Commitments and Contingencies (Details) - Commitments and Agreements (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012 agreements
Long-term Purchase Commitment [Line Items]
Drilling Plans, Agreement to Secure Drilling Rigs, Number of Agreements	3
Agreement Termination
Long-term Purchase Commitment [Line Items]
Loss Contingency, Range of Possible Loss, Maximum	27
Pending or threatened legal proceedings
Long-term Purchase Commitment [Line Items]
Loss Contingency Accrual, Carrying Value, Period Increase (Decrease)	1.3
Natural Gas \| Alabama Gas Corporation
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Time Period	August 2020
Long-term Purchase Commitment, Minimum Quantity Required	190
Recorded Unconditional Purchase Obligation, Time Period	March 2013
Recorded Unconditional Purchase Obligation	3.8
Recorded Unconditional Purchase Obligation, Market Value	2.8
Natural Gas, Delivery and Storage \| Alabama Gas Corporation
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	88
Long-term Purchase Commitment, Time Period	September 2024
Long Term Commitments Expense Recognized in Statements of Operations	14.3

Drilling Plans, Agreement to Secure Drilling Rigs, Number of Agreements

No definition available.

Name:	egn_DrillingPlansAgreementToSecureDrillingRigsNumberOfAgreements
Namespace Prefix:	egn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Long Term Commitments Expense Recognized in Statements of Operations

+ References

No definition available.

+ Details

Name:	egn_LongTermCommitmentsExpenseRecognizedInStatementsOfOperations
Namespace Prefix:	egn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Recorded Unconditional Purchase Obligation, Market Value

+ References

No definition available.

+ Details

Name:	egn_RecordedUnconditionalPurchaseObligationMarketValue
Namespace Prefix:	egn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Recorded Unconditional Purchase Obligation, Time Period

+ References

No definition available.

+ Details

Name:	egn_RecordedUnconditionalPurchaseObligationTimePeriod
Namespace Prefix:	egn_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Sets forth the number of units of goods that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentMinimumQuantityRequired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Specifies the time period covered by the arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentTimePeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The increase (decrease) in the period in loss contingency liabilities.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14326-108349

+ Details

Name:	us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14557-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 14

-Paragraph 3

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14435-108349

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossMaximum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying amount of the long-term purchase obligation as of the balance sheet date, which equals the sum of all payments due.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 440

-SubTopic 10

-Section 50

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25383-109308

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 6

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 10

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 440

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25287-109308

+ Details

Name:	us-gaap_RecordedUnconditionalPurchaseObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant