Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Operating Revenue	$ 842,103	$ 775,144	$ 2,420,122	$ 2,130,301
Operating Expenses:
Salaries, wages and employees' benefits	398,134	344,605	1,112,087	955,449
Purchased transportations	65,584	76,746	179,138	173,244
Fuel, operating expenses and supplies	158,733	144,282	475,935	419,397
Operating taxes and licenses	19,942	17,018	59,401	51,540
Claims and insurance	19,274	18,024	55,565	49,039
Depreciation and amortization	54,656	45,618	156,041	133,156
Other operating, net	609	416	1,279	643
Total operating expenses	716,932	646,709	2,039,446	1,782,468
Operating Income	125,171	128,435	380,676	347,833
Nonoperating (Income) Expenses:
Interest expense	2,997	454	5,951	1,600
Interest income	(45)	(2,423)	(910)	(3,050)
Other, net	(460)	157	(1,574)	(1,336)
Nonoperating (income) expenses, net	2,492	(1,812)	3,467	(2,786)
Income Before Income Taxes	122,679	130,247	377,209	350,619
Income Tax Provision	29,931	32,034	91,247	84,990
Net Income	$ 92,748	$ 98,213	$ 285,962	$ 265,629
Weighted average common shares outstanding - basic	26,695	26,644	26,686	26,626
Weighted average common shares outstanding - diluted	26,789	26,779	26,785	26,755
Basic Earnings Per Share	$ 3.47	$ 3.69	$ 10.72	$ 9.98
Diluted Earnings Per Share	$ 3.46	$ 3.67	$ 10.68	$ 9.93