Schedule I - Condensed Parent Company Finanical Statements (Details-Balance Sheet) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 44,738,000	$ 23,481,000
Other current assets	11,394,000	10,233,000
Total Current Assets	209,519,000	181,641,000
Other deferred assets and other
Other deferred assets and other	22,259,000	19,093,000
Investments:
Other investments	2,308,000	2,298,000
Total investments	94,676,000	88,492,000
Total Assets	2,253,651,000	2,081,664,000	$ 1,988,618,000
Current Liabilities:
Other current liabilities	6,015,000	14,676,000
Total Current Liabilities	190,926,000	128,820,000
Other Credits:
Deferred income taxes	231,471,000	243,302,000
Other deferred liabilities and other	72,211,000	63,013,000
Total Other Credits	567,422,000	573,427,000
Shareholders' Equity:
Retained earnings	545,429,000	504,740,000
Total Common Shareholders' Equity	976,000,000	855,676,000	$ 816,644,000	$ 778,187,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	2,253,651,000	2,081,664,000
MGE Energy [Member]
Current Assets:
Cash and cash equivalents	37,375,000	17,182,000
Other current assets	1,494,000	3,180,000
Total Current Assets	38,869,000	20,362,000
Other deferred assets and other
Other deferred assets and other	364,000	498,000
Investments:
Investments in affiliates	953,810,000	856,444,000
Other investments	15,634,000	12,910,000
Total investments	969,444,000	869,354,000
Total Assets	1,008,677,000	890,214,000
Current Liabilities:
Accounts payable to affiliates	530,000	530,000
Other current liabilities	66,000	2,314,000
Total Current Liabilities	596,000	2,844,000
Other Credits:
Deferred income taxes	29,926,000	29,006,000
Accounts payable to affiliates	2,118,000	2,647,000
Other deferred liabilities and other	37,000	41,000
Total Other Credits	32,081,000	31,694,000
Shareholders' Equity:
Common shareholders' equity	430,571,000	350,936,000
Retained earnings	545,429,000	504,740,000
Total Common Shareholders' Equity	976,000,000	855,676,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	$ 1,008,677,000	$ 890,214,000