Regulatory Assets and Liabilities - Regulatory Liabilities (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 163,663	$ 183,903
MGE [Member] | Public Service Commission of Wisconsin [Member] | Electric Rate Proceeding [Member]
Regulatory Liabilities [Line Items]
Return of unprotected excess deferred taxes	18,200
Deferred Fuel Savings [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	5,047
Deferred Derivative Gain (Loss) [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	617	0
Elm Road Regulatory Liability [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	1,957
Income Taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	110,817	129,856
Non Asset Retirement Obligation Removal Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	29,694	28,197
Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	11,451	7,524
Deferred Pension And Other Postretirement Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	8,112	0
Purchased Gas Adjustment [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,448	1,832
Renewable Energy Credits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,001	802
Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	223	7,669
Other Regulatory Liability [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 300	$ 1,019