Annual report pursuant to Section 13 and 15(d)

Subsequent Events (Details)

v3.10.0.1
Subsequent Events (Details)
2 Months Ended 12 Months Ended
Feb. 21, 2019
USD ($)
Feb. 21, 2019
USD ($)
store
Dec. 31, 2018
USD ($)
Dealerships
Dec. 31, 2017
USD ($)
Dealerships
Dec. 31, 2016
Dealerships
Subsequent Event [Line Items]          
Number of franchises disposed | Dealerships     7 3 0
Cash generated from disposition     $ 128,700,000 $ 38,200,000  
Subsequent event          
Subsequent Event [Line Items]          
Number of franchises disposed | store   2      
Cash generated from disposition   $ 108,600,000      
Subsequent event | Class A and Class B Common Stock          
Subsequent Event [Line Items]          
Dividends (usd per share) $ 0.10