Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
OPERATING REVENUES:
Operating revenues	$ 133,000	$ 135,302	$ 261,686	$ 254,761
OPERATING EXPENSES AND COSTS:
Salaries, wages and benefits	30,603	29,971	61,667	58,610
Operating supplies and expenses	24,520	23,506	48,032	46,176
Rent and purchased transportation	43,353	52,075	87,907	97,992
Depreciation	13,614	12,734	26,801	24,358
Insurance and claims	4,061	4,451	8,175	8,719
Other	3,539	3,067	6,533	5,648
Loss (gain) on sale or disposition of equipment	99	(519)	(327)	(515)
Total operating expenses and costs	119,789	125,285	238,788	240,988
OPERATING INCOME	13,211	10,017	22,898	13,773
NON-OPERATING (EXPENSE)/INCOME	(197)	632	3,275	(247)
INTEREST EXPENSE	(2,059)	(1,355)	(4,099)	(2,515)
INCOME BEFORE INCOME TAXES	10,955	9,294	22,074	11,011
FEDERAL AND STATE INCOME TAX EXPENSE:
Current	107	142	196	177
Deferred	2,194	1,863	4,923	2,158
Total federal and state income tax expense	2,301	2,005	5,119	2,335
NET INCOME	$ 8,654	$ 7,289	$ 16,955	$ 8,676
INCOME PER COMMON SHARE:
Basic (in dollars per share)	$ 1.47	$ 1.18	$ 2.87	$ 1.41
Diluted (in dollars per share)	$ 1.45	$ 1.17	$ 2.84	$ 1.39
AVERAGE COMMON SHARES OUTSTANDING:
Basic (in shares)	5,901	6,159	5,911	6,163
Diluted (in shares)	5,949	6,229	5,962	6,257
Freight Transportation Service [Member]
OPERATING REVENUES:
Operating revenues	$ 112,352	$ 112,881	$ 222,696	$ 211,985
Fuel Surcharge [Member]
OPERATING REVENUES:
Operating revenues	$ 20,648	$ 22,421	$ 38,990	$ 42,776