Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING REVENUE	$ 596,815	$ 610,803	$ 607,336
Operating Expenses
Salaries, wages and benefits	240,139	227,872	236,872
Rent and purchased transportation	7,984	18,700	30,002
Fuel	101,871	110,536	104,381
Operations and maintenance	24,479	27,143	29,609
Operating taxes and licenses	14,459	16,390	16,615
Insurance and claims	17,003	17,227	18,850
Communications and utilities	4,953	6,086	5,781
Depreciation and amortization	100,212	100,519	103,690
Other operating expenses	22,781	21,506	24,666
Gain on disposal of property and equipment	(31,341)	(24,963)	(26,674)
Total operating expenses	502,540	521,016	543,792
Operating income	94,275	89,787	63,544
Interest income	3,955	2,130	1,129
Interest expense	(1,052)	0	(175)
Income before income taxes	97,178	91,917	64,498
Federal and state income tax (benefit) expense	24,211	19,240	(10,675)
Net income	72,967	72,677	75,173
Other comprehensive income, net of tax	0	0	0
Comprehensive income	$ 72,967	$ 72,677	$ 75,173
Net income per share
Basic	$ 0.89	$ 0.88	$ 0.90
Diluted	$ 0.89	$ 0.88	$ 0.90
Weighted average shares outstanding
Basic	81,980	82,378	83,298
Diluted	82,024	82,410	83,336
Dividends declared per share	$ 0.08	$ 0.08	$ 0.08