Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Operating Revenue	$ 162,786	$ 187,523
Operating Expenses
Salaries, wages, and benefits	65,466	70,996
Rent and purchased transportation	6,700	9,327
Fuel	21,194	34,256
Operations and maintenance	6,639	8,134
Operating taxes and licenses	3,891	4,813
Insurance and claims	8,092	6,644
Communications and utilities	1,204	1,543
Depreciation and amortization	25,705	25,974
Other operating expenses	4,933	7,757
Gain on disposal of property and equipment	(1,288)	(10,181)
Total operating expenses	142,536	159,263
Operating income	20,250	28,260
Interest income	75	31
Interest expense	0	(19)
Income before income taxes	20,325	28,272
Federal and state income taxes	5,948	10,661
Net income	14,377	17,611
Other comprehensive income, net of tax	0	0
Comprehensive income	$ 14,377	$ 17,611
Net income per share
Basic	$ 0.17	$ 0.20
Diluted	$ 0.17	$ 0.20
Weighted average shares outstanding
Basic	83,369	87,791
Diluted	83,460	87,965
Dividends declared per share	$ 0.02	$ 0.02