Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Operating Revenue	$ 661,216	$ 484,074
Operating Expenses:
Salaries, wages and employees' benefits	289,463	244,437
Purchased transportation	78,248	45,031
Fuel, operating expenses and supplies	122,771	84,901
Operating taxes and licenses	16,573	14,338
Claims and insurance	10,736	11,480
Depreciation and amortization	39,952	35,372
Loss (gain) from property disposals, net	24	(199)
Total operating expenses	557,767	435,360
Operating Income	103,449	48,714
Nonoperating Expenses (Income):
Interest expense	692	852
Other, net	235	(131)
Nonoperating expenses, net	927	721
Income Before Income Taxes	102,522	47,993
Income Tax Provision	23,098	10,702
Net Income	$ 79,424	$ 37,291
Weighted average common shares outstanding – basic	26,391	26,285
Weighted average common shares outstanding – diluted	26,670	26,671
Basic Earnings Per Share	$ 3.01	$ 1.42
Diluted Earnings Per Share	$ 2.98	$ 1.40