Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy
Balance at beginning of period	$ 41,159	$ 195,127	$ 14,746
Total gains or (losses) (realized or unrealized):
Included in earnings	52,733	224,614	85,375
Included in other comprehensive income	(37,249)	(157,478)	181,346
Settlements	(52,733)	(221,489)	(86,340)
Transfers in and/or out of level 3		385
Balance at end of period	3,910	41,159	195,127
Natural Gas Revenues
Derivative disclosures
Unrealized loss included in natural gas revenues		$ (494)	$ (965)

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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Amount of gain (loss) recognized in the income statement of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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