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Summary of Significant Accounting Policies - Summary of Operating Lease Exit Accruals (Detail) - USD ($) $ in Thousands | 9 Months Ended
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Sep. 30, 2015 | Sep. 30, 2014
Accounting Policies [Abstract] |  |
Balance at December 31, 2014 | $ 18,962 |
Lease exit expense | 1,485 | $ (272)
Payments | (4,671) |
Balance at September 30, 2015 | $ 15,776 |

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- Definition Gain (loss) on exit of leased dealerships. + References No definition available. + Details
Name: | sah_GainLossOnExitOfLeasedDealerships
Namespace Prefix: | sah_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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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 payment. + References No definition available. + Details
Name: | sah_LeaseExitPayment
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