Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Statement of Cash Flows [Abstract]
Cash and Cash Equivalents, at Beginning of Period	$ 484,502	$ 429,784
Net income	112,143	87,459
Depreciation and amortization, net of accretion	181,045	171,426
Non-cash compensation and employee benefits	18,312	27,797
Increase in deferred income taxes	28,966	46,784
Provision for uncollectible accounts	2,394	5,045
Gain from sale of property and equipment, net	(8,543)	(6,169)
Receivables	(130,766)	(34,563)
Prepaid expense	11,611	14,334
Accounts payable	26,712	21,044
Accrued variable compensation	12,629	(22,896)
Accrued liabilities, excluding accrued variable compensation and employee benefits	36,217	29,675
Self-insurance accruals	9,845	758
Accrued income taxes	14,114	(7,344)
Employee benefits	(152,250)	(78,540)
Other	(1,769)	4,853
Net Cash Provided by Operating Activities	160,660	259,663
Capital expenditures	(214,329)	(212,549)
Software expenditures	(8,635)	(4,716)
Proceeds from sales of property and equipment	35,126	12,239
Purchases of marketable securities	(3,285)	0
Proceeds from sales of marketable securities	0	3,200
Net Cash Used in Investing Activities	(191,123)	(201,826)
Payment of capital leases	(9,544)	(9,598)
Repayment of short-term borrowings	(104)	(4,673)
Payments of debt issuance costs	0	(543)
Proceeds from exercise of stock options	33,420	19,757
Excess tax benefit from share-based compensation	3,075	2,486
Payments of common dividends	(20,051)	(16,930)
Repurchases of common stock	(4,111)	0
Net Cash Provided by (Used in) Financing Activities	2,685	(9,501)
Increase (Decrease) in Cash and Cash Equivalents	(27,778)	48,336
Cash and Cash Equivalents, at End of Period	456,724	478,120
Cash paid for income taxes, net	29,063	3,692
Cash paid for interest	42,040	42,349
Property, plant and equipment acquired through partial non-monetary exchanges	6,849	23,683
Property, plant and equipment acquired through capital leases	9,721	1,596
Property, plant and equipment acquired through increase in current liabilities	12,377	3,005
Repurchases of common stock included in current liabilities	$ 499	$ 0