Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Operating revenues		$ 121,576	$ 122,126	$ 269,103	$ 292,260
Depreciation and amortization		(11,114)	(10,995)	(22,146)	(21,844)
Other operating expenses		(82,250)	(87,082)	(189,214)	(214,516)
Operating income (loss)		28,212	24,049	57,743	55,900
Other income (deductions), net		2,179	2,446	4,621	4,551
Interest (expense) income, net		(4,957)	(5,008)	(9,957)	(10,099)
Income before income taxes		25,434	21,487	52,407	50,352
Income tax (provision) benefit		(9,284)	(8,008)	(19,229)	(18,595)
Net Income (Loss)		16,150	13,479	33,178	31,757
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		100,329	99,481	193,537	197,721
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,961	20,669	74,798	90,597
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		286	1,976	768	3,942
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		121,576	122,126	269,103	292,260
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		100,896	99,603	194,560	197,958
Depreciation and amortization		(7,259)	(7,456)	(14,422)	(14,788)
Other operating expenses		(78,291)	(79,961)	(153,670)	(159,761)
Operating income (loss)		15,346	12,186	26,468	23,409
Other income (deductions), net		118	16	314	106
Interest (expense) income, net		(2,776)	(2,768)	(5,566)	(5,587)
Income before income taxes		12,688	9,434	21,216	17,928
Income tax (provision) benefit		(4,158)	(3,164)	(6,694)	(5,547)
Net Income (Loss)		8,530	6,270	14,522	12,381
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		27,102	22,960	86,036	95,613
Depreciation and amortization		(2,015)	(1,662)	(3,996)	(3,304)
Other operating expenses		(21,295)	(19,089)	(69,036)	(79,157)
Operating income (loss)		3,792	2,209	13,004	13,152
Other income (deductions), net		(18)	(25)	(26)	(26)
Interest (expense) income, net		(799)	(790)	(1,607)	(1,594)
Income before income taxes		2,975	1,394	11,371	11,532
Income tax (provision) benefit		(1,195)	(557)	(4,554)	(4,638)
Net Income (Loss)		1,780	837	6,817	6,894
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,205	11,829	22,664	23,642
Depreciation and amortization		(1,828)	(1,866)	(3,704)	(3,729)
Other operating expenses		(35)	(36)	(82)	(86)
Operating income (loss)		9,342	9,927	18,878	19,827
Other income (deductions), net		0	0	0	0
Interest (expense) income, net		(1,449)	(1,507)	(2,912)	(3,025)
Income before income taxes		7,893	8,420	15,966	16,802
Income tax (provision) benefit		(3,168)	(3,380)	(6,408)	(6,744)
Net Income (Loss)		4,725	5,040	9,558	10,058
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		(3)	0	(4)	0
Operating income (loss)		(3)	0	(4)	0
Other income (deductions), net		1,767	2,290	4,000	4,171
Interest (expense) income, net		0	0	0	0
Income before income taxes		1,764	2,290	3,996	4,171
Income tax (provision) benefit		(709)	(919)	(1,606)	(1,675)
Net Income (Loss)		1,055	1,371	2,390	2,496
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Depreciation and amortization		(12)	(11)	(24)	(23)
Other operating expenses		(253)	(262)	(579)	(465)
Operating income (loss)		(265)	(273)	(603)	(488)
Other income (deductions), net		312	165	333	300
Interest (expense) income, net		67	57	128	107
Income before income taxes		114	(51)	(142)	(81)
Income tax (provision) benefit		(54)	12	33	9
Net Income (Loss)		60	(39)	(109)	(72)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(17,627)	(12,266)	(34,157)	(24,953)
Depreciation and amortization		0	0	0	0
Other operating expenses		17,627	12,266	34,157	24,953
Operating income (loss)		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		567	122	1,023	237
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		6,141	2,291	11,238	5,016
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,919	9,853	21,896	19,700
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		121,589	122,133	269,132	292,277
Depreciation and amortization		(11,102)	(10,984)	(22,122)	(21,821)
Other operating expenses	[1]	(90,473)	(93,868)	(206,217)	(230,885)
Operating income (loss)	[1]	20,014	17,281	40,793	39,571
Other income (deductions), net	[1]	1,100	1,302	2,579	2,464
Interest (expense) income, net		(5,024)	(5,065)	(10,085)	(10,206)
Income tax (provision) benefit		(8,464)	(7,041)	(17,554)	(16,817)
Net Income Including Noncontrolling Interest		16,090	13,518	33,287	31,829
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,952)	(6,626)	(12,204)	(13,179)
Net Income (Loss)		10,138	6,892	21,083	18,650
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		100,336	99,486	193,550	197,731
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,967	20,671	74,814	90,604
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		286	1,976	768	3,942
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		121,589	122,133	269,132	292,277
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		100,896	99,603	194,560	197,958
Depreciation and amortization		(7,259)	(7,456)	(14,422)	(14,788)
Other operating expenses	[1]	(82,405)	(83,079)	(160,284)	(165,221)
Operating income (loss)	[1]	11,232	9,068	19,854	17,949
Other income (deductions), net	[1]	74	(30)	234	19
Interest (expense) income, net		(2,776)	(2,768)	(5,566)	(5,587)
Net Income Including Noncontrolling Interest		8,530	6,270	14,522	12,381
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		8,530	6,270	14,522	12,381
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		27,102	22,960	86,036	95,613
Depreciation and amortization		(2,015)	(1,662)	(3,996)	(3,304)
Other operating expenses	[1]	(22,476)	(19,632)	(73,567)	(83,770)
Operating income (loss)	[1]	2,611	1,666	8,473	8,539
Other income (deductions), net	[1]	(32)	(39)	(49)	(51)
Interest (expense) income, net		(799)	(790)	(1,607)	(1,594)
Net Income Including Noncontrolling Interest		1,780	837	6,817	6,894
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		1,780	837	6,817	6,894
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,205	11,829	22,664	23,642
Depreciation and amortization		(1,828)	(1,866)	(3,704)	(3,729)
Other operating expenses	[1]	(3,203)	(3,416)	(6,490)	(6,830)
Operating income (loss)	[1]	6,174	6,547	12,470	13,083
Other income (deductions), net	[1]	0	0	0	0
Interest (expense) income, net		(1,449)	(1,507)	(2,912)	(3,025)
Net Income Including Noncontrolling Interest		4,725	5,040	9,558	10,058
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		4,725	5,040	9,558	10,058
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]	(3)	0	(4)	0
Operating income (loss)	[1]	(3)	0	(4)	0
Other income (deductions), net	[1]	1,058	1,371	2,394	2,496
Interest (expense) income, net		0	0	0	0
Net Income Including Noncontrolling Interest		1,055	1,371	2,390	2,496
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		1,055	1,371	2,390	2,496
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(17,614)	(12,259)	(34,128)	(24,936)
Depreciation and amortization		0	0	0	0
Other operating expenses	[1]	17,614	12,259	34,128	24,936
Operating income (loss)	[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		(5,952)	(6,626)	(12,204)	(13,179)
Net Income (Loss)		(5,952)	(6,626)	(12,204)	(13,179)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		560	117	1,010	227
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		6,135	2,289	11,222	5,009
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,919	9,853	21,896	19,700
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 MGE Consolidated Statement of Income.