Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Operating revenue	$ 1,074,880	$ 1,032,127	$ 3,159,224	$ 3,042,806
Operating expenses:
Salaries, wages and employee benefits	240,005	220,156	707,464	670,493
Operating supplies and expenses	88,459	85,204	253,361	236,267
Fuel	149,099	160,561	458,798	489,563
Purchased transportation	328,112	318,321	987,530	918,594
Rental expense	59,655	46,262	167,509	129,881
Insurance and claims	37,673	35,110	113,442	100,245
Depreciation and amortization of property and equipment	54,369	58,254	165,335	170,004
Asset Impairment Charges	2,308	0	2,308	0
Amortization of intangibles	4,204	4,204	12,611	12,611
Gain on disposal of property and equipment	(11,628)	(5,619)	(23,099)	(13,610)
Communication and utilities	7,321	6,679	22,207	19,145
Operating taxes and licenses	17,892	18,575	54,155	55,209
Total operating expenses	977,469	947,707	2,921,621	2,788,402
Operating income	97,411	84,420	237,603	254,404
Other (income) expenses:
Interest expense	20,372	24,595	65,050	75,719
Derivative interest expense	1,756	1,465	5,027	2,559
Interest income	(777)	(604)	(2,235)	(1,741)
Business Combination, Acquisition Related Costs	0	4,331	0	4,331
Loss on debt extinguishment	2,854	496	12,757	5,540
Gain on sale of real property	0	798	0	6,876
Other	(842)	(1,174)	(2,416)	(3,058)
Total other (income) expenses, net	23,363	28,311	78,183	76,474
Income before income taxes	74,048	56,109	159,420	177,930
Income tax expense (benefit)	23,890	26,156	56,759	67,806
Net income	$ 50,158	$ 29,953	$ 102,661	$ 110,124
Basic earnings per share	$ 0.35	$ 0.21	$ 0.73	$ 0.79
Diluted earnings per share	$ 0.35	$ 0.21	$ 0.72	$ 0.78
Shares used in per share calculations
Basic	141,557	140,327	141,282	140,004
Diluted	143,322	142,315	143,338	141,942