Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
OPERATING REVENUES:
Operating revenues	$ 135,302	$ 108,646	$ 254,761	$ 218,050
OPERATING EXPENSES AND COSTS:
Salaries, wages and benefits	29,971	25,263	58,610	51,167
Operating supplies and expenses	23,506	19,410	46,176	39,642
Rent and purchased transportation	52,075	43,717	97,992	86,839
Depreciation	12,734	10,485	24,358	21,156
Insurance and claims	4,451	4,439	8,719	9,135
Other	3,067	2,304	5,648	4,421
(Gain) loss on disposition of equipment	(519)	130	(515)	130
Total operating expenses and costs	125,285	105,748	240,988	212,490
OPERATING INCOME	10,017	2,898	13,773	5,560
NON-OPERATING INCOME/(EXPENSE)	632	650	(247)	2,702
INTEREST EXPENSE	(1,355)	(935)	(2,515)	(1,912)
INCOME BEFORE INCOME TAXES	9,294	2,613	11,011	6,350
FEDERAL AND STATE INCOME TAX EXPENSE:
Current	142	66	177	133
Deferred	1,863	938	2,158	2,325
Total federal and state income tax expense	2,005	1,004	2,335	2,458
NET INCOME	$ 7,289	$ 1,609	$ 8,676	$ 3,892
INCOME PER COMMON SHARE:
Basic (in dollars per share)	$ 1.18	$ 0.25	$ 1.41	$ 0.61
Diluted (in dollars per share)	$ 1.17	$ 0.25	$ 1.39	$ 0.61
AVERAGE COMMON SHARES OUTSTANDING:
Basic (in shares)	6,159	6,381	6,163	6,390
Diluted (in shares)	6,229	6,430	6,257	6,412
Freight Transportation Service [Member]
OPERATING REVENUES:
Operating revenues	$ 112,881	$ 93,097	$ 211,985	$ 186,700
Fuel Surcharge [Member]
OPERATING REVENUES:
Operating revenues	$ 22,421	$ 15,549	$ 42,776	$ 31,350