Income Taxes (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income tax provision components [Abstract]
Current payable: Federal		$ 4,811	$ 1,864	$ 2,102
Current payable: State		6,875	4,637	2,385
Net-deferred: Federal		(2,695)	16,317	14,770
Net-deferred: State		3,303	6,683	8,665
Amortized investment tax credits		(1,698)	(1,698)	(1,698)
Total income tax provision		$ 10,596	$ 27,803	$ 26,224
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate		21.00%	21.00%	21.00%
State income taxes, net of federal benefit		6.30%	6.20%	6.20%
Amortized investment tax credits		(2.10%)	(0.70%)	(0.70%)
Credit for electricity from wind energy		(10.50%)	(5.30%)	(5.40%)
AFUDC equity, net		(0.70%)	(0.60%)	(0.30%)
Amortization of utility excess deferred tax	[1]	(5.90%)	(1.50%)	(2.00%)
Other, net, individually insignificant		0.00%	0.00%	0.30%
Effective income tax rate		8.10%	19.10%	19.10%
Components of Deferred Tax Assets [Abstract]
Investment in ATC		$ 18,467	$ 19,287
Federal tax credits		21,252	43,281
Accrued expenses		11,614	10,408
Pension and other postretirement benefits		6,878	15,793
Deferred tax regulatory account		37,892	41,893
Derivatives		13	1,472
Leases		7,521	7,389
Other deferred tax assets		29,290	23,075
Gross deferred income tax assets		132,927	162,598
Less valuation allowance		0	0
Net deferred income tax assets		132,927	162,598
Components of Deferred Tax Liabilities [Abstract]
Property-related		334,728	316,305
Investment in ATC		54,262	53,137
Bond transactions		349	411
Pension and other postretirement benefits		26,801	34,824
Derivatives		13	1,472
Tax deductible prepayments		9,677	9,996
Leases		7,521	7,389
Other deferred tax liabilities		15,973	18,093
Gross deferred income tax liabilities		449,324	441,627
Deferred income taxes, net		316,397	279,029
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		21,252	43,281
Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits, beginning balance		1,615	2,485	$ 2,353
Additions based on tax positions related to current year		415	455	731
Additions based on tax positions related to prior year		0	0	0
Reductions based on tax positions related to prior years		(484)	(1,325)	(599)
Unrecognized tax benefits, ending balance		1,546	1,615	2,485
Interest on unrecognized tax benefits [Roll Forward]
Accrued interest on unrecognized tax benefits, beginning balance		130	189	150
Reduction in interest expense on uncertain tax positions		(77)	(149)	(95)
Interest expense on uncertain tax positions		64	90	134
Accrued interest on unrecognized tax benefits, ending balance		117	130	189
Federal
Components of Deferred Tax Assets [Abstract]
Federal tax credits		21,252	43,281
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		21,252	43,281
Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Excess deferred tax - Income statement effect		3,500	3,500	4,100
Return of unprotected excess deferred taxes		4,100
Deficient Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Collection of unprotected of deficient deferred taxes.			1,300	1,300
MGE [Member]
Income tax provision components [Abstract]
Current payable: Federal		3,206	1,329	934
Current payable: State		6,309	4,560	2,060
Net-deferred: Federal		(3,342)	15,345	14,397
Net-deferred: State		2,909	6,191	8,370
Amortized investment tax credits		(1,698)	(1,698)	(1,698)
Total income tax provision		$ 7,384	$ 25,727	$ 24,063
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate		21.00%	21.00%	21.00%
State income taxes, net of federal benefit		6.20%	6.20%	6.20%
Amortized investment tax credits		(2.30%)	(0.70%)	(0.70%)
Credit for electricity from wind energy		(11.50%)	(5.60%)	(5.70%)
AFUDC equity, net		(0.80%)	(0.60%)	(0.30%)
Amortization of utility excess deferred tax	[1]	(6.50%)	(1.60%)	(2.10%)
Other, net, individually insignificant		0.10%	(0.10%)	0.20%
Effective income tax rate		6.20%	18.60%	18.60%
Components of Deferred Tax Assets [Abstract]
Investment in ATC		$ 0	$ 0
Federal tax credits		21,252	43,281
Accrued expenses		11,566	10,406
Pension and other postretirement benefits		6,878	15,793
Deferred tax regulatory account		37,892	41,893
Derivatives		13	1,472
Leases		7,521	7,389
Other deferred tax assets		29,048	22,934
Gross deferred income tax assets		114,170	143,168
Less valuation allowance		0	0
Net deferred income tax assets		114,170	143,168
Components of Deferred Tax Liabilities [Abstract]
Property-related		334,728	316,305
Investment in ATC		0	0
Bond transactions		349	411
Pension and other postretirement benefits		26,801	34,824
Derivatives		13	1,472
Tax deductible prepayments		9,666	9,986
Leases		7,521	7,389
Other deferred tax liabilities		16,053	17,415
Gross deferred income tax liabilities		395,131	387,802
Deferred income taxes, net		280,961	244,634
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		21,252	43,281
MGE [Member] | Federal
Components of Deferred Tax Assets [Abstract]
Federal tax credits		21,252	43,281
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		$ 21,252	$ 43,281

[1] Included are impacts of the 2017 Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting in recognition of IRS rules that restrict the rate at which the excess deferred taxes may be returned to utility customers. For the years ended December 31, 2024, 2023, and 2022, MGE recognized $3.5 million, $3.5 million, and $4.1 million, respectively. For the year ended December 31, 2024, MGE recognized $4.1 million of deferred taxes not restricted by IRS normalization rules, compared to a net collection from customers of $1.3 million for both the years ended December 31, 2023 and 2022.