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Summary of Significant Accounting Policies - Summary of Lease Exit Accruals (Detail) $ in Thousands | 3 Months Ended
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Mar. 31, 2017 USD ($)
Accounting Policies [Abstract] |
Beginning balance | $ 9,790
Lease exit expense | 614
Payments | (1,189)
Other | (885)
Ending balance | $ 8,330

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

X
- Definition Lease exit other cash settlement. + References No definition available. + Details
Name: | sah_LeaseExitOtherCashSettlement
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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

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