Acquisitions - Pro Forma Information (Details) - USD ($)	4 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Assets Or Stock Of Multiple Dealership Locations Acquired
Acquisitions
Revenue		$ 210,700,000	$ 55,300,000
Pre-tax income (loss)		13,800,000	$ 1,700,000
Gander Mountain and Overton's
Acquisitions
Revenue	$ 22,300,000
Pre-tax income (loss)	$ (11,300,000)
TheHouse.com
Acquisitions
Revenue		3,700,000
Pre-tax income (loss)		200,000
W82
Acquisitions
Revenue		34,000
Pre-tax income (loss)		$ 8,000