Revenues - Retail Commercial Truck Dealership (Details) - Retail Commercial Truck Dealership - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Total revenues	$ 292.4
New vehicle
Revenues
Total revenues	170.4
Used vehicle
Revenues
Total revenues	26.5
Finance and insurance, net
Revenues
Total revenues	3.2
Service and parts
Revenues
Total revenues	90.4
Wholesale
Revenues
Total revenues	$ 1.9
Without Adoption of ASC 606
Revenues
Total revenues		$ 211.7
Without Adoption of ASC 606 | New vehicle
Revenues
Total revenues		110.7
Without Adoption of ASC 606 | Used vehicle
Revenues
Total revenues		19.0
Without Adoption of ASC 606 | Finance and insurance, net
Revenues
Total revenues		2.1
Without Adoption of ASC 606 | Service and parts
Revenues
Total revenues		78.0
Without Adoption of ASC 606 | Wholesale
Revenues
Total revenues		$ 1.9