Inventory And Vehicle Floorplan Payable (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Floorplan Payable [Line Items]
Vehicle floorplan facilities, amount outstanding	$ 3,203.8		$ 3,097.2
Used vehicle floorplan facilities, remaining borrowing capacity	186.7
Used vehicle floorplan facilities, current borrowing capacity	$ 160.2
Used Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, average LIBOR-based interest rates	1.70%	1.70%
Vehicle floorplan facilities, maximum borrowing capacity	$ 335.0
Vehicle floorplan facilities, amount outstanding	$ 148.3
New Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, average LIBOR-based interest rates	1.70%	1.80%
Vehicle floorplan facilities, maximum borrowing capacity	$ 4,100.0
Vehicle floorplan facilities, amount outstanding	$ 3,100.0