Interim Financial Statements (Business and Basis of Presentation) (Details)	9 Months Ended
	Sep. 30, 2017 brand store franchises
Product Information [Line Items]
Owned and operated new vehicle franchises | franchises	361
Number of brands | brand	33
Percentage of new vehicle sales from core brands (percent)	93.00%
Dealerships [Member]
Product Information [Line Items]
Number of stores	254
Collision Centers [Member]
Product Information [Line Items]
Number of stores	73