Acquisitions and Dispositions Acquisitions and Dispositions (Details textuals) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017
Acquisitions and Dispositions (Textual) [Abstract]
Business Combination, Consideration Transferred	$ 76.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 5.1
UNITED STATES
Acquisitions and Dispositions (Textual) [Abstract]
Number Of Dealerships Acquired	2
Number of Franchises Acquired	2
UNITED KINGDOM
Acquisitions and Dispositions (Textual) [Abstract]
Number Of Dealerships Acquired	5
Number of Franchises Acquired	8
Number Of Dealerships Opened	1	1
Number Of Franchises Awarded	1	1
BRAZIL
Acquisitions and Dispositions (Textual) [Abstract]
Number of Dealerships Disposed		2
Number of Franchises Disposed		2