Consolidated Statements Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Operating revenues	$ 521,812	$ 515,897	$ 1,020,188	$ 985,326
Operating expenses:
Salaries, wages and benefits	138,512	135,265	272,360	268,128
Fuel	99,322	110,502	202,259	208,433
Supplies and maintenance	44,741	43,085	86,578	84,274
Taxes and licenses	22,967	23,414	45,499	46,440
Insurance and claims	15,103	16,531	34,327	34,591
Depreciation	41,506	39,246	82,177	78,964
Rent and purchased transportation	108,496	98,605	209,006	187,102
Communications and utilities	3,344	3,843	7,163	7,766
Other	(3,292)	(1,361)	(5,696)	(4,581)
Total operating expenses	470,699	469,130	933,673	911,117
Operating income	51,113	46,767	86,515	74,209
Other expense (income):
Interest expense	65	10	207	38
Interest income	(433)	(345)	(855)	(690)
Other	(82)	263	(106)	289
Total other income	(450)	(72)	(754)	(363)
Income before income taxes	51,563	46,839	87,269	74,572
Income taxes	20,883	19,321	35,344	30,761
Net income	$ 30,680	$ 27,518	$ 51,925	$ 43,811
Earnings per share:
Basic	$ 0.42	$ 0.38	$ 0.71	$ 0.60
Diluted	$ 0.42	$ 0.38	$ 0.71	$ 0.60
Dividends declared per share	$ 0.050	$ 0.050	$ 0.100	$ 0.100
Weighted-average common shares outstanding:
Basic	72,859	72,794	72,857	72,749
Diluted	73,412	73,239	73,401	73,190