Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
New Vehicle [Member]
Revenues:
Revenues		$ 4,552,301	$ 3,077,670	$ 2,256,598
Cost of sales:
Cost of sales		4,271,931	2,879,486	2,105,480
Used Retail Vehicle [Member]
Revenues:
Revenues		1,927,016	1,362,481	1,032,224
Cost of sales:
Cost of sales		1,685,767	1,183,228	881,366
Used Wholesale Vehicle [Member]
Revenues:
Revenues		261,530	195,699	158,235
Cost of sales:
Cost of sales		257,073	192,053	155,524
Finance and Insurance [Member]
Revenues:
Revenues		283,018	190,381	139,007
Service, Body and Parts [Member]
Revenues:
Revenues		738,990	512,124	383,483
Cost of sales:
Cost of sales		375,069	262,388	197,913
Fleet and Other [Member]
Revenues:
Revenues		101,397	51,971	36,202
Cost of sales:
Cost of sales		98,778	49,849	34,513
Revenues		7,864,252	5,390,326	4,005,749
Cost of sales		6,688,618	4,567,004	3,374,796
Gross profit		1,175,634	823,322	$ 630,953
Asset impairments		20,124	1,853
Selling, general and administrative		811,175	563,207	$ 427,400
Depreciation and amortization		41,600	26,363	20,035
Operating income		302,735	231,899	183,518
Floor plan interest expense		(19,534)	(13,861)	(12,373)
Other interest expense		(19,491)	(10,742)	(8,350)
Other (expense) income, net		(1,006)	3,199	2,993
Income from continuing operations before income taxes	[1]	262,704	210,495	165,788
Income tax provision		(79,705)	(74,955)	(60,574)
Income from continuing operations, net of income tax		$ 182,999	135,540	105,214
Income from discontinued operations, net of income tax expense			3,180	786
Net income		$ 182,999	$ 138,720	$ 106,000
Basic income per share from continuing operations (in dollars per share)		$ 6.96	$ 5.19	$ 4.08
Basic income per share from discontinued operations (in dollars per share)			0.12	0.03
Basic net income per share (in dollars per share)		$ 6.96	$ 5.31	$ 4.11
Shares used in basic per share calculations (in shares)		26,290	26,121	25,805
Diluted income per share from continuing operations (in dollars per share)		$ 6.91	$ 5.14	$ 4.02
Diluted income per share from discontinued operations (in dollars per share)			0.12	0.03
Diluted net income per share (in dollars per share)		$ 6.91	$ 5.26	$ 4.05
Shares used in diluted per share calculations (in shares)		26,490	26,382	26,191

[1] Segment income for each of the segments is defined as Income from continuing operations before income taxes, depreciation and amortization, other interest expense and other (expense) income, net.