Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 47,859,000	$ 52,366,000	$ 44,343,000
First Mortgage Bonds [Member] | 7.70%, 2028 Series
Dividend Restrictions
Debt covenant, allowable amount available for payment of dividends	334,800,000
MGE [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	26,500,000	25,000,000	20,404,000
Dividend Restrictions
Dividend restrictions, minimum common equity ratio	0.55
Common equity ratio	0.569
MGE [Member] | First Mortgage Bonds [Member] | 7.70%, 2028 Series
Dividend Restrictions
Debt covenant, allowable amount available for payment of dividends	334,800,000
MGE Construct [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	0	0	239,000
MGE Power Elm Road [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	13,500,000	17,300,000	16,000,000
MGE Power [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	0	0	200,000
MGE Power West Campus [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	6,000,000	9,250,000	7,500,000
MGE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 1,859,000	$ 816,000	$ 0