Supplemental Guarantor/Non-Guarantor Financial Information (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 120,942	$ 83,708	$ 90,301	$ 89,313
Accounts receivable	53,702	49,311
Due from related parties	1,169	0
Inventories, net	69,780	68,683
Derivative financial instruments	0	752
Income tax receivable	1,145	1,601
Other prepaid and deferred charges	31,978	20,361
Other assets	1,762	741
Total current assets	280,478	225,157
Noncurrent assets
Property, plant and equipment, net	1,394,056	1,432,361
Goodwill	2,280	2,280
Deferred income taxes	0	0
Other assets	37,307	54,978
Total assets	1,714,121	1,714,776
Current liabilities
Accounts payable	29,288	27,678
Royalties and production taxes	59,251	63,018
Accrued expenses	39,892	35,857
Due to related parties	0	71
Other liabilities	2,555	2,567
Total current liabilities	130,986	129,191
Noncurrent liabilities
Senior notes	410,374	475,009
Asset retirement obligations, net of current portion	111,211	97,048	102,579
Accumulated postretirement medical benefit obligation, net of current portion	24,101	22,950
Royalties And Production Taxes Noncurrent	29,650	21,557
Other liabilities	16,839	17,360
Total liabilities	723,161	763,115
Commitments and Contingencies (Note 13)
Total equity	990,960	951,661
Total liabilities and equity	1,714,121	1,714,776
Eliminations
Current assets
Due from related parties	(36,296)	(116,486)
Total current assets	(36,296)	(116,486)
Noncurrent assets
Other assets	(2,279,123)	(2,316,517)
Total assets	(2,315,419)	(2,433,003)
Current liabilities
Due to related parties	(36,296)	(116,486)
Total current liabilities	(36,296)
Noncurrent liabilities
Total liabilities	(36,296)	(116,486)
Total equity	(2,279,122)	(2,316,517)
Total liabilities and equity	(2,315,419)	(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	6,510	0
Inventories, net	0	0
Derivative financial instruments	0	0
Income tax receivable	1,145	1,601
Other prepaid and deferred charges	485	278
Other assets	0	0
Total current assets	8,140	1,879
Noncurrent assets
Property, plant and equipment, net	0	0
Goodwill	0	0
Deferred income taxes	0	0
Other assets	992,565	1,019,289
Total assets	1,000,705	1,021,168
Current liabilities
Accounts payable	20	4
Royalties and production taxes	0	0
Accrued expenses	2,552	3,646
Due to related parties	0	59,638
Other liabilities	0	0
Total current liabilities	2,572	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	7,172	6,219
Total liabilities	9,744	69,507
Total equity	990,960	951,661
Total liabilities and equity	1,000,705	1,021,168
Issuers | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	120,812	83,673	89,931	87,054
Accounts receivable	0	0
Due from related parties	5,076	116,486
Inventories, net	0	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	125,888	200,229
Noncurrent assets
Property, plant and equipment, net	3,463	3,307
Goodwill	0	0
Deferred income taxes	0	0
Other assets	1,284,522	1,299,413
Total assets	1,413,873	1,502,949
Current liabilities
Accounts payable	25	1,748
Royalties and production taxes	0	0
Accrued expenses	10,887	6,879
Due to related parties	71	71
Other liabilities	0	0
Total current liabilities	10,983	8,698
Noncurrent liabilities
Senior notes	410,374	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	421,357	483,707
Total equity	992,516	1,019,241
Total liabilities and equity	1,413,873	1,502,948
Guarantor Subsidiaries | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	130	35	370	2,259
Accounts receivable	9,798	13,261
Due from related parties	25,879	0
Inventories, net	69,780	68,613
Derivative financial instruments	0	752
Income tax receivable	0	0
Other prepaid and deferred charges	31,493	20,083
Other assets	1,762	741
Total current assets	138,842	103,485
Noncurrent assets
Property, plant and equipment, net	1,390,593	1,429,054
Goodwill	2,280	2,280
Deferred income taxes	0	0
Other assets	38,960	52,793
Total assets	1,570,675	1,587,612
Current liabilities
Accounts payable	29,194	25,896
Royalties and production taxes	59,251	63,018
Accrued expenses	26,453	25,332
Due to related parties	0	27,250
Other liabilities	2,555	2,567
Total current liabilities	117,453	144,063
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	111,211	97,048
Accumulated postretirement medical benefit obligation, net of current portion	24,101	22,950
Royalties And Production Taxes Noncurrent	29,650	21,557
Other liabilities	9,667	11,141
Total liabilities	292,082	296,759
Total equity	1,278,593	1,290,854
Total liabilities and equity	1,570,675	1,587,613
Non-Guarantor Subsidiaries | Reportable Legal Entities [Member]
Current assets
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts receivable	43,904	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	43,904	36,050
Noncurrent assets
Property, plant and equipment, net	0	0
Goodwill	0	0
Deferred income taxes	0	0
Other assets	383	0
Total assets	44,287	36,050
Current liabilities
Accounts payable	49	30
Royalties and production taxes	0	0
Accrued expenses	0	0
Due to related parties	36,225	29,598
Other liabilities	0	0
Total current liabilities	36,274	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	36,274	29,628
Total equity	8,013	6,422
Total liabilities and equity	$ 44,287	$ 36,050