Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating revenue	$ 1,131,455	$ 1,263,878	$ 973,644
Operating expenses (income):
Salaries, wages and benefits	378,818	390,304	317,962
Purchased transportation	199,334	249,792	193,221
Fuel and fuel taxes	180,437	218,571	131,288
Supplies and maintenance	67,411	55,700	45,459
Depreciation	116,722	111,014	102,562
Operating taxes and licenses	11,053	10,763	10,534
Insurance and claims	56,014	50,513	41,987
Communications and utilities	10,149	9,177	8,350
Other	35,019	38,079	26,887
Total operating expenses	1,041,345	1,120,534	861,955
Operating income	90,110	143,344	111,689
Other	(3,806)	(827)	(43)
Income before income taxes	93,916	144,171	111,732
Income taxes expense	23,543	33,817	26,304
Net income	$ 70,373	$ 110,354	$ 85,428
Basic earnings per common share (in dollars per share)	$ 0.87	$ 1.35	$ 1.03
Diluted earnings per common share (in dollars per share)	0.86	1.35	1.02
Dividends declared per common share (in dollars per share)	$ 0.24	$ 0.24	$ 0.66
Revenue Equipment [Member]
Operating expenses (income):
Gain on disposition of property, plant and equipment	$ (13,612)	$ (13,379)	$ (16,295)