Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

Income Taxes - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Income Taxes [Line Items]    
Net short-term deferred tax asset 13,200,000us-gaap_DeferredTaxAssetsNetCurrent $ 15,900,000us-gaap_DeferredTaxAssetsNetCurrent
Net long-term deferred tax asset 3,800,000us-gaap_DeferredTaxAssetsNetNoncurrent 3,900,000us-gaap_DeferredTaxAssetsNetNoncurrent
Net long-term deferred tax liability 57,601,000us-gaap_DeferredTaxLiabilitiesNoncurrent 31,552,000us-gaap_DeferredTaxLiabilitiesNoncurrent
Gross deferred tax assets related to state net operating loss carryforwards 280,900,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration  
Valuation allowance related to certain state net operating loss carryforward deferred tax assets 6,500,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal  
Liabilities recorded related to unrecognized tax benefits   7,800,000sah_UnrecognizedTaxBenefitsRecordedLiability
Liabilities related to interest and penalties 1,200,000us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued 1,100,000us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
Unorganized tax benefit that would affect income tax rate if recognized 2,800,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate $ 3,000,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate
State and Local Jurisdiction [Member]    
Income Taxes [Line Items]    
Operating loss expiration date Net operating loss carryforwards that will expire between [2015 and 2032]  
Operating loss expiration, beginning year 2016  
Operating loss expiration, ending year 2034  
Income tax examination range upper limit 2014  
Income tax examination range lower limit 2006  
United States Federal Income Tax Authority [Member]    
Income Taxes [Line Items]    
Income tax examination range upper limit 2014  
Income tax examination range lower limit 2011