Schedule I - Condensed Parent Company Finanical Statements (Details-Balance Sheet) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current Assets:
Cash and cash equivalents	$ 65,755	$ 68,813	$ 46,357	$ 41,169
Accounts receivable, net:
Other current assets	10,711	8,225
Total Current Assets	253,959	220,601
Other deferred assets and other	4,837	5,853
Investments:
Other investments	159	0
Total investments	71,760	67,952
Total Assets	1,697,666	1,579,060	1,586,924
Current Liabilities:
Other current liabilities	13,931	9,489
Total Current Liabilities	89,996	96,666
Other Credits:
Deferred income taxes	342,045	284,791
Total Other Credits	553,013	465,470
Shareholders' Equity:
Retained income	308,007	266,197
Other comprehensive income (loss)	458	377
Total Common Shareholders' Equity	659,401	617,510	579,429	550,952
Commitments and contingencies (see Footnote 3)	0	0
Total Liabilities and Capitalization	1,697,666	1,579,060
MGE Energy [Member]
Current Assets:
Cash and cash equivalents	58,429	51,204	36,881	24,620
Accounts receivable, net:
Accounts receivable from affiliates	64	125
Other current assets	2,809	1,015
Total Current Assets	61,302	52,344
Other deferred assets and other	140	157
Investments:
Investments in affiliates	619,563	583,435
Other investments	1,177	948
Total investments	620,740	584,383
Total Assets	682,182	636,884
Current Liabilities:
Accounts payable to affiliates	7,096	530
Accrued taxes	663	4,297
Other current liabilities	2,601	3,076
Total Current Liabilities	10,360	7,903
Other Credits:
Deferred income taxes	7,125	5,646
Accounts payable to affiliates	5,296	5,825
Total Other Credits	12,421	11,471
Shareholders' Equity:
Common shareholders' equity	350,936	350,936
Retained income	308,007	266,197
Other comprehensive income (loss)	458	377
Total Common Shareholders' Equity	659,401	617,510
Commitments and contingencies (see Footnote 3)	0	0
Total Liabilities and Capitalization	$ 682,182	$ 636,884