Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
REVENUES:
REVENUES	$ 2,943,462	$ 2,672,195	$ 5,803,488	$ 5,191,024
COST OF SALES:
Cost of sales	2,505,299	2,267,303	4,945,562	4,402,610
GROSS PROFIT	438,163	404,892	857,926	788,414
SELLING, GENERAL AND ADMINISTRATIVE EXPENSES	308,092	298,568	632,439	588,347
DEPRECIATION AND AMORTIZATION EXPENSE	16,638	14,093	32,980	27,699
ASSET IMPAIRMENTS	4,268	0	4,268	0
INCOME FROM OPERATIONS	109,165	92,231	188,239	172,368
OTHER EXPENSE:
Floorplan interest expense	(14,563)	(13,226)	(28,650)	(25,168)
Other interest expense, net	(19,414)	(17,315)	(38,234)	(34,314)
INCOME BEFORE INCOME TAXES	75,188	61,690	121,355	112,886
PROVISION FOR INCOME TAXES	(18,725)	(22,557)	(29,078)	(39,814)
NET INCOME	$ 56,463	$ 39,133	$ 92,277	$ 73,072
BASIC EARNINGS PER SHARE (in dollars per share)	$ 2.72	$ 1.84	$ 4.42	$ 3.42
Weighted average common shares outstanding (in shares)	20,036	20,516	20,167	20,604
DILUTED EARNINGS PER SHARE (in dollars per share)	$ 2.72	$ 1.84	$ 4.42	$ 3.42
Weighted average common shares outstanding (in shares)	20,046	20,522	20,176	20,609
CASH DIVIDENDS PER COMMON SHARE (in dollars per share)	$ 0.256144440792765	$ 0.24	$ 0.516401846427567	$ 0.48
New vehicle retail sales
REVENUES:
REVENUES	$ 1,555,570	$ 1,448,768	$ 3,069,160	$ 2,785,981
COST OF SALES:
Cost of sales	1,478,988	1,373,857	2,917,151	2,641,843
Used vehicle retail sales
REVENUES:
REVENUES	821,853	685,949	1,602,423	1,346,876
COST OF SALES:
Cost of sales	770,639	641,036	1,507,714	1,256,958
Used vehicle wholesale sales
REVENUES:
REVENUES	92,854	99,377	196,883	203,534
COST OF SALES:
Cost of sales	92,613	99,644	194,987	203,701
Parts and service sales
REVENUES:
REVENUES	358,129	331,631	707,644	651,329
COST OF SALES:
Cost of sales	163,059	152,766	325,710	300,108
Finance, insurance and other, net
REVENUES:
REVENUES	$ 115,056	$ 106,470	$ 227,378	$ 203,304