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Business Acquisitions and Dispositions - Additional Information (Detail) - Franchise | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Business Combinations [Abstract] |  |  |  |
Number of franchises acquired | 0 | 0 | 0 | 0
Number of franchises disposed | 0 | 0 | 0 | 0

X
- Definition Number of franchises disposed. + References No definition available. + Details
Name: | sah_NumberOfFranchisesDisposed
Namespace Prefix: | sah_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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

X
- 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