Annual report pursuant to Section 13 and 15(d)

Business Acquisitions and Dispositions - Results Associated with Disposed Dealerships That Remain in Continued Operations (Detail)

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Business Acquisitions and Dispositions - Results Associated with Disposed Dealerships That Remain in Continued Operations (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Sep. 30, 2014
Jun. 30, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Business Combinations [Abstract]          
Income (loss) from operations     $ (787)sah_DisposalGroupNotDiscontinuedOperationOperatingIncomeLoss $ (485)sah_DisposalGroupNotDiscontinuedOperationOperatingIncomeLoss $ (424)sah_DisposalGroupNotDiscontinuedOperationOperatingIncomeLoss
Gain (loss) on disposal 3,200us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal 7,300us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal 11,079us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal   10us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal
Property impairment charges       (5,565)sah_DisposalGroupIncludingContinuedOperationAssetsImpairmentCharges  
Pre-tax income (loss)     10,292sah_DisposalGroupNotDiscontinuedOperationIncomeLossBeforeIncomeTax (6,050)sah_DisposalGroupNotDiscontinuedOperationIncomeLossBeforeIncomeTax (414)sah_DisposalGroupNotDiscontinuedOperationIncomeLossBeforeIncomeTax
Total revenues     $ 205,559sah_DisposalGroupNotDiscontinuedOperationRevenue $ 310,919sah_DisposalGroupNotDiscontinuedOperationRevenue $ 294,083sah_DisposalGroupNotDiscontinuedOperationRevenue