Supplemental Guarantor/Non-Guarantor Financial Information (Details 3) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Current assets
Cash and cash equivalents	$ 95,538	$ 168,745	$ 225,484	$ 231,633
Accounts receivable	52,214	86,838
Due from related parties	2,473	227
Inventories, net	78,714	79,802
Deferred income taxes	21,670	21,670
Derivative financial instruments	13,086	17,111
Other assets	20,622	9,840
Total current assets	284,317	384,233
Noncurrent assets
Property, plant and equipment, net	1,543,858	1,589,138
Port access contract rights, net	51,925	53,780
Goodwill	2,280	35,634
Deferred income taxes	63,254	56,468
Other assets	47,889	40,665
Total assets	1,993,523	2,159,918
Current liabilities
Accounts payable	47,620	52,035
Royalties and production taxes	110,830	126,212
Accrued expenses	38,045	52,213
Current portion of federal coal lease obligations	0	63,970
Other liabilities	1,632	1,632
Total current liabilities	198,127	296,062
Noncurrent liabilities
Senior notes	498,603	498,480
Asset retirement obligations, net of current portion	200,175	216,241	250,458
Accumulated postretirement medical benefit obligation, net of current portion	53,691	50,276
Other liabilities	10,375	11,025
Total liabilities	$ 960,971	$ 1,072,084
Commitments and Contingencies (Note 13)
Total equity	$ 1,032,552	$ 1,087,834
Total liabilities and equity	1,993,523	2,159,918
Eliminations
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable	0	0
Due from related parties	(528,454)	(601,313)
Inventories, net	0	0
Deferred income taxes	(45)	(46)
Derivative financial instruments	0	0
Other assets	0	0
Total current assets	(528,499)	(601,359)
Noncurrent assets
Property, plant and equipment, net	0	0
Port access contract rights, net	0	0
Goodwill	0	0
Deferred income taxes	(413)	0
Other assets	(2,919,662)	(3,013,443)
Total assets	(3,448,574)	(3,614,802)
Current liabilities
Accounts payable	0	0
Royalties and production taxes	0	0
Accrued expenses	0	0
Due to related parties	(528,454)	(601,313)
Current portion of federal coal lease obligations	0	0
Other liabilities	(45)	(46)
Total current liabilities	(528,499)	(601,359)
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Deferred income taxes	(413)
Accumulated postretirement medical benefit obligation, net of current portion	0	0
Other liabilities	0	0
Total liabilities	(528,912)	(601,359)
Total equity	(2,919,662)	(3,013,443)
Total liabilities and equity	(3,448,574)	(3,614,802)
Parent Guarantor (CPE Inc.)
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable	0	0
Due from related parties	0	0
Inventories, net	0	0
Deferred income taxes	0	0
Derivative financial instruments	0	0
Other assets	4,618	292
Total current assets	4,618	292
Noncurrent assets
Property, plant and equipment, net	0	0
Port access contract rights, net	0	0
Goodwill	0	0
Deferred income taxes	0	0
Other assets	1,050,926	1,108,101
Total assets	1,055,544	1,108,393
Current liabilities
Accounts payable	3	0
Royalties and production taxes	0	0
Accrued expenses	1,692	6,194
Due to related parties	20,884	14,365
Current portion of federal coal lease obligations	0	0
Other liabilities	0	0
Total current liabilities	22,579	20,559
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Deferred income taxes	413
Accumulated postretirement medical benefit obligation, net of current portion	0	0
Other liabilities	0	0
Total liabilities	$ 22,992	$ 20,559
Commitments and Contingencies (Note 13)
Total equity	$ 1,032,552	$ 1,087,834
Total liabilities and equity	1,055,544	1,108,393
Issuers
Current assets
Cash and cash equivalents	94,100	167,532	222,263	226,993
Accounts receivable	0	0
Due from related parties	0	0
Inventories, net	7,104	6,700
Deferred income taxes	0	0
Derivative financial instruments	0	0
Other assets	27	6
Total current assets	101,231	174,238
Noncurrent assets
Property, plant and equipment, net	5,480	6,167
Port access contract rights, net	0	0
Goodwill	0	0
Deferred income taxes	37,482	33,926
Other assets	1,881,030	1,919,464
Total assets	2,025,223	2,133,795
Current liabilities
Accounts payable	2,156	1,287
Royalties and production taxes	0	0
Accrued expenses	4,781	5,318
Due to related parties	468,760	520,611
Current portion of federal coal lease obligations	0	0
Other liabilities	45	46
Total current liabilities	475,742	527,262
Noncurrent liabilities
Senior notes	498,603	498,480
Asset retirement obligations, net of current portion	0	0
Deferred income taxes	0
Accumulated postretirement medical benefit obligation, net of current portion	0	0
Other liabilities	0	0
Total liabilities	$ 974,345	$ 1,025,742
Commitments and Contingencies (Note 13)
Total equity	$ 1,050,878	$ 1,108,053
Total liabilities and equity	2,025,223	2,133,795
Guarantor Subsidiaries
Current assets
Cash and cash equivalents	1,438	1,213	1,881	496
Accounts receivable	7,152	14,161
Due from related parties	530,927	601,540
Inventories, net	71,610	73,103
Deferred income taxes	21,715	21,716
Derivative financial instruments	13,086	17,111
Other assets	15,977	9,541
Total current assets	661,905	738,385
Noncurrent assets
Property, plant and equipment, net	1,538,378	1,582,971
Port access contract rights, net	51,925	53,780
Goodwill	2,280	35,634
Deferred income taxes	26,179	22,542
Other assets	35,595	26,543
Total assets	2,316,262	2,459,855
Current liabilities
Accounts payable	45,440	50,679
Royalties and production taxes	110,830	126,212
Accrued expenses	31,572	40,701
Due to related parties	0	0
Current portion of federal coal lease obligations	0	63,970
Other liabilities	1,632	1,632
Total current liabilities	189,474	283,194
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	200,175	216,241
Deferred income taxes	0
Accumulated postretirement medical benefit obligation, net of current portion	53,691	50,276
Other liabilities	10,375	11,025
Total liabilities	$ 453,715	$ 560,736
Commitments and Contingencies (Note 13)
Total equity	$ 1,862,547	$ 1,899,119
Total liabilities and equity	2,316,262	2,459,855
Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	0	0	$ 1,340	$ 4,144
Accounts receivable	45,062	72,676
Due from related parties	0	0
Inventories, net	0	0
Deferred income taxes	0	0
Derivative financial instruments	0	0
Other assets	0	0
Total current assets	45,062	72,676
Noncurrent assets
Property, plant and equipment, net	0	0
Port access contract rights, net	0	0
Goodwill	0	0
Deferred income taxes	6	0
Other assets	0	0
Total assets	45,068	72,676
Current liabilities
Accounts payable	20	68
Royalties and production taxes	0	0
Accrued expenses	0	0
Due to related parties	38,810	66,337
Current portion of federal coal lease obligations	0	0
Other liabilities	0	0
Total current liabilities	38,830	66,405
Noncurrent liabilities
Senior notes	0	0
Asset retirement obligations, net of current portion	0	0
Deferred income taxes	0
Accumulated postretirement medical benefit obligation, net of current portion	0	0
Other liabilities	0	0
Total liabilities	$ 38,830	$ 66,405
Commitments and Contingencies (Note 13)
Total equity	$ 6,238	$ 6,271
Total liabilities and equity	$ 45,068	$ 72,676