CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CONSOLIDATED STATEMENTS OF CASH FLOWS
Repayment of Sellers' Floor Plan Notes Payable Dealership Acquisitions	$ 117.8	$ 29.6	$ 74.9
Statement
Interest rate (as a percent)			3.50%
5.375% senior subordinated notes due 2024
Statement
Interest rate (as a percent)	5.375%
5.75% senior subordinated notes due 2022
Statement
Interest rate (as a percent)	5.75%	5.75%	5.75%
7.75% Notes
Statement
Interest rate (as a percent)			7.75%
3.5% Notes
Statement
Interest rate (as a percent)			3.50%