Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Total revenues	$ 8,678,157	$ 7,864,252	$ 5,390,326
Cost of sales:
Total cost of sales	7,376,842	6,688,618	4,567,004
Gross profit	1,301,315	1,175,634	823,322
Asset impairments	13,992	20,124	1,853
Selling, general and administrative	899,590	811,175	563,207
Depreciation and amortization	49,369	41,600	26,363
Operating income	338,364	302,735	231,899
Floor plan interest expense	(25,531)	(19,534)	(13,861)
Other interest expense	(23,207)	(19,491)	(10,742)
Other (expense) income, net	(6,103)	(1,006)	3,199
Income from continuing operations before income taxes	283,523	262,704	210,495
Income tax provision	(86,465)	(79,705)	(74,955)
Income from continuing operations, net of income tax	197,058	182,999	135,540
Income from discontinued operations, net of income tax expense			3,180
Net income	$ 197,058	$ 182,999	$ 138,720
Basic income per share from continuing operations (in dollars per share)	$ 7.76	$ 6.96	$ 5.19
Basic income per share from discontinued operations (in dollars per share)			0.12
Basic net income per share (in dollars per share)	$ 7.76	$ 6.96	$ 5.31
Shares used in basic per share calculations (in shares)	25,409	26,290	26,121
Diluted income per share from continuing operations (in dollars per share)	$ 7.72	$ 6.91	$ 5.14
Diluted income per share from discontinued operations (in dollars per share)			0.12
Diluted net income per share (in dollars per share)	$ 7.72	$ 6.91	$ 5.26
Shares used in diluted per share calculations (in shares)	25,521	26,490	26,382
Cash dividend declared per Class A and Class B share (in dollars per share)	$ 0.95	$ 0.76	$ 0.61
New Vehicle [Member]
Revenues:
Total revenues	$ 4,938,436	$ 4,552,301	$ 3,077,670
Cost of sales:
Total cost of sales	4,649,024	4,271,931	2,879,486
Used Retail Vehicle [Member]
Revenues:
Total revenues	2,226,951	1,927,016	1,362,481
Cost of sales:
Total cost of sales	1,963,267	1,685,767	1,183,228
Used Wholesale Vehicle [Member]
Revenues:
Total revenues	276,616	261,530	195,699
Cost of sales:
Total cost of sales	272,303	257,073	192,053
Finance and Insurance [Member]
Revenues:
Total revenues	330,922	283,018	190,381
Service, Body and Parts [Member]
Revenues:
Total revenues	844,505	738,990	512,124
Cost of sales:
Total cost of sales	434,222	375,069	262,388
Fleet and Other [Member]
Revenues:
Total revenues	60,727	101,397	51,971
Cost of sales:
Total cost of sales	$ 58,026	$ 98,778	$ 49,849