Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Additional Information (Details)

v3.10.0.1
Commitments and Contingencies - Additional Information (Details) - USD ($)
 9 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]    
Lease exit costs accrual $ 6,259,000 $ 6,478,000
Other Commitments [Line Items]    
Maximum exposure associated with general indemnifications $ 14,000,000.0 $ 5,000,000.0
General indemnifications minimum expiration period 1 year  
General indemnifications maximum expiration period 3 years  
Percentage of dealership that is accounted for under the equity method 50.00% 50.00%
Contingent liability reserve balance after reduction $ 2,800,000 $ 2,800,000
Acquired business, earnings targets, maximum term 10 years  
Maximum aggregate earnout payment $ 80,000,000.0  
Earnout accrual 23,300,000  
Earnout accrual recorded in other accrued liabilities 7,700,000  
Earnout accrual recorded in other long-term liabilities 15,600,000  
Other accrued liabilities    
Other Commitments [Line Items]    
Amount reserved for pending proceedings 2,100,000 3,000,000.0
Other long-term liabilities    
Other Commitments [Line Items]    
Amount reserved for pending proceedings $ 200,000 $ 200,000