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Fair Value of Financial Instruments (Tables) | 6 Months Ended
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Jun. 30, 2026
Fair Value Disclosures [Abstract] |
Estimated Fair Market Value of Financial Instruments | The estimated fair market value of the financial instruments are as follows:
|  | June 30, 2026 |  |  | December 31, 2025 |
(In thousands) |  | Carrying Amount |  |  | Fair Value |  |  | Carrying Amount |  |  | Fair Value |
Long-term debt(a) |  | $ | 904,217 |  |  | $ | 850,628 |  |  | $ | 818,115 |  |  | $ | 768,889 |
(a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.6 million and $4.3 million as of June 30, 2026, and December 31, 2025, respectively.
Assets and Liabilities Measured at Fair Value on a Recurring Basis | The following table presents the balances of assets and liabilities measured at fair value on a recurring basis for both MGE and MGE Energy.
|  | Fair Value as of June 30, 2026 |
(In thousands) |  | Total |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Assets: |  |  |  |  |  |  |  |  |  |  |  |
Derivatives, net(a) |  | $ | 1,376 |  |  | $ | 849 |  |  | $ | — |  |  | $ | 527 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |
Derivatives, net(a) |  | $ | 2,168 |  |  | $ | 1,432 |  |  | $ | — |  |  | $ | 736 |
Deferred compensation |  |  | 7,457 |  |  |  | — |  |  |  | 7,457 |  |  |  | — |
Total Liabilities |  | $ | 9,625 |  |  | $ | 1,432 |  |  | $ | 7,457 |  |  | $ | 736 |
|  | Fair Value as of December 31, 2025 |
(In thousands) |  | Total |  |  | Level 1 |  |  | Level 2 |  |  | Level 3 |
Assets: |  |  |  |  |  |  |  |  |  |  |  |
Derivatives, net(a) |  | $ | 1,151 |  |  | $ | 568 |  |  | $ | — |  |  | $ | 583 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |
Derivatives, net(a) |  | $ | 2,565 |  |  | $ | 1,331 |  |  | $ | — |  |  | $ | 1,234 |
Deferred compensation |  |  | 7,172 |  |  |  | — |  |  |  | 7,172 |  |  |  | — |
Total Liabilities |  | $ | 9,737 |  |  | $ | 1,331 |  |  | $ | 7,172 |  |  | $ | 1,234 |
(a) As of June 30, 2026, and December 31, 2025, collateral of $0.8 million and $1.8 million, respectively, was posted against and netted with derivative liability positions. The fair value of the derivatives disclosed in this table has not been adjusted for the collateral posted.
Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis | The following table summarizes the changes in Level 3 commodity derivative assets and liabilities measured at fair value on a recurring basis.
|  | Three Months Ended |  | Six Months Ended
|  | June 30, |  | June 30,
(In thousands) |  | 2026 |  | 2025 |  | 2026 |  | 2025
Realized and unrealized gains (losses): |  |  |  |  |  |  |  |  |  |  |  |
Included in regulatory assets |  |  | (284) |  |  | — |  |  | 442 |  |  | —
Included in regulatory liability |  |  | — |  |  | (318) |  | $ | — |  | $ | 642
Included in earnings |  |  | (564) |  |  | (665) |  |  | 817 |  |  | (1,262)
Settlements |  |  | 564 |  |  | 665 |  |  | (817) |  |  | 1,264
Gains and Losses Included in Income for Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis | The following table presents total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis(b).
|  | Three Months Ended |  | Six Months Ended
|  | June 30, |  | June 30,
(In thousands) |  | 2026 |  | 2025 |  | 2026 |  | 2025
Purchased power expense |  | $ | (564) |  | $ | (665) |  | $ | 817 |  | $ | (1,262)
(b) MGE's exchange-traded derivative contracts, over-the-counter party transactions, purchased power agreement, and FTRs are subject to regulatory deferral. These derivatives are therefore marked to fair value and are offset in the financial statements with a corresponding regulatory asset or liability.

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- Definition Tabular disclosure of the amount of gains or losses for the period included in earnings or resulted in a change to net assets, have arisen from the use of significant unobservable inputs (level 3) to measure the fair value of assets, liabilities, and financial instruments classified in shareholders' equity. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 102 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-102 + Details
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- Definition Tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482881/825-10-55-10 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482881/825-10-55-12 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-13 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 12 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-12 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-11 + Details
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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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