Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Details)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]      
Percentage of dealership that is accounted for under the equity method 50.00%   50.00%
Effective tax rate from continuing operations 47.80% 113.30%  
Discrete benefit related to vested or exercised stock compensation $ 0.9 $ 0.3  
Effective Income Tax Rate Reconciliation, Uncertain Tax Position, Amount $ 0.2 $ 0.6  
Minimum      
Schedule of Equity Method Investments [Line Items]      
Expected annual effective tax rate in future periods 26.00%    
Maximum      
Schedule of Equity Method Investments [Line Items]      
Expected annual effective tax rate in future periods 28.00%    
Dealership      
Schedule of Equity Method Investments [Line Items]      
Percentage of dealership that is accounted for under the equity method 50.00%