Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Operating Revenue	$ 2,792,057	$ 2,288,704	$ 1,822,366
Operating Expenses:
Salaries, wages and employees’ benefits	1,169,539	1,063,703	963,260
Purchased transportation	315,896	249,710	141,369
Fuel, operating expenses and supplies	558,456	381,904	299,234
Operating taxes and licenses	63,824	59,095	56,294
Claims and insurance	56,601	61,345	49,761
Depreciation and amortization	157,203	141,700	134,655
Operating (gains) losses, net	50	(3,894)	(2,528)
Total operating expenses	2,321,569	1,953,563	1,642,045
Operating Income	470,488	335,141	180,321
Non-operating Expenses (Income):
Interest expense	2,611	3,212	5,177
Other, net	(171)	(844)	(1,134)
Non-operating expenses, net	2,440	2,368	4,043
Income Before Income Taxes	468,048	332,773	176,278
Income Tax Expense	110,626	79,538	37,938
Net Income	$ 357,422	$ 253,235	$ 138,340
Weighted average common shares outstanding – basic	26,520	26,322	26,140
Weighted average common shares outstanding – diluted	26,674	26,707	26,592
Basic Earnings Per Share	$ 13.48	$ 9.62	$ 5.29
Diluted Earnings Per Share	$ 13.40	$ 9.48	$ 5.20