Supplemental Guarantor/Non-Guarantor Financial Information (Details 2) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 80,536	$ 83,708	$ 64,127	$ 89,313
Accounts receivable	49,042	49,311
Due from related parties	478	0
Inventories, net	70,022	68,683
Derivative financial instruments	0	752
Income tax receivable	1,516	1,601
Other prepaid and deferred charges	33,438	20,361
Other assets	802	741
Total current assets	235,834	225,157
Noncurrent assets
Property, plant and equipment, net	1,408,080	1,432,361
Goodwill	2,280	2,280
Deferred income taxes	0	0
Other assets	43,732	54,978
Total assets	1,689,926	1,714,776
Current liabilities
Accounts payable	32,925	27,678
Royalties and production taxes	57,335	63,018
Accrued expenses	31,375	35,857
Due to related parties	0	71
Other liabilities	2,552	2,567
Total current liabilities	124,187	129,191
Noncurrent liabilities
Senior notes	409,368	475,009
Asset retirement obligations, net of current portion	107,891	97,048	100,832
Accumulated postretirement medical benefit obligation, net of current portion	23,701	22,950
Royalties And Production Taxes Noncurrent	20,995	21,557
Other liabilities	15,276	17,360
Total liabilities	701,418	763,115
Commitments and Contingencies (Note 13)
Total equity	988,508	951,661
Total liabilities and equity	1,689,926	1,714,776
Eliminations
Current assets
Due from related parties	(63,679)	(116,486)
Total current assets	(63,679)	(116,486)
Noncurrent assets
Other assets	(2,258,028)	(2,316,517)
Total assets	(2,321,707)	(2,433,003)
Current liabilities
Due to related parties	(63,679)	(116,486)
Total current liabilities	(63,679)
Noncurrent liabilities
Total liabilities	(63,679)	(116,486)
Total equity	(2,258,028)	(2,316,517)
Total liabilities and equity	(2,321,707)	(2,433,003)
Parent Guarantor (CPE Inc.) | Reportable Legal Entities Member
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable	0	0
Due from related parties	0	0
Inventories, net	0	0
Derivative financial instruments	0	0
Income tax receivable	1,516	1,601
Other prepaid and deferred charges	687	278
Other assets	(1)	0
Total current assets	2,202	1,879
Noncurrent assets
Property, plant and equipment, net	0	0
Goodwill	0	0
Deferred income taxes	0	0
Other assets	994,161	1,019,289
Total assets	996,363	1,021,168
Current liabilities
Accounts payable	0	4
Royalties and production taxes	0	0
Accrued expenses	1,504	3,646
Due to related parties	1,062	59,638
Other liabilities	0	0
Total current liabilities	2,566	63,288
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Accumulated postretirement medical benefit obligation, net of current portion	0	0
Royalties And Production Taxes Noncurrent	0	0
Other liabilities	5,289	6,219
Total liabilities	7,855	69,507
Total equity	988,508	951,661
Total liabilities and equity	996,363	1,021,168
Issuers | Reportable Legal Entities Member
Current assets
Cash and cash equivalents	80,395	83,673	63,830	87,054
Accounts receivable	0	0
Due from related parties	63,608	116,486
Inventories, net	79	70
Derivative financial instruments	0	0
Income tax receivable	0	0
Other prepaid and deferred charges	0	0
Other assets	0	0
Total current assets	144,082	200,229
Noncurrent assets
Property, plant and equipment, net	3,339	3,307
Goodwill	0	0
Deferred income taxes	0	0
Other assets	1,262,565	1,299,413
Total assets	1,409,986	1,502,949
Current liabilities
Accounts payable	199	1,748
Royalties and production taxes	0	0
Accrued expenses	6,236	6,879
Due to related parties	71	71
Other liabilities	0	0
Total current liabilities	6,506	8,698
Noncurrent liabilities
Senior notes	409,368	475,009
Asset retirement obligations, net of current portion	0	0
Accumulated postretirement medical benefit obligation, net of current portion	0	0
Royalties And Production Taxes Noncurrent	0	0
Other liabilities	0	0
Total liabilities	415,874	483,707
Total equity	994,112	1,019,241
Total liabilities and equity	1,409,986	1,502,948
Guarantor Subsidiaries | Reportable Legal Entities Member
Current assets
Cash and cash equivalents	141	35	297	2,259
Accounts receivable	15,707	13,261
Due from related parties	549	0
Inventories, net	69,943	68,613
Derivative financial instruments	0	752
Income tax receivable	0	0
Other prepaid and deferred charges	32,751	20,083
Other assets	803	741
Total current assets	119,894	103,485
Noncurrent assets
Property, plant and equipment, net	1,404,741	1,429,054
Goodwill	2,280	2,280
Deferred income taxes	0	0
Other assets	44,610	52,793
Total assets	1,571,525	1,587,612
Current liabilities
Accounts payable	32,675	25,896
Royalties and production taxes	57,335	63,018
Accrued expenses	23,635	25,332
Due to related parties	36,991	27,250
Other liabilities	2,552	2,567
Total current liabilities	153,188	144,063
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	107,891	97,048
Accumulated postretirement medical benefit obligation, net of current portion	23,701	22,950
Royalties And Production Taxes Noncurrent	20,995	21,557
Other liabilities	9,987	11,141
Total liabilities	315,762	296,759
Total equity	1,255,763	1,290,854
Total liabilities and equity	1,571,525	1,587,613
Non-Guarantor Subsidiaries | Reportable Legal Entities Member
Current assets
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts receivable	33,335	36,050
Due from related parties	0	0
Inventories, net	0	0
Derivative financial instruments	0	0
Income tax receivable	0	0
Other prepaid and deferred charges	0	0
Other assets	0	0
Total current assets	33,335	36,050
Noncurrent assets
Property, plant and equipment, net	0	0
Goodwill	0	0
Deferred income taxes	0	0
Other assets	424	0
Total assets	33,759	36,050
Current liabilities
Accounts payable	51	30
Royalties and production taxes	0	0
Accrued expenses	0	0
Due to related parties	25,555	29,598
Other liabilities	0	0
Total current liabilities	25,606	29,628
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Accumulated postretirement medical benefit obligation, net of current portion	0	0
Royalties And Production Taxes Noncurrent	0	0
Other liabilities	0	0
Total liabilities	25,606	29,628
Total equity	8,153	6,422
Total liabilities and equity	$ 33,759	$ 36,050