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v3.19.3.a.u2

Fair Value of Financial Instruments (Details-3) | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Basis adjustment: |  |
Basis adjustment - on peak | 92.10% | 92.10%
Basis adjustment - off peak | 92.70% | 92.80%
US Treasury Bills [Member] |  |
Deferred compensation plan |  |
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: |  |
Internal generation | 40.00% | 50.00%
Purchased power | 40.00% | 25.00%
Maximum [Member] |  |
Counterparty fuel mix: |  |
Internal generation | 60.00% | 75.00%
Purchased power | 60.00% | 50.00%

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- Definition Investment maturity period used in deferred compensation interest calculation. + References No definition available. + Details
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- 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
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Period Type: | duration

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- 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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- References No definition available. + Details
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- References No definition available. + Details
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Namespace Prefix: | mgee_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- 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
Name: | mgee_FairValueInputsCounterpartyFuelMixInternalGeneration
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
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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 off peak electric future prices. Used as an input to measure fair value. + References No definition available. + Details
Name: | mgee_FairValueInputsDeliveryPointsBasisAdjustmentOffPeak
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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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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- Details
Name: | srt_RangeAxis=srt_MinimumMember
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- Details
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