Statements Of Consolidated Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Cash Flows [Abstract]
Cash and Cash Equivalents, Beginning of Period	$ 438,010	$ 421,420	$ 476,575
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Net Income	104,546	88,443	3,985
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization, net of accretion	215,202	201,638	189,517
Non-cash compensation and employee benefits	33,180	22,050	20,256
Increase in deferred income taxes	63,091	52,160	68,343
Provision for uncollectible accounts	6,358	6,761	7,319
Loss (Gain) from asset impairments and purchase-price adjustment	0	10,000	(19,181)
Loss from restructuring activities	0	0	(4,990)
Loss (Gain) from sales of property, equipment and investment, net	(8,649)	(7,120)	1,243
Increase (Decrease) in Operating Capital [Abstract]
Receivables	7,076	(42,315)	(61,264)
Prepaid expenses	(1,312)	(1,024)	(4,542)
Accounts payable	(14,824)	41,313	31,891
Accrued variable compensation	1,201	22,439	8,268
Accrued liabilities, excluding accrued variable compensation and employee benefits	1,988	3,808	(20,492)
Self-insurance accruals	(18,654)	(11,951)	30,487
Accrued income taxes	(2,316)	34,362	(39,583)
Employee benefits	(67,291)	(52,713)	(67,629)
Deferred charges and credits	(5,217)	(952)	(3,572)
Other	(2,968)	(2,189)	(3,526)
Net Cash Provided by Operating Activities	311,411	344,710	184,872
Net Cash Provided by (Used in) Investing Activities [Abstract]
Capital expenditures	(293,135)	(288,994)	(186,496)
Software expenditures	(8,963)	(8,667)	(8,101)
Proceeds from sales of property and equipment	20,840	13,213	12,403
Proceeds from sale-leaseback transactions	0	0	20,430
Proceeds from purchase-price adjustment	0	10,000	0
Purchases of marketable securities	(8,200)	(13,480)	(59,260)
Proceeds from sales of marketable securities	23,613	900	59,960
Net Cash Used in Investing Activities	(265,845)	(287,028)	(161,064)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Repayment of long-term debt and capital leases	(29,015)	(19,811)	(211,124)
Net proceeds from (repayments of) short-term borrowings	(7,621)	(4,691)	7,912
Payment of debt issuance costs	0	(661)	(2,123)
Net proceeds from issuance of common stock	0	0	143,325
Proceeds from exercise of stock options	3,560	5,532	3,459
Excess tax benefit from share-based compensation	1,641	716	433
Payments of common dividends	(22,357)	(22,177)	(20,845)
Net Cash Used in Financing Activities	(53,792)	(41,092)	(78,963)
Increase (Decrease) in Cash and Cash Equivalents	(8,226)	16,590	(55,155)
Cash and Cash Equivalents, End of Period	429,784	438,010	421,420
Supplemental Disclosure
Cash paid (refunded) for income taxes, net	6,163	(28,740)	(10,354)
Cash paid for interest, net of amounts capitalized	$ 53,806	$ 54,676	$ 62,869