Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Summary of Operating Lease Exit Accruals (Parenthetical) (Detail)

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Summary of Significant Accounting Policies - Summary of Operating Lease Exit Accruals (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Accounting Policies [Abstract]  
Component of lease exit expense in income (loss) from operations and the sale of dealerships $ 0.4sah_LeaseExitExpenseDiscontinuedOperations
Component of lease exit expense in selling, general and administrative expenses 0.1sah_LeaseExitExpenseSellingGeneralAndAdministrative
Component of lease exit payments in selling, general and administrative expenses 0.2sah_LeaseExitPaymentSellingGeneralAndAdministrative
Component of lease exit payments in income (loss) from operations and the sale of dealerships $ 1.4sah_LeaseExitPaymentDiscontinuedOperations