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Rate Matters (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014
MGE [Member] |  |  |
Purchased Gas Adjustment [Abstract] |  |  |
Purchased gas adjustment, overcollection | 6.7 us-gaap_RefundableGasCosts / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | 1.2 us-gaap_RefundableGasCosts / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |
PSCW [Member] | Legal Entity Type of Counterparty [Domain] |  |  |
Fuel Rules [Abstract] |  |  |
Fuel rules, bandwidth | 2.00%mgee_FuelRulesBandwidth / dei_LegalEntityAxis = us-gaap_LegalEntityTypeOfCounterpartyDomain / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |  |
Fuel rules, electric fuel deferred costs upper threshold | 102.00%mgee_FuelRulesElectricFuelDeferredCostsUpperThreshold / dei_LegalEntityAxis = us-gaap_LegalEntityTypeOfCounterpartyDomain / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |  |
Fuel rules, electric fuel deferred costs lower threshold | 98.00%mgee_FuelRulesElectricFuelDeferredCostsLowerThreshold / dei_LegalEntityAxis = us-gaap_LegalEntityTypeOfCounterpartyDomain / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |  |
PSCW [Member] | MGE [Member] |  |  |
Rate Proceedings [Abstract] |  |  |
Authorized return on equity, percentage | 10.20%us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember | 10.30%us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |
Fuel Rules [Abstract] |  |  |
Fuel rules, deferred electric cost | 2.4 mgee_FuelRulesDeferredElectricCost / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |  |
PSCW [Member] | MGE [Member] | Fuel Rules Surplus Credit, 2012 [Member] |  |  |
Rate Proceedings [Abstract] |  |  |
Return of electric fuel credit, total |  | 6.3 mgee_PublicUtilitiesReturnOfFuelRulesSurplusCredit / mgee_FuelRulesSurplusCreditYearAxis = mgee_FuelRulesSurplusCredit2012Member / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |
Fuel Rules [Abstract] |  |  |
Return of electric fuel credit, current period |  |  | 1.6 mgee_PublicUtilitiesReturnOfFuelRulesSurplusCreditCurrentYear / mgee_FuelRulesSurplusCreditYearAxis = mgee_FuelRulesSurplusCredit2012Member / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember
PSCW [Member] | Columbia Environmental Project [Member] | MGE [Member] |  |  |
Rate Proceedings [Abstract] |  |  |
Authorized AFUDC Rate |  | 100.00%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate / mgee_ConstructionProjectAxis = mgee_ColumbiaEnvironmentalProjectMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |
Electric [Member] | PSCW [Member] | MGE [Member] |  |  |
Rate Proceedings [Abstract] |  |  |
Authorized rate increase (decrease), percentage | 3.80%us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_ElectricRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember | 0.00%us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_ElectricRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |
Authorized rate increase (decrease), amount | 15.4 us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_ElectricRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember | 0 us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_ElectricRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |
Gas [Member] | PSCW [Member] | MGE [Member] |  |  |
Rate Proceedings [Abstract] |  |  |
Authorized rate increase (decrease), percentage | (2.00%)us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_GasRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember | 0.00%us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_GasRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |
Authorized rate increase (decrease), amount | (3.8)us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_GasRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember | 0 us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = mgee_GasRateProceedingMember / us-gaap_RegulatoryAgencyAxis = mgee_PublicServiceCommissionOfWisconsinMember |

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- Definition Pursuant to the provisions of the rate order, the fuel rules bandwidth will be plus or minus this percentage. + References No definition available. + Details
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- Definition The amount of electric fuel-related costs in which an entity has deferred outside the symmetrical cost tolerance band authorized by a regulatory agency in the most recent rate order. + References No definition available. + Details
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- Definition Under fuel rules, the amount in which MGE is required to defer the benefit of lower costs if actual electric fuel costs were less than the allowed electric fuel costs in latest rate order. + References No definition available. + Details
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- Definition Under fuel rules, the amount in which MGE would defer if actual electric fuel costs exceeded allowed electric fuel costs in latest rate order. + References No definition available. + Details
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- Definition The fuel rules surplus credit that is not required to be refunded to customers and will be amortized. The fuel credit will accrue interest at weighted cost of capital. + References No definition available. + Details
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- Definition The fuel rules surplus credit that is not required to be refunded to customers and will be amortized during the current period. The fuel credit will accrue interest at weighted cost of capital. + References No definition available. + Details
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- Details
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- Definition Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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- Definition Amount of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
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- Definition Percentage of public utility's approved rate increase (decrease) by regulatory agency. + References No definition available. + Details
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- Definition Percentage of public utility's approved return on equity. + References No definition available. + Details
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- Definition Gas costs of a regulated entity that are refundable through future rate adjustments. Such costs are a form of a regulatory liabilities and are expected to be refunded in less than one year through rate adjustments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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