Authorized electric fuel costs refund as a result of rate order.

Name:	mgee_AuthorizedElectricFuelCostsRefund
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Authorized percentage rate increase (decrease) for retail electric customers.

+ Details

Name:	mgee_AuthorizedPercentIncreaseDecreaseElectric
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Authorized percentage rate increase (decrease) for retail gas customers.

+ Details

Name:	mgee_AuthorizedPercentIncreaseDecreaseGas
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Authorized rate increase (decrease) for retail electric customers.

+ Details

Name:	mgee_AuthorizedRateIncreaseDecreaseElectric
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Authorized rate increase (decrease) for retail gas customers.

+ Details

Name:	mgee_AuthorizedRateIncreaseDecreaseGas
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Authorized return on common stock equity.

+ Details

Name:	mgee_AuthorizedReturnOnCommonStock
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	mgee_ElectricFuelDeferredCostsLowerThreshold
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	mgee_ElectricFuelDeferredCostsUpperThreshold
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	mgee_FuelRulesAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Pursuant to the provisions of the rate order, the fuel rules bandwidth will be plus or minus this percentage.

+ Details

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

- Definition

The amount of electric fuel-related costs in which MGE has deferred outside the 102% range authorized by the PSCW in the most recent rate order.

+ Details

Name:	mgee_IncreasedElectricFuelCostsDeferred
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Proposed percentage rate increase (decrease) for retail electric customers in the limited scope reopener 2012 rate case.

+ Details

Name:	mgee_ProposedPercentIncreaseDecreaseElectric
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Proposed percentage rate increase (decrease) for retail gas customers in the limited scope reopener 2012 rate case.

+ Details

Name:	mgee_ProposedPercentIncreaseDecreaseGas
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	mgee_PurchasedGasAdjustmentAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	mgee_PurchasedGasAdjustmentOverCollected
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	mgee_RateProceedingsAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Utility common equity.

+ Details

Name:	mgee_UtilityCommonEquity
Namespace Prefix:	mgee
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Rate Matters (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2011
Rate Proceedings [Abstract]
Authorized percentage increase (decrease) for electric		2.30%	3.30%
Authorized rate increase (decrease) for electric		$ 8.0	$ 11.9
Authorized percentage increase (decrease) for gas		1.00%	(0.74%)
Authorized rate increase (decrease) for gas		1.9	(1.5)
Fuel rules bandwidth		2.00%	2.00%
Authorized return on common stock		10.30%	10.40%
Utility common equity		58.10%	55.30%
Proposed percent increase (decrease) for electric	5.70%
Proposed percent increase (decrease) for gas	0.40%
Fuel Rules [Abstract]
Electric fuel deferred costs upper threshold		102.00%
Electric fuel deferred costs lower threshold		98.00%
Authorized electric fuel costs refund			0.3
Increased electric fuel costs deferred				0
Purchased Gas Adjustment [Abstract]
Purchased gas adjustment over collected			$ 4.8	$ 1.1