Rate Matters (Details) (PSCW [Member], USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended			9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2014 Legal Entity Type of Counterparty [Domain]	Sep. 30, 2014 MGE [Member]	Dec. 31, 2013 MGE [Member]	Sep. 30, 2014 MGE [Member] Fuel Rules Surplus Credit, 2012 [Member]	Sep. 30, 2014 MGE [Member] Fuel Rules Surplus Credit, 2013 [Member]	Sep. 30, 2014 Columbia Environmental Project [Member] MGE [Member]	Dec. 31, 2013 Columbia Environmental Project [Member] MGE [Member]	Sep. 30, 2014 Electric [Member] MGE [Member]	Dec. 31, 2013 Electric [Member] MGE [Member]	Dec. 31, 2015 Electric [Member] Proposed Future Rate Matters [Member] MGE [Member]	Dec. 31, 2015 Electric [Member] Proposed Future Rate Matters - Revised From Initial Filing [Member] MGE [Member]	Sep. 30, 2014 Gas [Member] MGE [Member]	Dec. 31, 2013 Gas [Member] MGE [Member]	Dec. 31, 2015 Gas [Member] Proposed Future Rate Matters [Member] MGE [Member]	Dec. 31, 2015 Gas [Member] Proposed Future Rate Matters - Revised From Initial Filing [Member] MGE [Member]
Rate Proceedings [Abstract]
Proposed rate increase (decrease), percentage										2.80%	4.30%			(2.30%)	(1.40%)
Authorized rate increase (decrease), percentage								0.00%	3.80%			0.00%	1.00%
Authorized rate increase (decrease), amount								$ 0	$ 14.9			$ 0	$ 1.6
Authorized AFUDC Rate						100.00%	50.00%
Return of electric fuel credit, total				6.2	6.7
Authorized return on equity, percentage		10.30%	10.30%
Fuel Rules [Abstract]
Fuel rules, bandwidth	2.00%
Fuel rules, electric fuel deferred costs upper threshold	102.00%
Fuel rules, electric fuel deferred costs lower threshold	98.00%
Return of electric fuel credit, current period				$ 4.7