Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues
Freight revenue		$ 1,103,573	$ 1,216,858	$ 1,046,003
Operating expenses:
Salaries, wages, and related expenses		400,491	402,276	350,246
Fuel expense		133,291	166,410	103,641
Operations and maintenance		63,753	79,051	59,269
Revenue equipment rentals and purchased transportation		271,893	325,624	331,685
Operating taxes and licenses		13,409	11,931	10,899
Insurance and claims		50,099	50,547	38,788
Communications and utilities		5,012	5,385	4,558
General supplies and expenses		49,444	37,762	29,673
Depreciation and amortization		69,943	57,512	53,881
Gain on disposition of property and equipment, net		(12,585)	(40,322)	(3,799)
Total operating expenses		1,044,750	1,096,176	978,841
Operating income		58,823	120,682	67,162
Interest expense, net		7,967	3,083	2,791
Income from equity method investment		(21,384)	(25,193)	(14,782)
Income from continuing operations		72,240	142,792	79,153
Income tax expense		17,611	34,860	20,962
Income from continuing operations		54,629	107,932	58,191
Income from discontinued operations, net of tax		600	750	2,540
Net income		$ 55,229	$ 108,682	$ 60,731
Basic income per share:
Income from continuing operations (in dollars per share)		$ 4.19	$ 7.19	$ 3.46
Income from discontinued operations (in dollars per share)		0.05	0.05	0.15
Net income per basic share(1) (in dollars per share)	[1]	4.23	7.24	3.61
Diluted income per share:
Income from continuing operations (in dollars per share)		3.95	6.95	3.42
Income from discontinued operations (in dollars per share)		0.04	0.05	0.15
Net income per diluted share (in dollars per share)		$ 3.99	$ 7	$ 3.57
Basic weighted average shares outstanding (in shares)		13,048	15,006	16,803
Diluted weighted average shares outstanding (in shares)		13,834	15,524	17,020
Cargo and Freight [Member]
Revenues
Freight revenue		$ 970,509	$ 1,046,396	$ 949,913
Fuel Surcharge [Member]
Revenues
Freight revenue		$ 133,064	$ 170,462	$ 96,090

[1] Total may not sum due to rounding.