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Fair Value Measurements - Additional Information (Detail) - Stand-Alone Pre-Owned Vehicle Businesses And Related Real Estate [Member]
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2016
Business
Sep. 30, 2017
USD ($)
Business
Sep. 30, 2016
Business
Business Acquisition [Line Items]      
Number of businesses acquired | Business 3   3
Impairment of goodwill | $   $ 0.9  
Impairment of property and equipment | $   $ 0.8  
Number of businesses closed | Business   2