Schedule I - Condensed Parent Company Finanical Statements (Details-Balance Sheet) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Assets:
Cash and cash equivalents	$ 83,102,000	$ 107,952,000
Other current assets	8,593,000	12,507,000
Total Current Assets	240,560,000	290,631,000
Other deferred assets and other
Other deferred assets and other	12,488,000	731,000
Investments:
Other investments	2,298,000	55,000
Total investments	78,000,000	67,772,000
Total Assets	1,988,618,000	1,855,182,000	$ 1,801,060,000
Current Liabilities:
Other current liabilities	14,113,000	18,758,000
Total Current Liabilities	120,628,000	126,514,000
Other Credits:
Deferred income taxes	231,952,000	225,130,000
Total Other Credits	558,003,000	552,320,000
Shareholders' Equity:
Retained earnings	465,708,000	426,874,000
Accumulated other comprehensive income, net of tax	0	377,000
Total Common Shareholders' Equity	816,644,000	778,187,000	$ 724,088,000	$ 690,458,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	1,988,618,000	1,855,182,000
MGE Energy [Member]
Current Assets:
Cash and cash equivalents	75,036,000	98,540,000
Other current assets	3,646,000	1,601,000
Total Current Assets	78,682,000	100,141,000
Other deferred assets and other
Other deferred assets and other	110,000	171,000
Investments:
Investments in affiliates	763,625,000	702,134,000
Other investments	7,672,000	5,640,000
Total investments	771,297,000	707,774,000
Total Assets	850,089,000	808,086,000
Current Liabilities:
Accounts payable to affiliates	617,000	665,000
Other current liabilities	2,500,000	2,047,000
Total Current Liabilities	3,117,000	2,712,000
Other Credits:
Deferred income taxes	27,151,000	23,480,000
Accounts payable to affiliates	3,177,000	3,707,000
Total Other Credits	30,328,000	27,187,000
Shareholders' Equity:
Common shareholders' equity	350,936,000	350,936,000
Retained earnings	465,708,000	426,874,000
Accumulated other comprehensive income, net of tax	0	377,000
Total Common Shareholders' Equity	816,644,000	778,187,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	$ 850,089,000	$ 808,086,000