Supplemental Guarantor Financial Information (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
ASSETS
Current assets	$ 1,265,139	$ 1,220,689
Current assets associated with discontinued operations	537	442
Total current assets	1,265,676us-gaap_AssetsCurrent	1,221,131us-gaap_AssetsCurrent
Property, plant and equipment, net	3,326,892us-gaap_PropertyPlantAndEquipmentNet	2,820,272us-gaap_PropertyPlantAndEquipmentNet	2,838,719us-gaap_PropertyPlantAndEquipmentNet
Goodwill	3,738us-gaap_Goodwill
Intangible and other assets, net	243,372exh_IntangibleAndOtherAssetsNet	164,836exh_IntangibleAndOtherAssetsNet
Long-term assets associated with discontinued operations	17,469	20,918
Total long-term assets	3,591,471us-gaap_AssetsNoncurrent	3,006,026us-gaap_AssetsNoncurrent
Total assets	4,857,147us-gaap_Assets	4,227,157us-gaap_Assets
LIABILITIES AND EQUITY
Current liabilities	608,652	637,473
Current liabilities associated with discontinued operations	2,066	3,233
Total current liabilities	610,718us-gaap_LiabilitiesCurrent	640,706us-gaap_LiabilitiesCurrent
Long-term debt	2,026,902	1,502,155
Other long-term liabilities	266,165	270,421
Long-term liabilities associated with discontinued operations	317	447
Total liabilities	2,904,102us-gaap_Liabilities	2,413,729us-gaap_Liabilities
Total equity	1,953,045	1,813,428	1,702,259	1,680,042
Total liabilities and equity	4,857,147	4,227,157
Eliminations
ASSETS
Investments in affiliates	(3,531,186)	(3,531,346)
Intangible and other assets, net		(11,230)
Intercompany receivables	(1,269,193)	(1,184,878)
Total long-term assets	(4,800,379)	(4,727,454)
Total assets	(4,800,379)	(4,727,454)
LIABILITIES AND EQUITY
Intercompany payables	(1,269,193)	(1,184,878)
Other long-term liabilities		(11,230)
Total liabilities	(1,269,193)	(1,196,108)
Total equity	(3,531,186)	(3,531,346)
Total liabilities and equity	(4,800,379)	(4,727,454)
Parent \| Reportable Legal Entities
ASSETS
Current assets	4,846	141
Total current assets	4,846	141
Investments in affiliates	1,786,572	1,851,131
Intangible and other assets, net	5,966	20,060
Intercompany receivables	727,896	536,382
Total long-term assets	2,520,434	2,407,573
Total assets	2,525,280	2,407,714
LIABILITIES AND EQUITY
Current liabilities	2,520	2,963
Total current liabilities	2,520	2,963
Long-term debt	725,500	742,661
Total liabilities	728,020	745,624
Total equity	1,797,260	1,662,090
Total liabilities and equity	2,525,280	2,407,714
Guarantor Subsidiaries \| Reportable Legal Entities
ASSETS
Current assets	649,719	710,801
Total current assets	649,719	710,801
Property, plant and equipment, net	1,124,786	1,143,111
Investments in affiliates	1,744,614	1,680,215
Intangible and other assets, net	33,292	29,555
Intercompany receivables	12,023	14,818
Total long-term assets	2,914,715	2,867,699
Total assets	3,564,434	3,578,500
LIABILITIES AND EQUITY
Current liabilities	353,851	369,829
Total current liabilities	353,851	369,829
Long-term debt	1,107	1,539
Intercompany payables	1,257,170	1,170,060
Other long-term liabilities	165,734	185,941
Total liabilities	1,777,862	1,727,369
Total equity	1,786,572	1,851,131
Total liabilities and equity	3,564,434	3,578,500
Other Subsidiaries \| Reportable Legal Entities
ASSETS
Current assets	610,574	509,747
Current assets associated with discontinued operations	537	442
Total current assets	611,111	510,189
Property, plant and equipment, net	2,202,106	1,677,161
Goodwill	3,738
Intangible and other assets, net	204,114	126,451
Intercompany receivables	529,274	633,678
Long-term assets associated with discontinued operations	17,469	20,918
Total long-term assets	2,956,701	2,458,208
Total assets	3,567,812	2,968,397
LIABILITIES AND EQUITY
Current liabilities	252,281	264,681
Current liabilities associated with discontinued operations	2,066	3,233
Total current liabilities	254,347	267,914
Long-term debt	1,300,295	757,955
Intercompany payables	12,023	14,818
Other long-term liabilities	100,431	95,710
Long-term liabilities associated with discontinued operations	317	447
Total liabilities	1,667,413	1,136,844
Total equity	1,900,399	1,831,553
Total liabilities and equity	$ 3,567,812	$ 2,968,397

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