CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenue	$ 1,401,457	$ 981,320	$ 2,699,580	$ 1,900,873
Transportation costs	1,154,619	860,759	2,237,725	1,671,565
Gross margin	246,838	120,561	461,855	229,308
Costs and expenses:
Salaries and benefits	68,041	54,375	136,967	111,326
General and administrative	30,064	20,370	50,140	39,613
Depreciation and amortization	11,097	8,868	22,052	17,370
Total costs and expenses	109,202	83,613	209,159	168,309
Operating income	137,636	36,948	252,696	60,999
Other income (expense):
Interest expense	(1,402)	(1,859)	(3,100)	(3,764)
Other, net	(194)	(192)	(63)	(284)
Total other expense, net	(1,596)	(2,051)	(3,163)	(4,048)
Income before provision for income taxes	136,040	34,897	249,533	56,951
Income tax expense	33,194	8,305	59,184	13,129
Net income	102,846	26,592	190,349	43,822
Other comprehensive (loss) income:
Foreign currency translation adjustments	(16)	25	4	15
Total comprehensive income	$ 102,830	$ 26,617	$ 190,353	$ 43,837
Basic earnings per common share	$ 3.06	$ 0.80	$ 5.66	$ 1.31
Diluted earnings per common share	$ 3.03	$ 0.78	$ 5.61	$ 1.30
Basic weighted average number of shares outstanding	33,651	33,428	33,647	33,423
Diluted weighted average number of shares outstanding	33,935	33,879	33,950	33,827