Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Long-term Debt [Line Items]
First Mortgage Bonds	$ 1,200	$ 1,200
Tax Exempt Debt	47,300	47,300
Medium-term Notes	120,000	120,000
Other Long-Term Debt	195,973	168,473
Long-term debt due within one year	(2,667)	(1,667)
Unamortized discount	(903)	(955)
Total Long-Term Debt	360,903	334,351
Long-Term Debt Maturities [Abstract]
Long term debt maturities in next twelve months	2,667
Long term debt maturities in year two	3,013
Long term debt maturities in year three	4,102
Long term debt maturities in year four	4,182
Long term debt maturities in year five	4,268
Long term debt maturities after year five	346,241
Total	364,473
7.70%, 2028 Series [Member]
Long-term Debt [Line Items]
First Mortgage Bonds	1,200	1,200
Interest rate on secured long-term debt	7.70%	7.70%
4.875% 2012 Series [Member]
Long-term Debt [Line Items]
Tax Exempt Debt	19,300	19,300
Interest rate on secured long-term debt	4.875%	4.875%
5.875% 2034 Series [Member]
Long-term Debt [Line Items]
Tax Exempt Debt	28,000	28,000
Interest rate on secured long-term debt	5.875%	5.875%
5.26%, due 2017 [Member]
Long-term Debt [Line Items]
Medium-term Notes	20,000	20,000
Interest rate on secured long-term debt	5.26%	5.26%
5.25%, due 2017 [Member]
Long-term Debt [Line Items]
Medium-term Notes	30,000	30,000
Interest rate on secured long-term debt	5.25%	5.25%
7.12%, due 2032 [Member]
Long-term Debt [Line Items]
Medium-term Notes	25,000	25,000
Interest rate on secured long-term debt	7.12%	7.12%
6.12%, due 2028 [Member]
Long-term Debt [Line Items]
Medium-term Notes	20,000	20,000
Interest rate on secured long-term debt	6.12%	6.12%
6.247%, due 2037 [Member]
Long-term Debt [Line Items]
Medium-term Notes	25,000	25,000
Interest rate on secured long-term debt	6.247%	6.247%
5.59%, due 2018 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	40,000	40,000
Interest rate on secured long-term debt	5.59%	5.59%
Disallowable ownership of stock by outside party	30.00%
Allowable ratio of indebtedness to capitalization	65.00%
Allowable ratio of priority debt to assets	20.00%
5.68%, due 2033 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	30,000	30,000
Interest rate on secured long-term debt	5.68%	5.68%
5.19%, due 2033 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	20,000	20,000
Interest rate on secured long-term debt	5.19%	5.19%
5.04%, due 2040 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	46,806	48,473	50,000
Interest rate on secured long-term debt	5.04%	5.04%
3.38%, due 2020 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	15,000	15,000
Interest rate on secured long-term debt	3.38%	3.38%
Disallowable ownership of stock by outside party	30.00%
Allowable ratio of indebtedness to capitalization	65.00%
Allowable ratio of priority debt to assets	20.00%
5.26%, due 2040 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	15,000	15,000
Interest rate on secured long-term debt	5.26%	5.26%
Disallowable ownership of stock by outside party	30.00%
Allowable ratio of indebtedness to capitalization	65.00%
Allowable ratio of priority debt to assets	20.00%
4.74%, due 2041 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	29,167	0
Interest rate on secured long-term debt	4.74%
MGE [Member]
Long-term Debt [Line Items]
First Mortgage Bonds	1,200	1,200
Tax Exempt Debt	47,300	47,300
Medium-term Notes	120,000	120,000
Other Long-Term Debt	195,973	168,473
Long-term debt due within one year	(2,667)	(1,667)
Unamortized discount	(903)	(955)
Total Long-Term Debt	360,903	334,351
Long-Term Debt Maturities [Abstract]
Long term debt maturities in next twelve months	2,667
Long term debt maturities in year two	3,013
Long term debt maturities in year three	4,102
Long term debt maturities in year four	4,182
Long term debt maturities in year five	4,268
Long term debt maturities after year five	346,241
Total	364,473
MGE [Member] | 7.70%, 2028 Series [Member]
Long-term Debt [Line Items]
First Mortgage Bonds	1,200	1,200
Interest rate on secured long-term debt	7.70%	7.70%
MGE [Member] | 4.875% 2012 Series [Member]
Long-term Debt [Line Items]
Tax Exempt Debt	19,300	19,300
Interest rate on secured long-term debt	4.875%	4.875%
MGE [Member] | 5.875% 2034 Series [Member]
Long-term Debt [Line Items]
Tax Exempt Debt	28,000	28,000
Interest rate on secured long-term debt	5.875%	5.875%
MGE [Member] | 5.26%, due 2017 [Member]
Long-term Debt [Line Items]
Medium-term Notes	20,000	20,000
Interest rate on secured long-term debt	5.26%	5.26%
MGE [Member] | 5.25%, due 2017 [Member]
Long-term Debt [Line Items]
Medium-term Notes	30,000	30,000
Interest rate on secured long-term debt	5.25%	5.25%
MGE [Member] | 7.12%, due 2032 [Member]
Long-term Debt [Line Items]
Medium-term Notes	25,000	25,000
Interest rate on secured long-term debt	7.12%	7.12%
MGE [Member] | 6.12%, due 2028 [Member]
Long-term Debt [Line Items]
Medium-term Notes	20,000	20,000
Interest rate on secured long-term debt	6.12%	6.12%
MGE [Member] | 6.247%, due 2037 [Member]
Long-term Debt [Line Items]
Medium-term Notes	25,000	25,000
Interest rate on secured long-term debt	6.247%	6.247%
MGE [Member] | 5.59%, due 2018 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	40,000	40,000
Interest rate on secured long-term debt	5.59%	5.59%
Disallowable ownership of stock by outside party	30.00%
Allowable ratio of indebtedness to capitalization	65.00%
Allowable ratio of priority debt to assets	20.00%
MGE [Member] | 5.68%, due 2033 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	30,000	30,000
Interest rate on secured long-term debt	5.68%	5.68%
MGE [Member] | 5.19%, due 2033 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	20,000	20,000
Interest rate on secured long-term debt	5.19%	5.19%
MGE [Member] | 5.04%, due 2040 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	46,806	48,473
Interest rate on secured long-term debt	5.04%	5.04%
MGE [Member] | 3.38%, due 2020 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	15,000	15,000
Interest rate on secured long-term debt	3.38%	3.38%
Disallowable ownership of stock by outside party	30.00%
Allowable ratio of indebtedness to capitalization	65.00%
Allowable ratio of priority debt to assets	20.00%
MGE [Member] | 5.26%, due 2040 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	15,000	15,000
Interest rate on secured long-term debt	5.26%	5.26%
Disallowable ownership of stock by outside party	30.00%
Allowable ratio of indebtedness to capitalization	65.00%
Allowable ratio of priority debt to assets	20.00%
MGE [Member] | 4.74%, due 2041 [Member]
Long-term Debt [Line Items]
Other Long-Term Debt	29,167	0
Interest rate on secured long-term debt	4.74%
MGE Power Elm Road [Member]
Long-term Debt [Line Items]
Debt service coverage ratio range, high	1.25
Debt service coverage ratio range, low	1.00
Long-Term Debt Maturities [Abstract]
Total	75,972	48,473
MGE Power Elm Road [Member] | 5.04%, due 2040 [Member]
Long-term Debt [Line Items]
Debt service coverage ratio range, high	1.25
Debt service coverage ratio range, low	1.00
MGE Power Elm Road [Member] | 4.74%, due 2041 [Member]
Long-term Debt [Line Items]
Debt service coverage ratio range, high	1.25
Debt service coverage ratio range, low	1.00
MGE Power West Campus [Member]
Long-term Debt [Line Items]
Debt service coverage ratio range, high	1.25
Debt service coverage ratio range, low	1.00
Debt to total capitalization ratio range, low	0.65
Debt to total capitalization ratio range, high	1.00
Long-Term Debt Maturities [Abstract]
Total	$ 50,000	$ 50,000
MGE Power West Campus [Member] | 5.68%, due 2033 [Member]
Long-term Debt [Line Items]
Debt service coverage ratio range, high	1.25
Debt service coverage ratio range, low	1.00
Debt to total capitalization ratio range, low	0.65
Debt to total capitalization ratio range, high	1.00
MGE Power West Campus [Member] | 5.19%, due 2033 [Member]
Long-term Debt [Line Items]
Debt service coverage ratio range, high	1.25
Debt service coverage ratio range, low	1.00
Debt to total capitalization ratio range, low	0.65
Debt to total capitalization ratio range, high	1.00