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Commitments and Contingencies - Summary of Lease Exit Accruals (Detail) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract] |
Beginning balance | $ 9,790
Lease exit expense | 2,157
Payments | (3,592)
Lease buyout/other | (1,877)
Ending balance | $ 6,478

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- Definition Lease exit accruals. + References No definition available. + Details
Name: | sah_LeaseExitAccruals
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Lease exit buyout other. + References No definition available. + Details
Name: | sah_LeaseExitBuyoutOther
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Lease exit expense. + References No definition available. + Details
Name: | sah_LeaseExitExpense
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Lease exit payment. + References No definition available. + Details
Name: | sah_LeaseExitPayment
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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