Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Operating Revenue	$ 152,402	$ 166,318
Operating Expenses
Salaries, wages, and benefits	64,782	70,254
Rent and purchased transportation	964	1,608
Fuel	24,157	25,941
Operating Costs and Expenses	5,688	6,800
Cost, Direct Tax and License	3,621	3,842
Insurance and claims	5,439	5,354
Communications and utilities	1,226	1,421
Depreciation and amortization	26,926	26,634
Other operating expenses	5,552	6,909
(Gain)/Loss on disposal of property and equipment	(4,232)	229
Total operating expenses	134,123	148,992
Operating income	18,279	17,326
Interest income	138	377
Income before income taxes	18,417	17,703
Federal and state income taxes	4,683	4,465
Net Income	13,734	13,238
Other comprehensive income, net of tax	0	0
Comprehensive income	$ 13,734	$ 13,238
Net income per share
Basic	$ 0.17	$ 0.16
Diluted	$ 0.17	$ 0.16
Weighted average shares outstanding
Basic	80,152	81,870
Diluted	80,206	81,945
Dividends declared per share	$ 0.02	$ 0.02