Store Divestitures (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) store	Mar. 31, 2017 USD ($) store
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on disposal | $	$ 6.5	$ 4.3
Premium Luxury Stores Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of stores divested	1
Domestic Stores Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of stores divested	7
Import Stores Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of stores divested	2	1
Collision Centers Divested [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of stores divested	1