Supplemental Guarantor/Non-Guarantor Financial Information (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	$ 301,673	$ 342,337		$ 863,374	$ 982,253
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	248,500	288,345		735,258	830,405
Depreciation and depletion	7,896	25,815		51,742	81,944
Amortization of port access contract rights	928	0		2,783	0
Accretion	3,070	3,848		9,960	12,066
Derivative financial instruments	10,235	(515)		17,781	(16,052)
Selling, general and administrative expenses	12,940	12,163		36,701	37,086
Goodwill impairment	0	0		33,355	0
Other operating costs	646	1,099		1,163	1,671
Total costs and expenses	284,215	330,755		888,743	947,120
Gain on sale of Decker Mine interest	0	(74,262)		0	(74,262)
Operating income (loss)	17,458	85,844		(25,369)	109,395
Other income (expense)
Interest income	37	37		137	222
Interest expense	(10,985)	(12,701)		(36,274)	(64,508)
Tax agreement benefit	0	58,595		0	58,595
Other, net	253	(31)		158	(262)
Total other income (expense)	(10,695)	45,900		(35,979)	(5,953)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	6,763	131,744		(61,348)	103,442
Income tax benefit (expense)	2,205	(40,688)		12,350	(30,709)
Income (loss) from unconsolidated affiliates, net of tax	(95)	13		294	562
Net income (loss)	8,873	91,069		(48,704)	73,295
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247		939	741
Write-off of prior service costs related to Decker Mine pension	0	3,183		0	3,183
Income tax on postretirement medical plan	(116)	(1,235)		(347)	(1,413)
Other comprehensive income (loss)	197	2,195		592	2,511
Total comprehensive income (loss)	9,070	93,264		(48,112)	75,806
Eliminations
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	(1,327)	(2,256)		(5,602)	(6,132)
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	0	0
Depreciation and depletion	0	0
Amortization of port access contract rights	0	0
Accretion	0	0
Derivative financial instruments	0	0
Selling, general and administrative expenses	(1,327)	(2,256)		(5,602)	(6,131)
Other operating costs	0	0
Total costs and expenses	(1,327)	(2,256)		(5,602)	(6,131)
Operating income (loss)	0	0
Other income (expense)
Interest income	0	0
Interest expense	0	0
Total other income (expense)	0	0
Income (loss) before income tax provision and earnings from unconsolidated affiliates	0	0
Income tax benefit (expense)	0	0
Earnings (losses) from consolidated affiliates, net of tax	(26,570)	(108,471)		68,290	(106,085)
Net income (loss)	(26,570)	(108,471)		68,290	(106,086)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	(626)	(494)		(1,878)	(1,482)
Write-off of prior service costs related to Decker Mine pension		(9,549)			(9,549)
Income tax on postretirement medical plan	232	3,616		694	3,972
Other comprehensive income (loss)	(394)	(6,427)		(1,184)	(7,059)
Total comprehensive income (loss)	(26,964)	(114,898)		67,106	(113,145)
Parent Guarantor (CPE Inc.)
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	1,327	2,256		5,602	6,131
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	0	0		0	0
Depreciation and depletion	0	0		0	0
Amortization of port access contract rights	0	0		0	0
Accretion	0	0		0	0
Derivative financial instruments	0	0		0	0
Selling, general and administrative expenses	1,878	2,257		6,162	6,132
Goodwill impairment	0			0	0
Other operating costs	0	0		0	0
Total costs and expenses	1,878	2,257		6,162	6,132
Gain on sale of Decker Mine interest		0			0
Operating income (loss)	(551)	(1)		(560)	(1)
Other income (expense)
Interest income	0	0		0	0
Interest expense	0	0		0	0
Tax agreement benefit		58,595			58,595
Other, net	0	0		0	0
Total other income (expense)	0	58,595		0	58,595
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(551)	58,594		(560)	58,594
Income tax benefit (expense)	111	(21,522)		112	(21,522)
Income (loss) from unconsolidated affiliates, net of tax	0	0		0	0
Earnings (losses) from consolidated affiliates, net of tax	9,313	53,997		(48,256)	36,223
Net income (loss)	8,873	91,069		(48,704)	73,295
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247		939	741
Write-off of prior service costs related to Decker Mine pension		3,183			3,183
Income tax on postretirement medical plan	(116)	(1,235)		(347)	(1,413)
Other comprehensive income (loss)	197	2,195		592	2,511
Total comprehensive income (loss)	9,070	93,264		(48,112)	75,806
Issuers
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	0	0		0	0
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	(1)	12		17	209
Depreciation and depletion	530	765		1,822	2,300
Amortization of port access contract rights	0	0		0	0
Accretion	0	0		0	0
Derivative financial instruments	0	0		0	0
Selling, general and administrative expenses	247	189		702	548
Goodwill impairment	0			0	0
Other operating costs	0	0		0	46
Total costs and expenses	776	966		2,541	3,103
Gain on sale of Decker Mine interest		0			0
Operating income (loss)	(776)	(966)		(2,541)	(3,103)
Other income (expense)
Interest income	37	37		137	222
Interest expense	(10,785)	(11,000)		(32,855)	(57,053)
Tax agreement benefit		0			0
Other, net	(41)	(84)		(172)	(865)
Total other income (expense)	(10,789)	(11,047)		(32,890)	(57,696)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(11,565)	(12,013)		(35,431)	(60,799)
Income tax benefit (expense)	3,578	12,084		7,133	24,866
Income (loss) from unconsolidated affiliates, net of tax	8	7		7	(8)
Earnings (losses) from consolidated affiliates, net of tax	17,292	53,919		(19,965)	72,164
Net income (loss)	9,313	53,997		(48,256)	36,223
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247		939	741
Write-off of prior service costs related to Decker Mine pension		3,183			3,183
Income tax on postretirement medical plan	(116)	(1,235)		(347)	(1,413)
Other comprehensive income (loss)	197	2,195		592	2,511
Total comprehensive income (loss)	9,510	56,192		(47,664)	38,734
Guarantor Subsidiaries
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	301,673	336,242		863,374	966,601
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	248,500	282,402		735,242	812,355
Depreciation and depletion	7,366	25,979		49,920	80,812
Amortization of port access contract rights	928	0		2,783	0
Accretion	3,070	3,077		9,960	9,263
Derivative financial instruments	10,235	(515)		17,781	(16,052)
Selling, general and administrative expenses	12,142	11,973		35,438	36,537
Goodwill impairment	0			33,355	0
Other operating costs	646	1,099		1,163	1,627
Total costs and expenses	282,887	324,015		885,642	924,542
Gain on sale of Decker Mine interest		(74,262)			(74,262)
Operating income (loss)	18,786	86,489		(22,268)	116,321
Other income (expense)
Interest income	0	0		0	0
Interest expense	(113)	(1,602)		(3,162)	(7,156)
Tax agreement benefit		0			0
Other, net	252	(30)		159	315
Total other income (expense)	139	(1,632)		(3,003)	(6,841)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	18,925	84,857		(25,271)	109,480
Income tax benefit (expense)	(1,495)	(31,499)		5,088	(35,585)
Income (loss) from unconsolidated affiliates, net of tax	(103)	6		287	571
Earnings (losses) from consolidated affiliates, net of tax	(35)	555		(69)	(2,302)
Net income (loss)	17,292	53,919		(19,965)	72,164
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247		939	741
Write-off of prior service costs related to Decker Mine pension		3,183			3,183
Income tax on postretirement medical plan	(116)	(1,235)		(347)	(1,413)
Other comprehensive income (loss)	197	2,195		592	2,511
Total comprehensive income (loss)	17,489	56,114		(19,373)	74,675
Non-Guarantor Subsidiaries
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	0	6,095		0	15,653
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	0	5,932		0	17,841
Depreciation and depletion	0	(929)		0	(1,168)
Amortization of port access contract rights	0	0		0	0
Accretion	0	771		0	2,803
Derivative financial instruments	0	0		0	0
Selling, general and administrative expenses	0	0		0	0
Goodwill impairment	0			0	0
Other operating costs	0	0		0	0
Total costs and expenses	0	5,774		0	19,475
Gain on sale of Decker Mine interest		0			0
Operating income (loss)	0	321		0	(3,823)
Other income (expense)
Interest income	0	0		0	0
Interest expense	(87)	(99)		(258)	(299)
Tax agreement benefit		0			0
Other, net	41	84		172	289
Total other income (expense)	(46)	(15)		(86)	(10)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(46)	306		(86)	(3,833)
Income tax benefit (expense)	11	249		17	1,531
Income (loss) from unconsolidated affiliates, net of tax	0	0	$ 0	0
Earnings (losses) from consolidated affiliates, net of tax	0	0		0	0
Net income (loss)	(35)	555		(69)	(2,302)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	0	0		0	0
Write-off of prior service costs related to Decker Mine pension		3,183			3,183
Income tax on postretirement medical plan	0	(1,146)		0	(1,146)
Other comprehensive income (loss)	0	2,037		0	2,037
Total comprehensive income (loss)	$ (35)	$ 2,592		$ (69)	$ (265)