Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Operating Revenue	$ 160,873	$ 142,144	$ 327,191	$ 281,681
Operating Expenses
Salaries, wages, and benefits	68,147	53,432	138,401	107,228
Rent and purchased transportation	1,028	1,868	2,636	4,280
Fuel	18,287	23,339	44,228	46,519
Operating Costs and Expenses	7,597	5,626	14,398	11,471
Cost, Direct Tax and License	3,724	3,500	7,566	7,391
Insurance and claims	5,852	3,985	11,206	8,774
Communications and utilities	1,272	1,104	2,692	2,327
Depreciation and amortization	27,168	22,615	53,803	44,842
Other operating expenses	6,056	5,187	12,965	10,358
Gain on disposal of property and equipment	(3,247)	(7,542)	(3,018)	(11,383)
Total operating expenses	135,884	113,114	284,877	231,807
Operating income	24,989	29,030	42,314	49,874
Interest income	157	1,229	534	2,374
Income before income taxes	25,146	30,259	42,848	52,248
Federal and state income taxes	5,964	7,898	10,428	12,569
Net Income	19,182	22,361	32,420	39,679
Other comprehensive income, net of tax	0	0	0	0
Comprehensive income	$ 19,182	$ 22,361	$ 32,420	$ 39,679
Net income per share
Basic	$ 0.24	$ 0.27	$ 0.40	$ 0.48
Diluted	$ 0.24	$ 0.27	$ 0.40	$ 0.48
Weighted average shares outstanding
Basic	81,351	81,968	81,611	81,952
Diluted	81,415	82,027	81,680	81,991
Dividends declared per share	$ 0.02	$ 0.02	$ 0.04	$ 0.04