Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING REVENUE	$ 736,345	$ 871,355	$ 582,257
Operating Expenses
Salaries, wages and benefits	277,318	278,126	178,736
Rent and purchased transportation	34,489	51,950	12,808
Fuel	123,714	219,261	172,315
Operations and maintenance	34,025	39,052	22,345
Operating taxes and licenses	18,095	20,370	10,516
Insurance and claims	21,618	17,946	14,888
Communications and utilities	6,001	6,494	3,552
Depreciation and amortization	110,973	108,566	68,908
Other operating expenses	28,572	31,266	19,157
Gain on disposal of property and equipment	(35,040)	(33,544)	(33,270)
Total operating expenses	619,765	739,487	469,955
Operating income	116,580	131,868	112,302
Interest income	210	195	462
Interest expense	(19)	(446)	(208)
Income before income taxes	116,771	131,617	112,556
Federal and state income taxes	43,715	46,783	41,974
Net income	73,056	84,834	70,582
Other comprehensive income, net of tax	0	0	1,284
Comprehensive income	$ 73,056	$ 84,834	$ 71,866
Net income per share
Basic	$ 0.84	$ 0.97	$ 0.83
Diluted	$ 0.84	$ 0.96	$ 0.83
Weighted average shares outstanding
Basic	86,974	87,748	85,209
Diluted	87,109	87,923	85,441
Dividends declared per share	$ 0.08	$ 0.08	$ 0.08