Equity and Financing Arrangements (Details) (USD $)	9 Months Ended				3 Months Ended							9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Jul. 18, 2013 Issuance of debt - 4.42%, due 2043 [Member]	Jul. 18, 2013 Issuance of debt - 4.47%, due 2048 [Member]	Jul. 18, 2013 Repayment of debt - 5.26%, due 2017 [Member]	Jul. 18, 2013 Repayment of debt - 5.59%, due 2018 [Member]	Jul. 18, 2013 5.59%, due 2018 [Member]	Sep. 16, 2013 Issuance of debt - 3.09%, due 2023 [Member]	Sep. 16, 2013 Issuance of debt - 3.29%, due 2026 [Member]	Sep. 30, 2013 MGE Energy [Member]	Jun. 19, 2013 MGE Energy [Member]	Sep. 30, 2013 MGE [Member]	Sep. 30, 2012 MGE [Member]	Jun. 19, 2013 MGE [Member]
Common Stock [Abstract]
Common stock issued during period	0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities	$ 0
Credit Facilities [Line Items]
Revolving credit facility										50,000,000	40,000,000	100,000,000		75,000,000
Floating rate-based borrowings adder minimum										0.00%		0.00%
Floating rate-based borrowings adder maximum										0.125%		0.125%
Eurodollar-based borrowings adder minimum										0.675%		0.675%
Eurodollar-based borrowings adder maximum										1.125%		1.125%
Federal funds fixed base rate										0.50%		0.50%
Eurodollar fixed base rate										1.00%		1.00%
Line of credit borrowings										0		0
Commercial paper outstanding												0
Debt Instruments [Line Items]
Unsecured debt			20,000,000	20,000,000				30,000,000	15,000,000
Interest rate			4.42%	4.47%	5.26%	5.59%	5.59%	3.09%	3.29%
Redeemed and retired debt					20,000,000	20,000,000
Debt make-whole premium	6,757,000	0			3,200,000	3,600,000						6,757,000	0
Secured debt							$ 20,000,000