Derivative Commodity Instruments - Derivative Transactions (Details)	6 Months Ended
Jun. 30, 2016 MBbls Bcf $ / Mcf $ / bbl
2016 \| NYMEX Swaps \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl and Bcf) \| MBbls	4,384,000
Average Contract Price (dollars per Bbl)	44.72
2016 \| WTI/WTI Basis Swaps \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl and Bcf) \| MBbls	3,762,000
Average Contract Price (dollars per Bbl)	(1.92)
2016 \| WTS/WTI Basis Swaps \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl and Bcf) \| MBbls	1,039,000
Average Contract Price (dollars per Bbl)	(1.64)
2016 \| Basin Specific Swaps - Permian \| Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl and Bcf) \| Bcf	3,600,000.0
Average contract price (dollars per Mcf) \| $ / Mcf	2.30
2017 \| NYMEX Swaps \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl and Bcf) \| MBbls	4,080,000
Average Contract Price (dollars per Bbl)	47.97
2017 \| NYMEX Three-Way Collars \| Crude Oil
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl and Bcf) \| MBbls	4,080,000
2017 \| Call \| Crude Oil \| Short [Member]
Derivatives, Fair Value [Line Items]
Ceiling sold price (call) (dollars per Bbl)	62.25
2017 \| Put \| Crude Oil \| Short [Member]
Derivatives, Fair Value [Line Items]
Floor price (dollars per Bbl)	35.00
2017 \| Put \| Crude Oil \| Long [Member]
Derivatives, Fair Value [Line Items]
Floor price (dollars per Bbl)	45.00
2017 \| Basin Specific Swaps - Permian \| Natural Gas
Derivatives, Fair Value [Line Items]
Total Hedged Volumes (in MBbl and Bcf) \| Bcf	13,200,000.0
Average contract price (dollars per Mcf) \| $ / Mcf	2.85

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

The cap rate on a price risk derivative such as a cap or collar. A payment or receipt is triggered if the market rate exceeds the cap rate on the contract.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeCapPrice
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

Floor rate on a price risk derivative such as a floor or a collar. A payment or receipt is triggered if the market rate falls below the floor rate on the contract.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFloorPrice
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
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_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract but not the derivative contract itself.

+ References

No definition available.

+ Details

Name:	us-gaap_UnderlyingDerivative
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract measured in volume but not the derivative contract itself.

+ References

No definition available.

+ Details

Name:	us-gaap_UnderlyingDerivativeVolume
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	egn_ProductionPeriodAxis=egn_ProductionPeriodYearOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=egn_NymexSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis=us-gaap_CrudeOilMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=egn_WtiwtiBasisSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=egn_WTSWTIBasisSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=egn_BasinSpecificSwapsPermainMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AverageSalesPriceAndProductionCostsPerUnitOfProductionProductionTypeAxis=us-gaap_NaturalGasReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	egn_ProductionPeriodAxis=egn_ProductionPeriodYearTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=egn_ThreeWayCollarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CallOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PositionAxis=us-gaap_ShortMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_PutOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PositionAxis=us-gaap_LongMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: