Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Assets or Liabilities Recorded at Fair Value (Parenthetical) (Detail)

v2.4.1.9
Fair Value Measurements - Assets or Liabilities Recorded at Fair Value (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Cash Flow Swaps Designated as Hedges [Member]    
Derivatives, Fair Value [Line Items]    
Amount included in other accrued liabilities $ 7.5sah_DerivativeLiabilityInOtherAccruedLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsDesignatedAsHedgesMember 		$ 10.6sah_DerivativeLiabilityInOtherAccruedLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsDesignatedAsHedgesMember
Amount included in other long-term liabilities 2.8sah_DerivativeLiabilityInOtherLongTermLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsDesignatedAsHedgesMember 		7.4sah_DerivativeLiabilityInOtherLongTermLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsDesignatedAsHedgesMember
Cash Flow Swaps Not Designated as Hedges [Member]    
Derivatives, Fair Value [Line Items]    
Amount included in other accrued liabilities 0.7sah_DerivativeLiabilityInOtherAccruedLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsNotDesignatedAsHedgesMember 		1.0sah_DerivativeLiabilityInOtherAccruedLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsNotDesignatedAsHedgesMember
Amount included in other long-term liabilities $ 0.8sah_DerivativeLiabilityInOtherLongTermLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsNotDesignatedAsHedgesMember 		$ 1.0sah_DerivativeLiabilityInOtherLongTermLiabilities
/ us-gaap_HedgingDesignationAxis
= sah_CashFlowSwapsNotDesignatedAsHedgesMember