Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
New Vehicle [Member]
Revenues:
Revenues	$ 1,096,055	$ 1,007,816
Cost of sales:
Cost of sales	1,029,289	946,042
Used Retail Vehicle [Member]
Revenues:
Revenues	532,726	462,931
Cost of sales:
Cost of sales	468,449	403,489
Used Wholesale Vehicle [Member]
Revenues:
Revenues	65,146	62,208
Cost of sales:
Cost of sales	63,316	60,047
Finance and Insurance [Member]
Revenues:
Revenues	77,638	64,604
Service, Body and Parts [Member]
Revenues:
Revenues	196,675	173,475
Cost of sales:
Cost of sales	100,556	89,036
Fleet and Other [Member]
Revenues:
Revenues	14,621	18,144
Cost of sales:
Cost of sales	14,069	17,189
Revenues	1,982,861	1,789,178
Cost of sales	1,675,679	1,515,803
Gross profit	307,182	273,375
Asset impairments	3,498	4,130
Selling, general and administrative	219,106	191,618
Depreciation and amortization	11,663	9,726
Operating income	72,915	67,901
Floor plan interest expense	(5,909)	(4,649)
Other interest expense	(5,459)	(4,828)
Other expense, net	(1,526)	(368)
Income before income taxes	60,021	58,056
Income tax provision	(19,751)	(17,403)
Net income	$ 40,270	$ 40,653
Basic net income per share (in dollars per share)	$ 1.56	$ 1.55
Shares used in basic per share calculations (in shares)	25,816	26,283
Diluted net income per share (in dollars per share)	$ 1.55	$ 1.53
Shares used in diluted per share calculations (in shares)	25,973	26,519