Reconciliation of Segment Information, Revenue and Other Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	$ 1,160,114	$ 1,084,041	$ 3,512,055	$ 3,584,805
Earnings Before Income Taxes:
Earnings Before Income Taxes	10,574	(31,371)	11,084	298,861
Revenue from Purchased Oil and Gas	1,608	953	4,372	2,443
Sales-Gas Royalty Interests	15,506	12,968	46,738	34,707
Freight-Outside	11,563	27,430	35,749	126,195
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	1,188,791	1,125,392	3,598,914	3,748,150
Total Assets	12,737,072	12,556,594	12,737,072	12,556,594	12,670,909
Depreciation, Depletion and Amortization	169,152	153,877	489,774	463,048
Capital Expenditures	437,909	437,622	1,195,909	1,152,021
Total Reportable Business Segments
Earnings Before Income Taxes:
Earnings Before Income Taxes	83,938	19,468	237,668	452,763
Total Assets	11,787,041	11,465,377	11,787,041	11,465,377
Coal
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	889,002	831,309	2,732,458	2,830,395
Earnings Before Income Taxes:
Earnings Before Income Taxes	85,805	7,804	244,785	427,455
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	11,563	27,430	35,749	126,195
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	900,565	858,739	2,768,207	2,956,590
Total Assets	5,792,969	5,594,926	5,792,969	5,594,926
Depreciation, Depletion and Amortization	104,530	95,702	307,992	297,148
Capital Expenditures	156,730	254,864	511,626	702,880
Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	192,782	165,102	531,860	473,404
Earnings Before Income Taxes:
Earnings Before Income Taxes	(1,867)	11,664	(7,117)	25,308
Revenue from Purchased Oil and Gas	1,608	953	4,372	2,443
Sales-Gas Royalty Interests	15,506	12,968	46,738	34,707
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	601	345	2,363	1,171
Segment Reporting Information, Revenue for Reportable Segment	210,497	179,368	585,333	511,725
Total Assets	5,994,072	5,870,451	5,994,072	5,870,451
Depreciation, Depletion and Amortization	58,444	52,215	163,079	148,344
Capital Expenditures	273,474	166,617	669,067	408,278
All Other Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	78,330	87,630	247,737	281,006
Earnings Before Income Taxes:
Earnings Before Income Taxes	(6,991)	8,494	(48,426)	27,539
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	32,213	37,987	100,118	111,332
Segment Reporting Information, Revenue for Reportable Segment	110,543	125,617	347,855	392,338
Total Assets	356,848	376,400	356,848	376,400
Depreciation, Depletion and Amortization	6,178	0	18,703	0
Capital Expenditures	7,705	16,141	15,216	40,863
Excludes Gas Segment [Member]
Earnings Before Income Taxes:
Interest Income (Expense), Net and Other Non-operating Activity	(57,482)	(56,338)	(166,548)	(175,323)
Fees for Disposing Non-core Assets	(8,891)	(2,995)	11,610	6,118
Intersegment Elimination [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	0	0	0	0
Earnings Before Income Taxes:
Earnings Before Income Taxes	(66,373)	(59,333)	(178,158)	(181,441)
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	(32,814)	(38,332)	(102,481)	(112,503)
Segment Reporting Information, Revenue for Reportable Segment	(32,814)	(38,332)	(102,481)	(112,503)
Total Assets	593,183	714,817	593,183	714,817
Depreciation, Depletion and Amortization	0	5,960	0	17,556
Capital Expenditures	0	0	0	0
Steam [Member] | Coal
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	753,692	667,372	2,212,909	2,227,728
Earnings Before Income Taxes:
Earnings Before Income Taxes	128,112	89,743	360,312	351,889
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	753,692	667,372	2,212,909	2,227,728
High Volatile Metallurgical [member] | Coal
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	29,608	48,484	145,345	180,302
Earnings Before Income Taxes:
Earnings Before Income Taxes	6,466	9,640	37,063	44,994
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	29,608	48,484	145,345	180,302
Low Volatile Metallurgical [Member] | Coal
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	98,232	110,239	356,066	403,460
Earnings Before Income Taxes:
Earnings Before Income Taxes	21,295	42,722	106,831	164,843
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	98,232	110,239	356,066	403,460
Other Coal [Member] | Coal
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	7,470	5,214	18,138	18,905
Earnings Before Income Taxes:
Earnings Before Income Taxes	(70,068)	(134,301)	(259,421)	(134,271)
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	11,563	27,430	35,749	126,195
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	19,033	32,644	53,887	145,100
Coalbed Methane [Member] | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	83,269	94,169	254,708	281,784
Earnings Before Income Taxes:
Earnings Before Income Taxes	20,909	30,983	64,345	91,717
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	83,269	94,169	254,708	281,784
Marcellus Shale [Member] | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	72,406	36,253	167,394	83,774
Earnings Before Income Taxes:
Earnings Before Income Taxes	27,941	6,347	53,389	14,433
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	72,406	36,253	167,394	83,774
Conventional Gas [Member] | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	32,957	32,288	99,138	100,868
Earnings Before Income Taxes:
Earnings Before Income Taxes	(2,124)	(3,439)	(11,861)	(9,571)
Revenue from Purchased Oil and Gas	0	0	0	0
Sales-Gas Royalty Interests	0	0	0	0
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	0	0	0	0
Segment Reporting Information, Revenue for Reportable Segment	32,957	32,288	99,138	100,868
Other Gas | Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-Outside	4,150	2,392	10,620	6,978
Earnings Before Income Taxes:
Earnings Before Income Taxes	(48,593)	(22,227)	(112,990)	(71,271)
Revenue from Purchased Oil and Gas	1,608	953	4,372	2,443
Sales-Gas Royalty Interests	15,506	12,968	46,738	34,707
Freight-Outside	0	0	0	0
Segment Reporting Information, Intersegment Revenue	601	345	2,363	1,171
Segment Reporting Information, Revenue for Reportable Segment	21,865	16,658	64,093	45,299
First Energy [Member] | Coal
Segment Reporting, Revenue Reconciling Item [Line Items]
Entity-Wide Revenue, Major Customer, Amount	$ 164,572	$ 129,014	$ 492,872	$ 409,745