Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
REVENUES:
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 sales	1,338,032	1,261,307	1,186,193
Finance, insurance and other, net	429,002	420,654	408,786
Total revenues	11,123,721	10,887,612	10,632,505
COST OF SALES:
New vehicle retail sales	5,835,526	5,729,697	5,695,829
Used vehicle retail sales	2,621,431	2,575,234	2,459,499
Used vehicle wholesale sales	402,912	406,305	399,171
Parts and service sales	618,343	581,307	544,034
Total cost of sales	9,478,212	9,292,543	9,098,533
GROSS PROFIT	1,645,509	1,595,069	1,533,972
SELLING, GENERAL AND ADMINISTRATIVE EXPENSES	1,226,195	1,170,763	1,120,833
DEPRECIATION AND AMORTIZATION EXPENSE	57,936	51,234	47,239
ASSET IMPAIRMENTS	19,506	32,838	87,562
INCOME FROM OPERATIONS	341,872	340,234	278,338
OTHER INCOME (EXPENSE):
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
BASIC EARNINGS PER SHARE	$ 10.08	$ 6.67	$ 3.91
Weighted average common shares outstanding	20,420	21,161	23,148
DILUTED EARNINGS PER SHARE	$ 10.08	$ 6.67	$ 3.90
Weighted average common shares outstanding	20,425	21,170	23,152
CASH DIVIDENDS PER COMMON SHARE	$ 0.97	$ 0.91	$ 0.83