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Business Acquisitions and Dispositions - Additional Information (Details) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2019 USD ($) Business | Mar. 31, 2018 USD ($) Business
Business Combinations [Abstract] |  |
Number of acquired franchises | Business | 0 |
Business Acquisition [Line Items] |  |
Number of franchises disposed | Business | 3 |
Net cash generated from disposition | $ | $ 121,700 |
Proceeds from sales of dealerships | $ | $ 121,700 | $ 7,461
Luxury franchise |  |
Business Acquisition [Line Items] |  |
Number of franchises terminated | Business |  | 1
Mid-line import franchise |  |
Business Acquisition [Line Items] |  |
Net cash generated from disposition | $ |  | $ 7,500

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- References No definition available. + Details
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Namespace Prefix: | sah_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | sah_NumberOfFranchisesTerminated
Namespace Prefix: | sah_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Proceeds From Dispositions Of Franchises + References No definition available. + Details
Name: | sah_ProceedsFromDispositionsOfFranchises
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of businesses acquired by the entity during the period. + References No definition available. + Details
Name: | us-gaap_NumberOfBusinessesAcquired
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition This element represents the cash inflow during the period from the sale of a component of the entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=sah_MidLineImportFranchiseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |