Consolidated Statements Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating revenues	$ 511,728	$ 506,504	$ 1,511,263	$ 1,526,692
Operating expenses:
Salaries, wages and benefits	137,834	134,923	406,175	407,283
Fuel	92,890	98,805	279,874	301,064
Supplies and maintenance	46,538	44,589	133,600	131,167
Taxes and licenses	21,548	22,251	64,758	67,750
Insurance and claims	16,714	14,469	53,835	48,796
Depreciation	42,612	41,901	127,310	124,078
Rent and purchased transportation	117,651	107,495	339,029	316,501
Communications and utilities	3,754	3,382	10,083	10,545
Other	(396)	(3,116)	(7,038)	(8,812)
Total operating expenses	479,145	464,699	1,407,626	1,398,372
Operating income	32,583	41,805	103,637	128,320
Other expense (income):
Interest expense	101	18	336	225
Interest income	(589)	(461)	(1,629)	(1,316)
Other	(35)	16	(127)	(90)
Total other income	(523)	(427)	(1,420)	(1,181)
Income before income taxes	33,106	42,232	105,057	129,501
Income taxes	11,847	17,104	40,447	52,448
Net income	$ 21,259	$ 25,128	$ 64,610	$ 77,053
Earnings per share:
Basic	$ 0.29	$ 0.34	$ 0.89	$ 1.06
Diluted	$ 0.29	$ 0.34	$ 0.88	$ 1.05
Dividends declared per share	$ 0.050	$ 0.050	$ 0.150	$ 0.150
Weighted-average common shares outstanding:
Basic	72,621	72,879	72,965	72,864
Diluted	73,216	73,445	73,530	73,414