Segment Information (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
MGE Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 117,259	$ 109,082	$ 281,864	$ 268,725
Interdepartmental revenues	0	0	0	0
Total operating revenues	117,259	109,082	281,864	268,725
Depreciation and amortization	(10,357)	(9,481)	(20,373)	(18,703)
Other operating expenses	(83,705)	(79,479)	(207,396)	(208,125)
Operating Income	23,197	20,122	54,095	41,897
Other (deductions) income, net	2,153	1,947	4,539	6,668
Interest (expense) income, net	(5,055)	(4,045)	(9,905)	(7,953)
Income before income taxes	20,295	18,024	48,729	40,612
Income tax provision	(7,572)	(6,472)	(18,223)	(14,800)
Net Income	12,723	11,552	30,506	25,812
MGE Energy [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	90,834	87,438	176,841	169,432
Interdepartmental revenues	121	127	228	237
Total operating revenues	90,955	87,565	177,069	169,669
Depreciation and amortization	(7,052)	(6,829)	(14,029)	(13,632)
Other operating expenses	(69,522)	(66,399)	(140,438)	(138,805)
Operating Income	14,381	14,337	22,602	17,232
Other (deductions) income, net	(124)	(112)	33	1,937
Interest (expense) income, net	(2,653)	(2,576)	(5,353)	(5,228)
Income before income taxes	11,604	11,649	17,282	13,941
Income tax provision	(4,121)	(4,003)	(5,722)	(4,301)
Net Income	7,483	7,646	11,560	9,640
MGE Energy [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	25,062	20,290	102,499	96,837
Interdepartmental revenues	2,173	1,543	3,164	5,844
Total operating revenues	27,235	21,833	105,663	102,681
Depreciation and amortization	(1,532)	(1,291)	(2,869)	(2,575)
Other operating expenses	(25,717)	(21,628)	(88,770)	(89,606)
Operating Income	(14)	(1,086)	14,024	10,500
Other (deductions) income, net	(35)	(32)	9	546
Interest (expense) income, net	(748)	(727)	(1,509)	(1,475)
Income before income taxes	(797)	(1,845)	12,524	9,571
Income tax provision	366	860	(4,882)	(3,641)
Net Income	(431)	(985)	7,642	5,930
MGE Energy [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,363	1,354	2,524	2,456
Interdepartmental revenues	9,581	7,144	18,977	14,620
Total operating revenues	10,944	8,498	21,501	17,076
Depreciation and amortization	(1,773)	(1,361)	(3,475)	(2,496)
Other operating expenses	(55)	(36)	(94)	(66)
Operating Income	9,116	7,101	17,932	14,514
Other (deductions) income, net	0	0	0	(104)
Interest (expense) income, net	(1,669)	(689)	(3,017)	(1,376)
Income before income taxes	7,447	6,412	14,915	13,034
Income tax provision	(2,990)	(2,604)	(5,987)	(5,220)
Net Income	4,457	3,808	8,928	7,814
MGE Energy [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	2,170	2,098	4,267	4,283
Interest (expense) income, net	0	0	0	0
Income before income taxes	2,170	2,098	4,267	4,283
Income tax provision	(870)	(842)	(1,722)	(1,719)
Net Income	1,300	1,256	2,545	2,564
MGE Energy [Member] | 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	(286)	(230)	(463)	(349)
Operating Income	(286)	(230)	(463)	(349)
Other (deductions) income, net	142	(7)	230	6
Interest (expense) income, net	15	(53)	(26)	126
Income before income taxes	(129)	(290)	(259)	(217)
Income tax provision	43	117	90	81
Net Income	(86)	(173)	(169)	(136)
MGE Energy [Member] | Corporate Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Interdepartmental revenues	(11,875)	(8,814)	(22,369)	(20,701)
Total operating revenues	(11,875)	(8,814)	(22,369)	(20,701)
Depreciation and amortization	0	0	0	0
Other operating expenses	11,875	8,814	22,369	20,701
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
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	117,259	109,082	281,864	268,725
Interdepartmental revenues	0	0	0	0
Total operating revenues	117,259	109,082	281,864	268,725
Depreciation and amortization	(10,357)	(9,481)	(20,373)	(18,703)
Other operating expenses	(90,083)	(85,015)	(223,487)	(219,880)
Operating Income	16,819	14,586	38,004	30,142
Other (deductions) income, net	1,062	1,131	2,553	3,885
Interest (expense) income, net	(5,070)	(3,992)	(9,879)	(8,079)
Net Income Including Noncontrolling Interest	12,811	11,725	30,678	25,948
Less net income attributable to noncontrolling interest, net of tax	(5,992)	(4,900)	(11,925)	(9,996)
Net Income	6,819	6,825	18,753	15,952
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	90,834	87,438	176,841	169,432
Interdepartmental revenues	121	127	228	237
Total operating revenues	90,955	87,565	177,069	169,669
Depreciation and amortization	(7,052)	(6,829)	(14,029)	(13,632)
Other operating expenses	(73,581)	(70,417)	(146,132)	(142,281)
Operating Income	10,322	10,319	16,908	13,756
Other (deductions) income, net	(185)	(97)	6	1,112
Interest (expense) income, net	(2,653)	(2,576)	(5,353)	(5,228)
Net Income Including Noncontrolling Interest	7,484	7,646	11,561	9,640
Less net income attributable to noncontrolling interest, net of tax	0	0	0	0
Net Income	7,484	7,646	11,561	9,640
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	25,062	20,290	102,499	96,837
Interdepartmental revenues	2,173	1,543	3,164	5,844
Total operating revenues	27,235	21,833	105,663	102,681
Depreciation and amortization	(1,532)	(1,291)	(2,869)	(2,575)
Other operating expenses	(25,333)	(20,772)	(93,644)	(93,014)
Operating Income	370	(230)	9,150	7,092
Other (deductions) income, net	(52)	(28)	2	313
Interest (expense) income, net	(748)	(727)	(1,509)	(1,475)
Net Income Including Noncontrolling Interest	(430)	(985)	7,643	5,930
Less net income attributable to noncontrolling interest, net of tax	0	0	0	0
Net Income	(430)	(985)	7,643	5,930
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,363	1,354	2,524	2,456
Interdepartmental revenues	9,581	7,144	18,977	14,620
Total operating revenues	10,944	8,498	21,501	17,076
Depreciation and amortization	(1,773)	(1,361)	(3,475)	(2,496)
Other operating expenses	(3,044)	(2,640)	(6,080)	(5,286)
Operating Income	6,127	4,497	11,946	9,294
Other (deductions) income, net	0	0	0	(104)
Interest (expense) income, net	(1,669)	(689)	(3,017)	(1,376)
Net Income Including Noncontrolling Interest	4,458	3,808	8,929	7,814
Less net income attributable to noncontrolling interest, net of tax	0	0	0	0
Net Income	4,458	3,808	8,929	7,814
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	1,299	1,256	2,545	2,564
Interest (expense) income, net	0	0	0	0
Net Income Including Noncontrolling Interest	1,299	1,256	2,545	2,564
Less net income attributable to noncontrolling interest, net of tax	0	0	0	0
Net Income	1,299	1,256	2,545	2,564
MGE [Member] | Corporate Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Interdepartmental revenues	(11,875)	(8,814)	(22,369)	(20,701)
Total operating revenues	(11,875)	(8,814)	(22,369)	(20,701)
Depreciation and amortization	0	0	0	0
Other operating expenses	11,875	8,814	22,369	20,701
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	(5,992)	(4,900)	(11,925)	(9,996)
Net Income	$ (5,992)	$ (4,900)	$ (11,925)	$ (9,996)