Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
OPERATING REVENUE	$ 610,803	$ 607,336	$ 612,937
Operating Expenses
Salaries, wages and benefits	227,872	236,872	231,980
Rent and purchased transportation	18,700	30,002	23,485
Fuel	110,536	104,381	91,494
Operations and maintenance	27,143	29,609	26,159
Operating taxes and licenses	16,390	16,615	15,559
Insurance and claims	17,227	18,850	24,449
Communications and utilities	6,086	5,781	4,485
Depreciation and amortization	100,519	103,690	105,578
Other operating expenses	21,506	24,666	13,385
Gain on disposal of property and equipment	(24,963)	(26,674)	(9,205)
Total operating expenses	521,016	543,792	527,369
Operating income	89,787	63,544	85,568
Interest income	2,130	1,129	481
Interest expense	0	(175)	0
Income before income taxes	91,917	64,498	86,049
Federal and state income tax (benefit) expense	19,240	(10,675)	29,663
Net income	72,677	75,173	56,386
Other comprehensive income, net of tax	0	0	0
Comprehensive income	$ 72,677	$ 75,173	$ 56,386
Net income per share
Basic	$ 0.88	$ 0.90	$ 0.68
Diluted	$ 0.88	$ 0.90	$ 0.68
Weighted average shares outstanding
Basic	82,378	83,298	83,297
Diluted	82,410	83,336	83,365
Dividends declared per share	$ 0.08	$ 0.08	$ 0.08