Property, Plant, and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
In-service plant, net	$ 975,053	$ 961,511
Construction work in progress	98,411	34,055
Total Property, Plant, and Equipment	1,073,464	995,566
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	912,273	886,589
Gas [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	332,767	319,502
Non Regulated Energy [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	308,043	307,182
Less: Accumulated depreciation and amortization	31,547	25,454
In-service plant, net	276,496	281,728
Construction work in progress	1,548	837
Utility [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	1,245,040	1,206,091
Less: Accumulated depreciation and amortization	546,483	526,308
In-service plant, net	698,557	679,783
Construction work in progress	96,863	33,218
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service plant, net	974,549	961,007
Construction work in progress	98,411	34,055
Total Property, Plant, and Equipment	1,072,960	995,062
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	912,289	886,606
MGE [Member] | Gas [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	332,779	319,513
MGE [Member] | Non Regulated Energy [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	307,511	306,650
Less: Accumulated depreciation and amortization	31,547	25,454
In-service plant, net	275,964	281,196
Construction work in progress	1,548	837
MGE [Member] | Utility [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	1,245,068	1,206,119
Less: Accumulated depreciation and amortization	546,483	526,308
In-service plant, net	698,585	679,811
Construction work in progress	$ 96,863	$ 33,218