Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING REVENUES:
Operating revenues	$ 514,177	$ 533,261	$ 437,838
OPERATING EXPENSES AND COSTS:
Salaries, wages and benefits	129,738	119,819	102,227
Operating supplies and expenses	98,420	93,130	79,505
Rents and purchased transportation	168,399	201,455	174,477
Depreciation	55,107	49,387	42,274
Insurance and claims	35,622	17,191	17,484
Other	13,761	11,983	9,249
Loss (gain) on disposition of equipment	583	(1,306)	(58)
Total operating expenses and costs	501,630	491,659	425,158
OPERATING INCOME	12,547	41,602	12,680
NON-OPERATING INCOME (EXPENSE)	6,222	(4,016)	5,853
INTEREST EXPENSE	(8,654)	(6,245)	(3,902)
INCOME BEFORE INCOME TAXES	10,115	31,341	14,631
FEDERAL & STATE INCOME TAX EXPENSE (BENEFIT):
Current	590	141	362
Deferred	1,625	7,206	(24,630)
Total federal & state income tax expense (benefit)	2,215	7,347	(24,268)
NET INCOME	$ 7,900	$ 23,994	$ 38,899
EARNINGS PER COMMON SHARE:
Basic (in dollars per share)	$ 1.35	$ 3.94	$ 6.14
Diluted (in dollars per share)	$ 1.34	$ 3.90	$ 6.08
AVERAGE COMMON SHARES OUTSTANDING:
Basic (in shares)	5,832	6,083	6,331
Diluted (in shares)	5,880	6,159	6,398
Freight Transportation Service [Member]
OPERATING REVENUES:
Operating revenues	$ 439,511	$ 445,855	$ 373,523
Fuel Surcharge [Member]
OPERATING REVENUES:
Operating revenues	$ 74,666	$ 87,406	$ 64,315