Consolidated Statements Of 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 revenues	$ 506,648	$ 521,812	$ 999,535	$ 1,020,188
Operating expenses:
Salaries, wages and benefits	135,236	138,512	268,341	272,360
Fuel	90,191	99,322	186,984	202,259
Supplies and maintenance	43,934	44,741	87,062	86,578
Taxes and licenses	21,586	22,967	43,210	45,499
Insurance and claims	17,320	15,103	37,121	34,327
Depreciation	42,367	41,506	84,698	82,177
Rent and purchased transportation	115,060	108,496	221,378	209,006
Communications and utilities	3,187	3,344	6,329	7,163
Other	(4,594)	(3,292)	(6,642)	(5,696)
Total operating expenses	464,287	470,699	928,481	933,673
Operating income	42,361	51,113	71,054	86,515
Other expense (income):
Interest expense	91	65	235	207
Interest income	(535)	(433)	(1,040)	(855)
Other	(82)	(82)	(92)	(106)
Total other income	(526)	(450)	(897)	(754)
Income before income taxes	42,887	51,563	71,951	87,269
Income taxes	17,047	20,883	28,600	35,344
Net income	$ 25,840	$ 30,680	$ 43,351	$ 51,925
Earnings per share:
Basic	$ 0.35	$ 0.42	$ 0.59	$ 0.71
Diluted	$ 0.35	$ 0.42	$ 0.59	$ 0.71
Dividends declared per share	$ 0.050	$ 0.050	$ 0.100	$ 0.100
Weighted-average common shares outstanding:
Basic	73,022	72,859	73,140	72,857
Diluted	73,598	73,412	73,690	73,401