Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Operating Revenue	$ 142,144	$ 155,826	$ 281,681	$ 312,521
Operating Expenses
Salaries, wages, and benefits	53,432	57,558	107,228	119,568
Rent and purchased transportation	1,868	5,460	4,280	11,584
Fuel	23,339	28,941	46,519	57,880
Operating Costs and Expenses	5,626	6,637	11,471	14,501
Cost, Direct Tax and License	3,500	4,150	7,391	8,101
Insurance and claims	3,985	4,231	8,774	8,455
Communications and utilities	1,104	1,566	2,327	3,436
Depreciation and amortization	22,615	24,757	44,842	50,358
Other operating expenses	5,187	5,765	10,358	11,796
Gain on disposal of property and equipment	(7,542)	(5,386)	(11,383)	(8,254)
Total operating expenses	113,114	133,679	231,807	277,425
Operating income	29,030	22,147	49,874	35,096
Interest income	1,229	423	2,374	765
Income before income taxes	30,259	22,570	52,248	35,861
Federal and state income taxes	7,898	4,767	12,569	4,679
Net income	22,361	17,803	39,679	31,182
Other comprehensive income, net of tax	0	0	0	0
Comprehensive income	$ 22,361	$ 17,803	$ 39,679	$ 31,182
Net income per share
Basic	$ 0.27	$ 0.22	$ 0.48	$ 0.38
Diluted	$ 0.27	$ 0.22	$ 0.48	$ 0.38
Weighted average shares outstanding
Basic	81,968	82,330	81,952	82,817
Diluted	82,027	82,368	81,991	82,855
Dividends declared per share	$ 0.02	$ 0.02	$ 0.04	$ 0.04