Supplemental Guarantor and Non-Guarantor Financial Information (Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues:
Sales	$ 179,068	$ 319,542	$ 658,549	$ 1,102,753
Miscellaneous income	5,731	10,004	13,803	19,029
Total revenues	184,799	329,546	672,352	1,121,782
Costs and expenses:
Cost of sales (exclusive of depreciation and depletion)	216,647	297,925	727,207	991,561
Depreciation and depletion	43,487	58,413	154,147	204,653
Selling, general and administrative	14,233	16,598	63,523	56,379
Other postretirement benefits	12,333	13,869	36,999	41,607
Restructuring charges (benefit)	4,216	(2,463)	6,662	5,835
Asset impairments	0	37	2,897,928	23,081
Total costs and expenses	290,916	384,379	3,886,466	1,323,116
Operating loss	(106,117)	(54,833)	(3,214,114)	(201,334)
Interest expense, net	(42,222)	(79,231)	(195,309)	(218,065)
Gain on extinguishment of debt	0	3,394	58,626	902
Loss before reorganization items, net and income tax benefit	(148,339)	(129,246)	(3,350,797)	(417,851)
Reorganization items, net	(17,017)	0	(17,017)	0
Other income, net	0	1,424	0	646
Loss before income tax benefit	(165,356)	(129,246)	(3,367,814)	(417,851)
Income tax expense (benefit)	(6,713)	(30,344)	(673,911)	(75,380)
Equity in net losses of subsidiaries	0	0	0	0
Net loss	(158,643)	(98,902)	(2,693,903)	(342,471)
Reportable legal entities | Parent (Issuer)
Revenues:
Sales	0	0	0	0
Miscellaneous income	226	(40)	1,454	939
Total revenues	226	(40)	1,454	939
Costs and expenses:
Cost of sales (exclusive of depreciation and depletion)	0	0	0	0
Depreciation and depletion	493	612	1,667	1,873
Selling, general and administrative	4,822	1,387	24,663	4,501
Other postretirement benefits	(67)	(45)	(200)	(133)
Restructuring charges (benefit)	192	50	547	564
Asset impairments		0	0	0
Total costs and expenses	5,440	2,004	26,677	6,805
Operating loss	(5,214)	(2,044)	(25,223)	(5,866)
Interest expense, net	(42,535)	(77,856)	(194,125)	(222,598)
Gain on extinguishment of debt		3,394	58,626	902
Loss before reorganization items, net and income tax benefit	(47,749)		(160,722)
Reorganization items, net	(17,581)		(17,581)
Other income, net		1,424		705
Loss before income tax benefit	(65,330)	(75,082)	(178,303)	(226,857)
Income tax expense (benefit)	(3,144)	(404)	(6,383)	(2,837)
Equity in net losses of subsidiaries	(96,457)	(24,224)	(2,521,983)	(118,451)
Net loss	(158,643)	(98,902)	(2,693,903)	(342,471)
Reportable legal entities | Guarantor Subsidiaries
Revenues:
Sales	155,845	280,010	587,530	903,120
Miscellaneous income	1,910	1,834	4,795	5,564
Total revenues	157,755	281,844	592,325	908,684
Costs and expenses:
Cost of sales (exclusive of depreciation and depletion)	190,245	246,187	626,341	744,414
Depreciation and depletion	33,334	35,289	103,610	109,544
Selling, general and administrative	6,711	11,564	30,204	37,069
Other postretirement benefits	12,400	13,914	37,199	41,740
Restructuring charges (benefit)	3,178	(13)	4,500	667
Asset impairments		37	0	23,081
Total costs and expenses	245,868	306,978	801,854	956,515
Operating loss	(88,113)	(25,134)	(209,529)	(47,831)
Interest expense, net	(45)	(257)	(406)	6,726
Gain on extinguishment of debt		0	0	0
Loss before reorganization items, net and income tax benefit	(88,158)		(209,935)
Reorganization items, net	230		230
Other income, net		0		0
Loss before income tax benefit	(87,928)	(25,391)	(209,705)	(41,105)
Income tax expense (benefit)	0	17	0	(4,342)
Equity in net losses of subsidiaries	0	0	0	0
Net loss	(87,928)	(25,408)	(209,705)	(36,763)
Reportable legal entities | Non-Guarantor Subsidiaries
Revenues:
Sales	23,223	39,532	71,019	199,633
Miscellaneous income	3,595	8,210	7,554	12,526
Total revenues	26,818	47,742	78,573	212,159
Costs and expenses:
Cost of sales (exclusive of depreciation and depletion)	26,402	51,738	100,866	247,147
Depreciation and depletion	9,660	22,512	48,870	93,236
Selling, general and administrative	2,700	3,647	8,656	14,809
Other postretirement benefits	0	0	0	0
Restructuring charges (benefit)	846	(2,500)	1,615	4,604
Asset impairments		0	2,897,928	0
Total costs and expenses	39,608	75,397	3,057,935	359,796
Operating loss	(12,790)	(27,655)	(2,979,362)	(147,637)
Interest expense, net	358	(1,118)	(778)	(2,193)
Gain on extinguishment of debt		0	0	0
Loss before reorganization items, net and income tax benefit	(12,432)		(2,980,140)
Reorganization items, net	334		334
Other income, net		0		(59)
Loss before income tax benefit	(12,098)	(28,773)	(2,979,806)	(149,889)
Income tax expense (benefit)	(3,569)	(29,957)	(667,528)	(68,201)
Equity in net losses of subsidiaries	0	0	0	0
Net loss	(8,529)	1,184	(2,312,278)	(81,688)
Eliminations
Revenues:
Sales	0	0	0	0
Miscellaneous income	0	0	0	0
Total revenues	0	0	0	0
Costs and expenses:
Cost of sales (exclusive of depreciation and depletion)	0	0	0	0
Depreciation and depletion	0	0	0	0
Selling, general and administrative	0	0	0	0
Other postretirement benefits	0	0	0	0
Restructuring charges (benefit)	0	0	0	0
Asset impairments		0	0	0
Total costs and expenses	0	0	0	0
Operating loss	0	0	0	0
Interest expense, net	0	0	0	0
Gain on extinguishment of debt		0	0	0
Loss before reorganization items, net and income tax benefit	0		0
Other income, net		0		0
Loss before income tax benefit	0	0	0	0
Income tax expense (benefit)	0	0	0	0
Equity in net losses of subsidiaries	96,457	24,224	2,521,983	118,451
Net loss	$ 96,457	$ 24,224	$ 2,521,983	$ 118,451