Statements Of Consolidated Cash Flows (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Statements Of Consolidated Cash Flows [Abstract]
Cash and Cash Equivalents, Beginning of Period	$ 421,420	$ 476,575
Operating Activities
Net income	65,472	1,598
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization, net of accretion	150,905	140,619
Non-cash compensation and employee benefits	17,668	15,746
Increase in deferred income taxes	42,049	33,163
Provision for uncollectible accounts	4,973	5,519
Loss from impairment of goodwill and other intangible assets		19,181
Loss (Gain) from sales of property and equipment, net	(1,923)	972
Changes in assets and liabilities:
Receivables	(104,658)	(108,590)
Prepaid expenses	16,350	4,628
Accounts payable	53,788	57,052
Accrued variable compensation	12,806	7,873
Accrued liabilities, excluding accrued variable compensation and employee benefits	15,172	(5,347)
Self-insurance accruals	(11,970)	29,596
Accrued income taxes	31,218	(31,021)
Employee benefits	(51,430)	(70,701)
Deferred charges and credits	1,508	(1,075)
Other	(5,878)	(3,940)
Net Cash Provided by Operating Activities	236,050	95,273
Investing Activities
Capital expenditures	(176,677)	(119,989)
Software expenditures	(7,280)	(7,015)
Proceeds from sales of property and equipment	6,083	3,258
Purchases of marketable securities	(11,230)	(54,260)
Proceeds from sales of marketable securities	525	28,460
Net Cash Used in Investing Activities	(188,579)	(149,546)
Financing Activities
Repayment of long-term debt and capital leases	(14,884)	(207,704)
Net proceeds from (repayments of) short-term borrowings	(3,732)	8,154
Payment of debt issuance costs	(661)
Proceeds from issuance of common stock		143,325
Proceeds from exercise of stock options	5,374	1,148
Excess tax benefit from stock-option exercises	713	150
Payments of common dividends	(16,617)	(15,367)
Net Cash Used in Financing Activities	(29,807)	(70,294)
Increase (Decrease) in Cash and Cash Equivalents	17,664	(124,567)
Cash and Cash Equivalents, End of Period	439,084	352,008
Supplemental Disclosures
Cash paid (refunded) for income taxes, net	(28,005)	16,988
Cash paid for interest, net of amounts capitalized	43,765	51,878
Non-cash Investing and Financing Activities
Capital lease incurred to acquire revenue equipment		35,104
Revenue equipment acquired through partial non-monetary exchanges	25,708
Repurchased common stock issued under defined contribution plan	$ 17,307	$ 27,383