Annual report pursuant to Section 13 and 15(d)

Related Parties - Additional Information (Detail)

v2.4.1.9
Related Parties - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Oil Chem Research Company [Member]      
Related Party Transaction [Line Items]      
Purchase from related party $ 2.1us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_OilChemResearchCompanyMember 		$ 2.0us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_OilChemResearchCompanyMember 		$ 2.0us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_OilChemResearchCompanyMember
SFC [Member]      
Related Party Transaction [Line Items]      
Aggregate annual rent for leased aircraft usage 0.5us-gaap_LeaseAndRentalExpense
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_SonicFinancialCorporationMember 		0.9us-gaap_LeaseAndRentalExpense
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_SonicFinancialCorporationMember 		0.9us-gaap_LeaseAndRentalExpense
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_SonicFinancialCorporationMember
Speedway Motorsports, Inc. [Member]      
Related Party Transaction [Line Items]      
Aggregate annual rent for leased aircraft usage $ 0.6us-gaap_LeaseAndRentalExpense
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_SpeedwayMotorsportsIncMember 		$ 0.6us-gaap_LeaseAndRentalExpense
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_SpeedwayMotorsportsIncMember 		$ 0.4us-gaap_LeaseAndRentalExpense
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= sah_SpeedwayMotorsportsIncMember