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Pension Plans and Other Postretirement Benefits (Tables) | 12 Months Ended
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Dec. 31, 2025
Retirement Benefits [Abstract] |
Schedule of Benefit Obligations and Change in Plan Assets | a. Benefit Obligations and Plan Assets.
(In thousands) |  | Pension Benefits |  |  | Other Postretirement Benefits |
Change in Benefit Obligations: |  | 2025 |  |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Net benefit obligation as of January 1, |  | $ | 326,937 |  |  |  | $ | 346,460 |  |  | $ | 59,184 |  |  | $ | 64,973 |
Service cost |  |  | 2,612 |  |  |  |  | 3,078 |  |  |  | 743 |  |  |  | 856 |
Interest cost |  |  | 17,139 |  |  |  |  | 17,118 |  |  |  | 3,028 |  |  |  | 3,126 |
Plan participants' contributions |  |  | — |  |  |  |  | — |  |  |  | 1,081 |  |  |  | 1,045 |
Actuarial loss (gain)(a) |  |  | 11,028 |  |  |  |  | (16,669 | ) |  |  | 289 |  |  |  | (3,769 | )
Settlements(b) |  |  | — |  |  |  |  | — |  |  |  | — |  |  |  | (1,227 | )
Gross benefits paid |  |  | (22,239 | ) |  |  |  | (23,050 | ) |  |  | (6,299 | ) |  |  | (6,171 | )
Less: federal subsidy on benefits paid(c) |  |  | — |  |  |  |  | — |  |  |  | 354 |  |  |  | 351 |
Benefit obligation as of December 31, |  | $ | 335,477 |  |  |  | $ | 326,937 |  |  | $ | 58,380 |  |  | $ | 59,184 |
Change in Plan Assets: |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of plan assets as of January 1, |  | $ | 424,468 |  |  |  | $ | 404,735 |  |  | $ | 41,321 |  |  | $ | 43,149 |
Actual return on plan assets |  |  | 57,886 |  |  |  |  | 40,608 |  |  |  | 5,999 |  |  |  | 4,131 |
Employer contributions |  |  | 2,304 |  |  |  |  | 2,175 |  |  |  | 739 |  |  |  | 682 |
Plan participants' contributions |  |  | — |  |  |  |  | — |  |  |  | 1,081 |  |  |  | 1,045 |
Settlements(b) |  |  | — |  |  |  |  | — |  |  |  | — |  |  |  | (1,515 | )
Gross benefits paid |  |  | (22,239 | ) |  |  |  | (23,050 | ) |  |  | (6,299 | ) |  |  | (6,171 | )
Fair value of plan assets at end of year |  |  | 462,419 |  |  |  |  | 424,468 |  |  |  | 42,841 |  |  |  | 41,321 |
Funded Status as of December 31, |  | $ | 126,942 |  |  |  | $ | 97,531 |  |  | $ | (15,539 | ) |  | $ | (17,863 | )
(a) Changes in discount rates were the primary driver of the actuarial loss (gain) in 2025 and 2024. (b) In August 2024, MGE entered into an agreement to transfer the mortality and investment risk, as well as the administration of, its employer-paid life insurance plan to a third party. MGE accounted for the settlement under the scope of ASC 715. (c) In 2003, the Medicare Prescription Drug, Improvement and Modernization Act of 2003 was signed into law authorizing Medicare to provide prescription drug benefits to retirees. For both the years ended December 31, 2025 and 2024, the subsidy due to MGE was $0.3 million.
Schedule of Amounts Recognized in the Consolidated Balance Sheet | The amounts recognized in the consolidated balance sheets to reflect the funded status of the plans as of December 31 are as follows:
|  | Pension Benefits |  |  | Other Postretirement Benefits |
(In thousands) |  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Long-term asset |  | $ | 162,493 |  |  | $ | 131,418 |  |  | $ | 2,492 |  |  | $ | 846 |
Current liability |  |  | (2,477 | ) |  |  | (2,441 | ) |  |  | — |  |  |  | — |
Long-term liability |  |  | (33,074 | ) |  |  | (31,446 | ) |  |  | (18,031 | ) |  |  | (18,709 | )
Net asset (liability) |  | $ | 126,942 |  |  | $ | 97,531 |  |  | $ | (15,539 | ) |  | $ | (17,863 | )
Amounts Recognized in Regulatory Asset | The following table shows the amounts that have not yet been recognized in our net periodic benefit cost as of December 31 and are recorded as regulatory asset (liability) in the consolidated balance sheets:
|  | Pension Benefits |  |  | Other Postretirement Benefits |
(In thousands) |  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Net actuarial loss (gain) |  | $ | (14,444 | ) |  | $ | 3,699 |  |  | $ | (9,575 | ) |  | $ | (7,191 | )
Transition obligation |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 3 |
Total |  | $ | (14,444 | ) |  | $ | 3,699 |  |  | $ | (9,575 | ) |  | $ | (7,188 | )
Schedule of Projected Benefit Obligations in Excess of Plan Assets | The projected benefit obligation and fair value of plan assets for pension plans with a projected benefit obligation in excess of plan assets as of December 31 are as follows:
(In thousands) |  | Pension Benefits |
Projected Benefit Obligation in Excess of Plan Assets |  | 2025 |  |  | 2024 |
Projected benefit obligation, end of year |  | $ | 35,551 |  |  | $ | 33,887 |
Fair value of plan assets, end of year |  |  | — |  |  |  | — |
Schedule of Accumulated Benefit Obligations in Excess of Plan Assets | The accumulated benefit obligation and fair value of plan assets with an accumulated benefit obligation in excess of plan assets as of December 31 are as follows:
(In thousands) |  | Pension Benefits |  |  | Other Postretirement Benefits |
Accumulated Benefit Obligation in Excess of Plan Assets |  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Accumulated benefit obligation, end of year |  | $ | 33,553 |  |  | $ | 32,463 |  |  | $ | 44,007 |  |  | $ | 43,882 |
Fair value of plan assets, end of year |  |  | — |  |  |  | — |  |  |  | 25,976 |  |  |  | 25,172 |
Net Periodic Benefit Costs |
(In thousands) |  | Pension Benefits |  |  | Other Postretirement Benefits |
Components of Net Periodic Benefit Cost: |  | 2025 |  |  | 2024 |  |  | 2023 |  |  | 2025 |  |  | 2024 |  |  | 2023 |
Service cost |  | $ | 2,612 |  |  | $ | 3,078 |  |  | $ | 2,892 |  |  | $ | 743 |  |  | $ | 856 |  |  | $ | 780 |
Interest cost |  |  | 17,139 |  |  |  | 17,118 |  |  |  | 17,319 |  |  |  | 3,028 |  |  |  | 3,126 |  |  |  | 3,308 |
Expected return on assets |  |  | (29,014 | ) |  |  | (28,597 | ) |  |  | (25,248 | ) |  |  | (2,715 | ) |  |  | (2,725 | ) |  |  | (2,595 | )
Settlement cost |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 288 |  |  |  | — |
Amortization of: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Transition obligation |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 3 |  |  |  | 3 |  |  |  | 3 |
Prior service credit |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | (242 | ) |  |  | — |
Actuarial loss (gain) |  |  | 299 |  |  |  | 859 |  |  |  | 1,760 |  |  |  | (642 | ) |  |  | 380 |  |  |  | (190 | )
Net periodic benefit cost (credit) |  | $ | (8,964 | ) |  | $ | (7,542 | ) |  | $ | (3,277 | ) |  | $ | 417 |  |  | $ | 1,686 |  |  | $ | 1,306 |
Plan Assumptions | The weighted-average assumptions used to determine the benefit obligations were as follows for the years ended December 31:
|  | Pension Benefits |  | Other Postretirement Benefits
|  | 2025 |  | 2024 |  | 2025 |  | 2024
Discount rate |  |  | 5.45 |  | % |  |  | 5.64 |  | % |  |  | 5.34 |  | % |  |  | 5.59 |  | %
Rate of compensation increase |  |  | 3.58 |  | % |  |  | 3.81 |  | % |  | N/A |  |  |  | N/A |  |
Assumed health care cost trend rates: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Health care cost trend rate assumed for next year |  | N/A |  |  |  | N/A |  |  |  |  | 7.25 |  | % |  |  | 7.50 |  | %
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) |  | N/A |  |  |  | N/A |  |  |  |  | 4.75 |  | % |  |  | 4.75 |  | %
Year that the rate reaches the ultimate trend rate |  | N/A |  |  |  | N/A |  |  |  | 2036 |  |  |  | 2036 |  |
The weighted-average assumptions used to determine the net periodic cost were as follows for the years ended December 31:
|  | Pension Benefits |  | Other Postretirement Benefits
|  | 2025 |  | 2024 |  | 2023 |  | 2025 |  | 2024 |  | 2023
Discount rate |  |  | 5.64 |  | % |  |  | 5.10 |  | % |  |  | 5.47 |  | % |  |  | 5.59 |  | % |  |  | 5.11 |  | % |  |  | 5.45 |  | %
Expected rate of return on plan assets |  |  | 7.00 |  | % |  |  | 7.24 |  | % |  |  | 7.00 |  | % |  |  | 7.00 |  | % |  |  | 6.81 |  | % |  |  | 6.59 |  | %
Rate of compensation increase |  |  | 3.83 |  | % |  |  | 4.32 |  | % |  |  | 3.28 |  | % |  | N/A |  |  |  | N/A |  |  |  | N/A |  |
Fair Value of Plan Assets by Asset Category | The asset allocation for MGE's pension plans as of December 31, 2025 and 2024, and the target allocation for 2026, by asset category, follows:
|  | Target |  | Percentage of Plan Assets at Year End
|  | Allocation(b) |  | 2025 |  | 2024
Equity securities(a) |  |  | 45 |  | % |  |  | 48 |  | % |  |  | 56 |  | %
Fixed income securities |  |  | 50 |  | % |  |  | 47 |  | % |  |  | 38 |  | %
Real estate |  |  | 5 |  | % |  |  | 5 |  | % |  |  | 6 |  | %
(a) Target allocations for equity securities are broken out as follows: 32% United States equity and 13% non-United States equity. (b) The target allocation for MGE's pension plans were approved to be rebalanced in December 2025. The trades happened in two steps, the first in December 2025 and the second in January 2026. Other Postretirement Plan Assets Other Postretirement plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. The asset allocation for MGE's 401(h) assets as of December 31, 2025 and 2024, and the target allocation for 2026, by asset category, follows:
|  | Target |  | Percentage of Plan Assets at Year End
|  | Allocation |  | 2025 |  | 2024
Equity securities(a) |  |  | 63 |  | % |  |  | 65 |  | % |  |  | 66 |  | %
Fixed income securities |  |  | 30 |  | % |  |  | 29 |  | % |  |  | 28 |  | %
Real estate |  |  | 7 |  | % |  |  | 6 |  | % |  |  | 6 |  | %
(a) Target allocations for equity securities are broken out as follows: 45.5% United States equity and 17.5% non-United States equity. The fair values of MGE's plan assets by asset category as of December 31 are as follows:
(In thousands) |  | 2025 |  |  | 2024 |
Cash and Cash Equivalents |  | $ | 695 |  |  | $ | 772 |
Equity Securities: |  |  |  |  |  |
U.S. Large Cap |  |  | 118,871 |  |  |  | 128,262 |
U.S. Mid Cap |  |  | 23,180 |  |  |  | 27,960 |
U.S. Small Cap |  |  | 32,676 |  |  |  | 37,222 |
International Blend |  |  | 72,948 |  |  |  | 73,444 |
Fixed Income Securities: |  |  |  |  |  |
Short-Term Fund |  |  | 18,467 |  |  |  | 7,231 |
High Yield Bond |  |  | 25,154 |  |  |  | 24,231 |
Long Duration Bond |  |  | 185,688 |  |  |  | 139,631 |
Real Estate |  |  | 27,012 |  |  |  | 26,146 |
Fixed Rate Fund |  |  | 569 |  |  |  | 890 |
Total |  | $ | 505,260 |  |  | $ | 465,789 |
Benefit Payments, Fiscal Year Maturity | The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid as follows:
|  | Pension |  |  | Other Postretirement Benefits |
(In thousands) |  | Pension Benefits |  |  | Gross Postretirement Benefits |  |  | Expected Medicare Part D Subsidy |  |  | Net Postretirement Benefits |
2026 |  | $ | 22,689 |  |  | $ | 5,404 |  |  | $ | (461 | ) |  | $ | 4,943 |
2027 |  |  | 22,878 |  |  |  | 5,415 |  |  |  | (504 | ) |  |  | 4,911 |
2028 |  |  | 23,123 |  |  |  | 5,383 |  |  |  | (541 | ) |  |  | 4,842 |
2029 |  |  | 23,297 |  |  |  | 5,311 |  |  |  | (577 | ) |  |  | 4,734 |
2030 |  |  | 23,392 |  |  |  | 5,247 |  |  |  | (608 | ) |  |  | 4,639 |
2031 - 2035 |  |  | 118,606 |  |  |  | 24,843 |  |  |  | (3,410 | ) |  |  | 21,433 |

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- Definition Tabular disclosure of benefit obligation and plan assets of defined benefit plan with accumulated benefit obligation in excess of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-3 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-3 + Details
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