Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating revenue	$ 843,271	$ 787,594	$ 698,120
Operating expenses (income):
Salaries, wages and benefits	274,156	252,047	226,091
Purchased transportation	158,948	144,611	118,349
Fuel and fuel taxes	121,341	121,633	105,390
Supplies and maintenance	46,737	40,853	41,613
Depreciation	95,137	88,585	85,120
Operating taxes and licenses	10,100	9,473	8,993
Insurance and claims	38,201	38,657	38,585
Communications and utilities	7,709	6,634	6,047
Gain on disposition of revenue equipment	(8,680)	(7,244)	(5,499)
Other	23,124	21,997	16,569
Total operating expenses	766,773	717,246	641,258
Operating income	76,498	70,348	56,862
Other	(1,190)	(681)	389
Income before income taxes	77,688	71,029	56,473
Income taxes expense (benefit)	16,617	16,002	(33,811)
Net income	$ 61,071	$ 55,027	$ 90,284
Basic earnings per common share (in dollars per share)	$ 1.12	$ 1.01	$ 1.66
Diluted earnings per common share (in dollars per share)	1.11	1.00	1.65
Dividends declared per common share (in dollars per share)	$ 0.77	$ 0.10	$ 0.08