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Derivative and Hedging Instruments (Details-5) (USD $) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014
Counterparties in net liability position or default [Abstract] |  |  |
Derivative, net liability position of counterparties (less than $0.1 million) | $ 100,000 us-gaap_DerivativeNetLiabilityPositionAggregateFairValue |  | $ 100,000 us-gaap_DerivativeNetLiabilityPositionAggregateFairValue
Number of counterparties in default | 0 mgee_CounterpartiesInDefault |  |
Commodity Derivative Contracts [Member] | Fuel For Electric Generation Purchased Power [Member] |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |
Realized losses (gains) on income statement | 420,000 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_IncomeStatementLocationAxis = mgee_FuelForElectricGenerationPurchasedPowerMember | (4,795,000)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_IncomeStatementLocationAxis = mgee_FuelForElectricGenerationPurchasedPowerMember |
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member] |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |
Realized losses (gains) on income statement | 1,761,000 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_IncomeStatementLocationAxis = mgee_CostOfGasSoldExpenseMember | (1,220,000)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember / us-gaap_IncomeStatementLocationAxis = mgee_CostOfGasSoldExpenseMember |
Financial Transmission Rights [Member] | Fuel For Electric Generation Purchased Power [Member] |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |
Realized losses (gains) on income statement | (119,000)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember / us-gaap_IncomeStatementLocationAxis = mgee_FuelForElectricGenerationPurchasedPowerMember | (636,000)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember / us-gaap_IncomeStatementLocationAxis = mgee_FuelForElectricGenerationPurchasedPowerMember |
Financial Transmission Rights [Member] | Cost Of Gas Sold Expense [Member] |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |
Realized losses (gains) on income statement | 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember / us-gaap_IncomeStatementLocationAxis = mgee_CostOfGasSoldExpenseMember | 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_FinancialTransmissionRightsMember / us-gaap_IncomeStatementLocationAxis = mgee_CostOfGasSoldExpenseMember |
Purchased Power Agreement [Member] |  |  |
Derivative collateral required to be posted for ten-year PPA [Abstract] |  |  |
Minimum collateral that may be required to be posted | 20,000,000 mgee_DerivativeCollateralRequiredToPostMinimum / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember |  |
Maximum collateral that may be required to be posted | 40,000,000 mgee_DerivativeCollateralRequiredToPostMaximum / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember |  |
Collateral posted | 0 us-gaap_CollateralAlreadyPostedAggregateFairValue / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember |  |
Purchased Power Agreement [Member] | Fuel For Electric Generation Purchased Power [Member] |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |
Realized losses (gains) on income statement | 1,021,000 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember / us-gaap_IncomeStatementLocationAxis = mgee_FuelForElectricGenerationPurchasedPowerMember | (1,210,000)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember / us-gaap_IncomeStatementLocationAxis = mgee_FuelForElectricGenerationPurchasedPowerMember |
Purchased Power Agreement [Member] | Cost Of Gas Sold Expense [Member] |  |  |
Realized losses (gains) on income statement [Line Items] |  |  |
Realized losses (gains) on income statement | $ 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember / us-gaap_IncomeStatementLocationAxis = mgee_CostOfGasSoldExpenseMember | $ 0 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = mgee_PurchasedPowerAgreementMember / us-gaap_IncomeStatementLocationAxis = mgee_CostOfGasSoldExpenseMember |

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- Definition Maximum collateral that may be required to be posted. + References No definition available. + Details
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- Definition The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959 + Details
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- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959 + Details
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