Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Operating revenue	$ 534,060	$ 446,533	$ 429,099
Operating Expenses [Abstract]
Salaries, wages and employee benefits	130,407	122,297	122,408
Fuel and fuel taxes	55,158	45,853	43,179
Depreciation and amortization	28,324	28,463	29,954
Insurance and claims	23,240	25,628	21,154
Equipment rent	10,840	10,173	7,443
Operations and maintenance	33,356	31,001	34,252
Purchased transportation	211,132	164,012	148,972
Operating taxes and licenses	3,814	4,068	4,695
Communications and utilities	2,849	2,713	3,239
Gain on disposal of assets, net	(2,361)	(773)	(1,116)
Costs incurred	639	0	(5,264)
Impairment on assets held for sale	0	0	2,839
Other	16,721	15,166	14,332
Total operating expenses	512,841	448,601	436,615
Operating income (loss)	21,219	(2,068)	(7,516)
Other expenses
Interest expense, net	3,649	3,808	3,178
Other, net	992	387	524
Total other expenses, net	4,641	4,195	3,702
Income (loss) before income taxes	16,578	(6,263)	(11,218)
Income Tax Expense (Benefit)	4,374	(13,760)	(3,519)
Consolidated net income (loss) and comprehensive income (loss)	$ 12,204	$ 7,497	$ (7,699)
Net earnings (loss) per share
Average basic shares outstanding (in shares)	8,194	8,029	8,550
Basic earnings (loss) per share (in usd per share)	$ 1.49	$ 0.93	$ (0.90)
Average diluted shares outstanding (in shares)	8,218	8,056	8,550
Diluted earnings (loss) per share (in usd per share)	$ 1.49	$ 0.93	$ (0.90)