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Business Acquisitions and Dispositions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 Franchise | Mar. 31, 2014
Business Acquisition [Line Items] |  |
Number of franchise acquired | 0 us-gaap_NumberOfBusinessesAcquired |
Aggregate purchase price of franchise |  | $ 2.6 us-gaap_BusinessCombinationConsiderationTransferred1
Luxury Franchise [Member] |  |
Business Acquisition [Line Items] |  |
Number of franchise acquired |  | 1 us-gaap_NumberOfBusinessesAcquired / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = sah_LuxuryFranchiseMember

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- Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- 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

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- Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis=sah_LuxuryFranchiseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |