Consolidated Condensed Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating revenue	$ 171,511	$ 166,090	$ 344,670	$ 328,019
Operating expenses (income):
Salaries, wages and benefits	56,715	56,196	113,115	111,026
Purchased transportation	27,516	26,187	56,878	54,222
Fuel and fuel taxes	25,007	23,930	50,963	43,560
Supplies and maintenance	10,541	10,908	21,531	21,407
Depreciation	21,306	20,368	42,689	40,415
Operating taxes and licenses	2,252	2,250	4,499	4,435
Insurance and claims	8,848	7,696	17,762	15,051
Communications and utilities	1,487	1,497	3,068	3,117
Other	4,141	4,985	7,632	10,022
Total operating expenses	155,942	151,314	315,163	299,118
Operating income	15,569	14,776	29,507	28,901
Other	125	237	266	452
Income before income taxes	15,444	14,539	29,241	28,449
Provision for income taxes	6,303	6,008	11,886	11,725
Net income	$ 9,141	$ 8,531	$ 17,355	$ 16,724
Basic earnings per common share (in dollars per share)	$ 0.17	$ 0.16	$ 0.32	$ 0.31
Diluted earnings per common share (in dollars per share)	0.17	0.16	0.32	0.31
Dividends declared per common share (in dollars per share)	$ 0.015	$ 0.015	$ 0.03	$ 0.03
Revenue Equipment [Member]
Operating expenses (income):
Gain on disposition of assets	$ (1,871)	$ (2,703)	$ (2,974)	$ (4,137)