Statements Of Consolidated Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Statement of Cash Flows [Abstract]
Cash and Cash Equivalents, Beginning of Period	$ 438,010	$ 421,420
Operating Activities
Net Income	92,750	65,472
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Depreciation and amortization, net of accretion	159,936	150,905
Non-cash compensation and employee benefits	25,299	17,668
Increase in deferred income taxes	57,102	42,049
Provision for uncollectible accounts	3,267	4,973
Gain from sales of property, equipment and investment, net	(8,015)	(1,923)
Changes in assets and liabilities:
Receivables	(54,586)	(104,658)
Prepaid expenses	9,805	16,350
Accounts payable	8,716	53,788
Accrued variable compensation	(4,742)	12,806
Accrued liabilities, excluding accrued variable compensation and employee benefits	25,153	15,172
Self-insurance accruals	(10,042)	(11,970)
Accrued income taxes	(8,949)	31,218
Employee benefits	(55,865)	(51,430)
Deferred charges and credits	(3,915)	1,508
Other	(6,211)	(5,878)
Net Cash Provided by Operating Activities	229,703	236,050
Investing Activities
Capital expenditures	(213,217)	(176,677)
Software expenditures	(5,743)	(7,280)
Proceeds from sales of property and equipment	19,385	6,083
Purchases of marketable securities	(8,200)	(11,230)
Proceeds from sales of marketable securities	23,613	525
Net Cash Used in Investing Activities	(184,162)	(188,579)
Financing Activities
Repayment of capital leases	(25,868)	(14,884)
Net repayments of short-term borrowings	(3,891)	(3,732)
Payment of debt issuance costs	0	(661)
Proceeds from exercise of stock options	3,357	5,374
Excess tax benefit from share-based compensation	1,632	713
Payments of common dividends	(16,760)	(16,617)
Net Cash Used in Financing Activities	(41,530)	(29,807)
Increase in Cash and Cash Equivalents	4,011	17,664
Cash and Cash Equivalents, End of Period	442,021	439,084
Supplemental Disclosure
Cash paid (refunded) for income taxes, net	7,260	(28,005)
Cash paid for interest, net of amounts capitalized	43,105	43,765
Non-cash Investing and Financing Activities
Revenue equipment acquired through partial non-monetary exchanges	23,974	25,708
Repurchased common stock issued under defined contribution plan	$ 0	$ 17,307