Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Summary of Lease Exit Accruals (Parenthetical) (Detail)

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Commitments and Contingencies - Summary of Lease Exit Accruals (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Commitments And Contingencies Disclosure [Abstract]  
Component of lease exit expense in interest expense, other, net $ 0.2sah_LeaseExitExpenseInterestOther
Component of lease exit expense in selling, general and administrative expenses 0.3sah_LeaseExitExpenseSellingGeneralAndAdministrative
Component of lease exit expense in income (loss) from operations and the sale of dealerships 0.2sah_LeaseExitExpenseDiscontinuedOperations
Component of lease exit payments in selling, general and administrative expenses 0.8sah_LeaseExitPaymentSellingGeneralAndAdministrative
Component of lease exit payments in income (loss) from operations and the sale of dealerships $ 6.2sah_LeaseExitPaymentDiscontinuedOperations