CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Revenue	$ 1,355,407	$ 1,075,107	$ 4,054,987	$ 2,975,980
Transportation costs	1,132,174	917,507	3,369,899	2,589,072
Gross margin	223,233	157,600	685,088	386,908
Costs and expenses:
Salaries and benefits	65,502	65,370	202,469	176,696
General and administrative	28,109	23,445	78,249	63,058
Depreciation and amortization	11,884	8,912	33,936	26,282
Total costs and expenses	105,495	97,727	314,654	266,036
Operating income	117,738	59,873	370,434	120,872
Other income (expense):
Interest expense	(2,151)	(1,793)	(5,251)	(5,555)
Other, net	(383)	(96)	(446)	(382)
Total other expense, net	(2,534)	(1,889)	(5,697)	(5,937)
Income before provision for income taxes	115,204	57,984	364,737	114,935
Income tax expense	27,879	14,646	87,063	27,775
Net income	87,325	43,338	277,674	87,160
Other comprehensive (loss) income:
Foreign currency translation adjustments	(35)	(25)	(31)	(10)
Total comprehensive income	$ 87,290	$ 43,313	$ 277,643	$ 87,150
Basic earnings per common share	$ 2.63	$ 1.30	$ 8.29	$ 2.61
Diluted earnings per common share	$ 2.61	$ 1.28	$ 8.21	$ 2.58
Basic weighted average number of shares outstanding	33,145	33,433	33,480	33,427
Diluted weighted average number of shares outstanding	33,521	33,873	33,807	33,842