Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Operating revenues		$ 156,823	$ 147,527
Depreciation and amortization		(12,959)	(11,032)
Other operating expenses		(110,954)	(106,964)
Operating income (loss)		32,910	29,531
Other income (deductions), net		2,451	2,442
Interest (expense) income, net		(4,894)	(5,000)
Income before income taxes		30,467	26,973
Income tax (provision) benefit		(11,167)	(9,945)
Net Income (Loss)		19,300	17,028
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		98,324	93,208
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		58,426	53,837
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		73	482
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		156,823	147,527
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		98,219	93,664
Depreciation and amortization		(8,900)	(7,163)
Other operating expenses		(75,326)	(75,379)
Operating income (loss)		13,993	11,122
Other income (deductions), net		190	196
Interest (expense) income, net		(2,776)	(2,790)
Income before income taxes		11,407	8,528
Income tax (provision) benefit		(3,454)	(2,536)
Net Income (Loss)		7,953	5,992
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		62,820	58,934
Depreciation and amortization		(2,213)	(1,981)
Other operating expenses		(50,577)	(47,741)
Operating income (loss)		10,030	9,212
Other income (deductions), net		5	(8)
Interest (expense) income, net		(799)	(808)
Income before income taxes		9,236	8,396
Income tax (provision) benefit		(3,704)	(3,359)
Net Income (Loss)		5,532	5,037
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,143	11,459
Depreciation and amortization		(1,846)	(1,876)
Other operating expenses		(41)	(47)
Operating income (loss)		9,256	9,536
Other income (deductions), net		0	0
Interest (expense) income, net		(1,407)	(1,463)
Income before income taxes		7,849	8,073
Income tax (provision) benefit		(3,151)	(3,240)
Net Income (Loss)		4,698	4,833
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Depreciation and amortization		0	0
Other operating expenses		0	(1)
Operating income (loss)		0	(1)
Other income (deductions), net		2,478	2,233
Interest (expense) income, net		0	0
Income before income taxes		2,478	2,232
Income tax (provision) benefit		(997)	(897)
Net Income (Loss)		1,481	1,335
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Depreciation and amortization		0	(12)
Other operating expenses		(369)	(326)
Operating income (loss)		(369)	(338)
Other income (deductions), net		(222)	21
Interest (expense) income, net		88	61
Income before income taxes		(503)	(256)
Income tax (provision) benefit		139	87
Net Income (Loss)		(364)	(169)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(15,359)	(16,530)
Depreciation and amortization		0	0
Other operating expenses		15,359	16,530
Operating income (loss)		0	0
Other income (deductions), net		0	0
Interest (expense) income, net		0	0
Income before income taxes		0	0
Income tax (provision) benefit		0	0
Net Income (Loss)		0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		(105)	456
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		4,394	5,097
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,070	10,977
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues		156,836	147,543
Depreciation and amortization		(12,959)	(11,020)
Other operating expenses	[1]	(120,863)	(115,744)
Operating income (loss)	[1]	23,014	20,779
Other income (deductions), net	[1]	151	1,479
Interest (expense) income, net		(4,982)	(5,061)
Net Income Including Noncontrolling Interest		18,183	17,197
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,389)	(6,252)
Net Income (Loss)		12,794	10,945
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		98,328	93,214
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		58,435	53,847
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		73	482
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	[2]	0	0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		156,836	147,543
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		98,219	93,664
Depreciation and amortization		(8,900)	(7,163)
Other operating expenses	[1]	(78,746)	(77,879)
Operating income (loss)	[1]	10,573	8,622
Other income (deductions), net	[1]	156	160
Interest (expense) income, net		(2,776)	(2,790)
Net Income Including Noncontrolling Interest		7,953	5,992
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		7,953	5,992
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		62,820	58,934
Depreciation and amortization		(2,213)	(1,981)
Other operating expenses	[1]	(54,271)	(51,091)
Operating income (loss)	[1]	6,336	5,862
Other income (deductions), net	[1]	(5)	(17)
Interest (expense) income, net		(799)	(808)
Net Income Including Noncontrolling Interest		5,532	5,037
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		5,532	5,037
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,143	11,459
Depreciation and amortization		(1,846)	(1,876)
Other operating expenses	[1]	(3,192)	(3,287)
Operating income (loss)	[1]	6,105	6,296
Other income (deductions), net	[1]	0	0
Interest (expense) income, net		(1,407)	(1,463)
Net Income Including Noncontrolling Interest		4,698	4,833
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		4,698	4,833
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	[2]	0	0
Depreciation and amortization	[2]	0	0
Other operating expenses	[1],[2]	0	(1)
Operating income (loss)	[1],[2]	0	(1)
Other income (deductions), net	[1],[2]	0	1,336
Interest (expense) income, net	[2]	0	0
Net Income Including Noncontrolling Interest	[2]	0	1,335
Less Net Income Attributable to Noncontrolling Interest, net of tax	[2]	0	0
Net Income (Loss)	[2]	0	1,335
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(15,346)	(16,514)
Depreciation and amortization		0	0
Other operating expenses	[1]	15,346	16,514
Operating income (loss)	[1]	0	0
Other income (deductions), net	[1]	0	0
Interest (expense) income, net		0	0
Net Income Including Noncontrolling Interest		0	0
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,389)	(6,252)
Net Income (Loss)		(5,389)	(6,252)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		(109)	450
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		4,385	5,087
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,070	10,977
MGE [Member] | Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	[2]	$ 0	$ 0

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

[2] As of July 31, 2016, MGE no longer consolidates MGE Energy's proportionate share of equity earnings in MGE Transco. See Footnote 3 for additional information.