Segment Information Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
New vehicle retail sales									$ 6,157,531	$ 6,046,075	$ 6,001,306
Used vehicle retail sales									2,798,986	2,757,713	2,638,969
Used vehicle wholesale sales									400,170	401,863	397,251
Parts and service									1,338,032	1,261,307	1,186,193
Finance and insurance									429,002	420,654	408,786
Total revenues	$ 2,920,405	$ 3,012,292	$ 2,672,195	$ 2,518,829	$ 2,673,632	$ 2,823,176	$ 2,782,449	$ 2,608,355	11,123,721	10,887,612	10,632,505
Gross profit	425,675	431,420	$ 404,892	$ 383,522	389,181	406,668	410,119	389,101	1,645,509	1,595,069	1,533,972
Selling, general and administrative expense									1,226,195	1,170,763	1,120,833
Depreciation and amortization									57,936	51,234	47,239
ASSET IMPAIRMENTS	10,000	$ 9,500			20,000	$ 10,900	$ 1,000	$ 900	19,506	32,838	87,562
Floorplan interest expense									(52,372)	(44,927)	(39,264)
Other interest expense, net									(70,497)	(67,936)	(56,903)
Income before income taxes									219,003	227,371	182,171
Provision for income taxes									(5,561)	(80,306)	(88,172)
Net income									213,442	147,065	93,999
Capital expenditures									98,301	100,606	107,232
Total assets	4,871,065				4,461,903				4,871,065	4,461,903
U.S.
Segment Reporting Information [Line Items]
New vehicle retail sales									4,768,864	4,766,047	4,989,290
Used vehicle retail sales									2,160,699	2,242,508	2,204,728
Used vehicle wholesale sales									250,668	276,710	289,580
Parts and service									1,124,380	1,071,651	1,032,960
Finance and insurance									375,954	377,756	377,432
Total revenues									8,680,565	8,734,672	8,893,990
Gross profit									1,365,314	1,355,349	1,338,947
Selling, general and administrative expense									983,974	965,139	958,608
Depreciation and amortization									48,285	43,472	41,220
ASSET IMPAIRMENTS									12,762	21,794	18,983
Floorplan interest expense									(47,221)	(40,444)	(36,062)
Other interest expense, net									(66,493)	(62,320)	(52,277)
Income before income taxes									206,579	222,180	231,797
Provision for income taxes									(5,679)	(82,541)	(89,433)
Net income									200,900	139,639	142,364
Capital expenditures									77,477	86,692	97,504
Goodwill and intangible franchise rights	1,091,248				1,066,469				1,091,248	1,066,469
Total assets	4,087,039				3,855,701				4,087,039	3,855,701
U.K.
Segment Reporting Information [Line Items]
New vehicle retail sales									1,092,612	987,538	641,888
Used vehicle retail sales									546,266	434,203	351,311
Used vehicle wholesale sales									136,847	121,747	100,706
Parts and service									165,755	143,362	102,183
Finance and insurance									44,523	36,305	24,117
Total revenues									1,986,003	1,723,155	1,220,205
Gross profit									225,253	192,982	137,646
Selling, general and administrative expense									191,570	158,636	108,719
Depreciation and amortization									8,198	6,594	4,307
ASSET IMPAIRMENTS									0	201	330
Floorplan interest expense									(4,727)	(4,222)	(2,276)
Other interest expense, net									(3,664)	(5,197)	(3,135)
Income before income taxes									17,094	18,132	18,879
Provision for income taxes									(2,142)	(3,697)	(3,655)
Net income									14,952	14,435	15,224
Capital expenditures									19,944	12,602	9,395
Goodwill and intangible franchise rights	94,517				74,391				94,517	74,391
Total assets	654,154				482,937				654,154	482,937
Brazil
Segment Reporting Information [Line Items]
New vehicle retail sales									296,055	292,490	370,128
Used vehicle retail sales									92,021	81,002	82,930
Used vehicle wholesale sales									12,655	3,406	6,965
Parts and service									47,897	46,294	51,050
Finance and insurance									8,525	6,593	7,237
Total revenues									457,153	429,785	518,310
Gross profit									54,942	46,738	57,379
Selling, general and administrative expense									50,651	46,988	53,506
Depreciation and amortization									1,453	1,168	1,712
ASSET IMPAIRMENTS									6,744	10,843	68,249
Floorplan interest expense									(424)	(261)	(926)
Other interest expense, net									(340)	(419)	(1,491)
Income before income taxes									(4,670)	(12,941)	(68,505)
Provision for income taxes									2,260	5,932	4,916
Net income									(2,410)	(7,009)	(63,589)
Capital expenditures									880	1,312	333
Goodwill and intangible franchise rights	12,901				20,779				12,901	20,779
Total assets	129,872				123,265				129,872	123,265
Consolidated Entities [Member]
Segment Reporting Information [Line Items]
Goodwill and intangible franchise rights	1,198,666				1,161,639				1,198,666	1,161,639
Total assets	$ 4,871,065				$ 4,461,903				4,871,065	4,461,903
Net of taxes [Member] | U.S.
Segment Reporting Information [Line Items]
ASSET IMPAIRMENTS									8,000	13,500	12,000
Net of taxes [Member] | Brazil
Segment Reporting Information [Line Items]
ASSET IMPAIRMENTS									$ 4,400	$ 6,900	$ 62,400