Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenues	$ 149,259	$ 164,605
Interdepartmental revenues	0	0
Total operating revenues	149,259	164,605
Depreciation and amortization	(9,624)	(10,016)
Other operating expenses	(111,191)	(123,691)
Operating Income	28,444	30,898
Other (deductions) income, net	2,570	2,386
Interest (expense) income, net	(5,104)	(4,850)
Income before income taxes	25,910	28,434
Income tax provision	(9,862)	(10,651)
Net Income	16,048	17,783
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,482,297		1,458,882
Capital Expenditures	15,467		65,176
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	89,936	86,007
Interdepartmental revenues	109	107
Total operating revenues	90,045	86,114
Depreciation and amortization	(6,478)	(6,977)
Other operating expenses	(72,788)	(70,916)
Operating Income	10,779	8,221
Other (deductions) income, net	164	157
Interest (expense) income, net	(2,727)	(2,700)
Income before income taxes	8,216	5,678
Income tax provision	(2,785)	(1,601)
Net Income	5,431	4,077
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	836,179		794,738
Capital Expenditures	13,987		47,206
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	57,019	77,437
Interdepartmental revenues	2,986	991
Total operating revenues	60,005	78,428
Depreciation and amortization	(1,370)	(1,337)
Other operating expenses	(49,741)	(63,053)
Operating Income	8,894	14,038
Other (deductions) income, net	46	44
Interest (expense) income, net	(769)	(761)
Income before income taxes	8,171	13,321
Income tax provision	(3,238)	(5,248)
Net Income	4,933	8,073
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	266,823		285,702
Capital Expenditures	1,151		15,830
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,304	1,161
Interdepartmental revenues	8,676	9,396
Total operating revenues	10,980	10,557
Depreciation and amortization	(1,776)	(1,702)
Other operating expenses	(12)	(39)
Operating Income	9,192	8,816
Other (deductions) income, net	0	0
Interest (expense) income, net	(1,645)	(1,348)
Income before income taxes	7,547	7,468
Income tax provision	(3,029)	(2,997)
Net Income	4,518	4,471
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	296,322		299,421
Capital Expenditures	329		2,140
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	0	0
Total operating revenues	0	0
Depreciation and amortization	0	0
Other operating expenses	0	0
Operating Income	0	0
Other (deductions) income, net	2,242	2,097
Interest (expense) income, net	0	0
Income before income taxes	2,242	2,097
Income tax provision	(910)	(852)
Net Income	1,332	1,245
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	57,863		57,006
Capital Expenditures	0		0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	0	0
Total operating revenues	0	0
Depreciation and amortization	0	0
Other operating expenses	(421)	(177)
Operating Income	(421)	(177)
Other (deductions) income, net	118	88
Interest (expense) income, net	37	(41)
Income before income taxes	(266)	(130)
Income tax provision	100	47
Net Income	(166)	(83)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	399,459		401,862
Capital Expenditures	0		0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	(11,771)	(10,494)
Total operating revenues	(11,771)	(10,494)
Depreciation and amortization	0	0
Other operating expenses	11,771	10,494
Operating Income	0	0
Other (deductions) income, net	0	0
Interest (expense) income, net	0	0
Income before income taxes	0	0
Income tax provision	0	0
Net Income	0	0
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(403,770)		(412,729)
Capital Expenditures	0		0
Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	29,421		32,882
Capital Expenditures	0		0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	149,259	164,605
Interdepartmental revenues	0	0
Total operating revenues	149,259	164,605
Depreciation and amortization	(9,624)	(10,016)
Other operating expenses	(119,739)	(133,404)
Operating Income	19,896	21,185
Other (deductions) income, net	1,459	1,491
Interest (expense) income, net	(5,141)	(4,809)
Income tax provision	(8,969)	(9,891)
Net Income Including Noncontrolling Interest	16,214	17,867
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,072)	(5,933)
Net Income	10,142	11,934
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,459,368		1,433,793
Capital Expenditures	15,467		65,176
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	89,936	86,007
Interdepartmental revenues	109	107
Total operating revenues	90,045	86,114
Depreciation and amortization	(6,478)	(6,977)
Other operating expenses	(75,508)	(72,551)
Operating Income	8,059	6,586
Other (deductions) income, net	99	191
Interest (expense) income, net	(2,727)	(2,700)
Net Income Including Noncontrolling Interest	5,431	4,077
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income	5,431	4,077
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	836,179		794,738
Capital Expenditures	13,987		47,206
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	57,019	77,437
Interdepartmental revenues	2,986	991
Total operating revenues	60,005	78,428
Depreciation and amortization	(1,370)	(1,337)
Other operating expenses	(52,961)	(68,311)
Operating Income	5,674	8,780
Other (deductions) income, net	28	54
Interest (expense) income, net	(769)	(761)
Net Income Including Noncontrolling Interest	4,933	8,073
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income	4,933	8,073
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	266,823		285,702
Capital Expenditures	1,151		15,830
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,304	1,161
Interdepartmental revenues	8,676	9,396
Total operating revenues	10,980	10,557
Depreciation and amortization	(1,776)	(1,702)
Other operating expenses	(3,041)	(3,036)
Operating Income	6,163	5,819
Other (deductions) income, net	0	0
Interest (expense) income, net	(1,645)	(1,348)
Net Income Including Noncontrolling Interest	4,518	4,471
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income	4,518	4,471
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	296,072		299,171
Capital Expenditures	329		2,140
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	0	0
Total operating revenues	0	0
Depreciation and amortization	0	0
Other operating expenses	0	0
Operating Income	0	0
Other (deductions) income, net	1,332	1,246
Interest (expense) income, net	0	0
Net Income Including Noncontrolling Interest	1,332	1,246
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income	1,332	1,246
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	57,863		57,006
Capital Expenditures	0		0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	(11,771)	(10,494)
Total operating revenues	(11,771)	(10,494)
Depreciation and amortization	0	0
Other operating expenses	11,771	10,494
Operating Income	0	0
Other (deductions) income, net	0	0
Interest (expense) income, net	0	0
Net Income Including Noncontrolling Interest	0	0
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,072)	(5,933)
Net Income	(6,072)	(5,933)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(26,990)		(35,706)
Capital Expenditures	0		0
MGE [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	29,421		32,882
Capital Expenditures	$ 0		$ 0