Quarterly report pursuant to Section 13 or 15(d)

Per Share Data and Stockholders' Equity - Dilutive Effect on Earnings Per Share (Detail)

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Per Share Data and Stockholders' Equity - Dilutive Effect on Earnings Per Share (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Earnings Per Share [Abstract]    
Weighted Average Shares, Earning (loss) and shares 50,854us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 52,418us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Weighted Average Shares, Stock compensation plans 549us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements 528us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
Weighted Average Shares, Diluted earnings (loss) and shares 51,403us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 52,946us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Income (Loss) From Continuing Operations, Amount $ 14,389us-gaap_IncomeLossFromContinuingOperations $ 19,984us-gaap_IncomeLossFromContinuingOperations
Participating securities income (loss) from continuing operations non-vested restricted stock and restricted stock units (5)us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic (63)us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic
Income (Loss) From Continuing Operations, Basic 14,384sah_IncomeLossFromContinuingOperationsBasicAfterEffectOfParticipatingSecurities 19,921sah_IncomeLossFromContinuingOperationsBasicAfterEffectOfParticipatingSecurities
Income (Loss) From Continuing Operations Diluted, Amount 14,384sah_IncomeLossFromContinuingOperationsDiluted 19,921sah_IncomeLossFromContinuingOperationsDiluted
Income (Loss) From Continuing Operations, Basic earnings (loss), Per Share Amount $ 0.28us-gaap_IncomeLossFromContinuingOperationsPerBasicShare $ 0.38us-gaap_IncomeLossFromContinuingOperationsPerBasicShare
Income (Loss) From Continuing Operations, Diluted earnings (loss), Per Share Amount $ 0.28us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare $ 0.38us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare
Dilutive effect on earnings per share (422)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax (598)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax
Income (Loss) From Discontinued Operations, Basic earnings (loss), Amount (422)sah_IncomeLossFromDiscontinuedOperationsNetOfTaxBasicAfterEffectOfParticipatingSecurities (598)sah_IncomeLossFromDiscontinuedOperationsNetOfTaxBasicAfterEffectOfParticipatingSecurities
Income (Loss) From Discontinued Operations, Diluted earnings (loss), Amount (422)sah_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityDiluted (598)sah_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityDiluted
Income (Loss) From Discontinuing Operations, Basic earnings (loss), Per Share Amount $ (0.01)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare $ (0.01)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare
Income (Loss) From Discontinued Operations, Diluted earnings (loss), Per Share Amount $ (0.01)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare $ (0.02)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare
Net Income (Loss), Amount 13,967us-gaap_NetIncomeLoss 19,386us-gaap_NetIncomeLoss
Net Income (Loss), Basic, Amount 13,962sah_NetIncomeLossBasicAfterEffectOfParticipatingSecurities 19,323sah_NetIncomeLossBasicAfterEffectOfParticipatingSecurities
Net Income (Loss), Diluted, Amount $ 13,962us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted $ 19,323us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Net Income (Loss), Basic, Per Share Amount $ 0.27us-gaap_EarningsPerShareBasic $ 0.37us-gaap_EarningsPerShareBasic
Net Income (Loss), Diluted, Per Share Amount $ 0.27us-gaap_EarningsPerShareDiluted $ 0.36us-gaap_EarningsPerShareDiluted