Commitments and Contingencies (Details-1) (USD $)	9 Months Ended
	Sep. 30, 2011 MW Tons Dth MWh
Lenz Oil Site [Abstract]
Total remedy amount	$ 2,200,000
MGE's portion of remedy	100,000
Air Quality Regulations [Abstract]
Minimum capacity to be regulated by CSAPR - MW	25
Minimum GHG emmissions required to include GHGs as permitted air emmissions	25,000
Columbia Certificate Of Authority [Abstract]
MGE's share of total capital expenditures	140,000,000
Incurred costs to date	1,400,000
Carrying cost on pre-construction costs - AFUDC rate	100.00%
Columbia Clean Air Act Litigation [Abstract]
Columbia Clean Air Act litigation civil penalties	37,500
Columbia Units [Member]
Columbia Units [Line Items]
Generating capability	225
Columbia's share of MGE's net generating capability	27.00%
Ownership interest in jointly owned plant	22.00%
WPL ownership interest of Columbia	46.20%
WPSC ownership interest of Columbia	31.80%
One Year From Balance Sheet Date [Member]
Columbia Project [Line Items]
MGE's share of Columbia project capital expenditures	5,000,000
More Than One And Within Two Years From Balance Sheet Date [Member]
Columbia Project [Line Items]
MGE's share of Columbia project capital expenditures	53,000,000
More Than Two And Within Three Years From Balance Sheet Date [Member]
Columbia Project [Line Items]
MGE's share of Columbia project capital expenditures	68,000,000
More Than Three And Within Four Years From Balance Sheet Date [Member]
Columbia Project [Line Items]
MGE's share of Columbia project capital expenditures	$ 13,000,000