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Subsequent Events (Details) - USD ($)
3 Months Ended
Feb. 14, 2018
Feb. 12, 2018
Jan. 15, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Mar. 23, 2018
Subsequent Event [Line Items]                                
Cash dividend declared per Class A and Class B share (in dollars per share)       $ 0.27 $ 0.27 $ 0.27 $ 0.25 $ 0.25 $ 0.25 $ 0.25 $ 0.20 $ 0.20 $ 0.20 $ 0.20 $ 0.16  
Subsequent Event                                
Subsequent Event [Line Items]                                
Cash dividend declared per Class A and Class B share (in dollars per share)   $ 0.27                            
Dividends payable                               $ 6,800,000
Ray Laks Honda and Ray Laks Acura | Subsequent Event                                
Subsequent Event [Line Items]                                
Cash paid for acquisition     $ 26,200,000                          
Revolving line of credit | Line of Credit | Subsequent Event                                
Subsequent Event [Line Items]                                
Credit facility $ 150,000,000.0                              
LIBOR | Revolving line of credit | Line of Credit | Subsequent Event                                
Subsequent Event [Line Items]                                
Basis spread on variable rate (in percent) 1.50%