Fair Value of Financial Instruments (Details-3)	3 Months Ended
Mar. 31, 2014
Fair Value Inputs Assets Quantitative Information [Line Items]
Basis adjustment - on peak	95.50%
Basis adjustment - off peak	93.10%
US Treasury Bill Securities [Member]
Deferred compensation plan [Abstract]
Investment interest calculation, investment maturity period (26 weeks)	182 days
Investment interest calculation, monthly compounding rate	1.00%
Investment interest calculation, minimum annual rate compounded monthly	7.00%
Minimum [Member]
Counterparty fuel mix [Abstract]
Internal generation	50.00%
Purchased power	50.00%
Maximum [Member]
Counterparty fuel mix [Abstract]
Internal generation	70.00%
Purchased power	30.00%

Investment maturity period used in deferred compensation interest calculation.

No definition available.

Name:	mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationInvestmentMaturityPeriod
Namespace Prefix:	mgee_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Minimum annual rate compounded monthly used in deferred compensation interest calculation.

No definition available.

Name:	mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationMinimumAnnualRateCompoundedMonthly
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage increase compounded monthly used in deferred compensation interest calculation.

No definition available.

Name:	mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationMonthlyCompoundingRate
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Name:	mgee_FairValueInputsCounterpartyFuelMixAbstract
Namespace Prefix:	mgee_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Estimate of counterparty's internal generation as a portion of their fuel mix, used as an input to measure fair value.

No definition available.

Name:	mgee_FairValueInputsCounterpartyFuelMixInternalGeneration
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Estimate of counterparty's purchased power as a portion of their fuel mix, used as an input to measure fair value.

No definition available.

Name:	mgee_FairValueInputsCounterpartyFuelMixPurchasedPower
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Basis adjustment between delivery points for off peak electric future prices. Used as an input to measure fair value.

No definition available.

Name:	mgee_FairValueInputsDeliveryPointsBasisAdjustmentOffPeak
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Basis adjustment between delivery points for on peak electric future prices. Used as an input to measure fair value.

No definition available.

Name:	mgee_FairValueInputsDeliveryPointsBasisAdjustmentOnPeak
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

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