Derivative Activities (Details 4) (USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Effects of cash flow hedges and other hedges on accumulated other comprehensive income (loss)
Change in unrealized deferred hedging gains, Tax Effect	$ (34,195)	$ (42,683)	$ (41,609)	$ (72,301)
Realized Gain (Loss) Reclassified from AOCI into Revenue, Income taxes	(10,034)	(6,014)	(33,476)	(13,445)
Change in Hedge Derivative Fair Value, effects of cash flow hedges on accumulated other comprehensive income (loss), total	56,993	66,968	74,530	115,293
Realized gain on hedge derivative contract settlements reclassified into earnings from other comprehensive income, net of taxes	16,724	9,602	55,791	21,726
Collars [Member]
Effects of cash flow hedges and other hedges on accumulated other comprehensive income (loss)
Change in Hedge Derivative Fair Value	75,449	109,663	97,873	187,593
Realized Gain (Loss) Reclassified from AOCI into Revenue	26,758	15,616	80,660	35,171
Swap [Member]
Effects of cash flow hedges and other hedges on accumulated other comprehensive income (loss)
Change in Hedge Derivative Fair Value	15,739	0	17,854	0
Realized Gain (Loss) Reclassified from AOCI into Revenue	0	0	0	0
Collars discontinued operations [Member]
Effects of cash flow hedges and other hedges on accumulated other comprehensive income (loss)
Change in Hedge Derivative Fair Value	0	(12)	412	1
Realized Gain (Loss) Reclassified from AOCI into Revenue	$ 0	$ 0	$ (8,607)	$ 0

Pre tax change in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges, net of reclassifications into earnings during the period. A cash flow hedge is a hedge of the exposure to variability in the cash flows of a recognized asset or liability or a forecasted transaction that is attributable to a particular risk. Includes an entity's share of an equity investee's increase or decrease in deferred hedging gains or losses. While for technical reasons this element has no balance attribute, the default assumption is a credit balance consistent with its label.

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- Definition

Net of tax effect change in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges after taxes. A cash flow hedge is a hedge of the exposure to variability in the cash flows of a recognized asset or liability or a forecasted transaction that is attributable to a particular risk. The change includes an entity's share of an equity investee's increase or decrease in deferred hedging gains or losses. While for technical reasons this element has no balance attribute, the default assumption is a credit balance consistent with its label.

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- Definition

Pre tax change in accumulated gains and losses from derivative instrument designated and qualifying as the effective portion of cash flow hedges. A cash flow hedge is a hedge of the exposure to variability in the cash flows of a recognized asset or liability or a forecasted transaction that is attributable to a particular risk. Includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.

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Change in accumulated gains and losses from derivative instrument designated and qualifying as the effective portion of cash flow hedges, net of tax effect. The after tax effect change includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.

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