Supplemental Consolidating Financial Information (Schedule of Consolidating Statements of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash provided by (used in) operating activities	$ 55,742	$ 332,804	$ 642,242
Investing Activities
Payments to Acquire Businesses, Net of Cash Acquired		0	2,894,339
Increase (Decrease) in Restricted Cash and Investments			(5,167)
Capital expenditures	(296,984)	(395,225)	(540,936)
Additions to prepaid royalties	(14,947)	(13,269)	(29,957)
Proceeds from dispositions of property, plant and equipment	10,790	22,825	25,887
Proceeds from sale-leaseback transactions	34,919
Proceeds from sale of Canyon Fuel	422,663
Investments in and advances to affiliates	(15,260)	(17,758)	(61,909)
Purchases of short term investments	(213,726)	(236,862)
Proceeds from Sale of Short-term Investments	194,537	1,754
Change in restricted cash	3,453	6,869	5,167
Purchase of noncontrolling interest	0		0
Payments for (Proceeds from) Previous Acquisition		0	(829)
Cash provided by (used in) investing activities	125,445	(649,166)	(3,496,916)
Financing Activities
Proceeds from Contributions from Parent
Proceeds from Issuance of Long-term Debt	644,000	1,993,253
Proceeds from issuance of senior notes	350,000	359,753	2,000,000
Proceeds from the issuance of common stock, net		0	1,267,933
Payments to retire debt	(629,172)	(452,934)	(605,178)
Payments on term loan	(17,250)	(7,625)
Net decrease in borrowings under lines of credit		(481,300)	424,396
Net payments on other debt	(6,324)	(682)	5,334
Debt financing costs	(20,489)	(50,568)	(114,823)
Dividends paid	(25,475)	(42,440)	(80,748)
Proceeds from exercise of options under incentive plans		5,131	2,316
Transactions with affiliates, net
Cash provided by (used in) financing activities	(54,710)	962,835	2,899,230
Increase in cash and cash equivalents	126,477	646,473	44,556
Cash and cash equivalents, beginning of period	784,622	138,149	93,593
Cash and cash equivalents, end of period	911,099	784,622	138,149
Parent/Issuer [Member]
Cash provided by (used in) operating activities	(632,060)	(571,576)	(187,039)
Investing Activities
Payments to Acquire Businesses, Net of Cash Acquired			2,894,339
Increase (Decrease) in Restricted Cash and Investments			(5,167)
Capital expenditures	(3,320)	(4,424)	(12,809)
Additions to prepaid royalties
Proceeds from dispositions of property, plant and equipment
Proceeds from sale-leaseback transactions
Proceeds from sale of Canyon Fuel
Investments in and advances to affiliates	(5,451)	(6,287)	(633,534)
Purchases of short term investments	(213,726)	(236,862)
Proceeds from Sale of Short-term Investments	194,537	1,754
Change in restricted cash	3,453	6,869
Payments for (Proceeds from) Previous Acquisition			(829)
Cash provided by (used in) investing activities	(24,507)	(256,450)	(3,536,344)
Financing Activities
Proceeds from Contributions from Parent
Proceeds from Issuance of Long-term Debt	644,000	1,993,253
Proceeds from issuance of senior notes			2,000,000
Proceeds from the issuance of common stock, net			1,267,933
Payments to retire debt	(628,660)
Payments on term loan	(17,250)	(7,625)
Net decrease in borrowings under lines of credit		(375,000)	375,000
Net payments on other debt	(6,324)	(682)	5,334
Debt financing costs	(19,864)	(50,022)	(114,799)
Dividends paid	(25,475)	(42,440)	(80,748)
Proceeds from exercise of options under incentive plans		5,131	2,316
Transactions with affiliates, net	838,160	(84,651)	316,009
Cash provided by (used in) financing activities	784,587	1,437,964	3,771,045
Increase in cash and cash equivalents	128,020	609,938	47,662
Cash and cash equivalents, beginning of period	671,313	61,375	13,713
Cash and cash equivalents, end of period	799,333	671,313	61,375
Guarantor Subsidiaries [Member]
Cash provided by (used in) operating activities	637,193	781,551	998,082
Investing Activities
Payments to Acquire Businesses, Net of Cash Acquired
Increase (Decrease) in Restricted Cash and Investments
Capital expenditures	(293,664)	(390,801)	(528,021)
Additions to prepaid royalties	(14,947)	(13,269)	(29,957)
Proceeds from dispositions of property, plant and equipment	10,790	1,328	25,887
Proceeds from sale-leaseback transactions	34,919
Proceeds from sale of Canyon Fuel	422,663
Investments in and advances to affiliates	(10,321)	(13,134)	(33,553)
Purchases of short term investments
Proceeds from Sale of Short-term Investments
Change in restricted cash
Payments for (Proceeds from) Previous Acquisition
Cash provided by (used in) investing activities	149,440	(415,876)	(565,644)
Financing Activities
Proceeds from Contributions from Parent	512	1,663	605,178
Proceeds from issuance of senior notes
Proceeds from the issuance of common stock, net
Payments to retire debt	(512)	(452,934)	(605,178)
Payments on term loan
Net decrease in borrowings under lines of credit			(56,904)
Net payments on other debt
Debt financing costs			(16)
Dividends paid
Proceeds from exercise of options under incentive plans
Transactions with affiliates, net	(786,683)	110,639	(379,973)
Cash provided by (used in) financing activities	(786,683)	(340,632)	(436,893)
Increase in cash and cash equivalents	(50)	25,043	(4,455)
Cash and cash equivalents, beginning of period	100,468	75,425	79,880
Cash and cash equivalents, end of period	100,418	100,468	75,425
Non-Guarantor Subsidiaries [Member]
Cash provided by (used in) operating activities	50,609	122,829	(168,801)
Investing Activities
Payments to Acquire Businesses, Net of Cash Acquired
Increase (Decrease) in Restricted Cash and Investments
Capital expenditures			(106)
Additions to prepaid royalties
Proceeds from dispositions of property, plant and equipment		21,497
Proceeds from sale-leaseback transactions
Proceeds from sale of Canyon Fuel
Investments in and advances to affiliates
Purchases of short term investments
Proceeds from Sale of Short-term Investments
Change in restricted cash
Payments for (Proceeds from) Previous Acquisition
Cash provided by (used in) investing activities		21,497	(106)
Financing Activities
Proceeds from Contributions from Parent
Proceeds from issuance of senior notes
Proceeds from the issuance of common stock, net
Payments to retire debt
Payments on term loan
Net decrease in borrowings under lines of credit		(106,300)	106,300
Net payments on other debt
Debt financing costs	(625)	(546)	(8)
Dividends paid
Proceeds from exercise of options under incentive plans
Transactions with affiliates, net	(51,477)	(25,988)	63,964
Cash provided by (used in) financing activities	(52,102)	(132,834)	170,256
Increase in cash and cash equivalents	(1,493)	11,492	1,349
Cash and cash equivalents, beginning of period	12,841	1,349
Cash and cash equivalents, end of period	11,348	12,841	1,349
Eliminations [Member]
Cash provided by (used in) operating activities
Investing Activities
Payments to Acquire Businesses, Net of Cash Acquired
Increase (Decrease) in Restricted Cash and Investments
Capital expenditures
Additions to prepaid royalties
Proceeds from dispositions of property, plant and equipment
Proceeds from sale-leaseback transactions
Proceeds from sale of Canyon Fuel
Investments in and advances to affiliates	512	1,663	605,178
Purchases of short term investments
Proceeds from Sale of Short-term Investments
Change in restricted cash
Payments for (Proceeds from) Previous Acquisition
Cash provided by (used in) investing activities	512	1,663	605,178
Financing Activities
Proceeds from Contributions from Parent	(512)	(1,663)	(605,178)
Proceeds from issuance of senior notes
Proceeds from the issuance of common stock, net
Payments to retire debt
Payments on term loan
Net decrease in borrowings under lines of credit
Net payments on other debt
Debt financing costs
Dividends paid
Proceeds from exercise of options under incentive plans
Transactions with affiliates, net
Cash provided by (used in) financing activities	(512)	(1,663)	(605,178)
Increase in cash and cash equivalents
Cash and cash equivalents, beginning of period
Cash and cash equivalents, end of period