Consolidated Statements of Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating Revenue	$ 133,992	$ 139,710	$ 268,265	$ 274,543
Operating Expenses
Salaries, wages, and benefits	40,939	42,962	81,537	84,958
Rent and purchased transportation	1,325	1,596	2,623	3,257
Fuel	38,637	41,111	81,615	83,816
Operations and maintenance	3,828	6,251	9,269	11,903
Operating taxes and licenses	2,468	2,248	4,884	4,323
Insurance and claims	4,744	3,952	7,604	6,466
Communications and utilities	699	746	1,472	1,493
Depreciation	16,930	13,995	31,995	27,934
Other operating expenses	3,691	3,647	7,506	7,626
Gain on disposal of property and equipment	(8,644)	(3,546)	(19,823)	(7,760)
Total operating expenses	104,617	112,962	208,682	224,016
Operating income	29,375	26,748	59,583	50,527
Interest income	129	167	253	309
Income before income taxes	29,504	26,915	59,836	50,836
Federal and state income taxes	10,366	8,688	20,962	16,020
Net income	19,138	18,227	38,874	34,816
Other comprehensive income, net of tax	600	1,797	600	1,797
Comprehensive income	$ 19,738	$ 20,024	$ 39,474	$ 36,613
Net income per share
Basic	$ 0.23	$ 0.21	$ 0.46	$ 0.40
Diluted	$ 0.23	$ 0.21	$ 0.46	$ 0.40
Weighted average shares outstanding
Basic	84,789	86,451	84,780	86,463
Diluted	85,039	86,779	85,042	86,802
Dividends declared per share	$ 0.02	$ 0.02	$ 0.04	$ 0.04