CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Repayment of Sellers' Floor Plan Notes Payable Dealership Acquisitions	$ 101.6	$ 62.2	$ 60.3
3.75% senior subordinated notes due 2020
Interest rate (as a percent)	3.75%
5.50% senior subordinated notes due 2026
Interest rate (as a percent)	5.50%	5.50%