Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets
Loss carryforwards - federal	$ 44,076	$ 20,247
Loss carryforwards - state	43,270	41,379
Tax credit carryover	34,837	34,837
Derivative contracts	0	21,341
Enhanced oil recovery credit carryforwards	42,817	14,974
Stock-based compensation	29,994	34,635
Other	32,656us-gaap_DeferredTaxAssetsOther	37,679us-gaap_DeferredTaxAssetsOther
Total deferred tax assets	227,650us-gaap_DeferredTaxAssetsNet	205,092us-gaap_DeferredTaxAssetsNet
Deferred tax liabilities
Property and equipment	(2,806,850)	(2,541,426)
Derivative contracts	(185,385)	0
Other	(11,984)us-gaap_DeferredTaxLiabilitiesOther	(10,206)us-gaap_DeferredTaxLiabilitiesOther
Total deferred tax liabilities	(3,004,219)us-gaap_DeferredIncomeTaxLiabilities	(2,551,632)us-gaap_DeferredIncomeTaxLiabilities
Total net deferred tax liability	$ (2,776,569)us-gaap_DeferredTaxAssetsLiabilitiesNet	$ (2,346,540)us-gaap_DeferredTaxAssetsLiabilitiesNet

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