Concentration Risk, Number of Large Customers

No definition available.

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

- Definition

Sensitivity Analysis Of Fair Value, Fair Value Of Derivative Contracts, Impact Of Ten Percent Change In Commodity Prices

+ References

No definition available.

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

The cash inflow from sales of all investments, including securities and other assets, having ready marketability and intended by management to be liquidated, if necessary, within the current operating cycle. Includes cash flows from securities classified as trading securities that were acquired for reasons other than sale in the short-term.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfShortTermInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=egn_CustomerConcentrationRiskLargestOilGasPurchasersOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueGoodsNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=egn_CustomerConcentrationRiskLargestOilGasPurchasersTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=egn_CustomerConcentrationRiskOtherOilandNaturalGasPurchasersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

FAIR VALUE MEASUREMENTS - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) customer	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Concentration Risk [Line Items]
Impact of ten percent change in commodity prices	$ 9,200
Sale of short-term investments	$ 0	$ 0	$ 919,000
Number of large customers \| customer	2
Plains Marketing \| Accounts receivable
Concentration Risk [Line Items]
Concentration of credit risk	50.00%
Plains Marketing \| Total operating revenues
Concentration Risk [Line Items]
Concentration of credit risk	56.00%
Shell Trading \| Accounts receivable
Concentration Risk [Line Items]
Concentration of credit risk	18.00%
Shell Trading \| Total operating revenues
Concentration Risk [Line Items]
Concentration of credit risk	13.00%
Remaining Customer Concentration Risk \| Accounts receivable
Concentration Risk [Line Items]
Concentration of credit risk	7.00%
Other Oil and Natural Gas Purchasers \| Total operating revenues
Concentration Risk [Line Items]
Concentration of credit risk	10.00%
Estimate of Fair Value Measurement
Concentration Risk [Line Items]
Fair value of long-term debt	$ 798,900	559,900
Reported Value Measurement
Concentration Risk [Line Items]
Fair value of long-term debt	$ 785,000	$ 554,000