Annual report pursuant to Section 13 and 15(d)

Description of Business and Summary of Significant Accounting Policies - Additional Information (Details)

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Description of Business and Summary of Significant Accounting Policies - Additional Information (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
Store
Segment
reporting_unit
Dealerships
Brand
Franchise
Collision
State
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Jan. 01, 2019
USD ($)
Jan. 01, 2018
USD ($)
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Number of operating segments | Segment 2        
Number of new vehicle dealerships | Dealerships 108        
Number of states | State 13        
Number of different brands of cars and light trucks | Brand 23        
Number of collision repair centers | Collision 15        
Book overdraft position $ 0 $ 6,900,000      
Revenue allowances for commission reserves 25,800,000 20,900,000      
Amount recognized for floor plan assistance $ 42,200,000 45,300,000 $ 45,000,000.0    
Term for funding of finance contracts 10 days        
Contracts in transit included in receivables, net $ 227,800,000 267,600,000      
Receivables, net $ 438,186,000 482,126,000     $ 486,716,000
Number of reporting units | reporting_unit 2        
Goodwill $ 509,592,000 525,780,000 472,437,000    
Insurance reserves 22,900,000 22,000,000.0      
Concentrations of credit risk with respect to receivables are limited primarily to receivables from automobile manufacturers 93,800,000 102,500,000      
Deposits 0 3,000,000.0      
Reduction in interest expense 0 500,000 600,000    
Advertising expense 63,100,000 61,600,000 61,700,000    
Cooperative manufacturer credits advertising expenses $ 26,700,000 26,000,000.0 $ 26,200,000    
Number of reportable Segment | Segment 2        
Expected business interruption insurance proceeds          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Receivables, net $ 1,000,000.0        
Financial institutions          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Concentrations of credit risk with respect to receivables are limited primarily to receivables from financial institutions 258,700,000 299,600,000      
Franchise assets          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Franchise asset impairment charge 2,100,000 3,600,000      
Continuing operations | Franchise assets          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Franchise asset impairment charge $ 2,100,000 $ 3,600,000      
Number of franchises resulted in asset impairment charge | Franchise 1        
Dealership          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Percentage of dealership that is accounted for under the equity method 50.00%        
Franchised dealerships          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Goodwill $ 449,600,000        
EchoPark          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Goodwill $ 60,000,000.0        
Franchised dealerships          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Number of stores | Store 96        
Minimum | ASU 2016-02 | Subsequent event          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Operating lease liabilities       $ 350,000,000.0  
ROU assets       350,000,000.0  
Maximum | ASU 2016-02 | Subsequent event          
Description Of Business And Summary Of Significant Accounting Policies [Line Items]          
Operating lease liabilities       400,000,000.0  
ROU assets       $ 400,000,000.0