Income Taxes (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income tax provision components [Abstract]
Current payable: Federal		$ 1,864	$ 2,102	$ (2,589)
Current payable: State		4,637	2,385	3,002
Net-deferred: Federal		16,317	14,770	(1,473)
Net-deferred: State		6,683	8,665	6,310
Amortized investment tax credits		(1,698)	(1,698)	(1,135)
Total income tax provision		$ 27,803	$ 26,224	$ 4,115
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		(0.70%)	(0.70%)	(1.50%)
Credit for electricity from wind energy		(5.30%)	(5.40%)	(6.00%)
AFUDC equity, net		(0.60%)	(0.30%)	(0.90%)
Amortization of utility excess deferred tax	[1]	(1.50%)	(2.00%)	(14.80%)
Other, net, individually significant		0.00%	0.30%	(0.30%)
Effective income tax rate		19.10%	19.10%	3.70%
Components of Deferred Tax Assets [Abstract]
Investment in ATC		$ 19,287	$ 20,098
Federal tax credits		43,281	46,282
Accrued expenses		10,408	10,642
Pension and other postretirement benefits		15,793	20,687
Deferred tax regulatory account		41,893	42,999
Derivatives		1,472	1,416
Leases		7,389	7,137
Other deferred tax assets		23,075	17,438
Gross deferred income tax assets		162,598	166,699
Less valuation allowance		0	0
Net deferred income tax assets		162,598	166,699
Components of Deferred Tax Liabilities [Abstract]
Property-related		316,305	295,872
Investment in ATC		53,137	52,840
Bond transactions		411	472
Pension and other postretirement benefits		34,824	35,590
Derivatives		1,472	1,416
Tax deductible prepayments		9,996	10,308
Leases		7,389	7,137
Other deferred tax liabilities		18,093	15,254
Gross deferred income tax liabilities		441,627	418,889
Deferred income taxes, net		279,029	252,190
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		43,281	46,282
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning balance		2,485	2,353	$ 2,281
Additions based on tax positions related to current year		455	731	714
Additions based on tax positions related to prior year		0	0	0
Reductions based on tax positions related to prior years		(1,325)	(599)	(642)
Unrecognized tax benefits, ending balance		1,615	2,485	2,353
Interest on unrecognized tax benefits [Roll Forward]
Accrued interest on unrecognized tax benefits, beginning balance		189	150	154
Reduction in interest expense on uncertain tax positions		(149)	(95)	(98)
Interest expense on uncertain tax positions		90	134	94
Accrued interest on unrecognized tax benefits, ending balance		130	189	150
State
Operating loss deductions and tax credit carryforwards [Abstract]
State net operating losses		0	3
Valuation allowances for state net operating losses		0	(3)
Federal
Components of Deferred Tax Assets [Abstract]
Federal tax credits		43,281	46,282
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		43,281	46,282
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	4,100	2,600
Return of unprotected excess deferred taxes				13,200
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		1,329	934	(3,434)
Current payable: State		4,560	2,060	3,163
Net-deferred: Federal		15,345	14,397	(1,951)
Net-deferred: State		6,191	8,370	5,605
Amortized investment tax credits		(1,698)	(1,698)	(1,135)
Total income tax provision		$ 25,727	$ 24,063	$ 2,248
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		(0.70%)	(0.70%)	(1.50%)
Credit for electricity from wind energy		(5.60%)	(5.70%)	(6.40%)
AFUDC equity, net		(0.60%)	(0.30%)	(1.00%)
Amortization of utility excess deferred tax	[1]	(1.60%)	(2.10%)	(15.80%)
Other, net, individually significant		(0.10%)	0.20%	(0.30%)
Effective income tax rate		18.60%	18.60%	2.20%
Components of Deferred Tax Assets [Abstract]
Investment in ATC		$ 0	$ 0
Federal tax credits		43,281	46,282
Accrued expenses		10,406	10,644
Pension and other postretirement benefits		15,793	20,687
Deferred tax regulatory account		41,893	42,999
Derivatives		1,472	1,416
Leases		7,389	7,137
Other deferred tax assets		22,934	17,490
Gross deferred income tax assets		143,168	146,655
Less valuation allowance		0	0
Net deferred income tax assets		143,168	146,655
Components of Deferred Tax Liabilities [Abstract]
Property-related		316,305	295,872
Investment in ATC		0	0
Bond transactions		411	472
Pension and other postretirement benefits		34,824	35,590
Derivatives		1,472	1,416
Tax deductible prepayments		9,986	10,308
Leases		7,389	7,137
Other deferred tax liabilities		17,415	15,118
Gross deferred income tax liabilities		387,802	365,913
Deferred income taxes, net		244,634	219,258
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		43,281	46,282
MGE [Member] | State
Operating loss deductions and tax credit carryforwards [Abstract]
State net operating losses		0	3
Valuation allowances for state net operating losses		0	(3)
MGE [Member] | Federal
Components of Deferred Tax Assets [Abstract]
Federal tax credits		43,281	46,282
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		$ 43,281	$ 46,282

[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, 2023, 2022, and 2021, MGE recognized $3.5 million, $4.1 million, and $2.6 million, respectively. Included in the 2021 rate settlement was a one-time return to customers of the electric portion of excess deferred taxes related to the 2017 Tax Act not restricted by IRS normalization rules. For the year ended December 31, 2021, MGE recognized $13.2 million. Included in the 2022 and 2023 rate settlement was a net collection from customers of the gas portion of deficient deferred taxes related to the 2017 Tax Act not restricted by IRS normalization rules. For both the years ended December 31, 2023, and 2022, MGE recognized $1.3 million.