Industry Segment Results (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Sales-Outside	$ 1,226,165	$ 1,311,471
Sales-Purchased Gas	1,358	839
Sales-Gas Royalty Interests	14,204	12,206
Freight-Outside	14,061	49,293
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	1,255,788	1,373,809
Earnings Before Income Taxes	(1,299)	118,577
Total Assets	12,593,194	12,595,611	12,670,909
Depreciation, Depletion and Amortization	161,315	155,347
Capital Expenditures	405,972	306,446
Equity in Earnings of Unconsolidated Affiliates	(4,797)	(7,935)
Investments in Unconsolidated Equity Affiliates	248,127		222,830
Total Reportable Business Segments
Segment Reporting Information [Line Items]
Earnings Before Income Taxes	92,862	174,970
Total Assets	11,578,492	11,471,162
Coal
Segment Reporting Information [Line Items]
Sales-Outside	972,385	1,054,316
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	14,061	49,293
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	986,446	1,103,609
Earnings Before Income Taxes	93,502	162,470
Total Assets	5,698,504	5,360,577
Depreciation, Depletion and Amortization	102,711	100,762
Capital Expenditures	197,338	194,429
Equity in Earnings of Unconsolidated Affiliates	817	4,807
Investments in Unconsolidated Equity Affiliates	20,334	39,373
Gas
Segment Reporting Information [Line Items]
Sales-Outside	167,842	160,203
Sales-Purchased Gas	1,358	839
Sales-Gas Royalty Interests	14,204	12,206
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	836	466
Total Sales and Freight	184,240	173,714
Earnings Before Income Taxes	(640)	12,500
Total Assets	5,879,988	6,110,585
Depreciation, Depletion and Amortization	52,399	48,803
Capital Expenditures	207,130	98,455
Equity in Earnings of Unconsolidated Affiliates	3,182	1,944
Investments in Unconsolidated Equity Affiliates	167,058	108,858
All Other Segments [Member]
Segment Reporting Information [Line Items]
Sales-Outside	85,938	96,952
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	35,477	37,209
Total Sales and Freight	121,415	134,161
Earnings Before Income Taxes	(40,552)	4,083
Total Assets	358,663	358,746
Depreciation, Depletion and Amortization	6,205	5,782
Capital Expenditures	1,504	13,562
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Sales-Outside	0	0
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	(36,313)	(37,675)
Total Sales and Freight	(36,313)	(37,675)
Earnings Before Income Taxes	(53,609)	(60,476)
Total Assets	656,039	765,703
Depreciation, Depletion and Amortization	0	0
Capital Expenditures	0	0
All Other
Segment Reporting Information [Line Items]
Equity in Earnings of Unconsolidated Affiliates	798	1,184
Investments in Unconsolidated Equity Affiliates	60,735	51,990
Steam [Member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	761,272	812,053
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	761,272	812,053
Earnings Before Income Taxes	128,432	128,449
Low Volatile Metallurgical [Member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	146,828	172,740
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	146,828	172,740
Earnings Before Income Taxes	54,717	79,341
High Volatile Metallurgical [member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	58,622	60,568
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	58,622	60,568
Earnings Before Income Taxes	13,352	15,936
Other Coal [Member] | Coal
Segment Reporting Information [Line Items]
Sales-Outside	5,663	8,955
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	14,061	49,293
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	19,724	58,248
Earnings Before Income Taxes	(102,999)	(61,256)
Coalbed Methane [Member] | Gas
Segment Reporting Information [Line Items]
Sales-Outside	83,640	99,535
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	83,640	99,535
Earnings Before Income Taxes	21,312	36,390
Marcellus Shale [Member] | Gas
Segment Reporting Information [Line Items]
Sales-Outside	48,411	23,791
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	48,411	23,791
Earnings Before Income Taxes	13,768	3,251
Conventional Gas [Member] | Gas
Segment Reporting Information [Line Items]
Sales-Outside	32,436	34,373
Sales-Purchased Gas	0	0
Sales-Gas Royalty Interests	0	0
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	0	0
Total Sales and Freight	32,436	34,373
Earnings Before Income Taxes	(4,161)	(3,722)
Other Gas | Gas
Segment Reporting Information [Line Items]
Sales-Outside	3,355	2,504
Sales-Purchased Gas	1,358	839
Sales-Gas Royalty Interests	14,204	12,206
Freight-Outside	0	0
Segment Reporting Information, Intersegment Revenue	836	466
Total Sales and Freight	19,753	16,015
Earnings Before Income Taxes	(31,559)	(23,419)
First Energy [Member] | Coal
Segment Reporting Information [Line Items]
Entity-Wide Revenue, Major Customer, Amount	170,982	144,155
XCoal Energy and Resources [Member] | Coal
Segment Reporting Information [Line Items]
Entity-Wide Revenue, Major Customer, Amount	$ 183,121	$ 138,341