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Investment in ATC and ATC Holdco (Tables) | 6 Months Ended
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Jun. 30, 2026
Equity Method Investments and Joint Ventures [Abstract] |
Equity Method Investments Financial Data | MGE Transco recorded the following amounts related to its investment in ATC:
|  | Three Months Ended |  |  | Six Months Ended |
|  | June 30, |  |  | June 30, |
(In thousands) |  | 2026 |  |  | 2025 |  |  | 2026 |  |  | 2025 |
Equity earnings from investment in ATC |  | $ | 3,776 |  |  | $ | 3,066 |  |  | $ | 7,298 |  |  | $ | 6,056 |
Dividends received from ATC |  |  | 2,788 |  |  |  | 2,345 |  |  |  | 5,450 |  |  |  | 5,632 |
Capital contributions to ATC |  |  | 2,156 |  |  |  | 2,679 |  |  |  | 6,616 |  |  |  | 5,171 |
In July 2026, MGE Transco made a $3.6 million capital contribution to ATC. ATC's summarized financial data is as follows:
|  | Three Months Ended |  |  | Six Months Ended |
|  | June 30, |  |  | June 30, |
(In thousands) |  | 2026 |  |  | 2025 |  |  | 2026 |  |  | 2025 |
Operating revenues |  | $ | 274,048 |  |  | $ | 241,227 |  |  | $ | 539,307 |  |  | $ | 476,156 |
Operating expenses |  |  | (129,636 | ) |  |  | (117,564 | ) |  |  | (257,041 | ) |  |  | (234,309 | )
Other income, net |  |  | 1,228 |  |  |  | 550 |  |  |  | 1,928 |  |  |  | 633 |
Interest expense, net |  |  | (45,925 | ) |  |  | (43,254 | ) |  |  | (90,401 | ) |  |  | (82,447 | )
Earnings before members' income taxes |  | $ | 99,715 |  |  | $ | 80,959 |  |  | $ | 193,793 |  |  | $ | 160,033 |

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- Definition Tabular disclosure of equity method investments including, but not limited to, name of each investee or group of investments, percentage ownership, difference between recorded amount of an investment and the value of the underlying equity in the net assets, and summarized financial information. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483499/205-20-50-7 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 205 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5A -Publisher FASB -URI https://asc.fasb.org/1943274/2147483499/205-20-50-5A Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 323 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481687/323-10-50-3 + Details
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