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Employee Benefit Plans - Additional Information (Detail) (USD $)
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12 Months Ended |
3 Months Ended |
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Dec. 31, 2014
Plans
Employer
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Dec. 31, 2013
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Dec. 31, 2012
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Mar. 31, 2012
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Number of active stock compensation plans |
3sah_ShareBasedCompensationNumberOfStockCompensationPlans
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| Additional terminated plans with outstanding grants |
1sah_ShareBasedCompensationNumberOfAdditionalTerminatedPlans
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| Restricted stock shares |
504,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
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| Number of employers to make contribution under multi-employer plan |
200sah_NumberOfEmployerToMakeContributionUnderMultiEmployerPlan
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| Pension Protection |
2006
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2006
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| Number of employee increase / (decrease) under multi employer benefit percentage |
2.80%us-gaap_MultiemployerPlansEmployeesIncreaseDecreasePercentage
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7.10%us-gaap_MultiemployerPlansEmployeesIncreaseDecreasePercentage
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| Total contributions of multi employer Plan |
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5.00%sah_MultiemployerPlansContributionPercentIncreaseDecrease
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5.00%sah_MultiemployerPlansContributionPercentIncreaseDecrease
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| Plans In Red Zone [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Multi-Employer Benefit AI Pension Plan |
Less than 65 percent
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| Plans In Yellow Zone [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Multi-Employer Benefit AI Pension Plan |
Between 65 and less than 80 percent
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| Plans In Green Zone [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Multi-Employer Benefit AI Pension Plan |
At least 80 percent
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| Supplemental Employee Retirement Plans, Defined Benefit [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Members of senior management |
12sah_MembersOfSeniorManagement
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
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| Stock Option [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Tax benefits recognized related to the compensation expenses |
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100,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
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| Stock Option [Member] | Selling, General and Administrative Expenses [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Compensation expense |
0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
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0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
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100,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
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| Non-vested Restricted Stock Awards and Restricted Stock Units [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Tax benefits recognized related to the compensation expenses |
2,900,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= sah_NonVestedRestrictedStockAndRestrictedStockUnitsRSUMember
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2,700,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= sah_NonVestedRestrictedStockAndRestrictedStockUnitsRSUMember
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1,900,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= sah_NonVestedRestrictedStockAndRestrictedStockUnitsRSUMember
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| Compensation expense not yet recognized |
12,500,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= sah_NonVestedRestrictedStockAndRestrictedStockUnitsRSUMember
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| Non-vested Restricted Stock Awards and Restricted Stock Units [Member] | Selling, General and Administrative Expenses [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Compensation expense |
7,700,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= sah_NonVestedRestrictedStockAndRestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
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7,200,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= sah_NonVestedRestrictedStockAndRestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
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5,000,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= sah_NonVestedRestrictedStockAndRestrictedStockUnitsRSUMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SellingGeneralAndAdministrativeExpensesMember
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| Non-vested restricted stock [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Total compensation cost related to non-vested options expected to be recognized over weighted average period |
1 year 9 months 18 days
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| 401(k) plan [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Employer contribution |
7,400,000us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
/ us-gaap_PlanNameAxis
= sah_EmployeeBenefitPlansMember
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7,200,000us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
/ us-gaap_PlanNameAxis
= sah_EmployeeBenefitPlansMember
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4,400,000us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
/ us-gaap_PlanNameAxis
= sah_EmployeeBenefitPlansMember
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| 2012 Formula Plan [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Number of shares authorized |
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300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= sah_TwoThousandTwelveFormulaPlanMember
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| 2012 Formula Plan [Member] | Restricted Stock [Member] | Director [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Restricted stock shares |
23,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= sah_TwoThousandTwelveFormulaPlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
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| 2012 Plan [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Number of shares authorized |
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2,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= sah_TwoThousandTwelvePlanMember
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| 2004 Stock Incentive Plan and 2012 Formula Plan [Member] | Restricted Stock Units (RSUs) [Member] | Executive Officer and Other Key Associates [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Restricted stock shares |
481,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= sah_TwoThousandFourPlanAndTwoThousandTwelveFormulaPlanMember
/ us-gaap_TitleOfIndividualAxis
= sah_ExecutiveOfficerAndOtherKeyAssociatesMember
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| 2004 Stock Incentive Plan and 2012 Formula Plan [Member] | Common Class A [Member] | Stock Option [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Stock option expiration period |
10 years
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| 2004 Stock Incentive Plan and 2012 Formula Plan [Member] | Common Class A [Member] | Stock Option [Member] | Minimum [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Stock award vesting period |
6 months
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| 2004 Stock Incentive Plan and 2012 Formula Plan [Member] | Common Class A [Member] | Stock Option [Member] | Maximum [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Stock award vesting period |
3 years
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| 2004 Stock Incentive Plan and 2012 Formula Plan [Member] | Common Class A [Member] | Non-vested Restricted Stock Awards and Restricted Stock Units [Member] | Minimum [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Stock award vesting period |
1 year
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| 2004 Stock Incentive Plan and 2012 Formula Plan [Member] | Common Class A [Member] | Non-vested Restricted Stock Awards and Restricted Stock Units [Member] | Maximum [Member] |
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| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
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| Stock award vesting period |
3 years
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