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Equity and Financing Arrangements (Tables) | 6 Months Ended
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Jun. 30, 2026
Equity [Abstract] |
Schedule of Common Stock Outstanding Roll Forward [Table Text Block] | The share issuances discussed above, together with shares issued pursuant to stock-based compensation arrangements, resulted in the following changes in outstanding common stock:
|  | Three Months Ended |  | Six Months Ended
|  | June 30, |  | June 30,
|  | 2026 |  | 2025 |  | 2026 |  | 2025
Common stock shares outstanding at beginning of period |  | 36,753,208 |  | 36,536,628 |  | 36,541,849 |  | 36,489,641
Shares issued: |  |  |  |  |  |  |  |
At-the-market offering program |  | — |  | — |  | 154,321 |  | —
Stock-based compensation |  | — |  | — |  | 22,050 |  | 11,213
Stock plan |  | 37,444 |  | 5,221 |  | 72,432 |  | 40,995
Public offering |  | 990,099 |  | — |  | 990,099 |  | —
Common stock shares outstanding at end of period |  | 37,780,751 |  | 36,541,849 |  | 37,780,751 |  | 36,541,849
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] | Potentially dilutive securities for MGE Energy consist of restricted stock units and shares under the forward equity sale agreements, as discussed above.
|  | Three Months Ended |  | Six Months Ended
|  | June 30, |  | June 30,
(In thousands) |  | 2026 |  | 2025 |  | 2026 |  | 2025
Net income attributed to common shareholders |  | 33,353 |  | 26,498 |  | 81,834 |  | 68,090
Weighted average common shares outstanding - basic |  | 37,351 |  | 36,540 |  | 36,972 |  | 36,526
Effect of dilutive securities: |  |  |  |  |  |  |  |
Dilutive effect of stock-based compensation awards |  | 43 |  | 29 |  | 26 |  | 31
Dilutive effect of forward equity sale agreement |  | 62 |  | — |  | 31 |  | —
Weighted average common shares outstanding - diluted |  | 37,456 |  | 36,569 |  | 37,029 |  | 36,557
Basic earnings per share |  | $0.89 |  | $0.73 |  | $2.21 |  | $1.86
Diluted earnings per share |  | $0.89 |  | $0.72 |  | $2.21 |  | $1.86

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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 260 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482662/260-10-50-1 + Details
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