Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenues	$ 117,221	$ 117,259	$ 266,480	$ 281,864
Interdepartmental revenues	0	0	0	0
Total operating revenues	117,221	117,259	266,480	281,864
Depreciation and amortization	(9,712)	(10,357)	(19,336)	(20,373)
Other operating expenses	(82,428)	(83,705)	(193,619)	(207,396)
Operating Income	25,081	23,197	53,525	54,095
Other (deductions) income, net	2,549	2,153	5,119	4,539
Interest (expense) income, net	(4,764)	(5,055)	(9,868)	(9,905)
Income before income taxes	22,866	20,295	48,776	48,729
Income tax provision	(8,596)	(7,572)	(18,458)	(18,223)
Net Income	14,270	12,723	30,318	30,506
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,506,550		1,506,550		1,458,882
Capital Expenditures			39,553		65,176
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	96,339	90,834	186,275	176,841
Interdepartmental revenues	119	121	228	228
Total operating revenues	96,458	90,955	186,503	177,069
Depreciation and amortization	(6,546)	(7,052)	(13,024)	(14,029)
Other operating expenses	(72,265)	(69,522)	(145,053)	(140,438)
Operating Income	17,647	14,381	28,426	22,602
Other (deductions) income, net	96	(124)	260	33
Interest (expense) income, net	(2,465)	(2,653)	(5,192)	(5,353)
Income before income taxes	15,278	11,604	23,494	17,282
Income tax provision	(5,642)	(4,121)	(8,427)	(5,722)
Net Income	9,636	7,483	15,067	11,560
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	868,718		868,718		794,738
Capital Expenditures			33,479		47,206
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	18,629	25,062	75,648	102,499
Interdepartmental revenues	3,077	2,173	6,063	3,164
Total operating revenues	21,706	27,235	81,711	105,663
Depreciation and amortization	(1,389)	(1,532)	(2,759)	(2,869)
Other operating expenses	(21,746)	(25,717)	(71,487)	(88,770)
Operating Income	(1,429)	(14)	7,465	14,024
Other (deductions) income, net	27	(35)	73	9
Interest (expense) income, net	(695)	(748)	(1,464)	(1,509)
Income before income taxes	(2,097)	(797)	6,074	12,524
Income tax provision	933	366	(2,305)	(4,882)
Net Income	(1,164)	(431)	3,769	7,642
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	258,569		258,569		285,702
Capital Expenditures			5,601		15,830
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,253	1,363	4,557	2,524
Interdepartmental revenues	8,677	9,581	17,353	18,977
Total operating revenues	10,930	10,944	21,910	21,501
Depreciation and amortization	(1,777)	(1,773)	(3,553)	(3,475)
Other operating expenses	(37)	(55)	(49)	(94)
Operating Income	9,116	9,116	18,308	17,932
Other (deductions) income, net	0	0	0	0
Interest (expense) income, net	(1,639)	(1,669)	(3,284)	(3,017)
Income before income taxes	7,477	7,447	15,024	14,915
Income tax provision	(3,001)	(2,990)	(6,030)	(5,987)
Net Income	4,476	4,457	8,994	8,928
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	293,194		293,194		299,421
Capital Expenditures			473		2,140
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Interdepartmental revenues	0	0	0	0
Total operating revenues	0	0	0	0
Depreciation and amortization	0	0	0	0
Other operating expenses	0	0	0	0
Operating Income	0	0	0	0
Other (deductions) income, net	2,242	2,170	4,484	4,267
Interest (expense) income, net	0	0	0	0
Income before income taxes	2,242	2,170	4,484	4,267
Income tax provision	(900)	(870)	(1,810)	(1,722)
Net Income	1,342	1,300	2,674	2,545
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	58,875		58,875		57,006
Capital Expenditures			0		0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Interdepartmental revenues	0	0	0	0
Total operating revenues	0	0	0	0
Depreciation and amortization	0	0	0	0
Other operating expenses	(253)	(286)	(674)	(463)
Operating Income	(253)	(286)	(674)	(463)
Other (deductions) income, net	184	142	302	230
Interest (expense) income, net	35	15	72	(26)
Income before income taxes	(34)	(129)	(300)	(259)
Income tax provision	14	43	114	90
Net Income	(20)	(86)	(186)	(169)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	405,929		405,929		401,862
Capital Expenditures			0		0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Interdepartmental revenues	(11,873)	(11,875)	(23,644)	(22,369)
Total operating revenues	(11,873)	(11,875)	(23,644)	(22,369)
Depreciation and amortization	0	0	0	0
Other operating expenses	11,873	11,875	23,644	22,369
Operating Income	0	0	0	0
Other (deductions) income, net	0	0	0	0
Interest (expense) income, net	0	0	0	0
Income before income taxes	0	0	0	0
Income tax provision	0	0	0	0
Net Income	0	0	0	0
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(403,330)		(403,330)		(412,729)
Capital Expenditures			0		0
Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	24,595		24,595		32,882
Capital Expenditures			0		0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	117,221	117,259	266,480	281,864
Interdepartmental revenues	0	0	0	0
Total operating revenues	117,221	117,259	266,480	281,864
Depreciation and amortization	(9,712)	(10,357)	(19,336)	(20,373)
Other operating expenses	(89,811)	(90,083)	(209,550)	(223,487)
Operating Income	17,698	16,819	37,594	38,004
Other (deductions) income, net	1,391	1,062	2,850	2,553
Interest (expense) income, net	(4,799)	(5,070)	(9,940)	(9,879)
Income tax provision	(7,635)	(6,666)	(16,604)	(16,557)
Net Income Including Noncontrolling Interest	14,290	12,811	30,504	30,678
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,080)	(5,992)	(12,152)	(11,925)
Net Income	8,210	6,819	18,352	18,753
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,477,303		1,477,303		1,433,793
Capital Expenditures			39,553		65,176
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	96,339	90,834	186,275	176,841
Interdepartmental revenues	119	121	228	228
Total operating revenues	96,458	90,955	186,503	177,069
Depreciation and amortization	(6,546)	(7,052)	(13,024)	(14,029)
Other operating expenses	(77,849)	(73,581)	(153,357)	(146,132)
Operating Income	12,063	10,322	20,122	16,908
Other (deductions) income, net	38	(185)	137	6
Interest (expense) income, net	(2,465)	(2,653)	(5,192)	(5,353)
Net Income Including Noncontrolling Interest	9,636	7,484	15,067	11,561
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0	0	0
Net Income	9,636	7,484	15,067	11,561
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	868,718		868,718		794,738
Capital Expenditures			33,479		47,206
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	18,629	25,062	75,648	102,499
Interdepartmental revenues	3,077	2,173	6,063	3,164
Total operating revenues	21,706	27,235	81,711	105,663
Depreciation and amortization	(1,389)	(1,532)	(2,759)	(2,869)
Other operating expenses	(20,797)	(25,333)	(73,758)	(93,644)
Operating Income	(480)	370	5,194	9,150
Other (deductions) income, net	11	(52)	39	2
Interest (expense) income, net	(695)	(748)	(1,464)	(1,509)
Net Income Including Noncontrolling Interest	(1,164)	(430)	3,769	7,643
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0	0	0
Net Income	(1,164)	(430)	3,769	7,643
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	258,569		258,569		285,702
Capital Expenditures			5,601		15,830
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,253	1,363	4,557	2,524
Interdepartmental revenues	8,677	9,581	17,353	18,977
Total operating revenues	10,930	10,944	21,910	21,501
Depreciation and amortization	(1,777)	(1,773)	(3,553)	(3,475)
Other operating expenses	(3,038)	(3,044)	(6,079)	(6,080)
Operating Income	6,115	6,127	12,278	11,946
Other (deductions) income, net	0	0	0	0
Interest (expense) income, net	(1,639)	(1,669)	(3,284)	(3,017)
Net Income Including Noncontrolling Interest	4,476	4,458	8,994	8,929
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0	0	0
Net Income	4,476	4,458	8,994	8,929
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	292,944		292,944		299,171
Capital Expenditures			473		2,140
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Interdepartmental revenues	0	0	0	0
Total operating revenues	0	0	0	0
Depreciation and amortization	0	0	0	0
Other operating expenses	0	0	0	0
Operating Income	0	0	0	0
Other (deductions) income, net	1,342	1,299	2,674	2,545
Interest (expense) income, net	0	0	0	0
Net Income Including Noncontrolling Interest	1,342	1,299	2,674	2,545
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0	0	0
Net Income	1,342	1,299	2,674	2,545
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	58,875		58,875		57,006
Capital Expenditures			0		0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Interdepartmental revenues	(11,873)	(11,875)	(23,644)	(22,369)
Total operating revenues	(11,873)	(11,875)	(23,644)	(22,369)
Depreciation and amortization	0	0	0	0
Other operating expenses	11,873	11,875	23,644	22,369
Operating Income	0	0	0	0
Other (deductions) income, net	0	0	0	0
Interest (expense) income, net	0	0	0	0
Net Income Including Noncontrolling Interest	0	0	0	0
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,080)	(5,992)	(12,152)	(11,925)
Net Income	(6,080)	(5,992)	(12,152)	(11,925)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(26,398)		(26,398)		(35,706)
Capital Expenditures			0		0
MGE [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	24,595		24,595		32,882
Capital Expenditures			$ 0		$ 0