Quarterly report pursuant to Section 13 or 15(d)

Contingencies - Additional Information (Detail)

v2.4.1.9
Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Contingencies And Commitments [Line Items]    
Maximum exposure associated with general indemnifications $ 16.8us-gaap_AccrualForEnvironmentalLossContingenciesGross $ 16.8us-gaap_AccrualForEnvironmentalLossContingenciesGross
General indemnifications minimum expiration period 1 year  
General indemnifications maximum expiration period 2 years  
Joint venture ownership percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage  
Contingent liability reserve balance after reduction 2.8sah_ContingentLiabilityReserveBalance 2.8sah_ContingentLiabilityReserveBalance
Other Accrued Liabilities [Member]    
Contingencies And Commitments [Line Items]    
Amount reserved for pending proceedings 1.5sah_LegalMattersAmountReservedForPendingProceedings
/ us-gaap_BalanceSheetLocationAxis
= sah_OtherAccruedLiabilitiesMember 		2.0sah_LegalMattersAmountReservedForPendingProceedings
/ us-gaap_BalanceSheetLocationAxis
= sah_OtherAccruedLiabilitiesMember
Other Long-Term Liabilities [Member]    
Contingencies And Commitments [Line Items]    
Amount reserved for pending proceedings $ 0.3sah_LegalMattersAmountReservedForPendingProceedings
/ us-gaap_BalanceSheetLocationAxis
= sah_OtherLongTermLiabilitiesMember 		$ 0.3sah_LegalMattersAmountReservedForPendingProceedings
/ us-gaap_BalanceSheetLocationAxis
= sah_OtherLongTermLiabilitiesMember