Accumulated Other Comprehensive (Loss) (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Line items in income statement impacted by reclassifications out of accumulated other comprehensive income
Natural gas revenues	$ 1,590,625us-gaap_NaturalGasProductionRevenue	$ 1,405,262us-gaap_NaturalGasProductionRevenue	$ 934,134us-gaap_NaturalGasProductionRevenue
Crude oil and condensate revenues	313,889us-gaap_OilAndCondensateRevenue	291,418us-gaap_OilAndCondensateRevenue	227,933us-gaap_OilAndCondensateRevenue
Income before income taxes	32,401	485,538	237,840
Tax expense	72,067us-gaap_IncomeTaxExpenseBenefit	(205,765)us-gaap_IncomeTaxExpenseBenefit	(106,110)us-gaap_IncomeTaxExpenseBenefit
Net income	104,468	279,773	131,730
Amount Reclassified from Accumulated Other Comprehensive Income
Line items in income statement impacted by reclassifications out of accumulated other comprehensive income
Income before income taxes	(144,177)	56,361	222,199
Tax expense	57,467	(22,199)	(86,459)
Net income	(86,710)	34,162	135,740
Net Gains (Losses) on Cash Flow Hedges \| Amount Reclassified from Accumulated Other Comprehensive Income \| Commodity contracts
Line items in income statement impacted by reclassifications out of accumulated other comprehensive income
Natural gas revenues	(143,577)	52,733	225,108
Crude oil and condensate revenues	(626)	4,269	11,218
Amortization of net (gain) loss \| Amount Reclassified from Accumulated Other Comprehensive Income
Line items in income statement impacted by reclassifications out of accumulated other comprehensive income
Amortization of prior service cost	0	0	(221)
Amortization of net (gain) loss	$ 26	$ (641)	$ (13,906)

This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Revenue from natural gas production during the reporting period. Natural gas consists largely of the hydrocarbon methane, and is found in underground formations either by itself or with crude oil.

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