CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Income Statement [Abstract]
Operating revenue	$ 1,040,462	$ 1,401,456	$ 2,192,727	$ 2,699,579
Costs and expenses:
Purchased transportation and warehousing	763,609	1,062,983	1,630,540	2,058,248
Salaries and benefits	141,823	129,499	279,254	258,238
Depreciation and amortization	35,386	32,244	70,835	63,533
Insurance and claims	11,676	10,645	24,359	19,938
General and administrative	26,757	36,213	52,298	59,435
Gain on sale of assets, net	(859)	(7,764)	(4,834)	(12,509)
Total operating expenses	978,392	1,263,820	2,052,452	2,446,883
Operating income	62,070	137,636	140,275	252,696
Other income (expense):
Interest expense	(3,116)	(1,407)	(6,086)	(3,110)
Interest income	2,087	5	3,463	9
Other, net	69	(195)	108	(63)
Total other expense, net	(960)	(1,597)	(2,515)	(3,164)
Income before provision for income taxes	61,110	136,039	137,760	249,532
Provision for income taxes	14,605	33,193	29,475	59,183
Net income	46,505	102,846	108,285	190,349
Other comprehensive (loss) income:
Foreign currency translation adjustments	44	(16)	78	4
Total comprehensive income	$ 46,549	$ 102,830	$ 108,363	$ 190,353
Basic earnings per common share	$ 1.45	$ 3.06	$ 3.35	$ 5.66
Diluted earnings per common share	$ 1.44	$ 3.03	$ 3.33	$ 5.61
Basic weighted average number of shares outstanding	32,037	33,651	32,293	33,647
Diluted weighted average number of shares outstanding	32,293	33,935	32,566	33,950