Annual report pursuant to Section 13 and 15(d)

Business Acquisitions and Dispositions - Additional Information (Detail)

v2.4.1.9
Business Acquisitions and Dispositions - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended
Jun. 30, 2014
Franchise
Dec. 31, 2014
Dealerships
Franchise
Dec. 31, 2013
Dealerships
Dec. 31, 2012
Dealerships
Mar. 31, 2014
Franchise
Business Acquisition [Line Items]          
Purchase price for franchise operations and underlying assets, including real estate, acquired   $ 50,900,000us-gaap_BusinessCombinationConsiderationTransferred1      
Goodwill   475,929,000us-gaap_Goodwill 476,315,000us-gaap_Goodwill 454,224,000us-gaap_Goodwill  
Number of dealerships held for sale   0sah_HeldForSaleDealershipsNumber     0sah_HeldForSaleDealershipsNumber
Number of franchises disposed 2sah_NumberOfFranchisesDisposed 9sah_NumberOfFranchisesDisposed 0sah_NumberOfFranchisesDisposed 12sah_NumberOfFranchisesDisposed  
Cash generated from disposition   74,800,000sah_ProceedsFromDispositionsOfFranchises   72,200,000sah_ProceedsFromDispositionsOfFranchises  
Interest allocated to discontinued operations   0us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense 0us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense 700,000us-gaap_DisposalGroupIncludingDiscontinuedOperationInterestExpense  
Luxury Franchise [Member]          
Business Acquisition [Line Items]          
Number of franchise acquired   2us-gaap_NumberOfBusinessesAcquired
/ us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis
= sah_LuxuryFranchiseMember 		     
Mid-line Import Franchise [Member]          
Business Acquisition [Line Items]          
Number of franchise acquired   1us-gaap_NumberOfBusinessesAcquired
/ us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis
= sah_MidLineImportFranchiseMember 		     
Domestic Franchise [Member]          
Business Acquisition [Line Items]          
Number of franchise acquired   1us-gaap_NumberOfBusinessesAcquired
/ us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis
= sah_DomesticFranchiseMember 		     
2014 Acquisitions [Member]          
Business Acquisition [Line Items]          
Net assets relating to dealership operations   33,200,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
/ us-gaap_BusinessAcquisitionAxis
= sah_AcquisitionsTwoThousandThirteenMember 		     
Indefinite life intangible assets representing rights acquired under franchise agreements   7,500,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets
/ us-gaap_BusinessAcquisitionAxis
= sah_AcquisitionsTwoThousandThirteenMember 		     
Goodwill   $ 10,200,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= sah_AcquisitionsTwoThousandThirteenMember