Acquisitions - Pro Forma Information (Details) - Assets Or Stock Of Multiple Dealership Locations Acquired - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Acquisitions
Revenue	$ 11.5	$ 12.2
Pre-tax income	$ 0.5	$ 0.2

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration