Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Operating Revenue	$ 139,536	$ 156,695
Operating Expenses
Salaries, wages, and benefits	53,796	62,009
Rent and purchased transportation	2,412	6,125
Fuel	23,180	28,940
Operating Costs and Expenses	5,845	7,865
Cost, Direct Tax and License	3,891	3,952
Insurance and claims	4,789	4,224
Communications and utilities	1,223	1,870
Depreciation and amortization	22,227	25,601
Other operating expenses	5,171	6,030
Gain on disposal of property and equipment	(3,841)	(2,869)
Total operating expenses	118,693	143,747
Operating income	20,843	12,948
Interest income	1,145	342
Income before income taxes	21,988	13,290
Federal and state income taxes	4,670	(88)
Net income	17,318	13,378
Other comprehensive income, net of tax	0	0
Comprehensive income	$ 17,318	$ 13,378
Net income per share
Basic	$ 0.21	$ 0.16
Diluted	$ 0.21	$ 0.16
Weighted average shares outstanding
Basic	81,936	83,309
Diluted	81,956	83,349
Dividends declared per share	$ 0.02	$ 0.02