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v2.4.1.9

Fair Value of Financial Instruments (Details-3) | 3 Months Ended | 12 Months Ended
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Mar. 31, 2015 | Dec. 31, 2014
Fair Value Inputs Assets Quantitative Information [Line Items] |  |
Basis adjustment - on peak | 97.50%mgee_FairValueInputsDeliveryPointsBasisAdjustmentOnPeak | 98.10%mgee_FairValueInputsDeliveryPointsBasisAdjustmentOnPeak
Basis adjustment - off peak | 94.70%mgee_FairValueInputsDeliveryPointsBasisAdjustmentOffPeak | 95.00%mgee_FairValueInputsDeliveryPointsBasisAdjustmentOffPeak
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%mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationMonthlyCompoundingRate / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryBillSecuritiesMember |
Investment interest calculation, minimum annual rate compounded monthly | 7.00%mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationMinimumAnnualRateCompoundedMonthly / us-gaap_InvestmentTypeAxis = us-gaap_USTreasuryBillSecuritiesMember |
Minimum [Member] |  |
Counterparty fuel mix [Abstract] |  |
Internal generation | 60.00%mgee_FairValueInputsCounterpartyFuelMixInternalGeneration / us-gaap_RangeAxis = us-gaap_MinimumMember | 50.00%mgee_FairValueInputsCounterpartyFuelMixInternalGeneration / us-gaap_RangeAxis = us-gaap_MinimumMember
Purchased power | 40.00%mgee_FairValueInputsCounterpartyFuelMixPurchasedPower / us-gaap_RangeAxis = us-gaap_MinimumMember | 50.00%mgee_FairValueInputsCounterpartyFuelMixPurchasedPower / us-gaap_RangeAxis = us-gaap_MinimumMember
Maximum [Member] |  |
Counterparty fuel mix [Abstract] |  |
Internal generation | 75.00%mgee_FairValueInputsCounterpartyFuelMixInternalGeneration / us-gaap_RangeAxis = us-gaap_MaximumMember | 70.00%mgee_FairValueInputsCounterpartyFuelMixInternalGeneration / us-gaap_RangeAxis = us-gaap_MaximumMember
Purchased power | 25.00%mgee_FairValueInputsCounterpartyFuelMixPurchasedPower / us-gaap_RangeAxis = us-gaap_MaximumMember | 30.00%mgee_FairValueInputsCounterpartyFuelMixPurchasedPower / us-gaap_RangeAxis = us-gaap_MaximumMember

X
- Definition Investment maturity period used in deferred compensation interest calculation. + References No definition available. + Details
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Namespace Prefix: | mgee_
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Balance Type: | na
Period Type: | duration

X
- Definition Minimum annual rate compounded monthly used in deferred compensation interest calculation. + References No definition available. + Details
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Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage increase compounded monthly used in deferred compensation interest calculation. + References No definition available. + Details
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Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: | mgee_
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Balance Type: | na
Period Type: | duration

X
- Definition Estimate of counterparty's internal generation as a portion of their fuel mix, used as an input to measure fair value. + References No definition available. + Details
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Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Estimate of counterparty's purchased power as a portion of their fuel mix, used as an input to measure fair value. + References No definition available. + Details
Name: | mgee_FairValueInputsCounterpartyFuelMixPurchasedPower
Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Basis adjustment between delivery points for off peak electric future prices. Used as an input to measure fair value. + References No definition available. + Details
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Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Basis adjustment between delivery points for on peak electric future prices. Used as an input to measure fair value. + References No definition available. + Details
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Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
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- Details
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Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
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- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
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Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |