per share) $ 39.29us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Volatility 0.315bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expected life (years) 8 years    
Assumed yield 5.28%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Risk-free rate 1.49%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Total value at grant date 1,518,050bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Estimated forfeitures 889,690bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expensed in previous years 0bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Future expense 209,461bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/4/2012 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 104,724us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/4/2012 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 157,083us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/4/2012 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 157,092us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayFourTwoThousandTwelveMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/10/2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 10, 2013    
Total grant (in shares) 202,500bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Vested (in shares) 50,625bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercised (in shares) 15,625bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Forfeited (in shares) 30,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercisable at December 31 (in shares) 35,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Remaining unexercised (in shares) 156,875bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercise price (in usd per share) $ 44.42us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Volatility 0.304bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expected life (years) 8 years    
Assumed yield 5.12%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Risk-free rate 1.49%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Total value at grant date 1,401,300bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Estimated forfeitures 280,468bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expensed in previous years 0bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Future expense 627,895bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/10/2013 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/10/2013 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 209,027us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/10/2013 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 283,910us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayTenTwoThousandThirteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/9/2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Grant date May 09, 2014    
Total grant (in shares) 170,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Vested (in shares) 0bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercised (in shares) 0bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Forfeited (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercisable at December 31 (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Remaining unexercised (in shares) 170,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercise price (in usd per share) $ 47.03us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Volatility 0.306bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsVolatility
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expected life (years) 7 years    
Assumed yield 4.89%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Risk-free rate 2.17%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Total value at grant date 1,349,800bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Estimated forfeitures 168,749bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expensed in previous years 0bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Future expense 984,203bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/9/2014 | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/9/2014 | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | 5/9/2014 | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 196,848us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_MayNineTwoThousandFourteenMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | Subtotals      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total grant (in shares) 1,045,000bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalGrantsInPeriodGross
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Vested (in shares) 398,750bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedInPeriod
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercised (in shares) 211,792bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsTotalExercisesInPeriod
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Forfeited (in shares) 290,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Exercisable at December 31 (in shares) 175,708us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Remaining unexercised (in shares) 543,208bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsRemainingUnexercisedNumber
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Total value at grant date 7,388,375bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Estimated forfeitures 1,823,557bfs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodFairValue
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Expensed in previous years 1,841,847bfs_AllocatedShareBasedCompensationExpenseInPreviousYears
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Future expense 1,891,071bfs_EmployeeAndNonEmployeeServiceSharebasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | Subtotals | Expensed in 2012      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 375,115us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodOneMember
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | Subtotals | Expensed in 2013      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation 601,460us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodTwoMember
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember		    
Officers | Subtotals | Expensed in 2014      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocated share based compensation $ 855,325us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_IncomeStatementLocationAxis
= bfs_ShareBasedCompensationExpensePeriodThreeMember
/ bfs_PeriodAxis
= bfs_SubtotalMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember