Income Taxes (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income tax provision components [Abstract]
Current payable: Federal		$ 2,102	$ (2,589)	$ 4,179
Current payable: State		2,385	3,002	5,095
Net-deferred: Federal		14,770	(1,473)	6,181
Net-deferred: State		8,665	6,310	4,182
Amortized investment tax credits		(1,698)	(1,135)	(214)
Total income tax provision		$ 26,224	$ 4,115	$ 19,423
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%	6.30%
Amortized investment tax credits		(0.70%)	(1.50%)	(0.20%)
Credit for electricity from wind energy		(5.40%)	(6.00%)	(6.20%)
AFUDC equity, net		(0.30%)	(0.90%)	(1.20%)
Amortization of utility excess deferred tax	[1]	(2.00%)	(14.80%)	(2.00%)
Other, net, individually significant		0.30%	(0.30%)	(0.30%)
Effective income tax rate		19.10%	3.70%	17.40%
Components of Deferred Tax Assets [Abstract]
Investment in ATC		$ 20,098	$ 20,868
Federal tax credits		46,282	39,161
Accrued expenses		10,642	11,053
Pension and other postretirement benefits		20,687	24,888
Deferred tax regulatory account		42,999	42,401
Derivatives		1,416	241
Leases		7,137	7,218
Other deferred tax assets		17,438	17,390
Gross deferred income tax assets		166,699	163,220
Less valuation allowance		0	0
Net deferred income tax assets		166,699	163,220
Components of Deferred Tax Liabilities [Abstract]
Property-related		295,872	274,613
Investment in ATC		52,840	52,731
Bond transactions		472	534
Pension and other postretirement benefits		35,590	34,781
Derivatives		1,416	241
Tax deductible prepayments		10,308	10,222
Leases		7,137	7,218
Other deferred tax liabilities		15,254	14,029
Gross deferred income tax liabilities		418,889	394,369
Deferred income taxes, net		252,190	231,149
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		46,282	39,161
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning balance		2,353	2,281	$ 2,093
Additions based on tax positions related to current year		731	714	796
Additions based on tax positions related to prior year		0	0	0
Reductions based on tax positions related to prior years		(599)	(642)	(608)
Unrecognized tax benefits, ending balance		2,485	2,353	2,281
Interest on unrecognized tax benefits [Roll Forward]
Accrued interest on unrecognized tax benefits, beginning balance		150	154	176
Reduction in interest expense on uncertain tax positions		(95)	(98)	(124)
Interest expense on uncertain tax positions		134	94	102
Accrued interest on unrecognized tax benefits, ending balance		189	150	154
Unrecognized Tax Benefits
Unrecognized tax benefits permanent differences		0	0	0
State
Operating loss deductions and tax credit carryforwards [Abstract]
State net operating losses		3	3
Valuation allowances for state net operating losses		(3)	(3)
Federal
Components of Deferred Tax Assets [Abstract]
Federal tax credits		46,282	39,161
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		46,282	39,161
Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Excess deferred tax - Income statement effect		4,100	2,600	2,200
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
MGE [Member]
Income tax provision components [Abstract]
Current payable: Federal		934	(3,434)	3,716
Current payable: State		2,060	3,163	4,790
Net-deferred: Federal		14,397	(1,951)	4,756
Net-deferred: State		8,370	5,605	3,787
Amortized investment tax credits		(1,698)	(1,135)	(214)
Total income tax provision		$ 24,063	$ 2,248	$ 16,835
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%	6.30%
Amortized investment tax credits		(0.70%)	(1.50%)	(0.20%)
Credit for electricity from wind energy		(5.70%)	(6.40%)	(6.80%)
AFUDC equity, net		(0.30%)	(1.00%)	(1.40%)
Amortization of utility excess deferred tax	[1]	(2.10%)	(15.80%)	(2.20%)
Other, net, individually significant		0.20%	(0.30%)	(0.30%)
Effective income tax rate		18.60%	2.20%	16.40%
Components of Deferred Tax Assets [Abstract]
Investment in ATC		$ 0	$ 0
Federal tax credits		46,282	39,161
Accrued expenses		10,644	11,047
Pension and other postretirement benefits		20,687	24,888
Deferred tax regulatory account		42,999	42,401
Derivatives		1,416	241
Leases		7,137	7,218
Other deferred tax assets		17,490	17,442
Gross deferred income tax assets		146,655	142,398
Less valuation allowance		0	0
Net deferred income tax assets		146,655	142,398
Components of Deferred Tax Liabilities [Abstract]
Property-related		295,872	274,613
Investment in ATC		0	0
Bond transactions		472	534
Pension and other postretirement benefits		35,590	34,781
Derivatives		1,416	241
Tax deductible prepayments		10,308	10,210
Leases		7,137	7,218
Other deferred tax liabilities		15,118	13,686
Gross deferred income tax liabilities		365,913	341,283
Deferred income taxes, net		219,258	198,885
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		46,282	39,161
MGE [Member] | State
Operating loss deductions and tax credit carryforwards [Abstract]
State net operating losses		3	3
Valuation allowances for state net operating losses		(3)	(3)
MGE [Member] | Federal
Components of Deferred Tax Assets [Abstract]
Federal tax credits		46,282	39,161
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		$ 46,282	$ 39,161

[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, 2022, 2021, and 2020, MGE recognized $4.1 million, $2.6 million, and $2.2 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 the year ended December 31, 2022, MGE recognized $1.3 million.