Acquisitions - Purchase Price (Details) - USD ($) $ in Thousands				9 Months Ended
	Sep. 22, 2017	Aug. 17, 2017	May 26, 2017	Sep. 30, 2017	Sep. 30, 2016
Acquisitions
Cash paid for acquisition, net of cash acquired				$ 345,140	$ 67,690
Assets Or Stock Of Multiple Dealership Locations Acquired
Acquisitions
Purchase Price				242,644	67,688
Inventory purchases financed via floor plan				(79,321)	(22,265)
Cash payment net of holdback and floor plan financing				163,323	45,423
Goodwill for tax purposes				$ 143,788	$ 35,786
Gander Mountain and Overton's
Acquisitions
Purchase Price			$ 35,400
Liability incurred/extinguished with acquistion			1,100
Cash paid for acquisition			35,578
Goodwill for tax purposes			$ 1,329
TheHouse.com
Acquisitions
Liability incurred/extinguished with acquistion		$ 35,300
Cash paid for acquisition		30,000
Cash paid for acquisition, net of cash acquired		64,811
Non-cash consideration - Class A shares issued		5,720
Goodwill for tax purposes		$ 3,400
W82
Acquisitions
Extinguishment of debt	$ 1,500
Cash paid for acquisition	600
Goodwill for tax purposes	$ 1,497