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Rate Matters (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2013
Rate Proceedings [Abstract] |  |  |  |
Authorized percentage increase (decrease) for electric |  | 3.80% | 4.30% |
Authorized rate increase (decrease) for electric |  | $ 14.9 | $ 15.7 |
Authorized percentage increase (decrease) for gas |  | 1.00% | 0.30% |
Authorized rate increase (decrease) for gas |  | 1.6 | 0.6 |
Fuel rules bandwidth |  | 2.00% |  |
Authorized return on common stock |  | 10.30% |  |
Proposed percent increase (decrease) for electric | 0.00% |  |  |
Proposed percent increase (decrease) for gas | 0.00% |  |  |
Proposed carrying cost on pre-construction costs - AFUDC rate | 100.00% |  |  |
Proposed return of electric fuel credit | 6.2 |  |  |
Fuel Rules [Abstract] |  |  |  |
Electric fuel deferred costs upper threshold |  | 102.00% |  |
Electric fuel deferred costs lower threshold |  | 98.00% |  |
Increased (decreased) electric fuel costs deferred |  |  |  | 0
Purchased Gas Adjustment [Abstract] |  |  |  |
Purchased gas adjustment over(under) collected |  |  | $ (0.1) | $ 5.3

X
- Definition Authorized percentage rate increase (decrease) for retail electric customers. + References No definition available. + Details
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Period Type: | duration

X
- Definition Authorized percentage rate increase (decrease) for retail gas customers. + References No definition available. + Details
Name: | mgee_AuthorizedPercentIncreaseDecreaseGas
Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Authorized rate increase (decrease) for retail electric customers. + References No definition available. + Details
Name: | mgee_AuthorizedRateIncreaseDecreaseElectric
Namespace Prefix: | mgee_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Authorized rate increase (decrease) for retail gas customers. + References No definition available. + Details
Name: | mgee_AuthorizedRateIncreaseDecreaseGas
Namespace Prefix: | mgee_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Authorized return on common stock equity. + References No definition available. + Details
Name: | mgee_AuthorizedReturnOnCommonStock
Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | mgee_ElectricFuelDeferredCostsLowerThreshold
Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | mgee_ElectricFuelDeferredCostsUpperThreshold
Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | mgee_FuelRulesAbstract
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Balance Type: | na
Period Type: | duration

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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
Name: | mgee_FuelRulesBandwidth
Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of electric fuel-related costs in which MGE has deferred outside the 102% or 98% range authorized by the PSCW in the most recent rate order. + References No definition available. + Details
Name: | mgee_IncreasedElectricFuelCostsDeferred
Namespace Prefix: | mgee_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Proposed rate MGE is entitled to for carrying cost on the related construction costs of the Columbia expenditures related to the construction of air emission reduction systems and associated equipment on Columbia Units 1 and 2. + References No definition available. + Details
Name: | mgee_ProposedCarryingCostOnPreConstructionCost
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Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Proposed percentage rate increase (decrease) for retail electric customers in the limited scope reopener 2012 rate case. + References No definition available. + Details
Name: | mgee_ProposedPercentIncreaseDecreaseElectric
Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Proposed percentage rate increase (decrease) for retail gas customers in the limited scope reopener 2012 rate case. + References No definition available. + Details
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Namespace Prefix: | mgee_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Proposed fuel rule surplus credit to be offset against MGE's increased costs. The fuel credit will accrue interest at MGE's weighted cost of capital during 2013. + References No definition available. + Details
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- Details
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- Definition Natural gas rates are subject to a fuel adjustment clause designed to recover or refund the difference between the actual cost of purchased gas and the amount included in rates. Differences between the amounts billed to customers and the actual costs recoverable are deferred and recovered or refunded in future periods by means of prospective monthly adjustments to rates. + References No definition available. + Details
Name: | mgee_PurchasedGasAdjustmentOverCollected
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- Details
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