Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues		$ 147,527	$ 170,134
Depreciation and amortization		(11,032)	(10,849)
Other operating expenses		(106,964)	(127,434)
Operating income (loss)		29,531	31,851
Other income (deductions), net		2,442	2,105
Interest (expense) income, net		(5,000)	(5,091)
Income before income taxes		26,973	28,865
Income tax (provision) benefit		(9,945)	(10,587)
Net Income (Loss)		17,028	18,278
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		93,208	98,240
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		53,837	69,928
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		482	1,966
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		147,527	170,134
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		93,664	98,355
Depreciation and amortization		(7,163)	(7,332)
Other operating expenses		(75,379)	(79,800)
Operating income (loss)		11,122	11,223
Other income (deductions), net		196	90
Interest (expense) income, net		(2,790)	(2,819)
Income before income taxes		8,528	8,494
Income tax (provision) benefit		(2,536)	(2,383)
Net Income (Loss)		5,992	6,111
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		58,934	72,653
Depreciation and amortization		(1,981)	(1,642)
Other operating expenses		(47,741)	(60,068)
Operating income (loss)		9,212	10,943
Other income (deductions), net		(8)	(1)
Interest (expense) income, net		(808)	(804)
Income before income taxes		8,396	10,138
Income tax (provision) benefit		(3,359)	(4,081)
Net Income (Loss)		5,037	6,057
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,459	11,813
Depreciation and amortization		(1,876)	(1,863)
Other operating expenses		(47)	(50)
Operating income (loss)		9,536	9,900
Other income (deductions), net		0	0
Interest (expense) income, net		(1,463)	(1,518)
Income before income taxes		8,073	8,382
Income tax (provision) benefit		(3,240)	(3,364)
Net Income (Loss)		4,833	5,018
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Depreciation and amortization		0	0
Other operating expenses		(1)	0
Operating income (loss)		(1)	0
Other income (deductions), net		2,233	1,881
Interest (expense) income, net		0	0
Income before income taxes		2,232	1,881
Income tax (provision) benefit		(897)	(756)
Net Income (Loss)		1,335	1,125
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Depreciation and amortization		(12)	(12)
Other operating expenses		(326)	(203)
Operating income (loss)		(338)	(215)
Other income (deductions), net		21	135
Interest (expense) income, net		61	50
Income before income taxes		(256)	(30)
Income tax (provision) benefit		87	(3)
Net Income (Loss)		(169)	(33)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(16,530)	(12,687)
Depreciation and amortization		0	0
Other operating expenses		16,530	12,687
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		456	115
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		5,097	2,725
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,977	9,847
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		147,543	170,144
Depreciation and amortization		(11,020)	(10,837)
Other operating expenses	[1]	(115,744)	(137,017)
Operating income (loss)	[1]	20,779	22,290
Other income (deductions), net	[1]	1,479	1,162
Interest (expense) income, net		(5,061)	(5,141)
Income tax (provision) benefit		(9,090)	(9,776)
Net Income Including Noncontrolling Interest		17,197	18,311
Less Net Income Attributable to Noncontrolling Interest, net of tax		(6,252)	(6,553)
Net Income (Loss)		10,945	11,758
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		93,214	98,245
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		53,847	69,933
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		482	1,966
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		147,543	170,144
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		93,664	98,355
Depreciation and amortization		(7,163)	(7,332)
Other operating expenses	[1]	(77,879)	(82,142)
Operating income (loss)	[1]	8,622	8,881
Other income (deductions), net	[1]	160	49
Interest (expense) income, net		(2,790)	(2,819)
Net Income Including Noncontrolling Interest		5,992	6,111
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		5,992	6,111
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		58,934	72,653
Depreciation and amortization		(1,981)	(1,642)
Other operating expenses	[1]	(51,091)	(64,138)
Operating income (loss)	[1]	5,862	6,873
Other income (deductions), net	[1]	(17)	(12)
Interest (expense) income, net		(808)	(804)
Net Income Including Noncontrolling Interest		5,037	6,057
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		5,037	6,057
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,459	11,813
Depreciation and amortization		(1,876)	(1,863)
Other operating expenses	[1]	(3,287)	(3,414)
Operating income (loss)	[1]	6,296	6,536
Other income (deductions), net	[1]	0	0
Interest (expense) income, net		(1,463)	(1,518)
Net Income Including Noncontrolling Interest		4,833	5,018
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		4,833	5,018
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Depreciation and amortization		0	0
Other operating expenses	[1]	(1)	0
Operating income (loss)	[1]	(1)	0
Other income (deductions), net	[1]	1,336	1,125
Interest (expense) income, net		0	0
Net Income Including Noncontrolling Interest		1,335	1,125
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		1,335	1,125
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(16,514)	(12,677)
Depreciation and amortization		0	0
Other operating expenses	[1]	16,514	12,677
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		(6,252)	(6,553)
Net Income (Loss)		(6,252)	(6,553)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		450	110
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		5,087	2,720
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,977	9,847
MGE [Member] | Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 0	$ 0

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