Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Income Statement [Abstract]
Operating Revenue	$ 817,115	$ 823,244	$ 1,604,690	$ 1,578,019
Operating Expenses:
Salaries, wages and employees' benefits	390,975	372,240	780,231	713,953
Purchased Transportation	57,699	61,047	117,548	113,554
Fuel, operating expenses and supplies	161,634	160,877	328,305	317,202
Operating taxes and licenses	22,014	19,693	42,451	39,459
Claims and insurance	22,826	18,828	44,371	36,291
Depreciation and amortization	62,546	52,536	121,589	101,385
Other operating, net	22	430	628	670
Total operating expenses	717,716	685,651	1,435,123	1,322,514
Operating Income	99,399	137,593	169,567	255,505
Nonoperating (Income) Expenses:
Interest expense	4,742	2,412	9,027	2,954
Interest income	(34)	(110)	(73)	(865)
Other, net	(873)	(326)	(516)	(1,114)
Nonoperating expenses, net	3,835	1,976	8,438	975
Income Before Income Taxes	95,564	135,617	161,129	254,530
Income Tax Provision	24,173	33,098	39,928	61,316
Net Income	$ 71,391	$ 102,519	$ 121,201	$ 193,214
Weighted average common shares outstanding - basic	26,739	26,691	26,730	26,682
Weighted average common shares outstanding - diluted	26,785	26,802	26,782	26,798
Basic Earnings Per Share	$ 2.67	$ 3.84	$ 4.53	$ 7.24
Diluted Earnings Per Share	$ 2.67	$ 3.83	$ 4.53	$ 7.21