Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Operating Revenue	$ 2,288,704	$ 1,822,366	$ 1,786,735
Operating Expenses:
Salaries, wages and employees’ benefits	1,063,703	963,260	947,911
Purchased transportation	249,710	141,369	129,980
Fuel, operating expenses and supplies	381,904	299,234	340,056
Operating taxes and licenses	59,095	56,294	54,397
Claims and insurance	61,345	49,761	43,073
Depreciation and amortization	141,700	134,655	119,135
Operating (gains) losses, net	(3,894)	(2,528)	(403)
Total operating expenses	1,953,563	1,642,045	1,634,149
Operating Income	335,141	180,321	152,586
Non-operating Expenses (Income):
Interest expense	3,212	5,177	6,688
Other, net	(844)	(1,134)	(754)
Non-operating expenses, net	2,368	4,043	5,934
Income Before Income Taxes	332,773	176,278	146,652
Income Tax Expense	79,538	37,938	32,933
Net Income	$ 253,235	$ 138,340	$ 113,719
Weighted average common shares outstanding – basic	26,322	26,140	25,952
Weighted average common shares outstanding – diluted	26,707	26,592	26,435
Basic Earnings Per Share	$ 9.62	$ 5.29	$ 4.38
Diluted Earnings Per Share	$ 9.48	$ 5.20	$ 4.30