Detail of Certain Balance Sheet Accounts (Inventories) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Summary of inventories
New Vehicles Inventory, Gross	$ 1,237,012		$ 1,194,632
Used Vehicles Inventory, Gross	359,725		350,760
Rental Vehicles Inventory, Gross	136,809		144,213
Parts, Accessories and Other Inventory, Gross	80,632		82,755
Inventory, Gross	1,814,178		1,772,360
Lower of cost or market reserves	10,002		9,067
Inventories, net	$ 1,804,176	$ 1,759,633	$ 1,763,293