Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Operating Revenue	$ 729,561	$ 616,216	$ 2,136,331	$ 1,671,623
Operating Expenses:
Salaries, wages and employees' benefits	297,247	277,087	881,762	790,310
Purchased Transportations	85,452	72,193	255,519	179,705
Fuel, operating expenses and supplies	145,461	98,834	413,762	274,399
Operating taxes and licenses	16,261	14,572	48,813	43,469
Claims and insurance	15,988	15,518	40,940	44,326
Depreciation and amortization	40,682	35,742	117,578	105,773
Loss (gain) from property disposals, net	115	(3,847)	160	(4,115)
Total operating expenses	601,206	510,099	1,758,534	1,433,867
Operating Income	128,355	106,117	377,797	237,756
Nonoperating Expenses (Income):
Interest expense	581	777	1,941	2,463
Other, net	68	14	1,072	(547)
Nonoperating expenses, net	649	791	3,013	1,916
Income Before Income Taxes	127,706	105,326	374,784	235,840
Income Tax Provision	29,815	25,617	88,224	56,366
Net Income	$ 97,891	$ 79,709	$ 286,560	$ 179,474
Weighted average common shares outstanding - basic	26,539	26,334	26,506	26,317
Weighted average common shares outstandin - diluted	26,676	26,713	26,663	26,699
Basic Earnings Per Share	$ 3.69	$ 3.03	$ 10.81	$ 6.82
Diluted Earnings Per Share	$ 3.67	$ 2.98	$ 10.75	$ 6.72