Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
OPERATING REVENUES:
Operating revenues	$ 183,085	$ 121,942	$ 493,206	$ 344,075
OPERATING EXPENSES AND COSTS:
Salaries, wages and benefits	34,937	30,618	102,173	90,991
Operating supplies and expenses	25,712	20,875	74,375	62,866
Rent and purchased transportation	72,698	41,402	192,387	114,688
Depreciation	12,740	13,403	41,426	41,936
Insurance and claims	3,443	3,145	9,806	5,701
Other	3,008	2,599	8,505	10,411
Gain on disposition of equipment	(276)	(174)	(962)	(71)
Total operating expenses and costs	152,262	111,868	427,710	326,522
OPERATING INCOME	30,823	10,074	65,496	17,553
NON-OPERATING INCOME (EXPENSE)	37	(94)	6,853	(6,209)
INTEREST EXPENSE	(1,899)	(2,211)	(6,372)	(6,601)
INCOME BEFORE INCOME TAXES	28,961	7,769	65,977	4,743
FEDERAL AND STATE INCOME TAX EXPENSE:
Current	2,141	106	2,368	106
Deferred	5,461	1,663	14,984	763
Total federal and state income tax expense	7,602	1,769	17,352	869
NET INCOME	$ 21,359	$ 6,000	$ 48,625	$ 3,874
INCOME PER COMMON SHARE:
Basic (in dollars per share)	$ 1.88	$ 0.52	$ 4.26	$ 0.34
Diluted (in dollars per share)	$ 1.87	$ 0.52	$ 4.24	$ 0.34
AVERAGE COMMON SHARES OUTSTANDING:
Basic (in shares)	11,362	11,526	11,421	11,516
Diluted (in shares)	11,430	11,536	11,481	11,550
Freight Transportation Service [Member]
OPERATING REVENUES:
Operating revenues	$ 166,331	$ 109,854	$ 446,647	$ 307,441
Fuel Surcharge [Member]
OPERATING REVENUES:
Operating revenues	$ 16,754	$ 12,088	$ 46,559	$ 36,634