Intangible Franchise Rights and Goodwill Goodwill (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 876,763,000	$ 854,915,000
Goodwill, Acquired During Period	32,002,000	33,499,000
Goodwill, Purchase Accounting Adjustments		1,052,000
Goodwill, Written off Related to Sale of Business Unit	(933,000)	(4,059,000)
Goodwill, Impairment Loss			$ 55,400,000
Goodwill, Foreign Currency Translation Gain (Loss)	5,202,000	(8,644,000)
Goodwill, Ending Balance	$ 913,034,000	876,763,000	854,915,000
Goodwill, Impaired, Accumulated Impairment Loss		97,800,000
U.S.
Goodwill [Line Items]
Number Of Dealerships Acquired	3
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 805,935,000	809,775,000
Goodwill, Acquired During Period	29,332,000	0
Goodwill, Purchase Accounting Adjustments		28,000
Goodwill, Written off Related to Sale of Business Unit	0	(3,868,000)
Goodwill, Foreign Currency Translation Gain (Loss)	0	0
Goodwill, Ending Balance	$ 835,267,000	$ 805,935,000	809,775,000
U.K.
Goodwill [Line Items]
Number Of Dealerships Acquired	12	12
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 57,054,000	$ 35,320,000
Goodwill, Acquired During Period	2,575,000	31,644,000
Goodwill, Purchase Accounting Adjustments		1,024,000
Goodwill, Written off Related to Sale of Business Unit	0	0
Goodwill, Foreign Currency Translation Gain (Loss)	5,405,000	(10,934,000)
Goodwill, Ending Balance	65,034,000	$ 57,054,000	35,320,000
Brazil
Goodwill [Line Items]
Number Of Dealerships Acquired		1
Goodwill [Roll Forward]
Goodwill, Beginning Balance	13,774,000	$ 9,820,000
Goodwill, Acquired During Period	95,000	1,855,000
Goodwill, Purchase Accounting Adjustments		0
Goodwill, Written off Related to Sale of Business Unit	(933,000)	(191,000)
Goodwill, Foreign Currency Translation Gain (Loss)	(203,000)	2,290,000
Goodwill, Ending Balance	$ 12,733,000	$ 13,774,000	$ 9,820,000