Risk Management and Derivative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2011 Dth
Contingent Features
Aggregate fair value of all derivative instruments with the credit-risk-related contingent features that are in a liability position	$ 0.7
Collateral which the entity would have been required to post with the counterparty if the credit-risk-related contingent features were triggered	$ 0.7
Gas
Price Risk Mitigation for Gas Segment
Target percentage of storage capacity utilization (as a percent)	95.00%
Volume of storage in pipelines that serve customers (in Dth)	700,000
Number of pipelines that serve customers	3
Storage capacity utilized (as a percent)	36.60%
Number of future winter seasons for which minimum of expected gas usage is hedged	2
Gas Usage Hedged By Winter Season
Dth Hedged Financial	770,000,000
Dth Hedged Physical	301,714,000
Dth in Storage	735,606,000
Gas \| Current Winter Season
Gas Usage Hedged By Winter Season
Minimum % Hedged (as a percent)	50.00%
Dth Hedged Financial	460,000,000
Dth Hedged Physical	301,714,000
Dth in Storage	735,606,000
Actual % Hedged (as a percent)	45.00%
Gas \| Second Winter Season
Gas Usage Hedged By Winter Season
Minimum % Hedged (as a percent)	50.00%
Dth Hedged Financial	310,000,000
Actual % Hedged (as a percent)	9.00%
Gas \| Third Winter Season
Gas Usage Hedged By Winter Season
Minimum % Hedged (as a percent)	20.00%

Represents the actual percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units.

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- Details

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- Definition

The amount of Dth hedged and held in storage.

+ Details

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Namespace Prefix:	ede
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

The notional amount of financial derivatives expressed in nonmonetary units.

+ Details

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Balance Type:	na
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- Details

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- Definition

Represents the number of future winter seasons for which minimum of expected gas usage is hedged to mitigate price volatility for the entity's customers.

+ Details

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Namespace Prefix:	ede
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of pipelines used to serve customers.

+ Details

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Namespace Prefix:	ede
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of storage capacity which was in place at the balance sheet date.

+ Details

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Namespace Prefix:	ede
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage of storage capacity which the entity targets to have full by November 1.

+ Details

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Namespace Prefix:	ede
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the volume of natural gas storage in pipelines that serve customers.

+ Details

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Namespace Prefix:	ede
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- 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

+ Details

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- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44D
-Subparagraph c
-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

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44D
-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.

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

+ Details

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