Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating revenue	$ 787,594	$ 698,120	$ 671,144
Operating expenses (income):
Salaries, wages and benefits	252,047	226,091	224,827
Purchased transportation	144,611	118,349	110,719
Fuel and fuel taxes	121,633	105,390	94,075
Supplies and maintenance	40,853	41,613	43,912
Depreciation	88,585	85,120	82,445
Operating taxes and licenses	9,473	8,993	9,099
Insurance and claims	38,657	38,585	32,223
Communications and utilities	6,634	6,047	6,287
Gain on disposition of assets	(7,244)	(5,499)	(10,502)
Other	21,997	16,569	19,756
	717,246	641,258	612,841
Operating income	70,348	56,862	58,303
Other	(681)	389	1,237
Income before income taxes	71,029	56,473	57,066
Income taxes expense (benefit)	16,002	(33,811)	23,602
Net income	$ 55,027	$ 90,284	$ 33,464
Basic earnings per common share (in dollars per share)	$ 1.01	$ 1.66	$ 0.62
Diluted earnings per common share (in dollars per share)	1	1.65	0.61
Dividends declared per common share (in dollars per share)	$ 0.10	$ 0.08	$ 0.06