Inventory And Vehicle Floorplan Payable (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Floorplan Payable [Line Items]
Vehicle floorplan facilities, amount outstanding	$ 4,039.4		$ 3,727.1
Used vehicle floorplan facilities, remaining borrowing capacity	41.5
Used vehicle floorplan facilities, current borrowing capacity	$ 0.4
Used Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, average LIBOR-based interest rates	1.90%	1.70%
Vehicle floorplan facilities, maximum borrowing capacity	$ 360.0
Vehicle floorplan facilities, amount outstanding	$ 318.5
New Vehicle Floorplan Facilities [Member]
Floorplan Payable [Line Items]
Vehicle floorplan facilities, average LIBOR-based interest rates	2.00%	1.70%
Vehicle floorplan facilities, maximum borrowing capacity	$ 4,600.0
Vehicle floorplan facilities, amount outstanding	$ 3,700.0