Statements Of Consolidated Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Statements Of Consolidated Cash Flows [Abstract]
Cash and Cash Equivalents, Beginning of Period	$ 438,010	$ 421,420
Operating Activities
Net income	25,646	6,922
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization, net of accretion	51,593	50,078
Non-cash compensation and employee benefits	8,720	6,106
Increase in deferred income taxes	15,532	11,702
Provision for uncollectible accounts	1,158	1,963
Gain from sales of property and equipment, net	(1,450)	(161)
Changes in assets and liabilities:
Receivables	(68,093)	(90,497)
Prepaid expenses	(13,482)	(16,667)
Accounts payable	40,366	59,150
Accrued variable compensation	(35,459)	(15,618)
Accrued liabilities, excluding accrued variable compensation and employee benefits	42,359	36,995
Self-insurance accruals	1,009	(11,392)
Accrued income taxes	(4,509)	17,240
Employee benefits	(8,236)	3,119
Deferred charges and credits	617	5,732
Other	(2,942)	(3,267)
Net Cash Provided by Operating Activities	52,829	61,405
Investing Activities
Capital expenditures	(82,486)	(51,485)
Software expenditures	(873)	(1,938)
Proceeds from sales of property and equipment	5,759	1,458
Purchases of marketable securities	(5,000)
Proceeds from sales of marketable securities	2,115	125
Net Cash Used in Investing Activities	(80,485)	(51,840)
Financing Activities
Repayment of capital leases	(4,816)	(4,618)
Net proceeds from (repayments of) short-term borrowings	1,248	(410)
Proceeds from exercise of stock options	279	2,078
Excess tax benefit from share-based compensation	1,360	150
Payments of common dividends	(5,579)	(5,510)
Net Cash Used in Financing Activities	(7,508)	(8,310)
Increase (Decrease) in Cash and Cash Equivalents	(35,164)	1,255
Cash and Cash Equivalents, End of Period	402,846	422,675
Supplemental Disclosure
Cash paid (refunded) for income taxes, net	3,400	(18,204)
Cash paid for interest, net of amounts capitalized	16,200	16,376
Non-cash Financing Activities
Revenue equipment acquired through partial non-monetary exchanges	6,908	6,933
Repurchased common stock issued under defined contribution plan		$ 8,589