Supplemental Guarantor/Non-Guarantor Financial Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	$ 317,553us-gaap_Revenues	$ 319,066us-gaap_Revenues
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	264,317us-gaap_CostOfGoodsSold	271,939us-gaap_CostOfGoodsSold
Depreciation and depletion	24,536us-gaap_Depreciation	26,928us-gaap_Depreciation
Amortization	928us-gaap_AmortizationOfIntangibleAssets	0us-gaap_AmortizationOfIntangibleAssets
Accretion	3,541	4,130
Derivative financial instruments	4,785	(12,734)
Selling, general and administrative expenses	11,249	12,441
Other operating costs	213us-gaap_OtherCostAndExpenseOperating	238us-gaap_OtherCostAndExpenseOperating
Total costs and expenses	309,569us-gaap_CostsAndExpenses	302,942us-gaap_CostsAndExpenses
Operating income (loss)	7,984us-gaap_OperatingIncomeLoss	16,124us-gaap_OperatingIncomeLoss
Other income (expense)
Interest income	49us-gaap_InvestmentIncomeInterest	124us-gaap_InvestmentIncomeInterest
Interest expense	(12,668)us-gaap_InterestExpense	(37,994)us-gaap_InterestExpense
Other, net	(337)us-gaap_OtherNonoperatingIncomeExpense	(465)us-gaap_OtherNonoperatingIncomeExpense
Total other income (expense)	(12,956)us-gaap_NonoperatingIncomeExpense	(38,335)us-gaap_NonoperatingIncomeExpense
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(4,972)	(22,211)
Income tax benefit (expense)	280us-gaap_IncomeTaxExpenseBenefit	6,490us-gaap_IncomeTaxExpenseBenefit
Earnings from unconsolidated affiliates, net of tax	12	95
Net income (loss)	(4,680)us-gaap_NetIncomeLoss	(15,626)us-gaap_NetIncomeLoss
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247
Income tax on postretirement medical plan and pension adjustments	116	89
Other comprehensive income (loss)	197	158
Total comprehensive income (loss)	(4,483)us-gaap_ComprehensiveIncomeNetOfTax	(15,468)us-gaap_ComprehensiveIncomeNetOfTax
Eliminations
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	(2,120)	(1,900)
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	0	0
Depreciation and depletion	0	0
Amortization	0	0
Accretion	0	0
Derivative financial instruments	0	0
Selling, general and administrative expenses	(2,120)	(1,900)
Other operating costs	0	0
Total costs and expenses	(2,120)	(1,900)
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 from unconsolidated affiliates, net of tax	0	0
Earnings (losses) from consolidated affiliates, net of tax	(2,047)	4,907
Net income (loss)	(2,047)	4,907
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	(626)	(494)
Income tax on postretirement medical plan and pension adjustments	(232)	(178)
Other comprehensive income (loss)	(394)	(316)
Total comprehensive income (loss)	(2,441)	4,591
Parent Guarantor (CPE Inc.)
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	2,120	1,900
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	0	0
Depreciation and depletion	0	0
Amortization	0	0
Accretion	0	0
Derivative financial instruments	0	0
Selling, general and administrative expenses	2,120	1,900
Other operating costs	0	0
Total costs and expenses	2,120	1,900
Operating income (loss)	0	0
Other income (expense)
Interest income	0	0
Interest expense	0	0
Other, net	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 from unconsolidated affiliates, net of tax	0	0
Earnings (losses) from consolidated affiliates, net of tax	(4,680)	(15,626)
Net income (loss)	(4,680)	(15,626)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247
Income tax on postretirement medical plan and pension adjustments	116	89
Other comprehensive income (loss)	197	158
Total comprehensive income (loss)	(4,483)	(15,468)
Issuers
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	0	0
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	8	169
Depreciation and depletion	647	757
Amortization	0	0
Accretion	0	0
Derivative financial instruments	0	0
Selling, general and administrative expenses	288	198
Other operating costs	0	45
Total costs and expenses	943	1,169
Operating income (loss)	(943)	(1,169)
Other income (expense)
Interest income	49	124
Interest expense	(11,102)	(35,116)
Other, net	(87)	(664)
Total other income (expense)	(11,140)	(35,656)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(12,083)	(36,825)
Income tax benefit (expense)	679	9,129
Earnings from unconsolidated affiliates, net of tax	(1)	(16)
Earnings (losses) from consolidated affiliates, net of tax	6,725	12,086
Net income (loss)	(4,680)	(15,626)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247
Income tax on postretirement medical plan and pension adjustments	116	89
Other comprehensive income (loss)	197	158
Total comprehensive income (loss)	(4,483)	(15,468)
Guarantor Subsidiaries
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	317,553	315,101
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	264,309	266,596
Depreciation and depletion	23,889	26,389
Amortization	928	0
Accretion	3,541	3,114
Derivative financial instruments	4,785	(12,734)
Selling, general and administrative expenses	10,961	12,243
Other operating costs	213	193
Total costs and expenses	308,626	295,801
Operating income (loss)	8,927	19,300
Other income (expense)
Interest income	0	0
Interest expense	(1,481)	(2,779)
Other, net	(337)	113
Total other income (expense)	(1,818)	(2,666)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	7,109	16,634
Income tax benefit (expense)	(399)	(3,291)
Earnings from unconsolidated affiliates, net of tax	13	110
Earnings (losses) from consolidated affiliates, net of tax	2	(1,367)
Net income (loss)	6,725	12,086
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	313	247
Income tax on postretirement medical plan and pension adjustments	116	89
Other comprehensive income (loss)	197	158
Total comprehensive income (loss)	6,922	12,244
Non-Guarantor Subsidiaries
Supplemental Condensed Consolidating Statement of Operations and Comprehensive Income
Revenue	0	3,965
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	0	5,174
Depreciation and depletion	0	(218)
Amortization	0	0
Accretion	0	1,016
Derivative financial instruments	0	0
Selling, general and administrative expenses	0	0
Other operating costs	0	0
Total costs and expenses	0	5,972
Operating income (loss)	0	(2,007)
Other income (expense)
Interest income	0	0
Interest expense	(85)	(99)
Other, net	87	87
Total other income (expense)	2	(12)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	2	(2,019)
Income tax benefit (expense)	0	652
Earnings from unconsolidated affiliates, net of tax	0	0
Earnings (losses) from consolidated affiliates, net of tax	0	0
Net income (loss)	2	(1,367)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service cost	0	0
Income tax on postretirement medical plan and pension adjustments	0	0
Other comprehensive income (loss)	0	0
Total comprehensive income (loss)	$ 2	$ (1,367)

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