Commitments and Contingencies (Details) (USD $)	6 Months Ended
Jun. 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
Timeframe Columbia project will be under construction	2011 - 2014
Carrying cost on pre-construction costs - AFUDC rate	100.00%
Incurred costs to date	1,100,000
Columbia Clean Air Act Litigation [Abstract]
Columbia Clean Air Act litigation civil penalties	37,500
Chattel Paper Purchase Agreement [Abstract]
Chattel paper purchase agreement maximum interest	10,000,000
Outstanding interest in chattel paper receivables	4,100,000
Servicing asset recognized	200,000
Smart Grid Investment Grant [Abstract]
Smart Grid grant approval amount	5,500,000
Total cost of proposed projects	11,000,000
Smart grid expenditures to date	4,400,000
Smart grid commitments to date	700,000
Columbia Units [Member]
Columbia Units [Line Items]
Generating capability	225
Columbia's share of MGE's net generating capability	27.00%
Ownership interest	22.00%
WPL ownership interest of Columbia	46.20%
WPSC ownership interest of Columbia	31.80%
One Year From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	334,000
Natural Gas Transportation And Storage Commitments [Abstract]
Natural gas transportation and storage commitments	7,803,000
Natural Gas Supply Commitments [Abstract]
Natural gas supply commitments	15,590,000
Coal Commitments [Abstract]
Coal commitments	13,410,000
More Than One And Within Two Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	561,000
Natural Gas Transportation And Storage Commitments [Abstract]
Natural gas transportation and storage commitments	17,226,000
Natural Gas Supply Commitments [Abstract]
Natural gas supply commitments	15,832,000
Coal Commitments [Abstract]
Coal commitments	29,515,000
More Than Two And Within Three Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	605,000
Natural Gas Transportation And Storage Commitments [Abstract]
Natural gas transportation and storage commitments	17,037,000
Natural Gas Supply Commitments [Abstract]
Natural gas supply commitments	0
Coal Commitments [Abstract]
Coal commitments	13,340,000
More Than Three And Within Four Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	423,000
Natural Gas Transportation And Storage Commitments [Abstract]
Natural gas transportation and storage commitments	16,843,000
Natural Gas Supply Commitments [Abstract]
Natural gas supply commitments	0
Coal Commitments [Abstract]
Coal commitments	3,661,000
More Than Four And Within Five Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	732,000
Natural Gas Transportation And Storage Commitments [Abstract]
Natural gas transportation and storage commitments	16,689,000
Natural Gas Supply Commitments [Abstract]
Natural gas supply commitments	0
Coal Commitments [Abstract]
Coal commitments	$ 0

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Coal commitments for the Columbia and Elm Road Units.

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Natural gas supply commitments.

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Natural gas transportation and storage commitments.

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