Statements Of Consolidated Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Cash Flows [Abstract]
Cash and Cash Equivalents, Beginning of Period	$ 429,784	$ 438,010
Operating Activities
Net Income	14,005	25,646
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Depreciation and amortization, net of accretion	55,673	51,593
Non-cash compensation and employee benefits	9,180	8,720
Increase in deferred income taxes	5,556	15,532
Provision for uncollectible accounts	401	1,158
Loss (Gain) from sales of property, equipment and investment, net	249	(1,450)
Changes in assets and liabilities:
Receivables	(49,353)	(68,093)
Prepaid expenses	(9,307)	(13,482)
Accounts payable	26,290	40,366
Accrued variable compensation	(44,256)	(35,459)
Accrued liabilities, excluding accrued variable compensation and employee benefits	39,831	42,359
Self-insurance accruals	(1,157)	1,009
Accrued income taxes	(5,483)	(4,509)
Employee benefits	(15,675)	(8,236)
Other	1,393	(2,325)
Net Cash Provided by Operating Activities	27,347	52,829
Investing Activities
Capital expenditures	(49,686)	(82,486)
Software expenditures	(960)	(873)
Proceeds from sales of property and equipment	1,396	5,759
Purchases of marketable securities	0	(5,000)
Proceeds from sales of marketable securities	3,200	2,115
Net Cash Used in Investing Activities	(46,050)	(80,485)
Financing Activities
Repayment of capital leases	(3,173)	(4,816)
Net proceeds from (repayments of) short-term borrowings	(4,162)	1,248
Proceeds from exercise of stock options	5,669	279
Excess tax benefit from share-based compensation	733	1,360
Payments of common dividends	(5,617)	(5,579)
Net Cash Used in Financing Activities	(6,550)	(7,508)
Decrease in Cash and Cash Equivalents	(25,253)	(35,164)
Cash and Cash Equivalents, End of Period	404,531	402,846
Supplemental Disclosure
Cash paid for income taxes, net	1,897	3,400
Cash paid for interest, net of amounts capitalized	15,929	16,200
Non-cash Investing and Financing Activities
Revenue equipment acquired through partial non-monetary exchanges	$ 6,394	$ 6,908