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

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- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
Name: | us-gaap_LeaseAndRentalExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=sah_OilChemResearchCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=sah_SonicFinancialCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=sah_SpeedwayMotorsportsIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |