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Investment in ATC (Details-1) (USD $) | 3 Months Ended | 0 Months Ended |
--- | --- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Apr. 30, 2015 | Dec. 31, 2014
Schedule Of Equity Method Investments [Line Items] |  |  |  |
Equity earnings from investment | $ 1,881,000 us-gaap_IncomeLossFromEquityMethodInvestments | $ 2,481,000 us-gaap_IncomeLossFromEquityMethodInvestments |  |
Dividend income from investment | 1,420,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions | 1,917,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions |  |
Capital contributions to investment | 280,000 us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates | 693,000 us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates |  |
MGE Transco [Member] | ATC [Member] |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |
Equity earnings from investment | 1,881,000 us-gaap_IncomeLossFromEquityMethodInvestments / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember | 2,481,000 us-gaap_IncomeLossFromEquityMethodInvestments / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember |  |
Dividend income from investment | 1,420,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember | 1,917,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember |  |
Capital contributions to investment | 178,000 us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember | 533,000 us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember |  |
Equity method investment | 68,300,000 us-gaap_EquityMethodInvestments / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember |  |  | 67,700,000 us-gaap_EquityMethodInvestments / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember
MGE Transco [Member] | ATC [Member] | Subsequent Event [Member] |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |
Capital contributions to investment |  |  | $ 200,000 us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates / dei_LegalEntityAxis = mgee_MgeTranscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_EquityMethodInvesteeMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |

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