Summary of Significant Accounting Principles (Details-1) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2023
Supplemental Cash Flow Information [Abstract]
Income taxes paid (receipts), net	[1]	$ 12,516	$ (4,911)
Accrued capital expenditures	[2]	14,785	9,194
Short-Term Debt [Abstract]
Short-Term Debt		76,001		$ 0
Cash, Cash Equivalents, And Restricted Cash [Abstract]
Cash and cash equivalents		10,141		21,302
Restricted cash		665		1,113
Receivable - margin account		3,214		2,081
Cash, cash equivalents, and restricted cash		14,020	18,406	24,496	$ 15,026
Notes Payable, Other Payables [Member]
Short-Term Debt [Abstract]
Short-Term Debt		2,000
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Effects of The Inflation Reduction Act [Abstract]
Guarantor Obligations, Liquidation Proceeds, Monetary Amount			7,100
MGE [Member]
Supplemental Cash Flow Information [Abstract]
Income taxes paid (receipts), net	[1],[3]	10,770	(7,266)
Accrued capital expenditures	[2],[3]	14,785	9,194
Short-Term Debt [Abstract]
Short-Term Debt		76,001		0
Cash, Cash Equivalents, And Restricted Cash [Abstract]
Cash and cash equivalents		3,249		16,865
Restricted cash		665		1,113
Receivable - margin account		3,214		2,081
Cash, cash equivalents, and restricted cash		$ 7,128	$ 6,671	$ 20,059	$ 6,705

[1] Cash received for income taxes in September 2024 includes $7.1 million related to PTCs generated in 2023 and 2024 that were sold to a third party

[2] Includes a $2.0 million unsecured promissory note, for an acquisition of land, issued to the seller, with all principal and interest due January 2026.

[3] MGE Energy files a consolidated federal income tax return with its subsidiaries. While taxes are filed on a consolidated basis, MGE calculates its respective share of tax liability and makes intercompany tax payments to or from its parent company.