Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Operating Revenue	$ 166,318	$ 139,536
Operating Expenses
Salaries, wages, and benefits	70,254	53,796
Rent and purchased transportation	1,608	2,412
Fuel	25,941	23,180
Operating Costs and Expenses	6,800	5,845
Cost, Direct Tax and License	3,842	3,891
Insurance and claims	5,354	4,789
Communications and utilities	1,421	1,223
Depreciation and amortization	26,634	22,227
Other operating expenses	6,909	5,171
Loss (gain) on disposal of property and equipment	229	(3,841)
Total operating expenses	148,992	118,693
Operating income	17,326	20,843
Interest income	377	1,145
Income before income taxes	17,703	21,988
Federal and state income taxes	4,465	4,670
Net income	13,238	17,318
Other comprehensive income, net of tax	0	0
Comprehensive income	$ 13,238	$ 17,318
Net income per share
Basic	$ 0.16	$ 0.21
Diluted	$ 0.16	$ 0.21
Weighted average shares outstanding
Basic	81,870	81,936
Diluted	81,945	81,956
Dividends declared per share	$ 0.02	$ 0.02