| Income Taxes - Summary of Changes in Liability Related to Unrecognized Tax Benefits (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended | ||
|---|---|---|---|
| Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | |
| Income Tax Disclosure [Abstract] | |||
| Unrecognized tax benefit liability, Beginning Balance | $ 6,693us-gaap_UnrecognizedTaxBenefits | $ 9,097us-gaap_UnrecognizedTaxBenefits | $ 13,689us-gaap_UnrecognizedTaxBenefits | 
| Prior period positions: | |||
| Increases | 181us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 409us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 35us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 
| Decreases | (66)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions | (233)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions | (1,101)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions | 
| Increases from current period positions | 195us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 799us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 1,155us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 
| Settlements | (897)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities | (1,721)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities | (2,924)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities | 
| Lapse of statute of limitations | (170)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations | (1,164)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations | (1,275)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations | 
| Other | (196)sah_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromOtherAdjustments | (494)sah_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromOtherAdjustments | (482)sah_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromOtherAdjustments | 
| Unrecognized tax benefit liability, Ending Balance | $ 5,740us-gaap_UnrecognizedTaxBenefits | $ 6,693us-gaap_UnrecognizedTaxBenefits | $ 9,097us-gaap_UnrecognizedTaxBenefits | 
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- Definition Unrecognized tax benefits increase decrease resulting from other adjustments. No definition available. 
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- Details 
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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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