Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Operating revenues	$ 130,946	$ 133,572	$ 117,259	$ 164,605	$ 135,928	$ 127,938	$ 109,082	$ 159,643	$ 546,382	$ 532,591	$ 533,819
Interdepartmental revenues									0	0	0
Total operating revenues									546,382	532,591	533,819
Depreciation and amortization									(40,942)	(37,960)	(41,080)
Other operating expenses									(397,572)	(398,029)	(408,074)
Operating Income	17,439	36,334	23,197	30,898	20,353	34,352	20,122	21,775	107,868	96,602	84,665
Other (deductions) income, net									9,214	11,093	8,096
Interest (expense) income, net									(20,162)	(16,157)	(13,594)
Income before income taxes									96,920	91,538	79,167
Income tax provision	(5,274)	(12,495)	(7,572)	(10,651)	(6,030)	(12,990)	(6,472)	(8,328)	(35,992)	(33,820)	(28,170)
Net Income	9,384	21,038	12,723	17,783	11,997	19,909	11,552	14,260	60,928	57,718	50,997
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	1,458,882				1,317,893				1,458,882	1,317,893	1,281,885
Capital Expenditures									65,176	60,082	77,929
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									375,858	360,729	332,324
Interdepartmental revenues									495	504	524
Total operating revenues									376,353	361,233	332,848
Depreciation and amortization									(28,323)	(27,498)	(28,779)
Other operating expenses									(292,080)	(279,389)	(258,988)
Operating Income									55,950	54,346	45,081
Other (deductions) income, net									71	2,353	(110)
Interest (expense) income, net									(10,849)	(10,548)	(10,678)
Income before income taxes									45,172	46,151	34,293
Income tax provision									(15,334)	(15,983)	(10,373)
Net Income									29,838	30,168	23,920
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	794,738				721,721				794,738	721,721	695,897
Capital Expenditures									47,206	33,655	37,014
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									165,271	165,915	192,334
Interdepartmental revenues									12,440	11,509	7,681
Total operating revenues									177,711	177,424	200,015
Depreciation and amortization									(5,593)	(5,237)	(9,557)
Other operating expenses									(155,444)	(158,146)	(171,313)
Operating Income									16,674	14,041	19,145
Other (deductions) income, net									20	664	(31)
Interest (expense) income, net									(3,060)	(2,975)	(3,012)
Income before income taxes									13,634	11,730	16,102
Income tax provision									(5,249)	(4,299)	(6,234)
Net Income									8,385	7,431	9,868
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	285,702				257,505				285,702	257,505	249,610
Capital Expenditures									15,830	13,719	13,734
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									5,253	5,947	9,161
Interdepartmental revenues									38,148	28,462	14,899
Total operating revenues									43,401	34,409	24,060
Depreciation and amortization									(7,026)	(5,225)	(2,744)
Other operating expenses									(174)	(136)	(129)
Operating Income									36,201	29,048	21,187
Other (deductions) income, net									0	0	0
Interest (expense) income, net									(6,331)	(2,659)	(2,690)
Income before income taxes									29,870	26,389	18,497
Income tax provision									(11,988)	(10,581)	(7,424)
Net Income									17,882	15,808	11,073
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	299,421				300,862				299,421	300,862	292,101
Capital Expenditures									2,140	12,708	27,181
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Interdepartmental revenues									0	0	0
Total operating revenues									0	0	0
Depreciation and amortization									0	0	0
Other operating expenses									0	0	(1)
Operating Income									0	0	(1)
Other (deductions) income, net									8,614	8,501	8,172
Interest (expense) income, net									0	0	(1)
Income before income taxes									8,614	8,501	8,170
Income tax provision									(3,467)	(3,443)	(3,280)
Net Income									5,147	5,058	4,890
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	57,006				54,241				57,006	54,241	51,728
Capital Expenditures									0	0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Interdepartmental revenues									0	0	0
Total operating revenues									0	0	0
Depreciation and amortization									0	0	0
Other operating expenses									(957)	(833)	(747)
Operating Income									(957)	(833)	(747)
Other (deductions) income, net									509	(425)	65
Interest (expense) income, net									78	25	2,787
Income before income taxes									(370)	(1,233)	2,105
Income tax provision									46	486	(859)
Net Income									(324)	(747)	1,246
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	401,862				376,219				401,862	376,219	389,744
Capital Expenditures									0	0	0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Interdepartmental revenues									(51,083)	(40,475)	(23,104)
Total operating revenues									(51,083)	(40,475)	(23,104)
Depreciation and amortization									0	0	0
Other operating expenses									51,083	40,475	23,104
Operating Income									0	0	0
Other (deductions) income, net									0	0	0
Interest (expense) income, net									0	0	0
Income before income taxes									0	0	0
Income tax provision									0	0	0
Net Income									0	0	0
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	(412,729)				(414,734)				(412,729)	(414,734)	(419,537)
Capital Expenditures									0	0	0
Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	32,882				22,079				32,882	22,079	22,342
Capital Expenditures									0	0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues									546,382	532,591	533,819
Interdepartmental revenues									0	0	0
Total operating revenues									546,382	532,591	533,819
Depreciation and amortization									(40,942)	(37,960)	(41,080)
Other operating expenses									(428,903)	(426,752)	(431,299)
Operating Income									76,537	67,879	61,440
Other (deductions) income, net									4,955	6,768	4,693
Interest (expense) income, net									(20,240)	(16,182)	(16,381)
Income tax provision									(36,039)	(34,305)	(27,311)
Net Income Including Noncontrolling Interest									61,252	58,465	49,752
Less Net Income Attributable to Noncontrolling Interest, net of tax									(23,970)	(20,740)	(13,883)
Net Income									37,282	37,725	35,869
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	1,433,793				1,318,941				1,433,793	1,318,941	1,273,555
Capital Expenditures									65,176	60,082	77,929
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									375,858	360,729	332,324
Interdepartmental revenues									495	504	524
Total operating revenues									376,353	361,233	332,848
Depreciation and amortization									(28,323)	(27,498)	(28,779)
Other operating expenses									(307,193)	(294,353)	(269,316)
Operating Income									40,837	39,382	34,753
Other (deductions) income, net									(150)	1,334	(155)
Interest (expense) income, net									(10,849)	(10,548)	(10,678)
Net Income Including Noncontrolling Interest									29,838	30,168	23,920
Less Net Income Attributable to Noncontrolling Interest, net of tax									0	0	0
Net Income									29,838	30,168	23,920
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	794,738				721,721				794,738	721,721	695,897
Capital Expenditures									47,206	33,655	37,014
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									165,271	165,915	192,334
Interdepartmental revenues									12,440	11,509	7,681
Total operating revenues									177,711	177,424	200,015
Depreciation and amortization									(5,593)	(5,237)	(9,557)
Other operating expenses									(160,631)	(162,157)	(177,534)
Operating Income									11,487	10,030	12,924
Other (deductions) income, net									(42)	376	(44)
Interest (expense) income, net									(3,060)	(2,975)	(3,012)
Net Income Including Noncontrolling Interest									8,385	7,431	9,868
Less Net Income Attributable to Noncontrolling Interest, net of tax									0	0	0
Net Income									8,385	7,431	9,868
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	285,702				257,505				285,702	257,505	249,610
Capital Expenditures									15,830	13,719	13,734
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									5,253	5,947	9,161
Interdepartmental revenues									38,148	28,462	14,899
Total operating revenues									43,401	34,409	24,060
Depreciation and amortization									(7,026)	(5,225)	(2,744)
Other operating expenses									(12,162)	(10,717)	(7,552)
Operating Income									24,213	18,467	13,764
Other (deductions) income, net									0	0	0
Interest (expense) income, net									(6,331)	(2,659)	(2,690)
Net Income Including Noncontrolling Interest									17,882	15,808	11,074
Less Net Income Attributable to Noncontrolling Interest, net of tax									0	0	0
Net Income									17,882	15,808	11,074
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	299,171				300,612				299,171	300,612	291,856
Capital Expenditures									2,140	12,708	27,181
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Interdepartmental revenues									0	0	0
Total operating revenues									0	0	0
Depreciation and amortization									0	0	0
Other operating expenses									0	0	(1)
Operating Income									0	0	(1)
Other (deductions) income, net									5,147	5,058	4,892
Interest (expense) income, net									0	0	(1)
Net Income Including Noncontrolling Interest									5,147	5,058	4,890
Less Net Income Attributable to Noncontrolling Interest, net of tax									0	0	0
Net Income									5,147	5,058	4,890
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	57,006				54,241				57,006	54,241	51,728
Capital Expenditures									0	0	0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Interdepartmental revenues									(51,083)	(40,475)	(23,104)
Total operating revenues									(51,083)	(40,475)	(23,104)
Depreciation and amortization									0	0	0
Other operating expenses									51,083	40,475	23,104
Operating Income									0	0	0
Other (deductions) income, net									0	0	0
Interest (expense) income, net									0	0	0
Net Income Including Noncontrolling Interest									0	0	0
Less Net Income Attributable to Noncontrolling Interest, net of tax									(23,970)	(20,740)	(13,883)
Net Income									(23,970)	(20,740)	(13,883)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	(35,706)				(37,217)				(35,706)	(37,217)	(37,878)
Capital Expenditures									0	0	0
MGE [Member] | Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	32,882				22,079				32,882	22,079	22,342
Capital Expenditures									$ 0	$ 0	$ 0