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Square-miles included in the franchised electric territory.

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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.

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For each income statement presented, the amount charged to expense for amortization of capitalized computer software costs.

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The carrying amount of capitalized computer software costs net of accumulated amortization as of the balance sheet date.

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Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

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The amount of excise and sales taxes included in sales and revenues, which are then deducted as a cost of sales. Includes excise taxes, which are applied to specific types of transactions or items (such as gasoline or alcohol); and sales, use and value added taxes, which are applied to a broad class of revenue-producing transactions involving a wide range of goods and services.

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 sqmi	Dec. 31, 2013	Dec. 31, 2012
Receivable - Margin Account [Abstract]
Receivable, margin account balance, net of collateral posted against derivative positions	$ 2,200,000us-gaap_MarginDepositAssets	$ 500,000us-gaap_MarginDepositAssets
Derivative liability, collateral offset	2,200,000
Derivative asset, collateral offset		200,000
Trade Receivables, Allowance for Doubtful Accounts, and Concentration Risk
Late payment charge on upaid receivables	1.00%
Electric territory (in square miles)	316
Gas territory (in square miles)	1,678
Inventories
Emissions allowance included in inventory	100,000	100,000
Renewable energy credit allowance included in inventory	800,000	600,000
Purchased Gas Adjustment Clause
Purchased gas adjustment, over (under) collected	1,200,000	1,700,000
Capitalized Software Costs
Capitalized software	8,400,000us-gaap_CapitalizedComputerSoftwareNet	9,000,000us-gaap_CapitalizedComputerSoftwareNet
Capitalized software amortization	1,600,000	1,500,000	1,300,000
Impairment of Long-Lived Assets
Impairment of long-lived assets	0	0	0
Excise taxes
License fee tax rate, electric, retail sales	3.19%
License fee tax rate, electric, resale by purchaser	1.59%
License fee tax rate, natural gas	0.97%mgee_LicenseFeeTaxRateNaturalGas
License fee tax expense	$ 14,600,000us-gaap_ExciseAndSalesTaxes	$ 13,800,000us-gaap_ExciseAndSalesTaxes	$ 13,500,000us-gaap_ExciseAndSalesTaxes
Treasury Stock
Treasury stock outstanding (in shares)	0us-gaap_TreasuryStockShares	0us-gaap_TreasuryStockShares
Minimum [Member] \| Capitalized Software [Member]
Capitalized Software Costs
Property, plant, and equipment, useful life	5 years
Maximum [Member] \| Capitalized Software [Member]
Capitalized Software Costs
Property, plant, and equipment, useful life	10 years
PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate	50.00%	50.00%	50.00%
Rate at which AFUDC was capitalized	8.21%	8.21%	8.36%
Columbia Environmental Project [Member] \| PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate	100.00%	50.00%	100.00%
Electric [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	2.60%	2.70%	2.90%
Gas [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	1.70%	1.70%	1.70%
Non Regulated Energy [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	2.40%	2.30%	2.30%
MGE Power Elm Road [Member]
Principles of Consolidation
Ownership percentage by parent	100.00%
MGE Power West Campus [Member]
Principles of Consolidation
Ownership percentage by parent	100.00%