Annual report pursuant to Section 13 and 15(d)

Long-Term Debt - Long-Term Debt (Parenthetical) (Detail)

v2.4.1.9
Long-Term Debt - Long-Term Debt (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 5.00%us-gaap_DebtInstrumentInterestRateStatedPercentage  
7.0% Senior Subordinated Notes Due 2022 [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 7.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= sah_SevenPercentSeniorSubordinateNoteDueTwoThousandTwentyTwoMember
7.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= sah_SevenPercentSeniorSubordinateNoteDueTwoThousandTwentyTwoMember
Discount associated with notes $ 1.5us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_LongtermDebtTypeAxis
= sah_SevenPercentSeniorSubordinateNoteDueTwoThousandTwentyTwoMember
$ 1.6us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_LongtermDebtTypeAxis
= sah_SevenPercentSeniorSubordinateNoteDueTwoThousandTwentyTwoMember
5.0% Senior Subordinated Notes due 2023 [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 5.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= sah_FivePercentSeniorSubordinateNoteDueTwoThousandTwentyThreeMember
5.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= sah_FivePercentSeniorSubordinateNoteDueTwoThousandTwentyThreeMember
Notes Payable to Finance Company [Member]    
Debt Instrument [Line Items]    
Interest on notes 10.19%us-gaap_LongtermDebtWeightedAverageInterestRate
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
 
Premium associated with notes 0.1us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
0.4us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
Notes Payable to Finance Company [Member] | Minimum [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 9.52%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Notes Payable to Finance Company [Member] | Maximum [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 10.52%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_NotesPayableToBanksMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
2011 Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Interest rate 2.00%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
/ us-gaap_LongtermDebtTypeAxis
= sah_TwoThousandElevenRevolvingCreditFacilityMember
 
2014 Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Interest rate   2.25%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
/ us-gaap_LongtermDebtTypeAxis
= sah_TwoThousandFourteenRevolvingCreditFacilityMember
Mortgage Notes Payable [Member]    
Debt Instrument [Line Items]    
Discount associated with notes $ 0.4us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_LongtermDebtTypeAxis
= sah_MortgageNotesPayableMember
$ 0.6us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_LongtermDebtTypeAxis
= sah_MortgageNotesPayableMember
Mortgage Loan at Fix Interest Rate [Member] | Minimum [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 3.51%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= sah_MortgageLoanAtFixInterestRateMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Mortgage Loan at Fix Interest Rate [Member] | Maximum [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 7.03%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= sah_MortgageLoanAtFixInterestRateMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
Mortgage Loan at Variable Interest Rate [Member] | Minimum [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 1.25%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_VariableRateAxis
= sah_MortgageLoanAtVariableInterestRateMember
 
Mortgage Loan at Variable Interest Rate [Member] | Maximum [Member]    
Debt Instrument [Line Items]    
Stated interest rate on debt agreement 3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_VariableRateAxis
= sah_MortgageLoanAtVariableInterestRateMember