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Summary of Significant Accounting Policies - Summary of Lease Exit Accruals (Parenthetical) (Detail) $ in Millions | 6 Months Ended
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Jun. 30, 2017 USD ($)
Accounting Policies [Abstract] |
Component of lease exit expense in selling, general and administrative expenses | $ 1.1
Component of lease exit expense in income (loss) from operations and the sale of dealerships before tax | 0.7
Component of lease exit payments in selling, general and administrative expenses | 0.4
Component of lease exit payments in income (loss) from operations and the sale of dealerships before tax | $ 1.5

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

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- Definition Lease exit income (expense) discontinued operations. + References No definition available. + Details
Name: | sah_LeaseExitIncomeExpenseDiscontinuedOperations
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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- Definition Lease exit payment selling general and administrative. + References No definition available. + Details
Name: | sah_LeaseExitPaymentSellingGeneralAndAdministrative
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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