Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Operating Revenue	$ 754,775	$ 660,535
Operating Expenses:
Salaries, wages and employees' benefits	341,713	298,956
Purchased transportations	52,507	46,727
Fuel, operating expenses and supplies	156,325	141,625
Operating taxes and licenses	19,766	17,065
Claims and insurance	17,463	14,059
Depreciation and amortization	48,849	42,880
Other operating, net	240	80
Total operating expenses	636,863	561,392
Operating Income	117,912	99,143
Nonoperating (Income) Expenses:
Interest expense	542	688
Interest income	(755)	(140)
Other, net	(788)	(503)
Nonoperating (income) expenses, net	(1,001)	45
Income Before Income Taxes	118,913	99,098
Income Tax Provision	28,218	23,001
Net Income	$ 90,695	$ 76,097
Weighted average common shares outstanding - basic	26,672	26,600
Weighted average common shares outstanding - diluted	26,794	26,702
Basic Earnings Per Share	$ 3.4	$ 2.86
Diluted Earnings Per Share	$ 3.38	$ 2.85