Quarterly report pursuant to Section 13 or 15(d)

Business Acquisitions and Dispositions - Additional Information (Details)

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Business Acquisitions and Dispositions - Additional Information (Details)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Business
Sep. 30, 2017
USD ($)
Business
Sep. 30, 2018
USD ($)
Business
Sep. 30, 2017
USD ($)
Franchise
Business Combinations [Abstract]        
Number of acquired franchises | Business 0   0  
Business Acquisition [Line Items]        
Number of franchises disposed | Business     6  
Net cash generated from disposition | $     $ 121,900  
Proceeds from sales of dealerships | $     $ 121,859 $ 22,578
Luxury franchise        
Business Acquisition [Line Items]        
Number of franchises terminated | Business   1    
EchoPark        
Business Acquisition [Line Items]        
Number of franchises ceased operations | Business   3    
Mid-line import franchise        
Business Acquisition [Line Items]        
Number of franchises disposed | Franchise       1
Net cash generated from disposition | $   $ 22,600    
Stand-alone pre-owned vehicle business        
Business Acquisition [Line Items]        
Business acquisition, consideration amount | $   $ 76,600