Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Statement [Abstract]
Operating Revenue	$ 660,535	$ 661,216
Operating Expenses:
Salaries, wages and employees' benefits	298,956	289,463
Purchased Transportations	46,727	78,248
Fuel, operating expenses and supplies	141,625	122,771
Operating taxes and licenses	17,065	16,573
Claims and insurance	14,059	10,736
Depreciation and amortization	42,880	39,952
Other operating, net	80	24
Total operating expenses	561,392	557,767
Operating Income	99,143	103,449
Nonoperating Expenses (Income):
Interest expense	688	692
Other, net	(643)	235
Nonoperating expenses, net	45	927
Income Before Income Taxes	99,098	102,522
Income Tax Provision	23,001	23,098
Net Income	$ 76,097	$ 79,424
Weighted average common shares outstanding - basic	26,600	26,391
Weighted average common shares outstandin - diluted	26,702	26,670
Basic Earnings Per Share	$ 2.86	$ 3.01
Diluted Earnings Per Share	$ 2.85	$ 2.98