Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Operating revenues		$ 122,126	$ 128,765	$ 292,260	$ 339,010
Depreciation and amortization		(10,995)	(10,069)	(21,844)	(19,815)
Other operating expenses		(87,082)	(94,255)	(214,516)	(250,783)
Operating Income		24,049	24,441	55,900	68,412
Other income (deductions), net		2,446	3,548	4,551	8,100
Interest (expense) income, net		(5,008)	(4,868)	(10,099)	(9,409)
Income before income taxes		21,487	23,121	50,352	67,103
Income tax (provision) benefit		(8,008)	(9,034)	(18,595)	(25,299)
Net Income (Loss)		13,479	14,087	31,757	41,804
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		99,481	96,697	197,721	195,549
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,669	31,218	90,597	141,931
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,976	850	3,942	1,530
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		122,126	128,765	292,260	339,010
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		99,603	96,824	197,958	195,794
Depreciation and amortization		(7,456)	(6,641)	(14,788)	(12,978)
Other operating expenses		(79,961)	(76,812)	(159,761)	(154,713)
Operating Income		12,186	13,371	23,409	28,103
Other income (deductions), net		16	1,036	106	2,863
Interest (expense) income, net		(2,768)	(2,534)	(5,587)	(4,739)
Income before income taxes		9,434	11,873	17,928	26,227
Income tax (provision) benefit		(3,164)	(4,491)	(5,547)	(8,844)
Net Income (Loss)		6,270	7,382	12,381	17,383
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		22,960	33,110	95,613	147,447
Depreciation and amortization		(1,662)	(1,562)	(3,304)	(3,125)
Other operating expenses		(19,089)	(29,865)	(79,157)	(122,708)
Operating Income		2,209	1,683	13,152	21,614
Other income (deductions), net		(25)	(17)	(26)	(52)
Interest (expense) income, net		(790)	(817)	(1,594)	(1,621)
Income before income taxes		1,394	849	11,532	19,941
Income tax (provision) benefit		(557)	(364)	(4,638)	(8,029)
Net Income (Loss)		837	485	6,894	11,912
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,829	11,523	23,642	22,873
Depreciation and amortization		(1,866)	(1,855)	(3,729)	(3,689)
Other operating expenses		(36)	(30)	(86)	(70)
Operating Income		9,927	9,638	19,827	19,114
Other income (deductions), net		0	0	0	0
Interest (expense) income, net		(1,507)	(1,559)	(3,025)	(3,131)
Income before income taxes		8,420	8,079	16,802	15,983
Income tax (provision) benefit		(3,380)	(3,242)	(6,744)	(6,414)
Net Income (Loss)		5,040	4,837	10,058	9,569
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
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 income (deductions), net		2,290	2,402	4,171	4,883
Interest (expense) income, net		0	0	0	0
Income before income taxes		2,290	2,402	4,171	4,883
Income tax (provision) benefit		(919)	(963)	(1,675)	(1,961)
Net Income (Loss)		1,371	1,439	2,496	2,922
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Depreciation and amortization		(11)	(11)	(23)	(23)
Other operating expenses		(262)	(240)	(465)	(396)
Operating Income		(273)	(251)	(488)	(419)
Other income (deductions), net		165	127	300	406
Interest (expense) income, net		57	42	107	82
Income before income taxes		(51)	(82)	(81)	69
Income tax (provision) benefit		12	26	9	(51)
Net Income (Loss)		(39)	(56)	(72)	18
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(12,266)	(12,692)	(24,953)	(27,104)
Depreciation and amortization		0	0	0	0
Other operating expenses		12,266	12,692	24,953	27,104
Operating Income		0	0	0	0
Other income (deductions), net		0	0	0	0
Interest (expense) income, net		0	0	0	0
Income before income taxes		0	0	0	0
Income tax (provision) benefit		0	0	0	0
Net Income (Loss)		0	0	0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		122	127	237	245
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		2,291	1,892	5,016	5,516
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		9,853	10,673	19,700	21,343
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues		122,133	128,775	292,277	339,031
Depreciation and amortization		(10,984)	(10,058)	(21,821)	(19,792)
Other operating expenses	[1]	(93,868)	(101,943)	(230,885)	(273,250)
Operating Income	[1]	17,281	16,774	39,571	45,989
Other income (deductions), net	[1]	1,302	2,279	2,464	5,288
Interest (expense) income, net		(5,065)	(4,910)	(10,206)	(9,491)
Income tax (provision) benefit		(7,041)	(7,918)	(16,817)	(22,842)
Net Income Including Noncontrolling Interest		13,518	14,143	31,829	41,786
Less Net Income Attributable to Noncontrolling Interest, net of tax		(6,626)	(6,621)	(13,179)	(13,131)
Net Income (Loss)		6,892	7,522	18,650	28,655
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		99,486	96,702	197,731	195,560
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,671	31,223	90,604	141,941
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,976	850	3,942	1,530
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		122,133	128,775	292,277	339,031
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		99,603	96,824	197,958	195,794
Depreciation and amortization		(7,456)	(6,641)	(14,788)	(12,978)
Other operating expenses	[1]	(83,079)	(81,165)	(165,221)	(163,211)
Operating Income	[1]	9,068	9,018	17,949	19,605
Other income (deductions), net	[1]	(30)	898	19	2,517
Interest (expense) income, net		(2,768)	(2,534)	(5,587)	(4,739)
Net Income Including Noncontrolling Interest		6,270	7,382	12,381	17,383
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		6,270	7,382	12,381	17,383
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		22,960	33,110	95,613	147,447
Depreciation and amortization		(1,662)	(1,562)	(3,304)	(3,125)
Other operating expenses	[1]	(19,632)	(30,188)	(83,770)	(130,638)
Operating Income	[1]	1,666	1,360	8,539	13,684
Other income (deductions), net	[1]	(39)	(58)	(51)	(151)
Interest (expense) income, net		(790)	(817)	(1,594)	(1,621)
Net Income Including Noncontrolling Interest		837	485	6,894	11,912
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		837	485	6,894	11,912
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,829	11,523	23,642	22,873
Depreciation and amortization		(1,866)	(1,855)	(3,729)	(3,689)
Other operating expenses	[1]	(3,416)	(3,272)	(6,830)	(6,484)
Operating Income	[1]	6,547	6,396	13,083	12,700
Other income (deductions), net	[1]	0	0	0	0
Interest (expense) income, net		(1,507)	(1,559)	(3,025)	(3,131)
Net Income Including Noncontrolling Interest		5,040	4,837	10,058	9,569
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		5,040	4,837	10,058	9,569
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Depreciation and amortization		0	0	0	0
Other operating expenses	[1]	0	0	0	0
Operating Income	[1]	0	0	0	0
Other income (deductions), net	[1]	1,371	1,439	2,496	2,922
Interest (expense) income, net		0	0	0	0
Net Income Including Noncontrolling Interest		1,371	1,439	2,496	2,922
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		1,371	1,439	2,496	2,922
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(12,259)	(12,682)	(24,936)	(27,083)
Depreciation and amortization		0	0	0	0
Other operating expenses	[1]	12,259	12,682	24,936	27,083
Operating Income	[1]	0	0	0	0
Other income (deductions), net	[1]	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		(6,626)	(6,621)	(13,179)	(13,131)
Net Income (Loss)		(6,626)	(6,621)	(13,179)	(13,131)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		117	122	227	234
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		2,289	1,887	5,009	5,506
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		9,853	10,673	19,700	21,343
MGE [Member] | Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 0	$ 0	$ 0	$ 0

[1] *Amounts are shown net of the related tax expense, consistent with the presentation on the consolidated MGE Income Statement.