Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory [Line Items]
New Vehicles Inventory, Gross	$ 1,194,632	$ 1,156,383
Used Vehicles Inventory, Gross	350,760	294,812
Rental Vehicles Inventory, Gross	144,213	131,080
Parts, Accessories and Other Inventory, Gross	82,755	77,762
Inventory, Gross	1,772,360	1,660,037
Summary of inventories
Lower of cost or market reserves	$ (9,067)	$ (8,222)