Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Operating Revenue	$ 162,282	$ 147,908	$ 489,473	$ 429,589
Operating Expenses
Salaries, wages, and benefits	67,178	60,909	205,579	168,137
Rent and purchased transportation	999	1,936	3,635	6,216
Fuel	21,218	25,211	65,445	71,730
Operating Costs and Expenses	7,118	6,260	21,516	17,730
Cost, Direct Tax and License	3,664	3,416	11,229	10,808
Insurance and claims	4,827	3,256	16,034	12,030
Communications and utilities	1,398	1,211	4,091	3,538
Depreciation and amortization	27,625	25,572	81,427	70,414
Other operating expenses	6,637	5,993	19,602	16,351
Gain on disposal of property and equipment	(5,721)	(12,595)	(8,739)	(23,978)
Total operating expenses	134,943	121,169	419,819	352,976
Operating income	27,339	26,739	69,654	76,613
Interest income	171	1,128	704	3,502
Interest Expense	0	(452)	0	(452)
Income before income taxes	27,510	27,415	70,358	79,663
Federal and state income taxes	6,796	6,914	17,224	19,483
Net Income	20,714	20,501	53,134	60,180
Other comprehensive income, net of tax	0	0	0	0
Comprehensive income	$ 20,714	$ 20,501	$ 53,134	$ 60,180
Net income per share
Basic	$ 0.25	$ 0.25	$ 0.65	$ 0.73
Diluted	$ 0.25	$ 0.25	$ 0.65	$ 0.73
Weighted average shares outstanding
Basic	81,370	81,992	81,530	81,965
Diluted	81,404	82,040	81,587	82,008
Dividends declared per share	$ 0.02	$ 0.02	$ 0.06	$ 0.06