Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING REVENUE	$ 612,937	$ 736,345	$ 871,355
Operating Expenses
Salaries, wages and benefits	231,980	277,318	278,126
Rent and purchased transportation	23,485	34,489	51,950
Fuel	91,494	123,714	219,261
Operations and maintenance	26,159	34,025	39,052
Operating taxes and licenses	15,559	18,095	20,370
Insurance and claims	24,449	21,618	17,946
Communications and utilities	4,485	6,001	6,494
Depreciation and amortization	105,578	110,973	108,566
Other operating expenses	13,385	28,572	31,266
Gain on disposal of property and equipment	(9,205)	(35,040)	(33,544)
Total operating expenses	527,369	619,765	739,487
Operating income	85,568	116,580	131,868
Interest income	481	210	195
Interest expense	0	(19)	(446)
Income before income taxes	86,049	116,771	131,617
Federal and state income taxes	29,663	43,715	46,783
Net income	56,386	73,056	84,834
Other comprehensive income, net of tax	0	0	0
Comprehensive income	$ 56,386	$ 73,056	$ 84,834
Net income per share
Basic	$ 0.68	$ 0.84	$ 0.97
Diluted	$ 0.68	$ 0.84	$ 0.96
Weighted average shares outstanding
Basic	83,297	86,974	87,748
Diluted	83,365	87,109	87,923
Dividends declared per share	$ 0.08	$ 0.08	$ 0.08