Statements Of Consolidated Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Cash Flows [Abstract]
Cash and Cash Equivalents, Beginning of Period	$ 484,502	$ 429,784	$ 438,010
Net Income	137,039	99,153	104,546
Adjustments to Reconcile Net Income to Cash Provided by Operating Activities [Abstract]
Depreciation and amortization, net of accretion	242,507	229,236	215,202
Non-cash compensation and employee benefits	34,040	38,496	33,180
Increase in deferred income taxes	55,946	57,423	63,091
Provision for uncollectible accounts	2,869	6,908	6,358
Gain from sales of property, equipment and investment, net	10,156	5,720	8,649
Increase (Decrease) in Operating Capital [Abstract]
Receivables	(82,990)	(12,869)	7,076
Prepaid expenses	(517)	21	(1,312)
Accounts payable	(15,401)	25,972	(14,824)
Accrued variable compensation	23,125	(17,140)	1,201
Accrued liabilities, excluding accrued variable compensation and employee benefits	10,687	11,572	1,988
Self-insurance accruals	14,797	(3,661)	(18,654)
Accrued income taxes	(15,716)	(4,846)	(2,316)
Employee benefits	(154,501)	(82,507)	(67,291)
Other	(1,845)	5,946	(8,185)
Net Cash Provided by Operating Activities	239,884	347,984	311,411
Net Cash Used in Investing Activities [Abstract]
Capital expenditures	289,776	281,943	293,135
Software expenditures	12,364	7,398	8,963
Proceeds from sales of property and equipment	47,238	14,202	20,840
Purchases of marketable securities	(8,285)	0	(8,200)
Proceeds from sales of marketable securities	0	3,200	23,613
Net Cash Used in Investing Activities	(263,187)	(271,939)	(265,845)
Net Cash Used in Financing Activities [Abstract]
Payments of capital leases	(21,098)	(16,068)	(29,015)
Net proceeds from (repayments of) short-term borrowings	147	(5,383)	(7,621)
Payment of debt issuance costs	0	(543)	0
Proceeds from exercise of stock options	33,902	20,777	3,560
Excess tax benefit from share-based compensation	3,128	2,510	1,641
Payments of common dividends	28,720	22,620	22,357
Repurchases of common stock	(15,799)	0	0
Net Cash Used in Financing Activities	(28,440)	(21,327)	(53,792)
Increase (Decrease) in Cash and Cash Equivalents	(51,743)	54,718	(8,226)
Cash and Cash Equivalents, End of Period	432,759	484,502	429,784
Supplemental Disclosure
Cash paid (refunded) for income taxes, net	30,597	(21)	6,163
Cash paid for interest, net of amounts capitalized	52,491	52,809	53,806
Property, plant and equipment acquired through partial non-monetary exchanges	17,597	27,711	34,759
Property, plant and equipment acquired through capital leases	10,483	5,575	0
Property, plant and equipment acquired through increase in current liabilities	6,756	32,336	14,034
Repurchases of common stock included in current liabilities	$ 984	$ 0	$ 0