Derivative Commodity Instruments (Details) - Derivative Instruments Change in Fair Value (Derivative Commodity Instruments, USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Derivative Commodity Instruments
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 13,446	$ 91,817	$ 42,755	$ 64,517
Realized (gains) losses	1,088	(455)	1,088	(455)
Unrealized gains relating to instruments held at the reporting date	32,235	26,282	28,681	102,169
Settlements during period	(10,565)	(30,767)	(36,320)	(79,354)
Balance at end of period	$ 36,204	$ 86,877	$ 36,204	$ 86,877

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

This element represents realized gains or losses for the period arising from assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ Details

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- Definition

This element represents unrealized gains or losses for the period arising from assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ Details

Name:	egn_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilityGainLossIncludedInEarningsUnrealized
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- Definition

Settlements that have taken place during the period in relation to assets and liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

This element represents an asset and liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ Details

Name:	egn_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilityValue
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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