Acquisitions - General Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Aug. 17, 2017 store	May 26, 2017 lease	May 25, 2017 store
Assets Or Stock Of Multiple Dealership Locations Acquired
Acquisitions
Real properties purchased | $	$ 12.2	$ 12.9
Real properties sold in sale-leaseback transactions | $	$ 6.0	$ 7.3
Gander Mountain
Acquisitions
Number of retail leases | lease				15
TheHouse.com
Acquisitions
Number of locations			2
Gander Mountain
Acquisitions
Number of locations					160
Overton's
Acquisitions
Number of locations					2