Consolidated Statements Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating revenues	$ 2,139,289	$ 2,029,183	$ 2,036,386
Operating expenses:
Salaries, wages and benefits	584,006	545,419	544,322
Fuel	346,058	371,789	401,417
Supplies and maintenance	188,437	179,172	172,505
Taxes and licenses	85,468	86,686	90,002
Insurance and claims	80,375	71,177	65,593
Depreciation	176,984	173,019	166,957
Rent and purchased transportation	498,782	456,885	420,480
Communications and utilities	14,220	13,506	13,745
Other	4,871	(8,196)	(10,079)
Total operating expenses	1,979,201	1,889,457	1,864,942
Operating income	160,088	139,726	171,444
Other expense (income):
Interest expense	881	454	288
Interest income	(2,538)	(2,269)	(1,837)
Other	(29)	(170)	(173)
Total other income	(1,686)	(1,985)	(1,722)
Income before income taxes	161,774	141,711	173,166
Income taxes	63,124	54,926	70,132
Net income	$ 98,650	$ 86,785	$ 103,034
Earnings per share:
Basic	$ 1.37	$ 1.19	$ 1.41
Diluted	$ 1.36	$ 1.18	$ 1.40
Weighted-average common shares outstanding:
Basic	72,122	72,866	72,909
Diluted	72,738	73,428	73,453