Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income tax disclosures of the Company
Percentage share of CPE resources pre-tax income on which income tax expenses recognized, before the Secondary Offering	51.00%
Percentage of pre-tax income on which income tax expenses recognized, after the Secondary Offering	100.00%
Deferred:
Total income tax provision	$ 62,614,000	$ 11,449,000	$ 31,982,000
CPE Inc
Current:
Federal	18,064,000	20,973,000	3,478,000
State	2,339,000	1,700,000
Total current	20,403,000	22,673,000	3,478,000
Deferred:
Federal	40,351,000	(11,261,000)	27,961,000
State	1,859,000	37,000	543,000
Total deferred	42,210,000	(11,224,000)	28,504,000
Total income tax provision	62,614,000	11,449,000	31,982,000
Deferred income tax assets:
Property, plant and equipment	30,770,000	62,379,000
Accrued expense and liabilities	32,484,000	32,324,000
Pension and other postretirement benefits	16,761,000	13,126,000
Investment in joint venture partnerships	8,450,000	7,349,000
Accrued reclamation and mine closure costs	41,854,000	38,091,000
Contract rights	31,838,000	30,679,000
Tax agreement liability	41,954,000	61,429,000
AMT credit	26,816,000	24,061,000
Other	5,263,000	6,433,000
Total deferred income tax assets	236,190,000	275,870,000
Less valuation allowance	(17,231,000)	(33,903,000)
Net deferred income tax asset	218,960,000	241,967,000
Deferred income tax liabilities:
Inventories	(2,919,000)	(3,332,000)
Mineral rights	(78,936,000)	(67,938,000)
Mark-to-market gain	(4,861,000)
Other	(3,057,000)	(341,000)
Total deferred income tax liabilities	(89,773,000)	(71,611,000)
Net deferred income tax assets (liabilities)	129,187,000	170,356,000
Operating loss carryforwards that expire	6,100,000
Net deferred income tax assets related to continuing operations as classified in the consolidated balance sheets
Net current deferred income tax assets	28,112,000	37,528,000
Net noncurrent deferred income tax assets	101,075,000	132,828,000
Net deferred income tax assets (liabilities)	129,187,000	170,356,000
CPE Resources
Current:
Federal	15,467,000	671,000
State	2,345,000	534,000
Total current	17,812,000	1,205,000
Deferred:
Federal	30,946,000	17,340,000	(755,000)
State	3,278,000	1,438,000	(25,000)
Total deferred	34,224,000	18,778,000	(780,000)
Total income tax provision	52,036,000	19,983,000	(780,000)
Deferred income tax assets:
Property, plant and equipment	30,770,000	62,379,000
Accrued expense and liabilities	32,484,000	32,324,000
Pension and other postretirement benefits	16,761,000	13,126,000
Investment in joint venture partnerships	8,450,000	7,349,000
Accrued reclamation and mine closure costs	41,854,000	38,091,000
Contract rights	31,838,000	30,679,000
AMT credit	26,816,000	24,061,000
Other	5,261,000	6,434,000
Total deferred income tax assets	194,235,000	214,443,000
Less valuation allowance	(17,231,000)	(33,903,000)
Net deferred income tax asset	177,004,000	180,540,000
Deferred income tax liabilities:
Inventories	(2,919,000)	(3,332,000)
Mineral rights	(78,936,000)	(67,938,000)
Mark-to-market gain	(4,861,000)
Other	(3,057,000)	(342,000)
Total deferred income tax liabilities	(89,773,000)	(71,612,000)
Net deferred income tax assets (liabilities)	87,232,000	108,928,000
Operating loss carryforwards that expire	6,100,000
Net deferred income tax assets related to continuing operations as classified in the consolidated balance sheets
Net current deferred income tax assets	21,096,000	30,648,000
Net noncurrent deferred income tax assets	66,136,000	78,280,000
Net deferred income tax assets (liabilities)	$ 87,232,000	$ 108,928,000