Property, Plant, and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
In-service plant, net	$ 961,511	$ 857,572
Construction work in progress	34,055	110,435
Total Property, Plant, and Equipment	995,566	968,007
Long-term debt instruments [Line Items]
First Mortgage Bonds	1,200	1,200
7.70%, 2028 Series [Member]
Long-term debt instruments [Line Items]
First Mortgage Bonds	1,200	1,200
Electric [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	886,589	841,256
Gas [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	319,502	304,117
Non Regulated Energy [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	307,182	232,754
Less: Accumulated depreciation and amortization	25,454	18,371
In-service plant, net	281,728	214,383
Construction work in progress	837	72,221
Utility [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	1,206,091	1,145,373
Less: Accumulated depreciation and amortization	526,308	502,184
In-service plant, net	679,783	643,189
Construction work in progress	33,218	38,214
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service plant, net	961,007	857,442
Construction work in progress	34,055	110,435
Total Property, Plant, and Equipment	995,062	967,877
Long-term debt instruments [Line Items]
First Mortgage Bonds	1,200	1,200
MGE [Member] | 7.70%, 2028 Series [Member]
Long-term debt instruments [Line Items]
First Mortgage Bonds	1,200	1,200
MGE [Member] | Electric [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	886,606	841,273
MGE [Member] | Gas [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	319,513	304,129
MGE [Member] | Non Regulated Energy [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	306,650	232,595
Less: Accumulated depreciation and amortization	25,454	18,371
In-service plant, net	281,196	214,224
Construction work in progress	837	72,221
MGE [Member] | Utility [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	1,206,119	1,145,402
Less: Accumulated depreciation and amortization	526,308	502,184
In-service plant, net	679,811	643,218
Construction work in progress	$ 33,218	$ 38,214