Consolidated Condensed Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating revenue	$ 232,442	$ 212,384	$ 455,488	$ 431,030
Operating expenses (income):
Salaries, wages and benefits	75,296	73,476	148,294	146,237
Purchased transportation	45,003	36,165	85,768	76,610
Fuel and fuel taxes	32,007	20,868	60,944	49,165
Supplies and maintenance	11,167	11,833	22,182	24,061
Depreciation	25,540	25,972	51,227	51,399
Operating taxes and licenses	2,718	2,615	5,430	5,254
Insurance and claims	9,391	11,633	20,837	23,917
Communications and utilities	2,056	1,977	4,139	3,962
Other	6,085	4,805	11,474	10,908
Total operating expenses	203,924	187,128	402,972	387,742
Operating income	28,518	25,256	52,516	43,288
Other	(9)	(13)	(19)	(110)
Income before income taxes	28,527	25,269	52,535	43,398
Income taxes expense	7,109	7,135	13,111	11,546
Net income	$ 21,418	$ 18,134	$ 39,424	$ 31,852
Basic earnings per common share (in dollars per share)	$ 0.26	$ 0.22	$ 0.48	$ 0.39
Diluted earnings per common share (in dollars per share)	0.26	0.22	0.47	0.38
Dividends declared per common share (in dollars per share)	$ 0.04	$ 0.027	$ 0.08	$ 0.053
Revenue Equipment [Member]
Operating expenses (income):
Gain on disposition of property, plant and equipment	$ (5,339)	$ (2,216)	$ (7,323)	$ (3,771)