Supplemental Guarantor/Non-Guarantor Financial Information (Details 2) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	$ 107,948	$ 83,708	$ 89,313	$ 168,745
Accounts receivable	50,075	49,311
Due from related parties	122	0
Inventories, net	72,904	68,683
Derivative financial instruments (Note 6)	0	752
Income tax receivable	256	1,601
Other prepaid and deferred charges	36,964	20,361
Other assets	1,765	741
Total current assets	270,034	225,157
Noncurrent assets
Property, plant and equipment, net (Note 7)	1,365,755	1,432,361
Goodwill	2,280	2,280	2,300
Income tax receivable	29,454	0
Other assets	31,178	54,978
Total assets	1,698,701	1,714,776	1,802,160
Current liabilities
Accounts payable	29,832	27,678
Royalties and production taxes	54,327	63,018
Accrued expenses	32,818	35,857
Due to related parties	0	71
Other liabilities	2,435	2,567
Total current liabilities	119,412	129,191
Noncurrent liabilities
Senior notes	405,266	475,009
Asset retirement obligations, net of current portion	99,297	97,048
Accumulated postretirement benefit obligation, net of current portion	24,958	22,950	60,845
Royalties And Production Taxes Noncurrent	21,896	21,557
Other liabilities	20,063	17,360
Total liabilities	690,892	763,115
Commitments and Contingencies (Note 17)
Total equity	1,007,809	951,661	887,881	1,087,834
Total liabilities and equity	1,698,701	1,714,776
Eliminations
Current assets
Cash and cash equivalents	0	0
Accounts receivable	0	0
Due from related parties	(69,272)	(116,486)
Inventories, net	0	0
Derivative financial instruments (Note 6)	0	0
Income tax receivable	0	0
Other prepaid and deferred charges	0	0
Other assets	0	0
Total current assets	(69,272)	(116,486)
Noncurrent assets
Property, plant and equipment, net (Note 7)	0	0
Goodwill	0	0
Income tax receivable	0	0
Other assets	(2,328,424)	(2,316,517)
Total assets	(2,397,696)	(2,433,003)
Current liabilities
Accounts payable	0	0
Royalties and production taxes	0	0
Accrued expenses	0	0
Due to related parties	(69,272)	(116,486)
Other liabilities	0	0
Total current liabilities	(69,272)	(116,486)
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Accumulated postretirement benefit obligation, net of current portion	0	0
Royalties And Production Taxes Noncurrent	0	0
Other liabilities	0	0
Total liabilities	(69,272)	(116,486)
Total equity	(2,328,424)	(2,316,517)
Total liabilities and equity	(2,397,696)	(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 (Note 6)	0	0
Income tax receivable	256	1,601
Other prepaid and deferred charges	283	278
Other assets	0	0
Total current assets	539	1,879
Noncurrent assets
Property, plant and equipment, net (Note 7)	0	0
Goodwill	0	0
Income tax receivable	29,454	0
Other assets	1,036,162	1,019,289
Total assets	1,066,155	1,021,168
Current liabilities
Accounts payable	1	4
Royalties and production taxes	0	0
Accrued expenses	3,160	3,646
Due to related parties	44,039	59,638
Other liabilities	0	0
Total current liabilities	47,200	63,288
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Accumulated postretirement benefit obligation, net of current portion	0	0
Royalties And Production Taxes Noncurrent	0	0
Other liabilities	11,146	6,219
Total liabilities	58,346	69,507
Total equity	1,007,809	951,661
Total liabilities and equity	1,066,155	1,021,168
Issuers | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	107,818	83,673	87,054	167,532
Accounts receivable	0	0
Due from related parties	46,350	116,486
Inventories, net	0	70
Derivative financial instruments (Note 6)	0	0
Income tax receivable	0	0
Other prepaid and deferred charges	0	0
Other assets	0	0
Total current assets	154,168	200,229
Noncurrent assets
Property, plant and equipment, net (Note 7)	3,480	3,307
Goodwill	0	0
Income tax receivable	0	0
Other assets	1,289,487	1,299,413
Total assets	1,447,135	1,502,949
Current liabilities
Accounts payable	24	1,748
Royalties and production taxes	0	0
Accrued expenses	5,659	6,879
Due to related parties	71	71
Other liabilities	0	0
Total current liabilities	5,754	8,698
Noncurrent liabilities
Senior notes	405,266	475,009
Asset retirement obligations, net of current portion	0	0
Accumulated postretirement benefit obligation, net of current portion	0	0
Royalties And Production Taxes Noncurrent	0	0
Other liabilities	0	0
Total liabilities	411,020	483,707
Total equity	1,036,115	1,019,241
Total liabilities and equity	1,447,135	1,502,948
Guarantor Subsidiaries | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	130	35	2,259	1,213
Accounts receivable	17,359	13,261
Due from related parties	23,044	0
Inventories, net	72,904	68,613
Derivative financial instruments (Note 6)	0	752
Income tax receivable	0	0
Other prepaid and deferred charges	36,681	20,083
Other assets	1,765	741
Total current assets	151,883	103,485
Noncurrent assets
Property, plant and equipment, net (Note 7)	1,362,275	1,429,054
Goodwill	2,280	2,280
Income tax receivable	0	0
Other assets	33,612	52,793
Total assets	1,550,050	1,587,612
Current liabilities
Accounts payable	29,748	25,896
Royalties and production taxes	54,327	63,018
Accrued expenses	23,999	25,332
Due to related parties	0	27,250
Other liabilities	2,435	2,567
Total current liabilities	110,509	144,063
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	99,297	97,048
Accumulated postretirement benefit obligation, net of current portion	24,958	22,950
Royalties And Production Taxes Noncurrent	21,896	21,557
Other liabilities	8,917	11,141
Total liabilities	265,577	296,759
Total equity	1,284,473	1,290,854
Total liabilities and equity	1,550,050	1,587,613
Non-Guarantor Subsidiaries | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts receivable	32,716	36,050
Due from related parties	0	0
Inventories, net	0	0
Derivative financial instruments (Note 6)	0	0
Income tax receivable	0	0
Other prepaid and deferred charges	0	0
Other assets	0	0
Total current assets	32,716	36,050
Noncurrent assets
Property, plant and equipment, net (Note 7)	0	0
Goodwill	0	0
Income tax receivable	0	0
Other assets	341	0
Total assets	33,057	36,050
Current liabilities
Accounts payable	59	30
Royalties and production taxes	0	0
Accrued expenses	0	0
Due to related parties	25,162	29,598
Other liabilities	0	0
Total current liabilities	25,221	29,628
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Accumulated postretirement benefit obligation, net of current portion	0	0
Royalties And Production Taxes Noncurrent	0	0
Other liabilities	0	0
Total liabilities	25,221	29,628
Total equity	7,836	6,422
Total liabilities and equity	$ 33,057	$ 36,050