Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Revenue	$ 5,562,298	$ 5,267,952
Lease and rental	247,549	238,238	$ 217,356
Total revenue	5,809,847	5,506,190	4,713,882
Cost of products sold
Lease and rental	206,200	197,271	183,091
Total cost of products sold	4,784,219	4,527,921	3,883,946
Gross profit	1,025,628	978,269	829,936
Selling, general and administrative	753,749	705,226	631,053
Depreciation and amortization	55,372	70,489	50,069
(Loss) gain on sale of assets	(102)	297	(105)
Operating income	216,405	202,851	148,709
Other income	1,925	0	0
Interest income (expense)
Interest income	1,680	1,376	891
Interest expense	(30,487)	(21,058)	(13,201)
Total interest expense, net	28,807	19,682	12,310
Income before taxes	189,523	183,169	136,399
Income tax provision (benefit)	47,940	44,107	(35,730)
Net income	$ 141,583	$ 139,062	$ 172,129
Earnings per common share
Basic (in dollars per share)	$ 3.86	$ 3.55	$ 4.34
Diluted (in dollars per share)	3.77	3.45	4.20
Dividends declared per common share (in dollars per share)	$ 0.50	$ 0.24	$ 0
New and Used Commercial Vehicle [Member]
Revenues
Revenue	$ 3,757,584	$ 3,558,637	$ 2,993,015
Cost of products sold
Cost of products sold	3,480,682	3,280,966	2,766,461
Parts and Service [Member]
Revenues
Revenue	1,762,510	1,670,052	1,471,266
Cost of products sold
Cost of products sold	1,097,337	1,049,684	934,394
Finance and Insurance [Member]
Revenues
Revenue	24,443	20,535	17,988
Product and Service, Other [Member]
Revenues
Revenue	$ 17,761	$ 18,728	$ 14,257