Common Stock Plans (Stock Options, Range of Exercise Prices) (Details) (USD $)	12 Months Ended
Dec. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of exercisable options, Weighted Average Remaining Contractual Life (in years)	5 years 9 months 5 days
Stock options \| Stock Incentive Plan
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices, Lower Range Limit	14.86
Number of outstanding options, Range of Exercise Prices, Upper Range Limit	60.56
Number of outstanding options, Shares	1,648,475
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	6 years 9 months 29 days
Stock options \| Stock Incentive Plan \| $14.86
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	14.86
Number of outstanding options, Shares	16,270
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	29 days
Stock options \| Stock Incentive Plan \| $21.38
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	21.38
Number of outstanding options, Shares	5,560
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	1 year 0 months 29 days
Stock options \| Stock Incentive Plan \| $46.45
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	46.45
Number of outstanding options, Shares	150,710
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	4 years
Stock options \| Stock Incentive Plan \| $55.08
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	55.08
Number of outstanding options, Shares	7,260
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	4 years 6 months
Stock options \| Stock Incentive Plan \| $60.56
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	60.56
Number of outstanding options, Shares	184,565
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	5 years
Stock options \| Stock Incentive Plan \| $29.79
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	29.79
Number of outstanding options, Shares	333,232
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	6 years
Stock options \| Stock Incentive Plan \| $43.30
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	43.30
Number of outstanding options, Shares	4,750
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	6 years 8 months 1 day
Stock options \| Stock Incentive Plan \| $46.69
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	46.69
Number of outstanding options, Shares	281,110
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	7 years
Stock options \| Stock Incentive Plan \| $54.99
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	54.99
Number of outstanding options, Shares	293,978
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	8 years
Stock options \| Stock Incentive Plan \| $54.11
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of outstanding options, Range of Exercise Prices	54.11
Number of outstanding options, Shares	371,040
Number of outstanding options, Weighted Average Remaining Contractual Life (in years)	9 years

Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range

No definition available.

Name:	egn_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRange
Namespace Prefix:	egn_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average remaining contractual term of exercisable stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageRemainingContractualTerm2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64

-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 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(1)(a, 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.

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration