Impairments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 132,224	$ 0	$ 132,224	$ 28,481
Other Asset Impairment Charges	0	700	0	835
Asset Impairment Charges	132,224	700	132,224	29,316
Granite Wash [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use	121,800
Marcellus Shale [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use	9,500
Selma Chalk [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use	900
Estimate of Fair Value, Fair Value Disclosure [Member] | Long-lived Assets Held for Use [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	93,945		93,945
Estimate of Fair Value, Fair Value Disclosure [Member] | Long-lived Assets Sold During the Year [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		96,099		96,099
Level 1 | Long-lived Assets Held for Use [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0		0
Level 1 | Long-lived Assets Sold During the Year [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0		0
Level 2 | Long-lived Assets Held for Use [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0		0
Level 2 | Long-lived Assets Sold During the Year [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0		0
Level 3 | Long-lived Assets Held for Use [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	93,945		93,945
Level 3 | Long-lived Assets Sold During the Year [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		$ 96,099		$ 96,099