Industry Segment Results (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 Information [Line Items]
Sales-Outside	$ 1,160,114	$ 1,084,041	$ 3,512,055	$ 3,584,805
Sales-Purchased 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
Total Sales and Freight	1,188,791	1,125,392	3,598,914	3,748,150
Earnings Before Income Taxes	10,574	(31,371)	11,084	298,861
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
Equity in Earnings of Unconsolidated Affiliates			(20,276)	(22,676)
Investments in Unconsolidated Equity Affiliates	261,218		261,218		222,830
Total Reportable Business Segments
Segment Reporting Information [Line Items]
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 Information [Line Items]
Sales-Outside	889,002	831,309	2,732,458	2,830,395
Sales-Purchased 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
Total Sales and Freight	900,565	858,739	2,768,207	2,956,590
Earnings Before Income Taxes	85,805	7,804	244,785	427,455
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
Equity in Earnings of Unconsolidated Affiliates	(1,682)	(3,504)	10,661	7,588
Investments in Unconsolidated Equity Affiliates	20,131	19,750	20,131	19,750
Gas
Segment Reporting Information [Line Items]
Sales-Outside	192,782	165,102	531,860	473,404
Sales-Purchased 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
Total Sales and Freight	210,497	179,368	585,333	511,725
Earnings Before Income Taxes	(1,867)	11,664	(7,117)	25,308
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
Equity in Earnings of Unconsolidated Affiliates	5,307	2,503	9,519	6,484
Investments in Unconsolidated Equity Affiliates	183,895	135,048	183,895	135,048
All Other Segments [Member]
Segment Reporting Information [Line Items]
Sales-Outside	78,330	87,630	247,737	281,006
Sales-Purchased 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
Total Sales and Freight	110,543	125,617	347,855	392,338
Earnings Before Income Taxes	(6,991)	8,494	(48,426)	27,539
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
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Sales-Outside	0	0	0	0
Sales-Purchased 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)
Total Sales and Freight	(32,814)	(38,332)	(102,481)	(112,503)
Earnings Before Income Taxes	(66,373)	(59,333)	(178,158)	(181,441)
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
All Other
Segment Reporting Information [Line Items]
Equity in Earnings of Unconsolidated Affiliates	(16)	8,574	96	8,604
Investments in Unconsolidated Equity Affiliates	57,192	58,910	57,192	58,910
Steam [Member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	753,692	667,372	2,212,909	2,227,728
Sales-Purchased 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
Total Sales and Freight	753,692	667,372	2,212,909	2,227,728
Earnings Before Income Taxes	128,112	89,743	360,312	351,889
Low Volatile Metallurgical [Member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	98,232	110,239	356,066	403,460
Sales-Purchased 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
Total Sales and Freight	98,232	110,239	356,066	403,460
Earnings Before Income Taxes	21,295	42,722	106,831	164,843
High Volatile Metallurgical [member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	29,608	48,484	145,345	180,302
Sales-Purchased 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
Total Sales and Freight	29,608	48,484	145,345	180,302
Earnings Before Income Taxes	6,466	9,640	37,063	44,994
Other Coal [Member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	7,470	5,214	18,138	18,905
Sales-Purchased 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
Total Sales and Freight	19,033	32,644	53,887	145,100
Earnings Before Income Taxes	(70,068)	(134,301)	(259,421)	(134,271)
Coalbed Methane [Member] | Gas
Segment Reporting Information [Line Items]
Sales-Outside	83,269	94,169	254,708	281,784
Sales-Purchased 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
Total Sales and Freight	83,269	94,169	254,708	281,784
Earnings Before Income Taxes	20,909	30,983	64,345	91,717
Marcellus Shale [Member] | Gas
Segment Reporting Information [Line Items]
Sales-Outside	72,406	36,253	167,394	83,774
Sales-Purchased 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
Total Sales and Freight	72,406	36,253	167,394	83,774
Earnings Before Income Taxes	27,941	6,347	53,389	14,433
Conventional Gas [Member] | Gas
Segment Reporting Information [Line Items]
Sales-Outside	32,957	32,288	99,138	100,868
Sales-Purchased 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
Total Sales and Freight	32,957	32,288	99,138	100,868
Earnings Before Income Taxes	(2,124)	(3,439)	(11,861)	(9,571)
Other Gas | Gas
Segment Reporting Information [Line Items]
Sales-Outside	4,150	2,392	10,620	6,978
Sales-Purchased 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
Total Sales and Freight	21,865	16,658	64,093	45,299
Earnings Before Income Taxes	(48,593)	(22,227)	(112,990)	(71,271)
First Energy [Member] | Coal
Segment Reporting Information [Line Items]
Entity-Wide Revenue, Major Customer, Amount	164,572	129,014	492,872	409,745
XCoal Energy and Resources [Member] | Coal
Segment Reporting Information [Line Items]
Entity-Wide Revenue, Major Customer, Amount	$ 119,707		$ 441,528	$ 382,950