Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Operating Revenue	$ 2,881,433	$ 2,792,057	$ 2,288,704
Operating Expenses:
Salaries, wages and employees’ benefits	1,301,280	1,169,539	1,063,703
Purchased transportation	238,688	315,896	249,710
Fuel, operating expenses and supplies	563,688	558,456	381,904
Operating taxes and licenses	69,542	63,824	59,095
Claims and insurance	67,984	56,601	61,345
Depreciation and amortization	178,845	157,203	141,700
Operating losses (gains), net	910	50	(3,894)
Total operating expenses	2,420,937	2,321,569	1,953,563
Operating Income	460,496	470,488	335,141
Non-operating (Income) Expenses:
Interest expense	2,535	2,611	3,212
Interest income	(6,208)	(217)	(11)
Other, net	(2,058)	46	(833)
Non-operating (income) expenses, net	(5,731)	2,440	2,368
Income Before Income Taxes	466,227	468,048	332,773
Income Tax Expense	111,370	110,626	79,538
Net Income	$ 354,857	$ 357,422	$ 253,235
Weighted average common shares outstanding – basic	26,632	26,520	26,322
Weighted average common shares outstanding – diluted	26,763	26,674	26,707
Basic Earnings Per Share	$ 13.32	$ 13.48	$ 9.62
Diluted Earnings Per Share	$ 13.26	$ 13.40	$ 9.48