Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Revenue	$ 5,267,952
Lease and rental	238,238	$ 217,356	$ 208,154
Total revenue	5,506,190	4,713,882	4,214,614
Cost of products sold:
Lease and rental	197,271	183,091	182,040
Total cost of products sold	4,527,921	3,883,946	3,496,602
Gross profit	978,269	829,936	718,012
Selling, general and administrative	705,226	631,053	587,778
Depreciation and amortization	70,489	50,069	51,261
Gain (loss) on sale of assets	297	(105)	1,755
Operating income	202,851	148,709	80,728
Interest income (expense):
Interest income	1,376	891	621
Interest expense	(21,058)	(13,201)	(14,900)
Total interest expense, net	19,682	12,310	14,279
Income before taxes	183,169	136,399	66,449
Income tax provision (benefit)	44,107	(35,730)	25,867
Net income	$ 139,062	$ 172,129	$ 40,582
Earnings per common share:
Basic (in dollars per share)	$ 3.55	$ 4.34	$ 1.02
Diluted (in dollars per share)	$ 3.45	$ 4.20	$ 1
New and Used Commercial Vehicle [Member]
Revenues:
Revenue	$ 3,558,637	$ 2,993,015	$ 2,640,019
Cost of products sold:
Cost of products sold	3,280,966	2,766,461	2,463,124
Aftermarket Products and Services [Member]
Revenues:
Revenue	1,670,052	1,471,266	1,332,356
Cost of products sold:
Cost of products sold	1,049,684	934,394	851,438
Finance and Insurance [Member]
Revenues:
Revenue	20,535	17,988	18,582
Product and Service, Other [Member]
Revenues:
Revenue	$ 18,728	$ 14,257	$ 15,503