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v2.4.1.9

Derivative and Hedging Instruments (Details-1) (USD $) | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2015 Dth MWh | Dec. 31, 2014 Dth MWh | Mar. 31, 2014 | Dec. 31, 2013
Gross Notional Volume of Open Derivatives |  |  |  |
Derivative, right to reclaim collateral (receivable) | $ 600,000 us-gaap_DerivativeCollateralRightToReclaimCash |  |  |
Other Current Assets [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Derivative fair value, net | 268,000 us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember | 1,001,000 us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember | 351,000 us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember | 411,000 us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember
Commodity Contracts And Financial Transimission Rights [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Derivative fair value, net | (600,000)us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_CommodityContractsAndFinancialTransimissionRightsMember | (1,600,000)us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_CommodityContractsAndFinancialTransimissionRightsMember |  |
Commodity Derivative Contracts [Member] |  |  |  |
Gross Notional Volume of Open Derivatives |  |  |  |
Notional amount, energy measure (in MWh) | 408,920 us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 448,000 us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Notional amount, decatherm measure (in Dth) | 2,785,000 mgee_DerivativeNonmonetaryNotionalAmountDecathermMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 4,405,000 mgee_DerivativeNonmonetaryNotionalAmountDecathermMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Derivative fair values [Abstract] |  |  |  |
Asset Derivatives, fair value, gross basis | 343,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 223,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Liability Derivatives, fair value, gross basis | 937,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 2,433,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Commodity Derivative Contracts [Member] | Other Current Assets [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Asset Derivatives, fair value, gross basis | 336,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 130,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Asset Derivatives, fair value, gross basis | 7,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 93,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherNoncurrentAssetsMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Liability Derivatives, fair value, gross basis | 821,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesCurrentMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 2,262,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesCurrentMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Liability Derivatives, fair value, gross basis | 116,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesNoncurrentMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 171,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesNoncurrentMember / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember |  |
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member] |  |  |  |
Derivatives Fair Value [Line Items] |  |  |  |
Maximum term of derivative hedging contract | 4 years |  |  |
Financial Transmission Rights [Member] |  |  |  |
Gross Notional Volume of Open Derivatives |  |  |  |
Notional amount, power measure (in MW) | 691 mgee_DerivativeNonmonetaryNotionalAmountPowerMeasure / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember | 1,854 mgee_DerivativeNonmonetaryNotionalAmountPowerMeasure / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember |  |
Derivative fair values [Abstract] |  |  |  |
Asset Derivatives, fair value, gross basis | 38,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember | 642,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember |  |
Financial Transmission Rights [Member] | Other Current Assets [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Asset Derivatives, fair value, gross basis | 38,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember | 642,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherCurrentAssetsMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember |  |
Financial Transmission Rights [Member] | Derivative Liability (Current) [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Liability Derivatives, fair value, gross basis | 0 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesCurrentMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember | 0 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesCurrentMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember |  |
Ten-year PPA [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Derivative fair value, net | (53,400,000)us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember | (53,400,000)us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember |  |
Liability Derivatives, fair value, gross basis | 53,410,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember | 53,430,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember |  |
Ten-year PPA [Member] | Derivative Liability (Current) [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Liability Derivatives, fair value, gross basis | 7,090,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesCurrentMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember | 6,870,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesCurrentMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember |  |
Ten-year PPA [Member] | Derivative Liability (Long-term) [Member] |  |  |  |
Derivative fair values [Abstract] |  |  |  |
Liability Derivatives, fair value, gross basis | $ 46,320,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesNoncurrentMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember | $ 46,560,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_BalanceSheetLocationAxis = mgee_DerivativeLiabilitiesNoncurrentMember / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember |  |

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