Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating revenue	$ 1,263,878	$ 973,644	$ 874,374
Operating expenses (income):
Salaries, wages and benefits	390,304	317,962	300,155
Purchased transportation	249,792	193,221	154,613
Fuel and fuel taxes	218,571	131,288	98,133
Supplies and maintenance	55,700	45,459	47,815
Depreciation	111,014	102,562	102,893
Operating taxes and licenses	10,763	10,534	10,840
Insurance and claims	50,513	41,987	47,454
Communications and utilities	9,177	8,350	8,011
Other	38,079	26,887	21,665
Total operating expenses	1,120,534	861,955	781,128
Operating income	143,344	111,689	93,246
Other	(827)	(43)	(140)
Income before income taxes	144,171	111,732	93,386
Income taxes expense	33,817	26,304	23,886
Net income	$ 110,354	$ 85,428	$ 69,500
Basic earnings per common share (in dollars per share)	$ 1.35	$ 1.03	$ 0.84
Diluted earnings per common share (in dollars per share)	1.35	1.02	0.84
Dividends declared per common share (in dollars per share)	$ 0.24	$ 0.66	$ 0.633
Revenue Equipment [Member]
Operating expenses (income):
Gain on disposition of property, plant and equipment	$ (13,379)	$ (16,295)	$ (8,733)
Facility [Member]
Operating expenses (income):
Gain on disposition of property, plant and equipment	$ 0	$ 0	$ (1,718)