Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Operating Revenue	$ 154,128	$ 160,873	$ 306,530	$ 327,191
Operating Expenses
Salaries, wages, and benefits	62,931	68,147	127,713	138,401
Rent and purchased transportation	1,009	1,028	1,973	2,636
Fuel	24,804	18,287	48,961	44,228
Operating Costs and Expenses	5,670	7,597	11,358	14,398
Cost, Direct Tax and License	3,413	3,724	7,034	7,566
Insurance and claims	4,678	5,852	10,117	11,206
Communications and utilities	967	1,272	2,193	2,692
Depreciation and amortization	25,956	27,168	52,882	53,803
Other operating expenses	5,204	6,056	10,756	12,965
Gain on disposal of property and equipment	(7,855)	(3,247)	(12,088)	(3,018)
Total operating expenses	126,777	135,884	260,899	284,877
Operating income	27,351	24,989	45,631	42,314
Interest income	175	157	312	534
Income before income taxes	27,526	25,146	45,943	42,848
Federal and state income taxes	6,784	5,964	11,466	10,428
Net Income	20,742	19,182	34,477	32,420
Other comprehensive income, net of tax	0	0	0	0
Comprehensive income	$ 20,742	$ 19,182	$ 34,477	$ 32,420
Net income per share
Basic	$ 0.26	$ 0.24	$ 0.43	$ 0.40
Diluted	$ 0.26	$ 0.24	$ 0.43	$ 0.40
Weighted average shares outstanding
Basic	79,906	81,351	80,028	81,611
Diluted	79,957	81,415	80,081	81,680
Dividends declared per share	$ 0.02	$ 0.02	$ 0.04	$ 0.04