Acquisitions - General Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	May 26, 2017 lease	May 25, 2017 store
Assets Or Stock Of Multiple Dealership Locations Acquired
Acquisitions
Real properties purchased | $	$ 11.1	$ 10.4
Real properties sold in sale-leaseback transactions | $	$ 6.0	$ 2.8
Gander Mountain
Acquisitions
Number of retail leases | lease			15
Gander Mountain
Acquisitions
Number of locations | store				160
Overton's
Acquisitions
Number of locations | store				2