Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
New and used commercial vehicle sales	$ 2,993,015	$ 2,640,019	$ 3,360,808
Aftermarket products and services sales	1,471,266	1,332,356	1,382,447
Lease and rental	217,356	208,154	199,867
Finance and insurance	17,988	18,582	21,150
Other	14,257	15,503	15,461
Total revenue	4,713,882	4,214,614	4,979,733
Cost of products sold:
New and used commercial vehicle sales	2,766,461	2,463,124	3,138,754
Aftermarket products and services sales	934,394	851,438	879,141
Lease and rental	183,091	182,040	176,891
Total cost of products sold	3,883,946	3,496,602	4,194,786
Gross profit	829,936	718,012	784,947
Selling, general and administrative	631,053	587,778	619,268
Depreciation and amortization	50,069	51,261	43,859
Gain (loss) on sale of assets	(105)	1,755	(544)
Operating income	148,709	80,728	121,276
Interest income (expense):
Interest income	891	621	490
Interest expense	(13,201)	(14,900)	(13,963)
Total interest expense, net	12,310	14,279	13,473
Income before taxes	136,399	66,449	107,803
Income tax (benefit) provision	(35,730)	25,867	41,750
Net income	$ 172,129	$ 40,582	$ 66,053
Earnings per common share:
Basic (in dollars per share)	$ 4.34	$ 1.02	$ 1.64
Diluted (in dollars per share)	$ 4.20	$ 1	$ 1.61