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Regulatory Assets and Liabilities | 12 Months Ended
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Dec. 31, 2025
Regulatory Assets and Liabilities Disclosure [Abstract] |
Schedule of Regulatory Assets and Liabilities [Text Block] | Regulator y Assets and Liabilities - MGE Energy and MGE. The following regulatory assets and liabilities are reflected in MGE's consolidated balance sheets as of December 31:
(In thousands) |  | Recovery/Refund Period |  | 2025 |  |  | 2024 |
Regulatory Assets |  |  |  |  |  |  |  |
Asset retirement obligation |  | ARO Asset lives |  | $ | 9,592 |  |  | $ | 6,813 |
Bad debt expense |  | One to two years |  |  | 2,250 |  |  |  | 5,200 |
Debt related costs |  | Term of related debt |  | $ | 6,077 |  |  | $ | 6,538 |
Derivatives |  | One to four years |  |  | 1,595 |  |  |  | — |
Leases |  | Lease term |  |  | 5,031 |  |  |  | 4,598 |
Pension and other postretirement costs |  | One to four years |  |  | — |  |  |  | 642 |
Tax recovery related to AFUDC equity |  | Plant lives |  |  | 14,859 |  |  |  | 13,440 |
Transmission |  | One to two years |  |  | 2,258 |  |  |  | 1,216 |
West Riverside |  | One to two years |  |  | 3,453 |  |  |  | 1,276 |
Other |  | Various |  |  | 6,522 |  |  |  | 5,563 |
Total Regulatory Assets |  |  |  | $ | 51,637 |  |  | $ | 45,286 |
(In thousands) |  | Recovery/Refund Period |  | 2025 |  |  | 2024 |
Regulatory Liabilities |  |  |  |  |  |  |  |
Cost of removal |  | Various |  | $ | 46,022 |  |  | $ | 41,714 |
Elm Road |  | One to two years |  |  | 1,444 |  |  |  | 1,700 |
Fuel savings |  | One year |  |  | 7,140 |  |  |  | 3,043 |
Income taxes |  | Various |  |  | 90,963 |  |  |  | 94,110 |
Pension and other postretirement costs |  | One to four years |  |  | 4,919 |  |  |  | — |
Pension and other postretirement non-service costs |  | Plant lives |  |  | 23,115 |  |  |  | 20,342 |
Purchased gas adjustment |  | Less than one year |  |  | 4,736 |  |  |  | 1,441 |
Renewable project savings |  | One to two years |  |  | 5,407 |  |  |  | 5,222 |
Unfunded pension and other postretirement asset |  | Various |  |  | 24,019 |  |  |  | 3,489 |
Other |  | Various |  |  | 1,097 |  |  |  | 241 |
Total Regulatory Liabilities |  |  |  | $ | 208,862 |  |  | $ | 171,302 |
MGE expects to recover its regulatory assets and return its regulatory liabilities through rates charged to customers based on PSCW decisions made during the ratemaking process or based on PSCW long-standing policies and guidelines. The adjustments to rates for these regulatory assets and liabilities will occur over the periods either specified by the PSCW or over the corresponding period related to the asset or liability. Management believes it is probable that MGE will continue to recover from customers the regulatory assets described above based on prior and current ratemaking treatment for such costs. All regulatory assets for which a cash outflow had been made are earning a return. Asset Retirement Obligation (ARO) The recovery of the underlying asset investments and related removal and monitoring costs of recorded AROs is approved by the PSCW in depreciation rates. MGE records a regulatory asset and a regulatory liability for timing differences between the recognition of AROs for financial reporting purposes and the recovery of these costs from customers. The recovery period approximates the useful life of the assets to be removed. See Footnote 17 for a discussion of asset retirement obligations. Bad debt expense In March 2020, the PSCW issued an order authorizing deferral of expenditures incurred to ensure the provision of safe, reliable, and affordable access to utility services during the COVID-19 pandemic and late payment charges. Expenditures include items such as bad debt expense. Recovery of these expenditures occurred during 2024 and 2025. Beginning in 2021, the PSCW approved MGE to defer any differential between bad debt expense reflected in rates and actual costs incurred in its next rate filing. Debt Related Costs This balance includes debt issuance costs of extinguished debt and other debt related expenses, including make-whole premiums paid on redemptions of long-term debt. The PSCW has allowed rate recovery on unamortized issuance costs for extinguished debt facilities. When the facility replacing the old facility is deemed by the PSCW to be more favorable for the ratepayers, the PSCW will allow rate recovery of any unamortized issuance costs related to the old facility. Derivatives MGE has physical and financial contracts that are accounted for as derivatives. The amounts recorded for the net mark-to-market value of the commodity based contracts is offset with a corresponding regulatory asset or liability because these transactions are part of the PGA or fuel rules clause authorized by the PSCW. See Footnote 18 for further discussion. Leases For ratemaking all leases are treated as operating leases. MGE has regulatory treatment and recognizes regulatory assets or liabilities for timing differences between net lease costs recognized and lease cash payments made. See Footnote 5 for further information. Pension and Other Postretirement Costs The current accounting treatment for Pension and Other Postretirement costs allows MGE to reflect any differential between pension and other postretirement costs reflected in rates and actual costs incurred in its next rate filing. Tax Recovery Related to AFUDC Equity AFUDC equity represents the after-tax equity cost associated with utility plant construction and results in a temporary difference between the book and tax basis of such plant. Tax recovery related to AFUDC equity represents the revenue requirement related to recovery of these future taxes payable, calculated at current statutory tax rates. Transmission Costs The current accounting treatment for transmission costs allows MGE to reflect any differential between transmission costs reflected in rates and actual costs incurred in its next rate filing. West Riverside Recovery of costs related to MGE's investment in the West Riverside Energy Center. Cost of Removal The PSCW allows MGE to collect amounts from customers through depreciation rates to fund future asset removal activities. This regulatory liability is reduced as costs are incurred to remove the assets at the end of their useful lives. Elm Road Costs associated with Elm Road for lease payments, management fees, community impact mitigation, and operating costs. Fuel Costs/Savings See Footnote 9.b. for discussion regarding the rules affecting our fuel-related costs. Income Taxes Excess deferred income taxes result from a decrease in tax rates subsequent to ratemaking settlements. The settlements were reached using tax rates that are higher than the currently applicable rates, and MGE is required to return these tax benefits to customers. The regulatory liability and deferred investment tax credit reflects the revenue requirement associated with the return of these tax benefits to customers. Changes in income taxes are generally passed through in customer rates for the regulated utility. The one-time 2017 impact on timing differences related to income taxes passed through to customer rates of the 2017 Tax Act was recorded as a regulatory liability. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, which will be subject to review by the PSCW. A portion of the regulatory liability will be returned to customers based on a mandated timeframe dictated by applicable tax laws. Pension and Other Postretirement Non-Service Costs These Pension and Other Postretirement non-service costs represents the non-service components of net periodic benefit cost capitalized in rates. The FASB issued authoritative guidance within the codification's Compensation-Retirement Benefits topic that only allows the service cost component of net periodic benefit cost to be eligible for capitalization within the consolidated balance sheets, all non-service costs are expensed. Under the current rate structure non-service cost is eligible for capitalization. The portion of net periodic benefit costs that are capitalized are being recovered as a component of depreciation expense. The non-service capitalized costs will be recovered in rates over the depreciable life of the asset for which net periodic benefit costs was applied. See Footnote 11 for further discussion. Purchased Gas Adjustment MGE's 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. Renewable Project Savings The PSCW requires MGE to defer the revenue requirement impact for the change of the in-service date for Paris to a future rate proceeding. Unfunded or funded Pension and Other Postretirement Asset or Liability MGE records unrecognized net actuarial gains and losses as a net regulatory asset or liability in lieu of accumulated other comprehensive gain or loss on the balance sheet, as these amounts are expected to be recovered or refunded in future rates. See Footnote 11 for further discussion.

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- Definition The entire disclosure for detailed information about regulatory assets and liabilities, including current and noncurrent assets created when regulatory agencies permit the deferral of costs to the balance sheet that would otherwise be required to appear on the company's income statement and would be charged against current expenses or revenues, as well as current and noncurrent liabilities created when regulatory agencies permit. + References No definition available. + Details
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