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Fair Value of Financial Instruments (Details-1) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Carrying Amount [Member] |  |  |  |
Assets: |  |  |  |
Cash and cash equivalents | $ 70,703 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | $ 65,755 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Liabilities: |  |  |  |
Short-term debt - commercial paper | 0 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 7,000 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Long-term debt | 398,653 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1] | 399,690 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1]
Fair Value [Member] |  |  |  |
Assets: |  |  |  |
Cash and cash equivalents | 70,703 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 65,755 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Liabilities: |  |  |  |
Short-term debt - commercial paper | 0 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |  | 7,000 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember |
Long-term debt | 465,534 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [1] | 457,420 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember | [1]
MGE [Member] | Carrying Amount [Member] |  |  |  |
Assets: |  |  |  |
Cash and cash equivalents | 17,156 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |  | 4,562 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |
Liabilities: |  |  |  |
Short-term debt - commercial paper | 0 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |  | 7,000 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |
Long-term debt | 398,653 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | [1] | 399,690 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | [1]
MGE [Member] | Fair Value [Member] |  |  |  |
Assets: |  |  |  |
Cash and cash equivalents | 17,156 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |  | 4,562 us-gaap_CashAndCashEquivalentsFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |
Liabilities: |  |  |  |
Short-term debt - commercial paper | 0 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |  | 7,000 mgee_CommercialPaperFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember |
Long-term debt | $ 465,534 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | [1] | $ 457,420 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_EstimateOfFairValueFairValueDisclosureMember / dei_LegalEntityAxis = us-gaap_SubsidiariesMember | [1]
[1] | *Includes long-term debt due within one year.

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- Definition Fair value portion of commercial paper. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
Period Type: | instant

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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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