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EQUITY COMPENSATION (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
EQUITY COMPENSATION      
Compensation Expense $ 3,688,000us-gaap_AllocatedShareBasedCompensationExpense $ 2,577,000us-gaap_AllocatedShareBasedCompensationExpense $ 1,863,000us-gaap_AllocatedShareBasedCompensationExpense
Tax Benefit Recognized 1,359,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 929,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 649,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
2015 Stock Incentive Plan      
Fair value      
Number of shares of common stock provided for grant 500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= ede_StockIncentivePlanMember
   
Time-Vested Restricted Stock Awards      
Assumptions used for estimating fair value of grants outstanding      
Vesting period 3 years    
Period from date of termination of employment due to death, retirement or disability during which the pro-rata portion of the awards are distributed 6 months    
Changes in restricted stock awards      
Nonvested, balance at the beginning of the period (in shares) 24,900us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
3,300us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
3,433us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
Granted (in shares) 22,600us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
21,600us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
 
Distributed (in shares) (4,010)ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDistributedInPeriod
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
  (133)ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDistributedInPeriod
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
Forfeited (in shares) (2,490)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
   
Nonvested, balance at the end of the period (in shares) 41,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
24,900us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
3,300us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
Vested (in shares) 6,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
   
Weighted Average Grant Date Price      
Nonvested, balance at the beginning of the period (in dollars per share) $ 21.42us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
$ 21.84us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
$ 21.84us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
Granted (in dollars per share) $ 22.40us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
$ 21.36us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
 
Distributed (in dollars per share) $ 21.77ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDistributedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
  $ 20.13ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDistributedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
Not Awarded (in dollars per share) $ 21.99ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedButNotAwardedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
   
Nonvested, balance at the end of the period (in dollars per share) $ 21.89us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
$ 21.42us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
$ 21.84us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
Vested (in dollars per share) $ 21.86us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
   
Fair value      
Unrecognized compensation expense 400,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
200,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
 
Recognition period 1 year 1 month 6 days    
Fair value (in dollars per share) $ 26.82ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEndOfPeriodTotalFairValuePerShare
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
$ 19.88ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsEndOfPeriodTotalFairValuePerShare
/ us-gaap_AwardTypeAxis
= ede_TimeVestedRestrictedAwardsMember
 
Time-Vested Restricted Stock Awards | Low end of range      
Fair value      
Recognition period   1 month 6 days  
Time-Vested Restricted Stock Awards | High end of range      
Fair value      
Recognition period 2 years 1 month 6 days 2 years 1 month 6 days  
Performance-Based Restricted Stock Awards      
Assumptions used for estimating fair value of grants outstanding      
Vesting period 3 years    
Changes in restricted stock awards      
Nonvested, balance at the beginning of the period (in shares) 47,200us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
33,900us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
37,400us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Granted (in shares) 27,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
26,300us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
10,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Awarded (in shares)   (4,460)ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
(7,823)ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Not Awarded (in shares) (10,900)ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedButNotAwardedInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
(8,540)ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedButNotAwardedInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
(5,677)ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedButNotAwardedInPeriod
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Nonvested, balance at the end of the period (in shares) 63,300us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
47,200us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
33,900us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Weighted Average Grant Date Price      
Nonvested, balance at the beginning of the period (in dollars per share) $ 21.39us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 20.25us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 19.28us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Granted (in dollars per share) $ 22.40us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 21.36us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 20.97us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Awarded (in dollars per share)   $ 18.36ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 18.12ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAwardedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Not Awarded (in dollars per share) $ 21.84ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedButNotAwardedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 18.36ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedButNotAwardedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 18.12ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedButNotAwardedInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Nonvested, balance at the end of the period (in dollars per share) $ 21.74us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 21.39us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 20.25us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Assumptions for valuation of shares      
Risk-free interest rate, low end of range (as a percent) 0.25%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
0.13%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
0.16%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Risk-free interest rate, high end of range (as a percent) 0.67%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
0.38%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
0.25%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Expected dividend yield (as a percent) 3.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
4.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
4.90%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Expected forfeiture rates (as a percent) 3.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
3.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
3.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Plan cycle 3 years 3 years 3 years
Weighted average fair value per share (in dollars per share) $ 43.80ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 18.47ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 10.94ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageFairValue
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Expected volatility (as a percent) 14.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
20.20%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
20.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Fair value      
Unrecognized compensation expense $ 1,100,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
$ 500,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
 
Threshold performance level set at percentile level of peer group (as a percent) 20.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
20.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
20.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardThresholdPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Target performance level set at percentile level of peer group (as a percent) 50.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
50.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
50.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Maximum performance level set at percentile level of peer group (as a percent) 80.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
80.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
80.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumPerformanceLevelAsPercentileLevelOfPeerGroup
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
Percentage of shares granted on reaching target performance level 100.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfSharesGrantedOnReachingTargetPerformanceLevel
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
   
Percentage of shares granted on reaching threshold performance level 50.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfSharesGrantedOnReachingThresholdPerformanceLevel
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
   
Percentage of shares granted on reaching maximum performance level 200.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfSharesGrantedOnReachingMaximumPerformanceLevel
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
   
Performance-Based Restricted Stock Awards | Low end of range      
Assumptions for valuation of shares      
Expected volatility of peer group stock (as a percent) 12.40%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateOfPeerGroupStock
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
12.30%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateOfPeerGroupStock
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
12.40%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateOfPeerGroupStock
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Fair value percentage 140.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePercentage
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
0.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePercentage
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
18.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePercentage
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Performance-Based Restricted Stock Awards | High end of range      
Assumptions for valuation of shares      
Expected volatility of peer group stock (as a percent) 24.80%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateOfPeerGroupStock
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
27.50%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateOfPeerGroupStock
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
29.20%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateOfPeerGroupStock
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Fair value percentage 157.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePercentage
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
108.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePercentage
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
96.00%ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePercentage
/ us-gaap_AwardTypeAxis
= ede_PerformanceBasedRestrictedAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Stock Options      
Assumptions used for estimating fair value of grants outstanding      
Vesting period 3 years    
Stock options, expiration term 10 years    
Assumptions for valuation of shares      
Risk-free interest rate, low end of range (as a percent)   0.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
0.11%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Risk-free interest rate, high end of range (as a percent)   0.38%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
0.44%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Expected dividend yield (as a percent)   4.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
4.90%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Expected volatility (as a percent)   24.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
24.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Expected life in months     78 months
Market value (in dollars per share)   $ 22.69ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsMarketValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
$ 20.38ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsMarketValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Weighted average fair value per option (in dollars per share)   $ 1.57ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
$ 1.34ede_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Fair value      
Recognition period     1 month
Stock Options | Low end of range      
Assumptions for valuation of shares      
Expected life in months   6 months 15 days  
Stock Options | High end of range      
Assumptions for valuation of shares      
Expected life in months   24 months 15 days