Acquisitions - General Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets Or Stock Of Multiple Dealership Locations Acquired
Acquisitions
Real properties purchased	$ 15.3	$ 17.0	$ 3.8	$ 13.6