Quarterly report pursuant to Section 13 or 15(d)

Business Acquisitions and Dispositions - Additional Information (Detail)

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Business Acquisitions and Dispositions - Additional Information (Detail) (USD $)
3 Months Ended 9 Months Ended
Sep. 30, 2013
Dealerships
Sep. 30, 2013
Dealerships
Dec. 31, 2012
Business Acquisition [Line Items]      
Purchase price for franchise operations and underlying assets, including real estate, acquired $ 88,200,000 $ 88,184,000  
Goodwill 478,951,000 478,951,000 454,224,000
Number of dealerships held for sale 0 0  
2013 Acquisitions [Member]
     
Business Acquisition [Line Items]      
Net assets relating to dealership operations 43,500,000 43,500,000  
Indefinite life intangible assets representing rights acquired under franchise agreements 20,000,000 20,000,000  
Goodwill $ 24,700,000 $ 24,700,000