Consolidated Statements Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating revenues	$ 2,029,183	$ 2,036,386	$ 2,002,850
Operating expenses:
Salaries, wages and benefits	545,419	544,322	536,509
Fuel	371,789	401,417	412,905
Supplies and maintenance	179,172	172,505	169,386
Taxes and licenses	86,686	90,002	92,917
Insurance and claims	71,177	65,593	67,523
Depreciation	173,019	166,957	158,634
Rent and purchased transportation	456,885	420,480	387,472
Communications and utilities	13,506	13,745	15,181
Other	(8,196)	(10,079)	(11,351)
Total operating expenses	1,889,457	1,864,942	1,829,176
Operating income	139,726	171,444	173,674
Other expense (income):
Interest expense	454	288	85
Interest income	(2,269)	(1,837)	(1,448)
Other	(170)	(173)	131
Total other income	(1,985)	(1,722)	(1,232)
Income before income taxes	141,711	173,166	174,906
Income taxes	54,926	70,132	72,149
Net income	$ 86,785	$ 103,034	$ 102,757
Earnings per share:
Basic earnings per share	$ 1.19	$ 1.41	$ 1.41
Diluted earnings per share	$ 1.18	$ 1.40	$ 1.40
Weighted-average common shares outstanding:
Basic	72,866	72,909	72,787
Diluted	73,428	73,453	73,225