MGE Energy (MGEE) 10-K 22 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 01, 2019	Jun. 30, 2018
Document and Entity Information [Line Items]
Entity Registrant Name	MGE Energy Inc
Entity Central Index Key	1,161,728
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Trading Symbol	MGEE
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 2,180,572,457
Entity Common Stock Shares Outstanding		34,668,370
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
MGE [Member]
Document and Entity Information [Line Items]
Entity Registrant Name	Madison Gas and Electric Company
Entity Central Index Key	61,339
Entity Well known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding		17,347,894

MGE Energy Inc Consolidated Sta

MGE Energy Inc Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Operating Revenues:
Electric revenues	$ 402,001	$ 414,274		$ 410,202
Gas revenues	157,767	148,825		134,543
Total Operating Revenues	559,768	563,099		544,745
Operating Expenses:
Fuel for electric generation	56,141	53,029		60,736
Purchased power	50,807	58,690		56,313
Cost of gas sold	84,968	76,644		66,771
Other operations and maintenance	177,823	177,740		172,335
Depreciation and amortization	56,412	53,077		44,646
Other general taxes	19,410	19,294		20,062
Total Operating Expenses	445,561	438,474		420,863
Operating Income (Loss)	114,207	124,625		123,882
Other income, net	17,055	14,399	[1]	14,057	[1]
Interest expense, net	(19,609)	(19,324)		(19,866)
Income before income taxes	111,653	119,700		118,073
Income tax provision	(27,434)	(22,094)	[2]	(42,513)
Net Income	$ 84,219	$ 97,606		$ 75,560
Earnings Per Share of Common Stock (basic and diluted)	$ 2.43	$ 2.82		$ 2.18
Dividends per share of common stock	$ 1.32	$ 1.26		$ 1.21
Weighted Average Shares Outstanding (basic and diluted)	34,668	34,668		34,668
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for further information.
[2]	In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.

Madison Gas and Electric Compan

Madison Gas and Electric Company Consolidated Statements of Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Operating Revenues:
Electric revenues		$ 402,001	$ 414,274		$ 410,202
Gas revenues		157,767	148,825		134,543
Total Operating Revenues		559,768	563,099		544,745
Operating Expenses:
Fuel for electric generation		56,141	53,029		60,736
Purchased power		50,807	58,690		56,313
Cost of gas sold		84,968	76,644		66,771
Other operations and maintenance		177,823	177,740		172,335
Depreciation and amortization		56,412	53,077		44,646
Other general taxes		19,410	19,294		20,062
Total Operating Expenses		445,561	438,474		420,863
Operating Income (Loss)		114,207	124,625		123,882
Other Income and Deductions:
AFUDC - equity funds		2,500
Equity earnings in MGE Transco		8,821	10,125		8,428
Total Other Income and Deductions		17,055	14,399	[1]	14,057	[1]
Interest Expense:
Net Interest Expense		19,609	19,324		19,866
Net Income		84,219	97,606		75,560
MGE [Member]
Operating Revenues:
Electric revenues		402,001	414,277		410,226
Gas revenues		157,767	148,834		134,572
Total Operating Revenues		559,768	563,111		544,798
Operating Expenses:
Fuel for electric generation		56,141	53,031		60,745
Purchased power		50,807	58,692		56,327
Cost of gas sold		84,968	76,652		66,800
Other operations and maintenance		176,762	176,729		171,423
Depreciation and amortization		56,412	53,077		44,622
Other general taxes		19,410	19,294		20,062
Income tax provision		25,098	18,280		39,616
Total Operating Expenses		469,598	455,755		459,595
Operating Income (Loss)	[2]	90,170	107,356		85,203
Other Income and Deductions:
AFUDC - equity funds		3,284	1,222		1,207
Equity earnings in MGE Transco		0	0		6,366
Income tax provision		(363)	(710)		(2,175)
Other income (deductions), net		7,142	5,228		4,129
Total Other Income and Deductions	[2]	10,063	5,740	[1]	9,527	[1]
Income before interest expense		100,233	113,096		94,730
Interest Expense:
Interest on long-term debt		21,967	20,273		20,351
Other interest, net		338	163		182
AFUDC - borrowed funds		(1,108)	(412)		(395)
Net Interest Expense		21,197	20,024		20,138
Net Income Including Noncontrolling Interest		79,036	93,072		74,592
Less Net Income Attributable to Noncontrolling Interest, net of tax		(22,552)	(43,237)		(23,358)
Net Income		$ 56,484	$ 49,835		$ 51,234
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for further information.
[2]	Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.

MGE Energy Inc Consolidated S_2

MGE Energy Inc Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Other Comprehensive Income [Abstract]
Net Income	$ 16,361	$ 29,506	$ 18,351	$ 20,001	$ 36,134	$ 26,629	$ 15,543	$ 19,300	$ 84,219	$ 97,606	$ 75,560
Other comprehensive income, net of tax:
Unrealized gain (loss) on available for sale securities, net of tax									0	175	(155)
Comprehensive Income									$ 84,219	$ 97,781	$ 75,405

Madison Gas and Electric Comp_2

Madison Gas and Electric Company Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other comprehensive income, net of tax:
Unrealized gain (loss) on available for sale securities, net of tax	$ 0	$ 175	$ (155)
Comprehensive Income	84,219	97,781	75,405
MGE [Member]
Net Income	79,036	93,072	74,592
Other comprehensive income, net of tax:
Unrealized gain (loss) on available for sale securities, net of tax	0	(47)	(4)
Comprehensive Income Including Noncontrolling Interest	79,036	93,025	74,588
Less: Comprehensive Income Attributable to Noncontrolling Interest, net of tax	(22,552)	(43,237)	(23,358)
Comprehensive Income	$ 56,484	$ 49,788	$ 51,230

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrealized gain (loss) on available-for-sale securities, taxes expense (benefit)	$ 0	$ 117	$ (104)
MGE [Member]
Unrealized gain (loss) on available-for-sale securities, taxes expense (benefit)	$ 0	$ (31)	$ (2)

MGE Energy Inc Consolidated S_3

MGE Energy Inc Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net Income	$ 84,219	$ 97,606	$ 75,560
Items not affecting cash:
Depreciation and amortization	56,412	53,077	44,646
Deferred income taxes	3,749	(4,082)	22,421
Provision for doubtful receivables	1,366	1,016	1,196
Employee benefit plan (credit) cost	(2,002)	831	295
Equity earnings in ATC	(8,821)	(10,125)	(8,428)
Gain on sale of property	0	(1,547)	0
Other items	(814)	641	2,462
Changes in working capital items:
Trade and other receivables (change)	(2,235)	(4,502)	(3,594)
Inventories (change)	2,724	(2,568)	7,273
Unbilled revenues (change)	3,157	(1,554)	(4,838)
Prepaid taxes (change)	10,320	101	8,616
Other current assets (change)	251	(2,786)	15
Accounts payable (change)	(4,855)	(5,290)	9,881
Other current liabilities (change)	11,957	3,948	(1,738)
Dividends from investment	6,958	8,803	5,854
Cash contributions to pension and other postretirement plans	(5,584)	(11,304)	(14,452)
Other noncurrent items, net	(3,762)	9,108	2,695
Cash Provided by Operating Activities	153,040	131,373	147,864
Investing Activities:
Capital expenditures	(212,197)	(108,131)	(83,659)
Capital contributions to investments	(5,926)	(11,081)	(2,958)
Proceeds from sale of property	0	2,819	0
Other	(205)	118	(196)
Cash Used for Investing Activities	(218,328)	(116,275)	(86,813)
Financing Activities:
Cash dividends paid on common stock	(45,762)	(43,682)	(41,775)
Repayment of long-term debt	(24,453)	(34,358)	(4,267)
Issuance of long-term debt	100,000	70,000	0
Proceeds from short-term debt	9,000	4,000	0
Other	(662)	(597)	(70)
Cash Provided by (Used for) Financing Activities	38,123	(4,637)	(46,112)
Change in cash, cash equivalents, and restricted cash:	(27,165)	10,461	14,939
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633	86,694
Cash, cash equivalents, and restricted cash at end of period	84,929	112,094	101,633
Supplemental disclosures of cash flow information:
Interest paid	20,018	19,176	19,415
Income taxes paid	12,597	27,149	21,831
Income taxes received	(59)	0	(10,000)
Significant noncash investing activities:
Accrued capital expenditures	$ 11,129	$ 16,602	$ 16,376

Madison Gas and Electric Comp_3

Madison Gas and Electric Company Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Items not affecting cash:
Depreciation and amortization	$ 56,412	$ 53,077	$ 44,646
Deferred income taxes	3,749	(4,082)	22,421
Provision for doubtful receivables	1,366	1,016	1,196
Employee benefit plan (credit) cost	(2,002)	831	295
Equity earnings in MGE Transco	(8,821)	(10,125)	(8,428)
Gain on sale of property	0	(1,547)	0
Other items	(814)	641	2,462
Changes in working capital items:
Trade and other receivables (change)	(2,235)	(4,502)	(3,594)
Inventories (change)	2,724	(2,568)	7,273
Unbilled revenues (change)	3,157	(1,554)	(4,838)
Prepaid taxes (change)	10,320	101	8,616
Other current assets (change)	251	(2,786)	15
Accounts payable (change)	(4,855)	(5,290)	9,881
Other current liabilities (change)	11,957	3,948	(1,738)
Dividend income from MGE Transco	6,958	8,803	5,854
Cash contributions to pension and other postretirement plans	(5,584)	(11,304)	(14,452)
Other noncurrent items, net	(3,762)	9,108	2,695
Cash Provided by Operating Activities	153,040	131,373	147,864
Investing Activities:
Capital expenditures	(212,197)	(108,131)	(83,659)
Capital contributions to investments	(5,926)	(11,081)	(2,958)
Proceeds from sale of property	0	2,819	0
Other	(205)	118	(196)
Cash Used for Investing Activities	(218,328)	(116,275)	(86,813)
Financing Activities:
Repayment of long-term debt	(24,453)	(34,358)	(4,267)
Issuance of long-term debt	100,000	70,000	0
Proceeds from short-term debt	9,000	4,000	0
Other	(662)	(597)	(70)
Cash Provided by (Used for) Financing Activities	38,123	(4,637)	(46,112)
Change in cash, cash equivalents, and restricted cash:	(27,165)	10,461	14,939
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633	86,694
Cash, cash equivalents, and restricted cash at end of period	84,929	112,094	101,633
Supplemental disclosures of cash flow information:
Interest paid	20,018	19,176	19,415
Income taxes paid	12,597	27,149	21,831
Income taxes received	(59)	0	(10,000)
Significant noncash investing activities:
Accrued capital expenditures	11,129	16,602	16,376
MGE [Member]
Operating Activities:
Net Income	79,036	93,072	74,592
Items not affecting cash:
Depreciation and amortization	56,412	53,077	44,622
Deferred income taxes	(69)	(7,760)	20,876
Provision for doubtful receivables	1,366	1,016	1,196
Employee benefit plan (credit) cost	(2,002)	831	295
Equity earnings in MGE Transco	0	0	(6,366)
Gain on sale of property	0	(1,547)	0
Other items	(107)	1,408	2,990
Changes in working capital items:
Trade and other receivables (change)	(2,160)	(4,113)	(3,583)
Inventories (change)	2,724	(2,568)	7,273
Unbilled revenues (change)	3,157	(1,554)	(4,838)
Prepaid taxes (change)	9,283	725	8,481
Other current assets (change)	255	(2,788)	14
Accounts payable (change)	(4,817)	(5,312)	9,941
Accrued interest and taxes (change)	4,761	118	419
Other current liabilities (change)	9,685	1,941	(2,137)
Dividend income from MGE Transco	0	0	5,032
Cash contributions to pension and other postretirement plans	(5,584)	(11,304)	(14,452)
Other noncurrent items, net	(3,946)	8,878	2,497
Cash Provided by Operating Activities	147,994	124,120	146,852
Investing Activities:
Capital expenditures	(212,197)	(108,131)	(83,659)
Capital contributions to investments	0	0	(1,598)
Proceeds from sale of property	0	1,721	0
Other	(1,105)	(162)	(378)
Cash Used for Investing Activities	(213,302)	(106,572)	(85,635)
Financing Activities:
Cash dividends paid to parent by MGE	0	(45,000)	(50,000)
Distributions to parent from noncontrolling interest	(22,000)	(18,000)	(24,113)
Equity contribution received by noncontrolling interest	0	0	1,598
Repayment of long-term debt	(24,453)	(34,358)	(4,267)
Issuance of long-term debt	100,000	70,000	0
Proceeds from short-term debt	9,000	4,000	0
Other	(662)	(539)	(63)
Cash Provided by (Used for) Financing Activities	61,885	(23,897)	(76,845)
Change in cash, cash equivalents, and restricted cash:	(3,423)	(6,349)	(15,628)
Cash, cash equivalents, and restricted cash at beginning of period	10,093	16,442	32,070
Cash, cash equivalents, and restricted cash at end of period	6,670	10,093	16,442
Supplemental disclosures of cash flow information:
Interest paid	20,018	19,176	19,415
Income taxes paid	0	1	29
Income taxes received	(59)	0	0
Significant noncash investing activities:
Accrued capital expenditures	11,129	16,602	16,376
Dividend in kind to parent	$ 0	$ 0	$ 15,822

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)		Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents		$ 83,102,000	$ 107,952,000
Accounts receivable, less reserves		43,593,000	42,299,000
Other accounts receivables, less reserves		6,262,000	9,440,000
Unbilled revenues		28,243,000	31,400,000
Materials and supplies, at average cost		24,093,000	22,614,000
Fuel for electric generation, at average cost		6,599,000	8,256,000
Stored natural gas, at average cost		11,303,000	12,923,000
Prepaid taxes		16,215,000	26,535,000
Regulatory assets - current		9,477,000	7,888,000
Assets held for sale		3,080,000	8,817,000
Other current assets		8,593,000	12,507,000
Total Current Assets		240,560,000	290,631,000
Other long-term receivables		2,709,000	4,788,000
Regulatory assets		145,424,000	142,567,000
Pension and other postretirement benefit asset		0	7,336,000
Other deferred assets and other		12,488,000	731,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,369,766,000	1,283,313,000
Construction work in progress		139,671,000	58,044,000
Total Property, Plant, and Equipment		1,509,437,000	1,341,357,000
Investments		78,000,000	67,772,000
Total Assets		1,988,618,000	1,855,182,000
Current Liabilities:
Long-term debt due within one year		4,553,000	24,452,000
Short-term debt	[1]	13,000,000	4,000,000
Accounts payable		46,158,000	47,645,000
Accrued interest and taxes		7,384,000	5,602,000
Accrued payroll related items		13,044,000	12,244,000
Regulatory liabilities - current		13,826,000	5,633,000
Derivative liabilities		8,550,000	8,180,000
Other current liabilities		14,113,000	18,758,000
Total Current Liabilities		120,628,000	126,514,000
Other Credits:
Deferred income taxes		231,952,000	225,130,000
Investment tax credit - deferred		818,000	918,000
Regulatory liabilities		165,638,000	154,153,000
Accrued pension and other postretirement benefits		67,483,000	69,088,000
Derivative liabilities		23,980,000	33,990,000
Other deferred liabilities and other		68,132,000	69,041,000
Total Other Credits		558,003,000	552,320,000
Common shareholders' equity:
Common stock		34,668,000	34,668,000
Additional paid-in capital		316,268,000	316,268,000
Retained earnings		465,708,000	426,874,000
Accumulated other comprehensive income, net of tax		0	377,000
Total Common Shareholders' Equity		816,644,000	778,187,000
Long-term debt		493,343,000	398,161,000
Total Capitalization		1,309,987,000	1,176,348,000
Commitments and contingencies (see Footnote 17)
Total Liabilities and Capitalization		1,988,618,000	1,855,182,000
MGE [Member]
Current Assets:
Cash and cash equivalents		4,843,000	5,951,000
Accounts receivable, less reserves		43,593,000	42,299,000
Affiliate receivables		621,000	668,000
Other accounts receivables, less reserves		6,111,000	6,984,000
Unbilled revenues		28,243,000	31,400,000
Materials and supplies, at average cost		24,093,000	22,614,000
Fuel for electric generation, at average cost		6,599,000	8,256,000
Stored natural gas, at average cost		11,303,000	12,923,000
Prepaid taxes		15,790,000	25,073,000
Regulatory assets - current		9,477,000	7,888,000
Assets held for sale		3,080,000	8,817,000
Other current assets		8,541,000	12,484,000
Total Current Assets		162,294,000	185,357,000
Affiliate receivable long-term		3,177,000	3,707,000
Regulatory assets		145,424,000	142,567,000
Pension and other postretirement benefit asset		0	7,336,000
Other deferred assets and other		14,142,000	3,280,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,369,795,000	1,283,341,000
Construction work in progress		139,671,000	58,044,000
Total Property, Plant, and Equipment		1,509,466,000	1,341,385,000
Investments		388,000	409,000
Total Assets		1,834,891,000	1,684,041,000
Current Liabilities:
Long-term debt due within one year		4,553,000	24,452,000
Short-term debt		13,000,000	4,000,000
Accounts payable		46,165,000	47,614,000
Accrued interest and taxes		10,319,000	5,558,000
Accrued payroll related items		13,044,000	12,244,000
Regulatory liabilities - current		13,826,000	5,633,000
Derivative liabilities		8,550,000	8,180,000
Other current liabilities		11,614,000	16,749,000
Total Current Liabilities		121,071,000	124,430,000
Other Credits:
Deferred income taxes		204,616,000	201,486,000
Investment tax credit - deferred		818,000	918,000
Regulatory liabilities		165,638,000	154,153,000
Accrued pension and other postretirement benefits		67,483,000	69,088,000
Derivative liabilities		23,980,000	33,990,000
Other deferred liabilities and other		68,132,000	69,041,000
Total Other Credits		530,667,000	528,676,000
Common shareholders' equity:
Common stock		17,348,000	17,348,000
Additional paid-in capital		192,417,000	192,417,000
Retained earnings		338,591,000	282,135,000
Accumulated other comprehensive income, net of tax		0	(28,000)
Total Common Shareholders' Equity		548,356,000	491,872,000
Noncontrolling interest		141,454,000	140,902,000
Total Equity		689,810,000	632,774,000
Long-term debt		493,343,000	398,161,000
Total Capitalization		1,183,153,000	1,030,935,000
Commitments and contingencies (see Footnote 17)
Total Liabilities and Capitalization		$ 1,834,891,000	$ 1,684,041,000
[1]	MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Receivables, Net
Reserve for uncollectible accounts receivable	$ 2,614	$ 2,840
Reserve for uncollectible other accounts receivable	$ 540	$ 335
Common shareholders' equity
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	75,000	75,000
Common stock, shares issued	34,668	34,668
Common stock, shares outstanding	34,668	34,668
MGE [Member]
Receivables, Net
Reserve for uncollectible accounts receivable	$ 2,614	$ 2,840
Reserve for uncollectible other accounts receivable	$ 540	$ 335
Common shareholders' equity
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	50,000	50,000
Common stock, shares outstanding	17,348	17,348

MGE Energy Inc Consolidated S_4

MGE Energy Inc Consolidated Statements of Common Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]
Beginning balance, shares at Dec. 31, 2015		34,668
Beginning balance, value at Dec. 31, 2015	$ 690,458	$ 34,668	$ 316,268	$ 339,165	$ 357
Increase (Decrease) in Equity [Roll Forward]
Net Income	75,560			75,560
Other comprehensive income (loss)	(155)				(155)
Common stock dividends declared	(41,775)			(41,775)
Ending balance, shares at Dec. 31, 2016		34,668
Ending balance, value at Dec. 31, 2016	724,088	$ 34,668	316,268	372,950	202
Increase (Decrease) in Equity [Roll Forward]
Net Income	97,606			97,606
Other comprehensive income (loss)	175				175
Common stock dividends declared	(43,682)			(43,682)
Ending balance, shares at Dec. 31, 2017		34,668
Ending balance, value at Dec. 31, 2017	778,187	$ 34,668	316,268	426,874	377
Increase (Decrease) in Equity [Roll Forward]
Cumulative effect of new accounting principle	0			377	(377)
Beginning balance, value - Adjusted at Dec. 31, 2017	778,187			427,251	0
Increase (Decrease) in Equity [Roll Forward]
Net Income	84,219			84,219
Common stock dividends declared	(45,762)			(45,762)
Ending balance, shares at Dec. 31, 2018		34,668
Ending balance, value at Dec. 31, 2018	$ 816,644	$ 34,668	$ 316,268	$ 465,708	$ 0

Madison Gas and Electric Comp_4

Madison Gas and Electric Company Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	MGE [Member]		Common Stock [Member]	Common Stock [Member]MGE [Member]	Additional Paid-In Capital [Member]MGE [Member]	Retained Earnings [Member]	Retained Earnings [Member]MGE [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]MGE [Member]	Noncontrolling Interest [Member]MGE [Member]
Beginning balance, shares at Dec. 31, 2015				34,668	17,348
Beginning balance, value at Dec. 31, 2015		$ 641,984			$ 17,348	$ 192,417		$ 291,888		$ 23	$ 140,308
Increase (Decrease) in Equity [Roll Forward]
Net Income		74,592						51,234			23,358
Other comprehensive income (loss)	$ (155)	(4)							$ (155)	(4)
Cash dividends paid to parent by MGE		(50,000)	[1]					(50,000)
Dividend in kind to parent		(15,822)						(15,822)
Equity contribution received by noncontrolling interest		1,598									1,598
Distributions to parent from noncontrolling interest		(24,113)									(24,113)
Deconsolidation of noncontrolling interest		(25,486)									(25,486)
Ending balance, shares at Dec. 31, 2016				34,668	17,348
Ending balance, value at Dec. 31, 2016		602,749			$ 17,348	192,417		277,300		19	115,665
Increase (Decrease) in Equity [Roll Forward]
Net Income		93,072						49,835			43,237
Other comprehensive income (loss)	175	(47)							175	(47)
Cash dividends paid to parent by MGE		(45,000)						(45,000)
Dividend in kind to parent		0
Distributions to parent from noncontrolling interest		(18,000)									(18,000)
Ending balance, shares at Dec. 31, 2017				34,668	17,348
Ending balance, value at Dec. 31, 2017		632,774			$ 17,348	192,417		282,135		(28)	140,902
Increase (Decrease) in Equity [Roll Forward]
Cumulative effect of new accounting principle	0	0					$ 377	(28)	(377)	28
Beginning balance, value - Adjusted at Dec. 31, 2017	$ 778,187	632,774					$ 427,251	282,107	$ 0	0
Increase (Decrease) in Equity [Roll Forward]
Net Income		79,036						56,484			22,552
Cash dividends paid to parent by MGE		0
Dividend in kind to parent		0
Distributions to parent from noncontrolling interest		(22,000)									(22,000)
Ending balance, shares at Dec. 31, 2018				34,668	17,348
Ending balance, value at Dec. 31, 2018		$ 689,810			$ 17,348	$ 192,417		$ 338,591		$ 0	$ 141,454
[1]	Excludes $15.8 million dividend in kind to MGE Energy from MGE in 2016 .

Consolidated Statements of Comm

Consolidated Statements of Common Equity (Parentheticals) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dividends per share of common stock	$ 0.338	$ 0.338	$ 0.323	$ 0.3225	$ 0.323	$ 0.323	$ 0.308	$ 0.308	$ 1.32	$ 1.26	$ 1.21

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies. a. Basis of Presentation - MGE Energy and MGE. The consolidated financial statements are prepared in confor mity with accounting principles generally acce pted in the U nited States of America (GAAP), which give recognition to the rate making accounting policies for regulated operations prescribed by the regulatory authorities having jurisdiction, principally the PSCW and FERC. MGE's accounting records confor m to the FERC uniform system of accounts. b. Principles of Consolidation - MGE Energy and MGE. MGE, a wholly owned subsidiary of MGE Energy, is a regulated electric and gas utility headquartered in Madison, Wisconsin. MGE Energy and MGE consolidate all majority owned subsidiaries in which they have a controlling influence. Additional wholly owned subsidiaries of MGE Energy include CWDC, MAGAEL, MGE Power, MGE State Energy Services, MGE Services, MGE Transco, and MGEE Transco . CWDC owns 100% of North Mendota, a subsidiary created to serve as a d evel opment entity for property. MGE Power owns 100 % o f MGE Power Elm Road and MGE Power West Campus. MGE Power and its subsidiaries are part of MGE Energy' s nonregulated energy operations, which were formed to own and lease electric generation projects to assist MGE. MGE Transco and MGEE Transco are nonregul ated entities formed to manage the investments in ATC and ATC Holdco, respectively. On December 1, 2016, MGE ' s ownership interest in MGE Transco was transferred to MGE Energy. See Footnote 6 for further discussion of the transfer of MGE ' s investment in MGE Transco. MGE Energy and MGE consolidate variable interest entities (VIEs) for which it is the primary beneficiary. Variable interest entities are legal entities that possess any of the following characteristics: equity investors who have an insufficient amount of equity at risk to finance their activities, equity owners who do not have the power to direct the significant activities of the entity (or have voting rights that are disproportionate to their ownership interest), or equity holders who do not rec eive expected losses or returns significant to the VIE. If MGE Energy or MGE is not the primary beneficiary and an ownership interest is held, the VIE is accounted for under the equity method of accounting. When assessing the determination of the primary b eneficiary, all relevant facts and circumstances are considered, including: the power, through voting or similar rights, to direct the activities of the VIE that most significantly impact the VIE's economic performance and the obligation to absorb the expe cted losses and/or the right to receive the expected returns of the VIE. Ongoing reassessments of all VIEs are performed to determine if the primary beneficiary status has changed. MGE has consolidated MGE Power Elm Road and MGE Power West Campus. Both ent ities are VIEs. MGE is considered the primary beneficiary of these entities as a result of contractual agreements. See Footnote 3 for more discussion of these entities. Prior to December 1, 2016, MGE Transco was jointly owned by MGE Energy and MGE. MGE's ownership interest in MGE Transco declined below a majority in July 2016. As a result of the change in majority ownership, MGE deconsolidated MGE Energy's proportionate share of the equity in MGE Transco. See Footnote 20 for further discussion regarding th e deconsolidation of noncontrolling interest . The consolidated financial statements reflect the application of certain accounting policies described in this note. All intercompany accounts and transactions have been eliminated in consolidation. c. Use of Estimates - MGE Energy and MGE. In order to prepare consolidated financial statements in conformity with GAAP, management must make estimates and assumptions. These estimates could affect reported amounts of assets, liabilities, and disclosures at the date of the financial statements, as well as the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from management's estimates. d. Cash, Cash Equivalents, and Restricted Cash – MGE Energy and MGE. The following table presents the components of total cash, cash equivalents, and restricted cash on the consolidated balance sheets. (In thousands) MGE Energy MGE As of December 31, 2018 2017 2018 2017 Cash and cash equivalents $ 83,102 $ 107,952 $ 4,843 $ 5,951 Restricted cash 634 1,635 634 1,635 Receivable - margin account 1,193 2,507 1,193 2,507 Cash, cash equivalents, and restricted cash $ 84,929 $ 112,094 $ 6,670 $ 10,093 Cash Equivalents MGE Energy and MGE consider all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash MGE has certain cash accounts that are restricted to uses other than current operations and designated for a specific purpose. MGE's restricted cash accounts include cash held by trustees for certain employee benefits and cash deposits held by third parties. These are included in "Other current assets" on the consolidated balance s heets. Receivable – Margin Account Cash amounts held by counterparties as margin collateral for certain financial transactions are recorded as Receivable – margin account in "Other current assets" on the consolidated balance sheets. The costs being hedged are fuel for electric generation, purchased power, and cost of gas sold. Retrospective adjustments to cash flow amounts on MGE Energy's and MGE's consolidated statements of cash flows in accordance with the adoption of ASU 2016-18, Restricted Cash for th e years ended December 31, were as follows: (In thousands) 2017 2016 Cash provided by operating activities $ (1,618) $ 351 Cash used for investing activities 86 13 Change in cash, cash equivalents, and restricted cash (1,532) 364 Cash, cash equivalents, and restricted cash at beginning of period 5,674 5,310 Cash, cash equivalents, and restricted cash at end of period $ 4,142 $ 5,674 e. Trade Receivables, Allowance for Doubtful Accounts, and Concentration Risk - MGE Energy and MGE. Trade accounts receivable are recorded at the invoiced amount and do not bear interest. However, a 1 % late payment charge is recorded on all receivables unpaid after the due date. The allowance for doubtful accounts associated with these receivables represents our best estimate of the amount of probable credit losses in our existing accounts receivable. We determine our allowance for doubtful accounts based on historical write-off experience, regional economic data, and review of the accounts receivable aging . MGE manages this concentration and the related credit risk through its credit and collection pol icies, which are consistent with state regulatory requirements. f. Inventories - MGE Energy and MGE. Inventories consist of natural gas in storage, fuel for electric generation, materials and supplies, and renewable energy credits (R ECs). MGE values natural gas in storage, fuel for electric generation , and materials and supplies using average cost. REC allowances are included in "Materials and supplies" on the consolidated balance sheets and are recorded based on specific identification. These allo wances are charged to purchase power expense as they are used in operations. MGE's REC allowance balance as of December 31, 2018 and 2017 , was $ 0.7 million and $ 0.5 million, respectively. g. Chattel Paper Agreements - MGE Energy and MGE. MGE makes available to qualifying customers a financing program for the purchase and installation of energy-related equipment that will provide more efficient use of utility service at the customer's property. The energy-related equipment installed at the customer sites is used to secure the customer loans. MGE is a party to a chattel paper purchase agreement with a financial institution under which MGE can sell, transfer, and assign to the financial i nstitution an undivided interest with recourse, in up to $ 10.0 million of the financing program receivables, until July 31, 2019. The length of the MGE guarantee to the financial institution varies from one to ten years depending on the term of the underlying customer loan. The loan balances outstanding as of December 31, 2018 , approximates the fair value of the energy-related equipment acting as collateral. MGE accounts for these agreements as secured borrowings. As of December 31, 2018 , the remaining contractual maturities of the chattel paper agreements were as follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Repurchase-to-Maturity Transactions: Loans $ 396 $ 407 $ 392 $ 354 $ 510 $ 122 h. Regulatory Assets and Liabilities - MGE Energy and MGE. Regulatory assets and regulatory liabilities are recorded consistent with regulatory treatment. Regulatory assets represent costs which are deferred due to the probable future recovery from customers through regulated rates. Regulatory liabilities represent the excess recovery of costs or accrued credits which were deferred because MGE believes it is probable such amounts will be returned to customers through future regulated rates. Regulator y assets and liabilities are amortized in the consolidated statements of income consistent with the recovery or refund included in customer rates. MGE believes that it is probable that its recorded regulatory assets and liabilities will be recovered and re funded, respectively, in future rates. See Footnote 7 for further information. i. Debt Issuance Costs - MGE Energy and MGE. Premiums, discounts, and expenses incurred with the issuance of outstanding long-term debt are amortized over the life of the debt issue. Any call premiums or unamortized expenses associated with refinancing higher-cost debt obligations used to finance utility-regulated assets and operations are amortized consistent with regulatory treatment of those items. These costs are included as a direct r eduction to the related debt liability on the consolidated balance sheets. j. Property, Plant, and Equipment - MGE Energy and MGE. Property, plant, and equipment is recorded at original cost. Cost includes indirect costs consisting of payroll taxes, pensions, postretirement benefits, other fringe benefits, and administrative and general costs. Also, included in the cost is AFUDC for utility property and capitalized interest for nonregulated property. Additions for significant replacements of property are charged to property, plant, and equipment at cost; and minor items are ch arged to maintenance expense. Depreciation rates on utility property are approved by the PSCW, based on the estimated economic lives of property, and include estimates for salvage value and removal costs. Removal costs of utility property, less any salvage value, are adjusted through regulatory liabilities. Depreciation rates on nonregulated property are based on the estimated economic lives of the property. See Footnote 4 for further information. Provisions at composite straight-line depreciation rates ap proximate the following percentages for the cost of depreciable property: 2018 2017 2016 Electric (a)(b) 2.9 % 3.0 % 2.5 % Gas (a) 2.1 % 2.1 % 2.1 % Nonregulated 2.3 % 2.3 % 2.3 % (a ) In December 2015, the PSCW approved new depreciation rates, which were implemented and became effective as of January 1, 2016. (b) In September 2016, the PSCW approved new depreciation rates for Columbia effective January 1, 2017. k. Asset Retirement Obligations - MGE Energy and MGE. A liability is recorded for the fair value of an asset retirement o bligation (ARO) to be recognized in the period in which it is incurred if it can be reasonably estimated. The offsetting associated asset retirement costs are capitalized as a long-lived asset and depreciated over the asset ' s useful life. The expected present value technique used to calculate the fair value of ARO liabilities includes assumptions about costs, probabilities, settlement dates, interest accretion, and inflation. Revisions to the assumptions, including the timing or amount of expected asset retirement costs, could result in increases or decreases to the AROs. All asset retirement obligations are recorded as "O ther long-term liabilities " on the consolidated balance sheets. MGE has regulatory treatment and recognizes regulatory assets or liabilities for the timing differences between when it recover s legal AROs in rates and when it would recognize these costs. See Footnote 18 for further information. l . Repairs and Maintenance Expense - MGE Energy and MGE. MGE utilizes the direct expensing method for planned major maintenance projects. Under this method, MGE expenses all costs associated with major planned maintenance activities as incurred. m. Purchased Gas Adjustment Clause - MGE Energy and MGE. MGE's natural gas rates are subject to a fuel adjustment clause designed to recover or refund the difference between the actual cost of purchased gas and the amount included in rates. Differences between the amounts billed to customers and the actual costs recoverable are deferred and recovered or refunded in future periods by means of prospective monthly adjustments to rates. As of December 31, 2018 and 2017 , MGE had over collected $ 1.2 million and $ 1.4 million, respectively. These amounts are included in "Regulatory liabilities – current " on the consolidated balance sheets. n. Revenue Recognition - MGE Energy and MGE. Operating revenues are recorded as service is rendered or energy is delivered to customers. Meters are read on a systematic basis throughout the month based on established meter-reading schedules. At the end of the month, MGE accrues an estimate for the unbilled amount of energy delivered to customers. The unbilled revenue estimate is based on daily system demand volumes, weather factors, estimated line losses, estimated customer usage by class, and applicable customer rates. See Footnote 19 for further information. o. Utility Cost Recovery - MGE Energy and MGE. MGE's tariff rates include a provision for fuel cost recovery. The PSCW allows Wisconsin utilities to defer electric fuel-related costs, less excess revenues, that fall outside a symmetrical cost tolerance band. Any over/under recovery of the actual costs in a given year is determined in the following year and is then reflected in future billings to electric retail customers. Over-collection of fuel-related costs that are outside the approved range will be r ecognized as a reduction of revenue. Prior to adoption of the new revenue recognition guidance, effective January 1, 2018, over-collected fuel-related costs were reflected in "Purchased power" expense. Under-collection of these costs will continue to be re cognized in "Purchased power" expense in the consolidated statements of income of MGE Energy and MGE. The cumulative effects of these deferred amounts will be recorded in "Regulatory assets" or "Regulatory liabilities" on the consolidated balance sheets of MGE Energy and MGE until they are reflected in future billings to customers. See Footnote 8.b. for further information. p. Regional Transmission Organizations - MGE Energy and MGE. MGE reports on a net basis transactions on the MISO markets in which it buys and sells power within the same hour to meet electric energy delivery requirements. This treatment resulted in a $ 90.3 million , a $ 87.9 million, and a $ 77.2 million reduction to sales to the market and purchase power expense for MISO markets for the years ended December 31, 2018 , 2017 , and 2016 , r espectively. q. Allowance for Funds Used During Construction - MGE Energy and MGE. Allowance for funds used during construction is included in utility plant accounts and represents the cost of borrowed funds used during plant construction and a return on shareholder' s capital used for construction purposes. In the consolidated income statements, the cost of borrowed funds (AFUDC-debt) is presented as an offset to "Interest expense" and the return on shareholder's capital (AFUDC-equity funds) is shown as an item within "Other income." For both 2018 and 2017 , as approved by the PSCW, MGE capitalized AFUDC-debt and equity on 50 % of applicable average construction work in progress at 7.87 % . For 2016 , as app roved by the PSCW, MGE capitalized AFUDC-debt and equity on 50 % of applicable average construction work in progress at 7.93 %. For 2018 , 2017 , and 2016 , MGE received specific approval to recover 100 % AFUDC on certain environmental costs for Columbia. For 2018 and 2017 , MGE received specific approval to recover 100 % AFUDC on certain costs for the Saratoga Wind Farm project. These amounts are recovered under t he ratemaking process over the service lives of the related properties. r. Investments - MGE Energy and MGE. Investments in limited liability companies that have specific ownership accounts in which MGE Energy or MGE's ownership interest is more than minor and are considered to have significant influence are accounted for using the equity method. All other investments are carried at fair value, with changes in fair value recognized through net income . See Footnote 6 for further information. s. Capitalized Software Costs - MGE Energy and MGE. Property, plant, and equipment includes the net book value of capitalized costs of internal use software totaling $ 15.1 million and $ 11.1 million as of December 31, 2018 and 2017 , respectively. During 2018 , 2017 , and 2016 , MGE recorded $ 4.7 million, $ 3.3 million, and $ 3.0 million, respectively, of amortization expense related to these costs. These costs are amortized on a straight-line basis over the estimated useful lives of the assets. For internal use software, the useful lives range from five to fifteen years. t. Capitalized Software Assets – Hosting Arrangements – MGE Energy and MGE. The FASB issued authoritative guidance of accounting for software in a hosted arrangement. MGE Energy and MGE adopted the authoritative guidance as of September 30, 2018. See Footnote 2 for further information. T he net book value of capitalized costs of internal use software incurred in a hosting arrangement was $ 9.2 million and $ 0.5 million as of December 31, 2018 and 2017 , respectively. During 2018, MGE implemented an enterprise resource planning platform which was placed in service as of January 1, 2019. As of December 31, 2018 , accumulated a mortization expense was $ 0.1 million. There was no accumulated amortization expense a s of December 31, 2017 . Capitalized software assets for hosted arrangements and the related accumulated amortization expense are recorded in " Other deferred assets and other " on the consolidated balance sheets . During 2018 , MGE recorded $ 0.1 million of amortization expense related to software assets for hosted arrangements. During 2017 and 2016 , no amortization expense was recorded. These costs are recognized in " Other operations and maintenance " expense in the consolidated statements of income and are amortized on a straight-line basis over the estimated useful lives of the assets. Software ass ets for hosted arrangements have useful lives ranging from five to ten years. u. Impairment of Long-Lived Assets - MGE Energy and MGE. MGE reviews plant and equipment and other property for impairment when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. MGE's policy for determining when long-lived assets are impaired is to recognize an impairment loss if the sum of the expected future cash flows (undiscounted and without interest charges) from an asset are less than the carrying amount of that asset. If an impairment loss is recognized, the amount that will be recorded will be measured as the amount by which the carrying amount of the asset exceeds the fair value of the asset. There was no impairment of long-lived assets a s of December 31, 2018 , 2017 , and 2016 . v. Income Taxes and Excise Taxes - MGE Energy and MGE. Income taxes Under the liability method, income taxes are deferred for all temporary differences between pretax financial and taxable income and between the book and tax basis of assets and liabilities using the tax rates scheduled by law to be in effect when the temporary differences reverse. Future tax benefits are recognized to the extent that realization of suc h benefits is more likely than not. A valuation allowance is recorded for those benefits that do not meet this criterion. Accounting for uncertainty in income taxes applies to all tax positions and requires a recognition threshold and measurement standard for the financial statement recognition and measurement of a tax position taken, or expected to be taken, in an income tax return. The threshold is defined for recognizing tax return positions in the financial statements as "more likely than not" that the position is sustainable, based on its merits. Subsequent recognition, derecognition, and measurement is based on management's best judgment given the facts, circumstances, and information available at the reporting date. Regulatory and accounting princip les have resulted in a regulatory liability related to income taxes. Excess deferred income taxes result from past taxes provided at rates higher than current rates. The income tax regulatory liability and deferred investment tax credit reflect the revenue requirement associated with the return of these tax benefits to customers. Investment tax credits from regulated operations are amortized over related property service lives. Excise taxes MGE Energy, through its utility operations, pays a state license fee tax in lieu of property taxes on prope rty used in utility operations. License fee tax is calculated as a percentage of adjusted operating revenues of the prior year. The electric tax rate is 3.19 % for retail sales and 1.59 % for sales of electricity for resale by the purchaser. The tax rate on sales of natural gas is 0.97 % . The tax is required to be estimated and prepaid in the year prior to its computation and expensing. License fee tax expense, included in "Other general taxes ," was $ 14.4 million, $ 14.1 million, and $ 14.5 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively. Operating income taxes, including tax credits and license fee tax, are included in rates for utility related items. w. Share-Based Compensation - MGE Energy and MGE. Under two separate incentive plans, eligible participants, including employees and non-employee directors, may receive performance units that entitle the holder to receive a cash payment equal to the value of a designated number of shares of MGE Energy's common stock, plus dividend equivalent payments thereon, at the end of the set performance period set in th e award. Under the plans, these awards are subject to a prescribed vesting schedule and must be settled in cash. Accordingly, no new shares of common stock are issued in connection with the plans. On the grant, date the cost of the employee or director se rvices received in exchange for a performance unit award is measured based on the current market value of MGE Energy common stock. The fair value of the awards is re-measured quarterly through the settlement date. Changes in fair value as well as the origi nal grant are recognized as compensation cost. See Footnote 16 for additional information regarding the plans. x . Derivative and Hedging Instruments - MGE Energy and MGE. As part of regular operations, MGE enters into contracts, including options, swaps, futures, forwards, and other contractual commitments, to manage its exposure to commodity prices. MGE recognizes all derivatives in the consolidated balance sheets at fair value, with changes in the fair value of derivative instruments to be recorded in current earnings or deferred in accumulated other comprehensive income (loss), depending on whether a de rivative is designated as, and is effective as, a hedge and on the type of hedge transaction. Derivative activities are in accordance with the company's risk management policy. If the derivative qualifies for regulatory deferral, the derivatives are mark ed to fair value and are offset with a corresponding regulatory asset or liability. Cash flows from such derivative instruments are classified on a basis consistent with the nature of the underlying hedged item.

New Accounting Standards

New Accounting Standards	12 Months Ended
	Dec. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements	Adoption of Accounting Principles and Recently Issued Accounting Pronouncements - MGE Energy and MGE. a. Recently Adopted R evenue from Contracts with Customers. The FASB issued authoritative guidance within the codification's Revenue Recognition topic that provides guidance on the recognition, measurement, and disclosure of revenue from contracts with customers. The new standard establishes a five-step model for recognizing and measuring revenue from contracts with customers and replaces existing guidance on revenue recognition. The underlying principle is that an entity will recognize revenue to present the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. Th is authoritative guidance became effective January 1, 2018, and MGE Energy and MGE adopted the standard upon the effective date. Adoption of this standard was permitted under one of two methods: the full retrospective method or the modified retrospective m ethod. MGE Energy and MGE implemented the standard using the modified retrospective method. The cumulative impact of this guidance on our financial statements is not material, except for additional footnote disclosures. See Footnote 19 for further informat ion. Financial Instruments. In January 2016, the FASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018, and required equity investments to be measured at fair value with changes in fair value recognized in net income rather than in other comprehensive income. As a result of this guidance, MGE Energy and MGE will no longer have other comprehensive income rela ted to equity investments. This standard was applied using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the fiscal year of adoption. As of January 1, 2018, MGE Energy re corded a $0.4 million increase in retained earnings and a corresponding decrease in accumulated other comprehensive income related to equity investments within the scope of this standard. As of January 1, 2018, MGE recorded less than a $0.1 million decreas e in retained earnings and a corresponding increase in accumulated other comprehensive income related to equity investments within the scope of this standard. Restricted Cash. In November 2016, the FASB issued authoritative guidance within the codificati on's Statement of Cash Flows topic that provides guidance on the classification and presentation of changes in restricted cash within the statement of cash flows. Under the new guidance, reporting entities are required to explain the changes in the total o f restricted and unrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, i nvesting, or financing activities within the statement of cash flows based on the nature of the restriction. Reporting entities are now also required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restrictions of cash. This authoritative guidance became effective January 1, 2018. Upon the effective date, MGE Energy and MGE changed the presentation of restricted cash on the consolidated statements of cash flows to reflect the new accounting gu idance retrospectively for all periods presented. See Footnote 1.d. for further information. Pension and Other Postretirement Benefits. In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net benefit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be pre sented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense " increased and "Other income, net" increas ed $4.1 million and $4.3 million for the years ended December 31, 2017 and 2016 , respectively . The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronouncement (wh ereas under previous GAAP all components of net benefit cost were eligible for capitalization). See Footnote 13 for further information. Internal-Use Software – Hosting Arrangements . In August 2018, the FASB issued amended authoritative guidance within t he codification's Intangibles – Goodwill and Other – Internal-Use Software topic. The amended authoritative guidance aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement (hosting arrangement) that is a ser vice contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangement that include an internal-use software license). Costs for implementation activities in the development st age are capitalized depending on the nature of the costs and presented in the same line item on the balance sheet as amounts prepaid for the hosted service. Costs incurred during the preliminary and postimplementation stages are expensed as the activities are performed. The costs capitalized as part of implementation stage should be expensed over the term of the hosting contract, which includes any renewable option periods, and presented in the same line on the income statement as the fees for the associate d hosted service. This amended authoritative guidance will become effective January 1, 2020. Early adoption of the amendment is permitted, including adoption in any interim period. Entities can choose to adopt the new guidance either prospectively, for eligible costs incurred on or after the date this guidance is first applied, or retrospectively. MGE Energy and MGE early adopted these amendments retrospectively as of September 30, 2018 . The cumulative impact of this guidance on our financial statement w as not material, except for additional footnote disclosures. See Footnote 1.t. for disclosures required under this standard. b. Recently Issued Leases. In February 2016, the FASB issued authoritative guidance within the codification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liability. Prior to the authoritativ e guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance, as applied by lessors, is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optio nal practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE adopted this practical expedient. Management has completed a bottoms-up app roach to analyze the impact of the standard on our lease portfolio. MGE Energy and MGE have reviewed current accounting policies and procedures to identify potential differences in accounting treatment that would result from applying the requirements of th e new standard to our existing lease portfolio. In addition, we identified appropriate changes to our business processes, systems, and controls to support recognition and disclosure requirements under the new standard. This authoritative guidance became ef fective January 1, 2019. MGE Energy and MGE adopted the standard upon the effective date. In compliance with authorized transition guidance, MGE Energy and MGE began applying the new standard on January 1, 2019, but will continue to present periods prior t o that date according to the previous authoritative standard. MGE Energy and MGE expec t to recognize approximately $15-$17 million additional lease assets and liabilities under the new standard. We do not expect that it will have a material impact on our c onsolidated net income or cash flows.

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2018
Variable Interest Entities Disclosure [Abstract]
Variable Interest Entities	Variable Interest Entities - MGE Energy and MGE. a. Consolidated Variable Interest Entities. MGE Power Elm Road and MGE Power West Campus are not subsidiaries of MGE; but, they have been consolidated in the financial statements of MGE. MGE Power Elm Road and MGE Power West Campus were created for the purpose of owning new generating assets. Power Elm Road ' s sole principal asset is an undivided ownership interest in two coal-fired gen erating plants (the Elm Road Units) located in Oak Creek, Wisconsin, which it leases to MGE pursuant to long-term leases. Power West Campus ' s sole principal asset is the WCCF, which it leases to MGE pursuant to a long-term lease. Based on the nature and te rms of the contractual agreements, MGE is expected to absorb a majority of the expected losses or residual value associated with its ownership of MGE Power Elm Road and Power West Campus and therefore holds a variable interest despite the absence of an equ ity interest. In accordance with applicable accounting guidance, MGE Energy and MGE consolidate VIEs of which they are the primary beneficiary. MGE has the power to direct the activities that most significantly impact both the Elm Road Units ' and the WCC F ' s economic performance and is also the party most closely associated with MGE Power Elm Road and MGE Power West Campus. As a result, MGE is the primary beneficiary. As of December 31, MGE has included the following significant accounts on its consolidated b alance sheets related to its interest in these VIEs: MGE Power Elm Road MGE Power West Campus (In thousands) 2018 2017 2018 2017 Property, plant, and equipment, net $ 173,464 $ 176,002 $ 81,273 $ 80,282 Construction work in progress 530 1,225 478 610 Affiliate receivables - - 3,707 4,236 Deferred income taxes 30,595 29,256 14,222 13,795 Long-term debt (a) 56,806 59,416 41,496 43,262 Noncontrolling interest 97,519 97,635 43,935 43,267 b . Other Variable Interest Entities. MGE has a variable interest in entities through purchase power agreements relating to purchased energy from the facilities covered by the agreements. As of December 31, 2018 and 2017 , MGE had 11 megawatts and 61 megawatts, respectively, of capacity available under these agreements. MGE evaluated the variable interest entities for possible consolidation. The interest holder is considered the primary beneficiary of the entity and is required to consolidate the entity if the interest holder has the power to direct the activities that most significantly impact the economics of the variable interest entity. MGE examined qualitative factors such as the length of the remaining term of the contracts compared with the remaining lives of the plants, who has the power to direct the operations and maintenance of the facilities, and other factors, and determined MGE is not the primary beneficiary of the variable interest entities. There is not a significant potential exposure to loss as a result of involvement with these variable interest entities.

Property, Plant, and Equipment

Property, Plant, and Equipment	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant, and Equipment - MGE Energy and MGE. Property, plant, and equipm ent consisted of the following as of December 31: MGE Energy MGE (In thousands) 2018 2017 2018 2017 Utility: Electric (a)(b) $ 1,310,421 $ 1,209,336 $ 1,310,438 $ 1,209,353 Gas 442,581 415,542 442,593 415,553 Total utility plant 1,753,002 1,624,878 1,753,031 1,624,906 Less: Accumulated depreciation and amortization (a)(b) 639,486 599,469 639,486 599,469 In-service utility plant, net 1,113,516 1,025,409 1,113,545 1,025,437 Nonregulated: Nonregulated 322,855 319,611 322,855 319,611 Less: Accumulated depreciation and amortization 66,605 61,707 66,605 61,707 In-service nonregulated plant, net 256,250 257,904 256,250 257,904 Construction work in progress: Utility construction work in progress (a)(c) 138,663 56,208 138,663 56,208 Nonregulated construction work in progress 1,008 1,836 1,008 1,836 Total property, plant, and equipment $ 1,509,437 $ 1,341,357 $ 1,509,466 $ 1,341,385 (a ) As of December 31, 2018 and 2017 , MGE has classified $ 3.1 million and $ 8.8 million, respectively, of Columbia assets as held-for-sale on the consolidated balance sheets related to the partial sale of plant assets to WPL. See Footnote 5.a. for further discussion. (b) In April 2018, MGE, along with two other utilities, purchased the Forward Wind Energy Center (Forward Wind), which consists of 86 wind turbines located in Wisconsin. The aggregate purchase price was approximately $ 174 million, of which MGE's proportionate share is 12.8 %, or approximately $ 23 million. (c) In December 2017, the PSCW authorized construction of a 66 MW wind farm, consisting of 33 turbines, located near Saratoga, Iowa. MGE received specific approval to recover 100 % AFUDC on the project. As of December 31, 2018 , MG E has incurred $ 95.8 million of capital expenditures. After tax, MGE has recognized $ 2.5 million in AFUDC equity related to this project for the year ended December 31, 2018 . Construction of the project was completed in February 2019 . MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust. As of December 31, 2018 and 2017 , there was $1.2 million of bonds outstanding under that indenture. See Footnote 10 for further disc us sion of the mortgage indenture.

Joint Plant Ownership

Joint Plant Ownership	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Joint Plant Ownership	Joint Plant Ownership - MGE Energy and MGE. a. Columbia. MGE and two other utilities jointly own Columbia, a coal-fired generating facility located in Portage, Wisconsin, which, as of December 31, 2018 , accounts for 29 % ( 219 MW) of MGE's net summer rated capacity. Power from this facility is shared in proportion to each company's ownership interest. A s of December 31, 2018 , MGE had a 19.4 % ownership interest in Columbia. The other owners are WPL, which operates Columbia, and WPSC. MGE's share of fuel, operating, and maintenance expenses for Columbia was $ 36.5 million, $ 36.2 million, and $ 39.5 million for the years en ded December 31, 2018 , 2017 , and 2016 , respectively . Each owner provides its own financing and reflects its respective portion of facilities and operating costs in its financial statements. MGE's interest in Columbia' s gross utility plant in servic e, and the related accumulated depreciation reserves a s of December 31 were as follows: (In thousands) 2018 2017 Utility plant $ 292,157 $ 274,450 Accumulated depreciation (94,766) (87,144) Property, plant, and equipment, net 197,391 187,306 Construction work in progress 2,021 20,382 Total property, plant, and equipment $ 199,412 $ 207,688 In 2016, MGE and WPL negotiated an amendment to the existing Columbia joint operating agreement that has been approved by the PSCW. Under the terms of the amendments, MGE has reduced its obligation to pay certain capital expenditures (other than SCR-related expenditures) at Columbia in exchange for a proportional reduction in MGE's ownership in Columbia. On January 1 of each year from 2017 through 2019 and then on June 1, 2020, the ownership percentage is adjusted through a partial sale based on the amount of capital expenditures foregone. In June 2017, the FERC approved the ownership transfer in Columbia, effective January 1, 2017. During 2018 and 2017 , MGE accrued $ 3.1 million and $ 8.8 million , respectively, of foregone capital expenditures as part of the ownership transfer agreement with WPL . As of December 31, 2018 and 2017 , MGE classified $ 3.1 million and $ 8.8 million , respectively, of Columbia assets as held-for-sale on the consolidated balance sheets. In January 2018 , MGE reduced its ownership interest in Columbia from 20.4 % to 19.4 % and in January 2019, MGE further reduced its ownership to 19.1 % through the partial sale of plant assets to WPL . b . Elm Road. MGE Power Elm Road owns an 8.33 % ownership interest in each of two 615 MW coal-fired generating units in Oak Creek, Wisconsin, which, a s of December 31, 2018 , accounts for 14 % ( 106 MW) of MGE ' s net summer rated capacity. Unit 1 entered commercial operation on February 2, 2010. Unit 2 entered commercial operation on January 12, 2011. MGE Power Elm Road's sole principal asset is that ownership interest in those generating units. MGE Power Elm Road ' s interest in the Elm Road Units is leased to MGE pursuant to long-term leases . The remainder of the ownership interest in the Elm Road Units is held by two other entities, one of which is also responsible for the Unit s ' operation. Each owner provides its own financing and reflects its respective portion of the facility and costs in its financial statements. MGE ' s share of fuel, operating, and maintenance expenses for the Elm Road Units was $ 17.6 million, $ 17.3 million, and $ 21.2 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively. MGE Power Elm Road ' s interest in the portion of the Elm Road Units in-service and the related accumulated depreciation reserves a s of December 31 were as follows: (In thousands) 2018 2017 Nonregulated plant $ 207,361 $ 206,063 Accumulated depreciation (33,897) (30,061) Property, plant, and equipment, net 173,464 176,002 Construction work in progress 530 1,225 Total property, plant, and equipment $ 173,994 $ 177,227 c. Forward Wind . In April 2018, MGE, along with two other utilities, purchased the Forward Wind Energy Center (Forward Wind), which consists of 86 wind turbines located in Wisconsin. The aggregate purchase price was approximately $ 174 million, of which MGE's proportionate share is 12.8 %, or approximately $ 23 million. The purchase of Forward Wind replaced an existing purchase power agreement, under which MGE purchased 12.8 % of the facility's energy output. MGE's proportionate share of Forward Wind's total capacity is 18 MW. Each owner provides its own financing and reflects its respective portion of facilities and operating costs in its financial statements. MGE's share of operating and maintenance expenses for Forward Wind was $ 0.5 million for the year ended December 31, 2018 , which was deferred in a regulatory asset account and will be recovered in future rates. MGE's interest in the portion of Forward Wind ' s utility plant in service and the related accumulated depreciation reserves as of December 31 were as follows: (In thousands) 2018 Nonregulated plant $ 33,929 Accumulated depreciation (12,530) Property, plant, and equipment, net 21,399 Construction work in progress 67 Total property, plant, and equipment $ 21,466 d . WCCF. MGE Power West Campus and the UW jointly own the West Campus Cogeneration Facility (WCCF) located on the UW campus in Madison, Wisconsin . MGE Power West Campus owns 55 % of the facility and the UW owns 45 % of the facility. The UW owns a controlling interest in the chilled-water and steam plants, which are used to meet the growing needs for air-conditioning and steam-heat capacity for the UW campus. MGE Power West Campus owns a controlling interest in the elect ric generation plant, which is leased and operated by MGE. Each owner provides its own financing and reflects its respective portion of the facility and operating costs in its financial statements. MGE Power West Campus' interest in WCCF and the related a ccu mulated depreciation reserves as of December 31 were as follows: (In thousands) 2018 2017 Nonregulated plant $ 113,328 $ 111,386 Accumulated depreciation (32,055) (31,104) Property, plant, and equipment, net 81,273 80,282 Construction work in progress 478 610 Total property, plant, and equipment $ 81,751 $ 80,892 Operating charges are allocated to the UW based on formulas contained in the operating agreement. Under the provisions of this arrangement, the UW is required to reimburse MGE for their allocated portion of fuel and operating expenses. For the years ended December 31, 2018 , 2017 , and 2016 , the UW allocated share of fu el and operating costs was $ 6.3 million, $ 5.3 million, and $ 5.5 million, respectively .

Investments

Investments	12 Months Ended
	Dec. 31, 2018
Investments Disclosure [Abstract]
Investments	Investments - MGE Energy and MGE. a. Equity Securities, Equity Method Investments, and Other Investments. MGE Energy MGE (In thousands) 2018 2017 2018 2017 Equity securities (a) $ 9,363 $ 7,291 $ 388 $ 409 Equity method investments: ATC and ATC Holdco (b) 66,313 59,298 - - Other 26 1,128 - - Total equity method investments 66,339 60,426 - - Other investments 2,298 55 - - Total $ 78,000 $ 67,772 $ 388 $ 409 (a ) Reflects modified retrospective application of new authoritative guidance related to Financial Instruments as described in Footnote 2. Prior to January 1, 2018, investments were considered available for sale securities. As of December 31, 2017, MGE Energy had available for sale securities with a cost basis of $6.7 million, gross unrealized gains of $0.7 million, and gross unrealized losses of less than $0.1 million. As of December 31, 2017, MGE had available for sale securities with a cost basis of $ 0.5 million and gross unrealized losses of less than $0.1 million. (b) In December 2017, there was a $ 20.4 million one-time tax impact related to ATC as a result of the Tax Act. See Footnote 12 for further information. MGE Energy's and MG E's equity securities represent publicly traded securities and private equity investments in common stock of companies in various industries. During the years ended December 31, 2018 , 2017 , and 2016 , certain inves tments were liquidated. As a re sult of these liquidations, MGE Energy and MGE received the following: MGE Energy MGE (In thousands) 2018 2017 2016 2018 2017 2016 Cash proceeds $ 960 $ 677 $ 408 $ 3 $ - $ 16 Gain (loss) on sale 476 522 121 3 - (8) b. ATC and ATC Holdco. ATC owns and operates electric transmission facilities primarily in Wisconsin. MGE received an interest in ATC when it, like other Wisconsin electric utilities, contributed its electric transmission facilities to ATC as required by Wisconsin law. That interest is presently held by MGE Transco, which, since December 1, 2016, is owned by MGE Energy. ATC Holdco was formed by several members of ATC, including MGE Energy, to pursue electric transmission development and investments outsid e of Wisconsin. The ownership interest in ATC Holdco is held by MGEE Transco, a wholly-owned subsidiary of MGE Energy. MGE Transco and MGEE Transco have accounted for their investment in ATC and ATC Holdco, respectively, under the equity method of account ing. For the years ended December 31, 2018 , 2017 , and 2016 , MGE Transco recorded the following: (In thousands) 2018 2017 2016 Equity earnings from investment in ATC $ 8,821 $ 10,125 $ 8,670 Dividends received from ATC (a) 4,611 9,078 7,926 Capital contributions to ATC 2,841 3,551 2,486 (a ) MGE Transco recorded a $ 2.3 million and a $ 2.1 million dividend receivable from ATC as of December 31, 2017 and 2016 , respectively. A cash dividend was received in January of each of the proceeding years. ATC Holdco was formed in December 2016. In the near term, it is expected that ATC Holdco will be pursuing transmission development opportunities that typically have long development and investment lead times before becoming operational. In 2018 and 2017 , MGEE Transco recorded capital contributions of $ 0.3 million and $ 2.9 million, respectively, to ATC Holdco. As of December 31, 2018 and 2017 , MGE Transco held a 3.6 % ownership interest in ATC. A s of December 31, 2018 and 2017 , MGEE Transco held a 4.4 % ownership interest in ATC Holdco. In June 2016, the PSCW required MGE to transfer its interest in ATC to MGE Energy, which was to be completed by December 31, 2022. The re quirement arose in the context of requests for regulatory approvals by several owners of ATC in connection with a reorganization of ATC . MGE ' s ownership interest in ATC , held through MGE Transco, was tr ansferred net of deferred tax liabilities to MGE Energy by way of a dividend in kind of $ 15.8 m illion as of December 1, 2016. As a result of the transfer, MGE's ownership interest in MGE Transco was completely eliminated in favor of MGE Energy. The change had no effect on MGE Energy's consolidated financial statements. ATC's summarized financial data is as follows: (In thousands) Income statement data for the year ended December 31, 2018 2017 2016 Operating revenues $ 690,510 $ 721,672 $ 650,806 Operating expenses (358,703) (346,308) (323,947) Other income 2,405 7,402 5,361 Interest expense, net (110,725) (110,138) (99,464) Earnings before members' income taxes $ 223,487 $ 272,628 $ 232,756 Balance sheet data as of December 31, 2018 2017 Current assets $ 87,250 $ 87,730 Noncurrent assets 4,928,793 4,598,919 Total assets $ 5,016,043 $ 4,686,649 Current liabilities $ 640,040 $ 767,248 Long-term debt 2,013,997 1,790,590 Other noncurrent liabilities 295,281 240,286 Members' equity 2,066,725 1,888,525 Total members' equity and liabilities $ 5,016,043 $ 4,686,649 During 2018 , 2017 , and 2016 , MGE recorded $ 29.0 m illion, $ 29.2 million, and $ 29.1 million, respectively, for transmission services received from ATC. MGE also provides a variety of operational, maintenance, and project management work for ATC, which is reimbursed by ATC. As of December 31, 2018 and 2017 , MGE had a receivable due from ATC of $ 0.1 million and $ 0.2 million, respectively.

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	12 Months Ended
	Dec. 31, 2018
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities - MGE Energy and MGE. The following regulatory assets and liab ilities are reflected in MGE's c onsolidated b alance s heet s as of December 31: (In thousands) 2018 2017 Regulatory Assets Asset retirement obligation $ 9,199 $ 8,328 Conservation costs 81 222 Debt related costs 9,288 9,749 Derivatives 31,830 41,958 Tax recovery related to AFUDC equity 6,482 5,497 Unfunded pension and other postretirement liability 96,030 84,342 Other 1,991 359 Total Regulatory Assets $ 154,901 $ 150,455 Regulatory Liabilities Deferred fuel savings $ 9,504 $ 4,229 Elm Road 2,515 931 Income taxes 135,449 131,689 Non-ARO removal costs 19,891 18,536 Pension and other postretirement service costs 3,669 - Purchased gas adjustment 1,186 1,404 Renewable energy credits 700 454 Transmission 5,476 1,967 Other 1,074 576 Total Regulatory Liabilities $ 179,464 $ 159,786 MGE expects to recover its regulatory assets and return its regulatory liabilities through rates charged to customers based on PSCW decisions made during the ratemaking process or based on PSCW long-standing policies and guidelines. The adjustments to rates for these regulatory assets and liabilities will occur over the periods either specified by the PSCW or over the corresponding period related to the asset or liability. Management believes it is probable that MGE will continue to recover from custome rs the regulatory assets described above based on prior and current ratemaking treatment for such costs. All regulatory assets for which a cash outflow had been made are earning a return. Asset Retirement Obligation See Footnote 18 for further discussion . Conservation Costs MGE has received regulatory treatment for certain conservation expenditures. The expenditures are used for Focus on Energy programs, which is Wisconsin ' s statewide energy efficiency and renewable resource program, to promote energy ef ficiency on the customer's premises. Costs for Focus on Energy programs are estimated in MGE's rates utilizing escrow accounting. The escrow accounting allows the utility to true-up its actual costs incurred and reflect the amount of the true-up in its nex t rate case filing. Debt Related Costs This balance includes debt issuance costs of extinguished debt and other debt related expenses, including make-whole premiums. The PSCW has allowed rate recovery on unamortized issuance costs for extinguished debt fa cilities. When the facility replacing the old facility is deemed by the PSCW to be more favorable for the ratepayers, the PSCW will allow rate recovery of any unamortized issuance costs related to the old facility. These amounts are recovered over the term of the new facility. Derivatives MGE has physical and financial contracts that are accounted for as derivatives. The amounts recorded for the net mark-to-market value of the commodity based contracts is offset with a corresponding regulatory asset or lia bility because these transactions are part of the PGA or fuel rules clause authorized by the PSCW. A significant portion of the recorded amount is related to a purchased power agreement that provides MGE with firm capacity and energy during a base term tha t began on June 1, 2012, and ends on May 31, 2022. See Footnote 14 for further discussion. Tax Recovery Related to AFUDC Equity AFUDC equity represents the after-tax equity cost associated with utility plant construction and results in a temporary differe nce between the book and tax basis of such plant. It is probable under PSCW regulation that MGE will recover in future rates the future increase in taxes payable represented by the deferred income tax liability. The amounts will be recovered in rates over the depreciable life of the asset for which AFUDC was applied. Tax recovery related to AFUDC equity represents the revenue requirement related to recovery of these future taxes payable, calculated at current statutory tax rates. Unfunded Pension and Other Postretirement Liability MGE is required to recognize the unfunded status of defined benefit pension and other postretirement pension plans as a net liability or asset on the balance sheet with an offset to a regulatory asset or liability. The unfunded st atus represents future expenses that are expected to be recovered in rates. See Footnote 13 for further discussion. Deferred Fuel Savings The fuel rules require the PSCW and Wisconsin utilities to defer electric fuel-related costs that fall outside a symmetrical cost tolerance band. Any over/under recovery of the actual costs is determined on an annual basis and is adjusted in future billings to electric retail customers. See Footnote 8.b. for further discussion. Elm Road Costs associated with Elm Road are estimated in MGE ' s rates utilizing escrow accounting and include costs for lease payments, management fees, community impact mitigation, and operating costs. Costs are collected in rates over a one to two year period. Income Taxes Excess deferr ed income taxes result from past taxes provided at rates higher than current rates. The regulatory liability and deferred investment tax credit reflects the revenue requirement associated with the return of these tax benefits to customers. Changes in inco me taxes are generally passed through in customer rates for the regulated utility. The one-time 2017 impact on timing differences related to income taxes passed through to customer rates of the Tax Act was recorded as a regulatory liability. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, which will be subject to review by the PSCW. A portion of the regulatory liability will be returned to customers based on a mandated tim eframe dictated by applicable tax laws. See Footnote 12 for further information. Non-ARO Removal Costs In connection with accounting for asset retirement obligations, companies are required to reclassify cumulative collections for non-ARO removal costs as a regulatory liability, with an offsetting entry to accumulated depreciation. Under the current rate structure, these removal costs are being recovered as a component of depreciation expense. Pension and Other Postretirement Service Costs The FASB issued authoritative guidance within the codification's Compensation-Retirement Benefits topic that, beginning January 1, 2018, only allows the service cost component of net periodic benefit cost to be eligible for capitalization within the consolidated balance sheets. Under the current rate structure, non-service cost components of net periodic benefit cost are being recovered as a component of depreciation expense. MGE has regulatory treatment and recognizes regulatory assets or liabilities for timing differences between when net periodic benefit costs are recovered and when costs are recognized. See Footnote 13 for further discussion. Purchased Gas Adjustme nt MGE's natural gas rates are subject to a fuel adjustment clause designed to recover or refund the difference between the actual cost of purchased gas and the amount included in rates. Differences between the amounts billed to customers and the actual costs recoverable are deferred and recovered or refunded in future periods by means of prospective monthly adjustments to rates. Renewable Energy Credits MGE receives renewable energy credits from certain purchase power agreements. The value of the credit s are recorded as inventory and expensed when the credit is redeemed or expired. A regulatory liability has been established for the value of the renewable energy credits included in inventory. In Wisconsin, renewable energy credits expire four years after the year of acquisition. Transmission Costs The current accounting treatment for transmission costs allows MGE to reflect any differential between transmission costs reflected in rates and actual costs incurred in its next rate filing.

Rate Matters

Rate Matters	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Rate Matters	Rate Matters - MGE Energy and MGE. a. Rate P roceedings. In December 2018, the PSCW approved the settlement agreement between MGE and intervening parties in the rate case. The settlement decreases electric rates by 2.24 % or $ 9.2 million in 2019. MGE will maintain this rate level for 2020, with the exception that MGE will file a 2020 Fuel Cost Plan in 2019 and MGE's electric rates will be adjusted accordingly. The decrease reflects the ongoing tax imp acts of the Tax Act and the addition of lower-cost renewable generation capacity. The settlement agreement increases gas rates by 1.06 % or $ 1.7 million in 2019 and 1.46 % or $ 2.4 million in 2020. The gas increase covers infrastructure costs. It also reflects the impacts of the Tax Act. The return on common stock equity for 2019 and 2020 is 9.8 % based on a capital structure consisting of 56.6 % common equity in 2019 and 56.1 % common equity in 2020. I n December 2016, the PSCW authorized MGE , effective January 1, 2017, to decrease 2017 rates for retail electric customers by 0.8 % or $ 3.3 million on an annual basis and to increase rates for retail gas customers by 1.9 % or $ 3.1 million on an annual basis . The decrease in retail electr ic rates was attributable to declining fuel and purchased power costs. The increase in retail gas rates cover ed costs associated with MGE ' s natural gas system infrastructure improvements. The authorized return on common stock equity for 2017 was 9.8 % based on a capital structure consisting of 57.2 % common equity . MGE did not file a base rate case for 2018 and 2016. b. Fuel R ules. Fuel rules require the PSCW and Wisconsin utilities to defer electric fuel-related costs that fall outside a symmetrical cost tolerance band around the amount approved for a utility in its annual fuel proceedings. Any over/under recovery of the actual costs is determined in the following year and is then reflected in future billings to electric retail customers. The fuel rules bandwidth is currently set at plus or minus 2 %. Under fuel rules, MGE would defer costs, les s any excess revenues, if its actual electric fuel costs exceeded 102 % of the electric fuel costs allowed in its latest rate order. Excess revenues are defined as revenues in the year in question that provide MGE with a greater ret urn on common equity than authorized by the PSCW in MGE's latest rate order. Conversely, MGE is required to defer the benefit of lower costs if actual electric fuel costs were less than 98 % of the electric fuel costs allowed in th at order . These costs will be subject to the PSCW ' s annual review of fuel costs completed in the year following the deferral . In August 2015, the PSCW approved a $0.00256/kWh fuel credit that began on September 1, 2015, and continued throughout 2016. MGE returned $ 8.3 million of electric fuel-related savings during the year ended December 31, 2017 . The PSCW issued final decisions in the fuel rules proceedings for MGE to refund additional fuel savings incurred to its retail electric customers over a one-month period. MGE returned $ 4.2 million, $ 6.2 million, and $ 15.5 million of electric fuel-related savings in October 2018, October 2017, and September 2016, respectively. There was no change to the refund in the fuel rules proceedings from the amount MGE deferred in the previous respective years. In December 2017, the PSCW approved a surcharge for 2018 electric fuel-related costs. The surcharge increased electric retail revenue in 2018 by $ 0.5 million or 0.13 %. As of December 31, 2018 , MGE has deferred $ 9.5 million of 2018 fuel-related savings. These costs will be subject to the PSCW ' s annual review of 2018 fuel costs, expected to be completed in 2019 .

Common Equity

Common Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Common Equity	Common Equity. a. Common Stock - MGE Energy and MGE. MGE Energy sells shares of its common stock through its Stock Plan. Those shares may be newly issued shares or shares that MGE Energy has purchased in the open market for resale to participants in the Stock Plan. All sales under the Stock Plan are covered by a shelf registration statement that MGE Energy filed with the SEC. For the years ended December 31, 2018 and 2017 , MGE Energy did not issue any new shares of common stock under the Stock Plan. MGE Energy's transfer agent purchases shares on the open market to provide shares to meet obligations to participants in the Stock Plan. The shares are purchased on the open market through their securities broker-dealer and then are reissued under the Stock Plan as needed to meet share delivery requirements. The volume and timing of share repurchases in the open market depends upon the level of dividend reinvestment and optional share purchases being made from time to time by plan participants. As a result, there is no specific maximum number of shares to be repurchased and no specified termination date for the repurchases. During the years ended December 31, 2018 and 2017 , MGE Energy paid $ 45.8 million (or $ 1.32 per share) and $ 43.7 million (or $ 1.26 per share), respectively, in cash dividends on its common stock. Dividend payments by MGE to MGE Energy are subject to restrictions arising under a PSCW rate ord er and, to a lesser degree, MGE's first mortgage bonds. The PSCW order restricts any dividends, above the PSCW authorized amount that MGE may pay MGE Energy if its common equity ratio, calculated in th e manner used in the rate proceeding, is less than 55 %. This restriction did not impact MGE 's payment of dividends in 2018 . See Footnote 10 for further discussion of the mortgage indenture covenants. During the year ended December 31, 2017 , MGE paid $ 45.0 million in cash dividends to MGE Energy. MGE paid no dividends to MGE Energy during the year ended December 31, 2018 . b. Dilutive Shares Calculation - MGE Energy. MGE Energy has not issued any dilutive securities.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt - MGE Energy and MGE. a. Long-Term Debt . December 31, (In thousands) 2018 2017 First Mortgage Bonds: (a) 7.70%, 2028 Series $ 1,200 $ 1,200 Tax Exempt Debt: 3.45%, 2027 Series, Industrial Development Revenue Bonds 19,300 19,300 Medium-Term Notes: (b) 6.12%, due 2028 20,000 20,000 7.12%, due 2032 25,000 25,000 6.247%, due 2037 25,000 25,000 Total Medium-Term Notes 70,000 70,000 Other Long-Term Debt: (d) 5.59%, due 2018 (c)(e) - 20,000 3.38%, due 2020 (e) 15,000 15,000 3.09%, due 2023 (e) 30,000 30,000 3.29%, due 2026 (e) 15,000 15,000 3.11%, due 2027 (e) 30,000 30,000 5.68%, due 2033 (f) 25,064 26,121 5.19%, due 2033 (f) 16,561 17,290 5.26%, due 2040 (e) 15,000 15,000 5.04%, due 2040 (g) 35,139 36,806 4.74%, due 2041 (g) 22,167 23,166 4.38%, due 2042 (e) 28,000 28,000 4.42%, due 2043 (e) 20,000 20,000 4.47%, due 2048 (e) 20,000 20,000 3.76%, due 2052 (e) 40,000 40,000 4.19%, due 2048 (c)(e) 60,000 - 4.24%, due 2053 (c)(e) 20,000 - 4.34%, due 2058 (c)(e) 20,000 - Total Other Long-Term Debt 411,931 336,383 Long-term debt due within one year (4,553) (24,452) Unamortized discount and debt issuance costs (4,535) (4,270) Total Long-Term Debt $ 493,343 $ 398,161 (a) MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust, under which its first mortgage bonds are issued. The Mortgage Indenture provides that dividends or any other distribution or purchase of shares may not be made if the aggregate amount thereof since December 31, 1945 , would exceed the earned surplus (retained earnings) accumulated subsequent to December 31, 1945. As of December 31, 2018 , approximately $ 400.0 m illion was available for the payment of dividends under this covenant. (b ) T he indenture under which MGE's Medium-T erm notes are issued provides that those notes will be entitled to be equally and ratably secured in the event that MGE issues any additional firs t mortgage bonds. (c ) In July 2018, MGE issued a total of $ 4 0 million of new long-term unsecured debt. In September 2018, MGE issued $60 million of new long-term unsecured debt. MGE used the net proceeds from these debt financings to assist with financing capital expenditures, such as the Saratoga Wind Farm, and to refinance $20 million of long-term debt w hich matured in September 2018. (d ) Unsecured notes issued pursuant to various Note Purchase Agreements with one or more purchasers. The notes are not i ssued under, or governed by, MGE ' s Indenture dated as of September 1, 1998, which governs MGE ' s Medium-Term Notes. (e ) Issued by MGE. Under that Note Purchase Agreement: (i) note holders have the right to require MGE to repurchase their notes at par in the event of an acquisition of beneficial ownership of 30 % or more of the outstanding vot ing stock of MGE Energy, (ii) MGE must maintain a ratio of its consolidated indebtedness to consolidated total capitalization not to exceed a maximum of 65 %, and (iii) MGE cannot issue "Priority Debt" in an amount exceeding 20 % of its consolidated assets. Priority Debt is defined as any indebtedness of MGE secured by liens other than specified liens permitted by the Note Purchase Agreement and certain unsecured indebtedness of certain subsidiaries. As of December 31, 2018 , MGE was in compliance with the covenant requirements. (f ) Issued by MGE Power West Campus. The Note Purchase Agreements require it to maintain a projected debt service coverage ratio of not less than 1.25 to 1.00 , and debt to total capitalization ratio of not more than 0.65 to 1.00 . The notes are secured by a collateral assignment of lease payments that MGE is making to MGE Power West Campus for use of its ownership interest in the WCCF pursuant to a long-term lease. As of December 31, 2018 , MGE Power West Campus was in compliance with the covenant requirements. (g) Issued by M GE Power Elm Road. The Note Purchase Agreement requires MGE Power Elm Road to maintain a projected and actual debt service coverage ratio at the end of any calendar quarter of not less than 1.25 to 1.00 for the trailing 12-month period. The notes are secured by a collateral assignment of lease payments that MGE is making to MGE Power Elm Road for use of its ownership interest in the Elm Road Units pursuant to long-term leases. As of December 31, 2018 , MGE Power Elm Road was in compliance with the covenant requirements. b. Long-Term Debt Maturities . Below is MGE Energy's and MGE's aggregate maturities for all long-term debt for years following December 31, 2018 . (In thousands) 2019 2020 2021 2022 2023 Thereafter Long-term debt maturities $ 4,553 $ 19,659 $ 4,771 $ 4,889 $ 35,014 $ 433,545 MGE includes long-term debt held by MGE Power Elm Road and MGE Power West Campus in the consolidated financial statements (see Footnote 3 for further information).

Notes Payable to Banks, Commerc

Notes Payable to Banks, Commercial Paper, and Lines of Credit	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Notes Payable to Banks, Commercial Paper, and Lines of Credit	Notes Payable to Banks, Commercial Paper, and Lines of Credit. a. MGE Energy. A s of December 31, 2018 , MGE Energy had an unsecured, committed revolving line of credit of $ 50 m illion expiring June 1, 2020. As of December 31, 2018 , n o borrowings were outstanding under this facility. On February 7, 2019, MGE Energy amended and restated the credit agreement to extend the initial term expiration date to February 7, 2024. The agreement require s MGE Energy to maintain a ratio o f its consolidated indebtedness to consolidated total capitalizati on not to exceed a maximum of 65 %. A change in control constitutes a default under the agreement. Change in control events are defined as (i) a fa ilure by MGE Energy to hold 100 % of the outstanding voting equity interest in MGE or (ii) the acquisition of beneficial ownership of 30 % or more of the outstanding voting stock of MGE Energy by one person or two or more persons acting in concert. As of December 31, 2018 , MGE Energy was in compliance with the covenant requirements. b. MGE. For short-term borrowings, MGE generally iss ues commercial paper (issued at the prevailing discount rate at the time of issuance), which is supported by unused committed bank lines of credit. A s of December 31, 2018 , MGE had two unsecured, committed revolving lines of credit for a total of $ 100 m illion expiring June 1, 2020. As of December 31, 2018 , no borrowings were outstanding under these f acilities; however there was $ 13.0 million in commercial paper outstanding. On February 7, 2019, MGE amended and restated the credit agreements to extend the initial term expiration date to February 7, 2024. The agreement s require MGE to maintain a ratio of consolidated debt to consolidated total capitalization not to exceed a maximum of 65 %. The ratio calculation excludes assets, liabilities, revenues, and expenses included in MGE's financial statements as the result of the consolidation of VIEs, such as MGE Power West Campus and MGE Power Elm Road. A chang e in control constitutes a default under the agreements. Change in control events are defined as (i) a failure by MGE Energy to hold 100 % of the outstanding voting equity interest in MGE or (ii) the acquisition of beneficia l ownership of 30 % or more of the outstanding voting stock of MGE Energy by one person or two or more persons acting in concert. As of December 31, 2018 , MGE was in compliance with the covenant requirements. c. Short-Term Borrowings - MGE Energy and MGE. Information concerning short-term borrowings is shown below: (In thousands) MGE Energy (a) MGE As of December 31, 2018 2017 2018 2017 Available lines of credit $ 150,000 $ 150,000 $ 100,000 $ 100,000 Short-term debt outstanding $ 13,000 $ 4,000 $ 13,000 $ 4,000 Weighted-average interest rate 2.55 % 1.55 % 2.55 % 1.55 % Year Ended December 31, Maximum short-term borrowings $ 31,500 $ 7,500 $ 31,500 $ 7,500 Average short-term borrowings $ 9,211 $ 304 $ 9,211 $ 304 Weighted-average interest rate 1.92 % 1.18 % 1.92 % 1.18 % (a) MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes. a. MGE Energy and MGE Income Taxes. MGE Energy files a consolidated federal income tax return that includes the operations of all subsidiary companies. The subsidiaries calculate their respective federal income tax provisions as if they were separate taxable entities. On a consolidated and separate company basis, the income tax provision consists of the following provision (benefit) components for the years ended December 31 : MGE Energy MGE (In thousands) 2018 2017 2016 2018 2017 2016 Current payable: Federal $ 18,622 $ 21,125 $ 16,908 $ 19,926 $ 21,512 $ 17,521 State 5,163 5,129 3,287 5,704 5,316 3,497 Net-deferred: Federal 120 (8,346) 17,571 (2,563) (11,195) 16,391 State 3,629 4,264 4,850 2,494 3,435 4,485 Amortized investment tax credits (100) (78) (103) (100) (78) (103) Total income tax provision $ 27,434 $ 22,094 $ 42,513 $ 25,461 $ 18,990 $ 41,791 The consolidated income tax provision differs from the amount computed by applying the statutory federal income tax rate to income before income taxes, as follows: MGE Energy MGE 2018 2017 2016 2018 2017 2016 Statutory federal income tax rate 21.0 % 35.0 % 35.0 % 21.0 % 35.0 % 35.0 % State income taxes, net of federal benefit 6.3 % 5.1 % 5.1 % 6.2 % 5.1 % 5.1 % Amortized investment tax credits (0.1) % - % (0.1) % (0.1) % - % (0.1) % Credit for electricity from wind energy (0.3) % (1.6) % (1.6) % (0.4) % (1.7) % (1.7) % Domestic manufacturing deduction - % (1.4) % (1.3) % - % (1.5) % (1.3) % AFUDC equity, net (0.6) % (0.2) % (0.2) % (0.5) % (0.2) % (0.2) % Federal income tax rate reduction - % (18.1) % - % - % (19.3) % - % Amortization of utility excess deferred tax (a) (1.8) % - % - % (2.0) % - % - % Other, net, individually insignificant 0.1 % (0.3) % (0.9) % 0.2 % (0.4) % (0.9) % Effective income tax rate 24.6 % 18.5 % 36.0 % 24.4 % 17.0 % 35.9 % MGE Energy MGE (In thousands) 2018 2017 2018 2017 Deferred tax assets Investment in ATC 23,638 24,781 - - Accrued expenses 15,385 15,135 15,385 15,135 Pension and other postretirement benefits 34,914 32,196 34,914 32,196 Deferred tax regulatory account 37,121 36,124 37,121 36,124 Derivatives 8,861 11,525 8,861 11,525 Other 15,137 12,790 15,185 12,831 Gross deferred income tax assets 135,056 132,551 111,466 107,811 Less valuation allowance (86) (86) (86) (86) Net deferred income tax assets 134,970 132,465 111,380 107,725 Deferred tax liabilities Property-related $ 244,114 $ 238,437 $ 244,114 $ 238,544 Investment in ATC 50,771 48,324 - - Bond transactions 765 832 765 832 Pension and other postretirement benefits 47,644 42,919 47,644 42,919 Derivatives 8,861 11,525 8,861 11,525 Tax deductible prepayments 6,014 6,169 6,014 6,169 Other 8,753 9,389 8,598 9,222 Gross deferred income tax liabilities 366,922 357,595 315,996 309,211 Deferred income taxes $ 231,952 $ 225,130 $ 204,616 $ 201,486 On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the Tax Act). The Tax Act makes broad and complex changes to the U.S. tax code, including a reduction in the U.S. federal corporate tax rate from 35 percent to 21 percent. The SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118), which provides guidance on accounting for the tax effects of the Tax Act. SAB 118 provides a measurement period that should not extend beyo nd one year from the Tax Act enactment date for companies to complete the accounting for certain income tax effects. In accordance with S AB 118 any subsequent adjustment to these amounts would be recorded in 2018 when the analysis is complete. The analysis was completed and n o material adjustments have been recorded during 2018. The Tax Act reduce d the corporate tax rate to 21 percent, effective January 1, 2018. The one-time impacts recorded to remeasure deferred income tax balances at the 21 percent corpo rate federal income tax rate as of December 31, 2017 were as follows: (In thousands) MGE Energy MGE Net Decrease in Deferred Tax Liability $ 176,871 $ 156,493 Decrease in Regulatory Asset 4,347 4,347 Increase in Regulatory Liability (b) 130,497 130,497 Decrease in Investment ATC 20,375 - Net Deferred Income Tax Benefit Recorded (c) 21,651 21,649 b . Accounting for Uncertainty in Income Taxes - MGE Energy and MGE . T he difference between the tax benefit amount taken on prior year tax returns, or expected to be taken on a current year tax return, and the tax benefit amount recognized in the financial statements is accounted for as an unrecognized tax benefit. A tabular reconciliation o f unrecognized tax benefits and is as follows: (In thousands) Unrecognized Tax Benefits: 2018 2017 2016 Unrecognized tax benefits, January 1, $ 1,924 $ 2,487 $ 2,528 Additions based on tax positions related to the current year 425 552 452 Additions based on tax positions related to the prior years 272 19 39 Reductions based on tax positions related to the prior years (672) (1,134) (532) Unrecognized tax benefits, December 31, $ 1,949 $ 1,924 $ 2,487 (In thousands) Interest on Unrecognized Tax Benefits: 2018 2017 2016 Accrued interest on unrecognized tax benefits, January 1, $ 165 $ 388 $ 311 Reduction in interest expense on uncertain tax positions (136) (312) (27) Interest expense on uncertain tax positions 162 89 104 Accrued interest on unrecognized tax benefits, December 31, $ 191 $ 165 $ 388 Unrecognized tax benefits ar e classified with " Other deferred l iabilities " on the consolidated balance sheets. The interest component recoverable in rates is offset by a regulatory asset. As of December 31, 2018 , 2017 , and 2016 , unrecognized tax benefits primarily related to temporary tax differences associated with the change in income tax method of accounting for electric generation and electric and gas distr ibution repairs. In addition, as of December 31, 2018 , unrecognized tax benefits relatin g to permanent differen ces and tax credits was $ 0.3 million . As of December 31, 2017 and 2016 , unrecognized tax benefits relating to permanent differen ces and tax credits was less than $ 0.1 million . The unrecognized tax benefits as of December 31, 2018 , a re not expected to significantly increase or decrease within the next twelve months. In add ition, statutes of limitations will expire for MGE Energy and MGE tax returns. The impact of the statutes of limitations expiring is not anticipated to be material. The following table shows tax years that remain subject to examination by major jurisdictio n: Taxpayer Open Years MGE Energy and consolidated subsidiaries in federal return 2015 through 2018 MGE Energy Wisconsin combined reporting corporation return 2013 through 2018

Pension Plans and Other Postret

Pension Plans and Other Postretirement Benefits	12 Months Ended
	Dec. 31, 2018
Compensation and Retirement Disclosure [Abstract]
Pension Plans and Other Postretirement Benefits	Pension Plans and Other Postretirement Benefits - MGE Energy and MGE. MGE maintains qualified and nonqualified pension plans, health care , and life insurance benefits, and defined contribution 401(k) benefit plans for its employees and retirees. MGE's costs for the 401(k) plans were $ 3.9 million, $ 3.5 million, and $ 3.1 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively . A measurement date of December 31 is utilized for all pension and postretirement benefit plans. All employees hired after December 31, 2006, have been enrolled in the defined contribution pension plan, rather than the defined b enefit pension plan previously in place. a. Benefit Obligations and Plan Assets. (In thousands) Pension Benefits Other Postretirement Benefits Change in Benefit Obligations: 2018 2017 2018 2017 Net benefit obligation at beginning of year $ 391,269 $ 349,556 $ 82,290 $ 78,842 Service cost 5,723 5,383 1,283 1,231 Interest cost 12,859 12,625 2,612 2,666 Plan participants' contributions - - 950 894 Actuarial (gain) loss (a) (34,439) 37,689 (7,555) 2,749 Gross benefits paid (15,124) (13,984) (4,623) (4,262) Less: federal subsidy on benefits paid (b) - - 204 170 Benefit obligation at end of year $ 360,288 $ 391,269 $ 75,161 $ 82,290 Change in Plan Assets: Fair value of plan assets at beginning of year $ 361,651 $ 311,933 $ 48,470 $ 43,177 Actual return on plan assets (24,485) 56,987 (2,780) 7,104 Employer contributions 1,738 6,715 504 1,557 Plan participants' contributions - - 950 894 Gross benefits paid (15,124) (13,984) (4,623) (4,262) Fair value of plan assets at end of year $ 323,780 $ 361,651 $ 42,521 $ 48,470 Funded Status as of December 31 $ (36,508) $ (29,618) $ (32,640) $ (33,820) (a) In 2018, higher discount rates were the main driver of the actuarial gain. However, in 2017, lower discount rates were the main driver of the actuarial loss. (b) In 2003, the Medicare Prescription Drug, Improvement and Modernization Act of 2003 was signed into law authorizing Medicare to provide prescription drug benefits to retirees. For the years ended December 31, 2018 and 2017 , the subsidy due to MGE was $ 0.2 million. The accumulated benefit obligation for the def ined benefit pension plans as of December 31, 2018 and 2017 , was $ 335.8 million and $ 356.0 million , respectively . The amounts recognized in the consolidated balance sheets to reflect the funded status of the plans as of December 31 are as follows: Pension Benefits Other Postretirement Benefits (In thousands) 2018 2017 2018 2017 Long-term asset $ - $ 7,336 $ - $ - Current liability (1,732) (1,726) - - Long-term liability (34,776) (35,228) (32,640) (33,820) Net liability $ (36,508) $ (29,618) $ (32,640) $ (33,820) The following table shows the amounts that have not yet been recognized in our net periodic benefit cost as of December 31 and are recorded as regulatory assets in the consolidated balance sheets: Pension Benefits Other Postretirement Benefits (In thousands) 2018 2017 2018 2017 Net actuarial loss $ 92,978 $ 81,969 $ 10,569 $ 12,600 Prior service benefit (385) (429) (7,153) (9,821) Transition obligation - - 21 23 Total $ 92,593 $ 81,540 $ 3,437 $ 2,802 The projected benefit obligation and fair value of plan assets for pension plans with a projected benefit obligation in excess of plan assets were as follows: (In thousands) Pension Benefits Projected Benefit Obligation in Excess of Plan Assets 2018 2017 Projected benefit obligation, end of year $ 360,288 $ 36,954 Fair value of plan assets, end of year 323,780 - The accumulated benefit obligation and fair value of plan assets for pension plans with an accumulated benefit obligation in excess of plan assets were as follows: (In thousands) Pension Benefits Accumulated Benefit Obligation in Excess of Plan Assets 2018 2017 Accumulated benefit obligation, end of year $ 31,200 $ 32,813 Fair value of plan assets, end of year - - b . Net Periodic Benefit Cost. (In thousands) Pension Benefits Other Postretirement Benefits Components of Net Periodic Benefit Cost: 2018 2017 2016 2018 2017 2016 Service cost $ 5,723 $ 5,383 $ 5,365 $ 1,283 $ 1,231 $ 1,271 Interest cost 12,859 12,625 12,393 2,612 2,666 2,681 Expected return on assets (26,241) (22,963) (22,365) (3,232) (2,887) (2,829) Amortization of: Transition obligation - - - 3 3 3 Prior service (credit) cost (44) (17) 10 (2,669) (2,669) (2,669) Actuarial loss 5,278 6,352 5,600 488 660 589 Net periodic benefit cost (credit) $ (2,425) $ 1,380 $ 1,003 $ (1,515) $ (996) $ (954) The components of net periodic benefit cost, other than the service cost component, are recorded in " Other income, net " on the consolidated statements of income. The service cost component is recorded in " Other operations and maintenance " on the consolidated statements of income. Prior to January 1, 2018, a portion of all net periodic benefit cost components were capitalized within the consolidated balance sheets. The FASB issued authoritative guidance w ithin the codification ' s Compensation-Retirement Benefits topic that, beginning January 1, 2018, only allows the service cost component of net periodic benefit cost to be eligible for capitalization within the consolidated balance sheets. MGE has regulatory treatment and recognizes regulatory assets or liabilities for timing differences between when net periodic benefit costs are recovered and when costs are recognized. c. Plan Assumptions. The weighted-average assumptions used to determine the benefit obligations were as follows for the years ended December 31: Pension Benefits Other Postretirement Benefits 2018 2017 2018 2017 Discount rate 4.32 % 3.73 % 4.24 % 3.58 % Rate of compensation increase 3.20 % 3.67 % N/A N/A Assumed health care cost trend rates: Health care cost trend rate assumed for next year N/A N/A 6.25 % 6.00 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) N/A N/A 5.00 % 5.00 % Year that the rate reaches the ultimate trend rate N/A N/A 2024 2022 The weighted-average assumptions used to determine the net periodic cost were as follows for the years ended December 31: Pension Benefits Other Postretirement Benefits 2018 2017 2016 2018 2017 2016 Discount rate 3.73 % 4.30 % 4.51 % 3.60 % 4.09 % 4.32 % Expected rate of return on plan assets 7.40 % 7.40 % 7.65 % 6.94 % 6.80 % 6.96 % Rate of compensation increase 3.72 % 3.76 % 3.76 % N/A N/A N/A The assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. The following table shows how an assumed 1% increase or 1% decrease in health care cost trends could impact postretirement benefits in 2018 d ollars: (In thousands) 1% Increase 1% Decrease Effect on other postretirement benefit obligation $ 754 $ (980) Effect on total service and interest cost components 21 (30) MGE employs a building-block approach in determining the expected long-term rate of return for asset classes. Historical markets are studied and long-term historical relationships among asset classes are analyzed, consistent with the widely accepted capital market principle that assets with higher volatility generate a greater return over the long run. Current market factors , such as interest rates and dividend yields , are evaluated before long-term capital market assumptions are determined. The expe cted long-term nominal rate of return for plan assets is primarily a function of expected long-term real rates of return for component asset classes and the plan's target asset allocation in conjunction with an inflation assumption. Peer data and historica l returns are reviewed to check for appropriateness. d. Investment Strategy. MGE employs a total return investment approach whereby a mix of equities, fixed income, and real estate investments are used to maximize the expected long-term return of plan as sets for a prudent level of risk. Risk tolerance is established through careful consideration of plan liabilities, plan-funded status, and corporate financial condition. The investment portfolio contains a diversified blend of equity, fixed income, and rea l estate investments. Investment risk is measured and monitored on an ongoing basis through periodic investment portfolio reviews and liability measurements. The asset allocation for MGE's pension plans as of December 31, 2018 and 2017 , and the target al location for 2019 , by asset category, follows : Target Allocation Percentage of Plan Assets at Year End 2018 2017 Equity securities (a) 63.0 % 60.0 % 65.0 % Fixed income securities 30.0 % 33.0 % 29.0 % Real estate 7.0 % 7.0 % 6.0 % Total 100.0 % 100.0 % 100.0 % (a) Target allocations for equity securities are broken out as follows: 45.5 % United States equity, 17.5 % non- United States equity . The fair value of plan assets for the postretirement benefit plans is $ 42.5 million and $ 48.5 million as of December 31, 2018 and 2017 , respectively. Of this amount, $ 37.5 million and $ 43.1 million as of December 31, 2018 and 2017 , respectively, were held in the master pension trust and are allocable to postretirement health expenses. The target asset allocation and investment strategy for the portion of assets held in the master pension trust are the same as that ex plained for MGE's pension plans. The remainder of postretirement benefit assets are held either in an insurance continuance fund for the payment of retiree life benefits or health benefit trusts for payment of retiree health premiums. The asset allocation for the insurance continuance fund is determined by the life insurer. The target asset allocation for the health benefit trusts are established based on a similar investment strategy as assets held in the master pension trust, with consideration for liquid ity needs in the health benefit trusts. e. Concentrations of Credit Risk. MGE evaluated its pension and other postretirement benefit plans' asset portfolios for the existence of significant concentrations of credit risk as of December 31, 2018 . Types of concentrations that were evaluated include, but are not limited to, investment concentrations in a single entity, type of industry, and foreign country. As of December 31, 2018 , there were no significant concentrations (defined as greater than 10 percent of plan assets) of risk in MGE pension and postretirement benefit plan assets. f. Fair Value Measurements of Plan Assets. Pension and other postretirement benefit plan investments are recorded at fair value. See Foo tnote 15 for more information regarding the fair value hierarchy. The following descriptions are the categories of underlying plan assets held within the pension and other postretirement benefit plans as of December 31, 2018 : Cash and Cash Equivalents – This category includes highly liquid investments with maturities of less than three months which are traded in active markets. Equity Securities – These securities consist of U.S. and international stock funds. The U.S. stock funds are primarily invest ed in domestic equities. Securities in these funds are typically priced using the closing price from the applicable exchange, NYSE, Nasdaq, etc. The international funds are composed of international equities. Securities are priced using the closing price f rom the appropriate local stock exchange. Fixed Income Securities – These securities consist of U.S. bond funds and short-term funds. U.S. bond funds are priced by a pricing agent using inputs such as benchmark yields, reported trades, broker/dealer quotes, and issuer spreads. The short-term funds are valued initially a t cost and adjusted for amortization of any discount or premium. Real Estate – Real estate funds are funds with a direct investment in pools of real estate properties. These funds are valued by investment managers on a periodic basis using pricing models that use independent appraisals. The fair value of real estate investments is determined using net asset value. Insurance Continuance Fund (ICF) – The ICF is a supplemental retirement plan that includes assets that have been segregated and restricted to pay retiree term life insurance premiums. Fixed Rate Fund – The Fixed Rate fund is supported by an underlying portfolio of fixed income securities, including public bonds, commercial mortgages, and private placement bonds . Public market data and GAAP repo rted market values are used when available to determine fair value. All of the fair values of MGE's plan assets are measured using net asset value, except for cash and cash equivalents which are considered level 1 investments. The fair values of MGE ' s pla n assets by asset category as of December 31 are as follows: (In thousands) 2018 2017 Cash and Cash Equivalents $ 701 $ 488 Equity Securities: U.S. Large Cap 102,984 124,594 U.S. Mid Cap 23,683 29,138 U.S. Small Cap 28,573 37,782 International Blend 61,299 71,514 Fixed Income Securities: Short-Term Fund 4,053 4,641 High Yield Bond 19,437 19,400 Long Duration Bond 93,216 91,678 Real Estate 27,923 25,995 Insurance Continuance Fund 1,491 1,500 Fixed Rate Fund 2,941 3,391 Total $ 366,301 $ 410,121 g . Expected Cash Flows. MGE does not expect to need to make any required contributions to the qualified plans for 2019 and 2020 . The contributions for years after 2020 are not yet currently estimated. MGE has adopted the asset smoothing as permitted in accordance with the Pension Protection Act of 2006, including modifications made by WRERA. Due to uncertainties in the future economic performance of plan assets, discount rates, and other key assumptions, estimated contributions are subject to change. MGE may also elect to make additional discretionary contributions. In 2018 , MGE made $ 5.6 million in employer contributions to its pension and postretirement plans. h . Benefit Payments. The following benefit payments, which reflect expec ted future service, as appropriate, are expected to be paid as follows: Pension Other Postretirement Benefits (In thousands) Pension Benefits Gross Postretirement Benefits Expected Medicare Part D Subsidy Net Postretirement Benefits 2019 $ 16,362 $ 4,248 $ (228) $ 4,020 2020 17,087 4,585 (252) 4,333 2021 17,835 4,994 (276) 4,718 2022 18,956 5,325 (305) 5,020 2023 19,770 5,604 (334) 5,270 2024 - 2028 110,037 29,478 (2,103) 27,375

Derivative and Hedging Instrume

Derivative and Hedging Instruments	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and Hedging Instruments	Derivative and Hedging Instruments - MGE Energy and MGE. a. Purpose. As part of its regular operations, MGE enters into contracts, including options, swaps, futures, forwards, and other contractual commitments, to manage its exposure to commodity prices. To the extent that these contracts are derivatives, MGE assesses whether or not the normal purchases or normal sales exclusion applies. For contracts to which this exclusion cannot be applied, the derivatives are recognized in the consolidated bala nce sheets at fair value . MGE's financial commodity derivative activities are conducted in accordance with its electric and gas risk management program, which is approved by the PSCW and limits the volume MGE can hedge with specific risk management strateg ies. The maximum length of time over which cash flows related to energy commodities can be hedged is four years. If the derivative qualifies for regulatory deferral, the derivatives are marked to fair value and are offset with a corresponding regulatory as set or liability depending on whether the derivative is in a net loss or net gain position, respectively . The deferred gain or loss is recognized in earnings in the delivery month applicable to the instrument. Gains and losses related to hedges qualifying for regulatory treatment are recoverable in gas rates through the PGA or in electric rates as a component of the fuel rules mechanism. b. Notional Amounts. The gross notional volume of open derivatives is as follows: December 31, 2018 December 31, 2017 Commodity derivative contracts 386,440 MWh 552,310 MWh Commodity derivative contracts 5,260,000 Dth 5,460,000 Dth FTRs 2,252 MW 2,226 MW PPA 2,050 MW 2,650 MW c . Financial Statement Presentation . MGE purchases and sells exchange-traded and over-the-counter options, swaps, and future contracts. These arrangements are primarily entered into to help stabilize the price risk associated with gas or power purchases. These transactions are employed by both MGE ' s gas and electric segments. Additionally, as a result of the firm transmission agreements that MGE holds on electricity transmission paths in the MISO market , MGE holds financial transmission rights ( FTRs ) . An FTR is a financial instrument that entitles the holder to a stream of revenues or charges based on the differences in hourly day-ahead energy prices between two points on the transmission grid. The fair values of these instruments are offset with a corresp onding regulatory asset/liability depending on whether they are in a net loss/gain position. Depending on the nature of the instrument, the gain or loss associated with these transactions will be reflected as cost of gas sold, fuel for electric generation, or purchased power expense in the delivery month applicable to the instrument. As of December 31, 2018 and 2017 , the fair value of exchange traded derivatives and FTRs exceeded their cost basis by $ 0.7 million and $ 0.2 million, respectively. MGE is a party to a purchased power agreement that provides MGE with firm capacity and energy during a base term from June 1, 2012, through May 31, 2022. The agreement also allows MGE an option to extend the contract af ter the base term. The agreement is accounted for as a derivative contract and is recognized at its fair value on the consolidated balance sheet s . However, the derivative qualifies for regulatory deferral and is recognized with a corresponding regulatory asset or liability depending on whether the fair value is in a loss or gain position. The fair value of the contract a s of December 31, 2018 and 2017 , reflects a loss position of $ 32.5 million and $ 42.2 million , respectively . The actual cost will be recognized in purchased power e xpense in the month of purchase. The following table summarizes the fair value of the derivative instruments on the consolidated balance sheet s . All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreement as well a s the netting of collateral. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as we ll as the netting of collateral . (In thousands) Derivative Assets Derivative Liabilities Balance Sheet Location December 31, 2018 Commodity derivative contracts (a) $ 727 $ 270 Other current assets Commodity derivative contracts (a) 74 72 Other deferred charges FTRs 241 - Other current assets PPA N/A 8,550 Derivative liability (current) PPA N/A 23,980 Derivative liability (long-term) December 31, 2017 Commodity derivative contracts (a) $ 566 $ 603 Derivative liability (current) (b) Commodity derivative contracts (a) 110 190 Derivative liability (long-term) FTRs 329 - Other current assets PPA N/A 8,180 Derivative liability (current) PPA N/A 33,990 Derivative liability (long-term) (a ) As of December 31, 2017 , collateral of $ 0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions as of December 31, 2018 . (b) As of December 31, 2017 , MGE presented $ 0.1 million as other current assets on the consolidated balance sheets. The following tables show the effect of netting arrangements for recognized deriva tive assets and liabilities that are subject to a master netting arrangement or similar arrangement on the consolidated balance sheets. Offsetting of Derivative Assets (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets December 31, 2018 Commodity derivative contracts $ 801 $ (342) $ - $ 459 FTRs 241 - - 241 December 31, 2017 Commodity derivative contracts $ 676 $ (654) $ - $ 22 FTRs 329 - - 329 Offsetting of Derivative Liabilities (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets December 31, 2018 Commodity derivative contracts $ 342 $ (342) $ - $ - PPA 32,530 - - 32,530 December 31, 2017 Commodity derivative contracts $ 793 $ (654) $ (139) $ - PPA 42,170 - - 42,170 The following tables summarize the unrealized and realized gains/losses related to the derivative instruments on the consolidated balance sheets as of December 31, 2018 and 2017 , and the consolidated statements of income for the years ended December 31, 2018 and 2017 . 2018 2017 Current and Long-Term Regulatory Asset Other Current Assets Current and Long-Term Regulatory Asset Other Current Assets (In thousands) Balance as of January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized gain (11,094) - (2,743) - Realized gain (loss) reclassified to a deferred account 523 (523) (1,260) 1,260 Realized loss reclassified to income statement 443 94 (3,320) (684) Balance as of December 31, $ 31,830 $ 377 $ 41,958 $ 806 Realized Losses (Gains) 2018 2017 (In thousands) Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Year Ended December 31: Commodity derivative contracts $ (716) $ (199) $ 786 $ 634 FTRs (702) - (1,464) - PPA 1,080 - 4,048 - MGE's commodity derivative contracts, FTRs, and PPA are subject to regulatory deferral. These derivatives are marked to fair value and are offset with a corresponding regulatory asset or liability. Realized gains and losses are deferred on the consolidated balance sheet s and are recognized in earnings in the delivery month applicable to the instrument. As a result of the above described treatment, there are no unrealized gains or losses that flow through earnings. The PPA has a provision that may require MGE to post collateral if MGE's debt rating falls below investment grade (i.e., below BBB-). The amount of collateral that it may be required to post varies from $ 20.0 million to $ 40.0 million, depending on MGE's nominated capacity amount. As of December 31, 2018 , no collateral is required to be, or has been, posted. Certain counterparties extend MGE a credit limit. If MGE exceeds these limits, the counterparties may require collateral to be post ed. As of December 31, 2017 , certain counterparties were in a net liability of $ 0.1 million . As of December 31, 2018 , no counterparties were in a net liability position. Nonperformance of counterparties to the non-exchange traded derivatives could expose MGE to credit loss. However, MGE enters into transactions only with companies that meet or exceed strict credit guidelines, and it monitors these counterparties on an ongoing basis to mitigate nonperformance risk in its port folio. As of December 31, 2018 , n o counterparties have defaulted.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments - MGE Energy and MGE. Fair value is defined as the price that would be received to sell an asset or would be paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. The accounting standard clarifies that fair value should be based on the assumptions market participants would use when pricing the asset or liability including ass umptions about risk. The standard also establishes a three level fair value hierarchy based upon the observability of the assumptions used and requires the use of observable market data when available. The levels are: Level 1 - Pricing inputs are quoted p rices within active markets for identical assets or liabilities. Level 2 - Pricing inputs are quoted prices within active markets for similar assets or liabilities; quoted prices for identical or similar instruments in markets that are not active; and mod el-derived valuations that are correlated with or otherwise verifiable by observable market data. Level 3 - Pricing inputs are unobservable and reflect management's best estimate of what market participants would use in pricing the asset or liability. a. Fair Value of Financial Assets and Liabilities Recorded at the Carrying Amount. T he carrying amount of cash, cash equivalents, and outstanding commercial paper approximates fair market value due to the short maturity of those investments and obligations. The estimated fair market value of long-term debt is based on quoted market prices for similar financial instruments a s of December 31 . Since long-term debt i s not traded in an active market, it is classified as Level 2. The estimated fair market value of financial instruments are as follows: December 31, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 83,102 $ 83,102 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper 13,000 13,000 4,000 4,000 Long-term debt (a) 502,431 518,811 426,883 475,282 MGE Assets: Cash and cash equivalents $ 4,843 $ 4,843 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper 13,000 13,000 4,000 4,000 Long-term debt (a) 502,431 518,811 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.5 million and $4.3 million as of December 31, 2018 and 2017, respectively. b. Recurring Fair Value Measurements. The following table presents the balances of assets and liabilities measured at fair value on a recurring basis . Fair Value as of December 31, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,042 $ 296 $ - $ 746 Exchange-traded investments 848 848 - - Total Assets $ 1,890 $ 1,144 $ - $ 746 Liabilities: Derivatives, net $ 32,872 $ 124 $ - $ 32,748 Deferred compensation 3,078 - 3,078 - Total Liabilities $ 35,950 $ 124 $ 3,078 $ 32,748 MGE Assets: Derivatives, net $ 1,042 $ 296 $ - $ 746 Exchange-traded investments 43 43 - - Total Assets $ 1,085 $ 339 $ - $ 746 Liabilities: Derivatives, net $ 32,872 $ 124 $ - $ 32,748 Deferred compensation 3,078 - 3,078 - Total Liabilities $ 35,950 $ 124 $ 3,078 $ 32,748 Fair Value as of December 31, 2017 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 792 792 - - Total Assets $ 1,797 $ 1,070 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 MGE Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 64 64 - - Total Assets $ 1,069 $ 342 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 (b) These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of December 31, 2017. No transfers were made in or out of Level 1 or Level 2 for the year ended December 31 , 2018 . I nvestments include exchange-traded investment securities valued using quoted prices on active exchanges and are therefore classified as Level 1. Derivatives include exchange-traded derivative c ontracts, over-the-counter transactions, a purchased power agreement, and FTRs. Most exchange-traded derivative contracts are valued based on unadjusted quoted prices in active markets and are therefore classified as Le vel 1. A small number of exchange-traded derivative contracts are valued using quoted market pricing in markets with insufficient volumes and are therefore considered unobservable and classified as Level 3. Transactions done with an over-the-counter party are on inactive markets and are therefore classified as Level 3. These transactions are valued based on quoted prices from markets with similar exchange- traded transactions . FTRs are priced based upon monthly auction results for identical or similar instru ments in a closed market with limited data available and are therefore classified as Level 3 . The purchased power agreement (see Footnote 1 4 ) was valued using an internally-developed pricing model and therefore is classified as Level 3. The model project s future market energy prices and compares those prices to the projected power costs to be incurred under the contract . Inputs to the model require significant management judgment and estimation. Future energy prices are based on a forward power pricing cu rve using exchange-traded contracts in the electric futures market . A basis adjustment is applied to the market energy price to reflect the price differential between the market price delivery point and the counterparty delivery point. The historical relat ionship between the delivery points is reviewed and a discount (below 100%) or premium (above 100%) is derived. This comparison is done for both peak times when demand is high and off peak times when demand is low. If the basis adjustment is lowered, the f air value measurement will decrease , and if the basis adjustment is increased, the fair value measurement will increase. The projected power costs anticipated to be incurred under the purchased power agreement are determined using many factors, including historical generating costs, future prices, and expected fuel mix of the counterparty. An increase in the projected fuel costs would result in a decrease in the fair value measurement of the purchased power agreement. A significant input that MGE estimates is the counterparty's fuel mix in determining the projected power cost. MGE also considers the assumptions that market participants would use in valuing the asset or liability. This consideration includes assumptions about market risk such as liquidity, v olatility , and contract duration. The fair value model uses a discount rate that incorporates discounting, credit, and model risks. The following table presents the significant unobservable inputs used in the pricing model as of December 31: Model Input Significant Unobservable Inputs 2018 2017 Basis adjustment: On peak 92.1 % 92.3 % Off peak 92.8 % 94.1 % Counterparty fuel mix: Internal generation 50%-75% 55%-75% Purchased power 50%-25% 45%-25% The deferred compensation plan allows participants to defer certain cash compensation into a notional investment account. These amounts are included within other deferred liabilities in the consolidated balance sheets of MGE Energy and MGE. The notional investments earn interest based upon the semiannual rate of U.S. Treasury Bills having a 26 week maturity increased by 1 % compounded monthly with a minimu m annual rate of 7 %, compounded monthly . The notional investments are based upon observable market data, however, since the deferred compensation obligations themselves are not exchanged in an active market, they are classified as L evel 2 . The following table summarizes the changes in Level 3 commodity derivative assets and liabilities measured at fair value on a recurring basis . (In thousands) 2018 2017 2016 Balance as of January 1, $ (42,026) $ (50,306) $ (53,501) Realized and unrealized gains (losses): Included in regulatory liabilities 10,024 8,281 3,195 Included in other comprehensive income - - - Included in earnings 132 (3,718) (5,347) Included in current assets (47) (9) (142) Purchases 23,643 24,181 23,346 Sales - - - Issuances - - - Settlements (23,728) (20,455) (17,857) Transfers in and/or out of Level 3 - - - Balance as of December 31, $ (32,002) $ (42,026) $ (50,306) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, (c) $ - $ - $ - The following table presents total realized and unrealized gains (losses) included in income for Level 3 assets and liabiliti es measured at fair value on a recurring basis (c ) . (In thousands) Year Ended December 31, 2018 2017 2016 Purchased power expense $ 355 $ (3,314) $ (5,262) Cost of gas sold expense (223) (404) (85) Total $ 132 $ (3,718) $ (5,347) ( c ) MGE's exchange-traded derivative contracts, over-the-count er party transactions, purchased power agreement, and FTRs are subject to regulatory deferral. These derivatives are therefore marked to fair value and are offset in the financial statements with a corresponding regulatory asset or liability.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation - MGE Energy and MGE. Under MGE Energy ' s Director Incentive Plan and its Performance Unit Plan, non-employee directors and eligible employees , respectively, may receive performance units that entitle the holder to receive a cash payment equal to the value of a designated number of shares of MGE Energy's common stock, plus dividend equivalent payments thereon, at the end of the set performance period set in the award . In accor dance with the plans ' provisions, these awards are subject to prescribed vesting schedule s and must be settled in cash. Accordingly, no shares of common stock will be issued in connection with the plan s . On the grant d ate, the cost of the director or employee services received in exchange for a performance unit award is measured based on the current market value of MGE Energy common stock. The fair value of the awards is re measured quarterly, including as of December 31, 2018 , as required by applicable accounting standards. Changes in fair value as well as the original grant are recognized as compensation cost. Since this amount is re measured throughout the vesting period, the compensation co st is subject to variability. Units granted un der the Director Incentive Plan are subject to a three- year vesting schedule. The most recent three years of units granted under this plan are as follows: Grant Date MGE Energy Units Granted January 18, 2019 5,175 March 1, 2018 1,106 January 19, 2018 4,704 January 20, 2017 4,608 Units granted under the Performance Unit Plan are subject to a five-year vesting schedule. The most recent units granted under this plan are as follows: Grant Date MGE Energy Units Granted February 15, 2019 17,022 February 16, 2018 17,830 March 1, 2017 14,704 February 19, 2016 19,055 February 20, 2015 18,948 For nonretir ement eligible employees under the Performance Unit Plan , stock- based compensation costs are accrued and recognized using the graded vesting method. Compensation cost for retirement eligible employees or employees that will become retirement eligible during the vesting schedule are recognized on an abridged horizon as retirement eligibility accelerates vesting . During the years ended December 31, 2018 , 2017 and 2016 , MGE recorded $ 1.1 million, $ 1.0 million, and $ 3.1 million , respectively, in compensation expense as a r esult of awards under the plans . In January 2018 , cash payments of $ 1.6 million were distributed relating to awards that were granted under the plans . No forfeitures of units occurred during the years ended December 31, 2018 , 2017 , and 2016 . As of December 31, 2018 , $ 5.2 million of outstanding awards are vested . O f this amount, no cash settlements have occurred as cash payments are only made at the end of the period covered by the awards.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies. a. Purchase Contracts - MGE Energy and MGE. MGE Energy and MGE have entered into various commodity supply, transportation, and storage contracts to meet their obligations to deliver electricity and natural gas to customers. Management expects to recover these costs in future customer rates. As of December 31, 2018 , the future minimum commitments related to these purchase cont racts were as follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Coal (a) $ 25,167 $ 8,213 $ 828 $ - $ - $ - Natural gas Transportation and storage (b) 21,051 20,853 20,853 20,853 20,853 53,361 Supply (c) 15,423 - - - - - Purchase power (d) 27,577 28,082 28,675 15,533 5,641 21,751 Other 6,261 3,007 2,980 2,894 2,825 7 $ 95,479 $ 60,155 $ 53,336 $ 39,280 $ 29,319 $ 75,119 (a) Total coal commitments for the Columbia and Elm Road Units , including transportation . Fuel procurement for MGE's jointly owned Columbia and Elm Road Units is handled by WPL and WEPCO, respectively, who are the operators of those facilities . (b) MGE's natural gas transportation and storage contracts require fixed monthly payments for firm supply pipeline transportation and storage capacity. The pricing components of the fixed monthly payments for the transportation and storage contracts are established by FERC but may be subject to change. (c) These commitments include market-based pricing. (d) MGE has several purchase power agreements to help meet futu re electric supply requirements . b . Leases - MGE Energy and MGE. MGE has noncancelable operating leases, primarily for combustion turbines, railcars, and computer equipment. The operating leases generally do not contain renewal options, with the exception of certain railcar operating leases. These leases have a renewal option of one year or less. MGE is required to pay all executory costs , such as maintenanc e and insurance, for its leases. Future minimum rental payments as of December 31, 2018 , u nder agreements classified as operating leases with noncancelable terms in excess of one year are a s follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Minimum lease payments $ 1,646 $ 1,371 $ 1,095 $ 989 $ 975 $ 22,707 Rental expense under operating leases totaled $ 1.6 million , $ 1.7 million, and $ 2.0 million for 2018 , 2017 , and 2016 , respectively . c . Environmental - MGE Energy and MGE. Water Quality Water quality regulations promulgated by the EPA and WDNR in accordance with the Federal Water Pollution Control Act, or more commonly known as the Clean Water Act (CWA), impose restrictions on discharges of various pollutants into surface waters. The CWA also regulates surface water quality issues that affect aquatic life, such as water temperatures, intake structures, and wetlands filling. The CWA also includes discharge standards, which requir e the use of effluent-treatment processes equivalent to categorical "best practicable" or "best available" technologies. The CWA regulates discharges from "point sources," such as power plants, through establishing discharge limits in water discharge permi ts. MGE's power plants operate under Wisconsin Pollution Discharge Elimination System (WPDES) permits issued by the WDNR to ensure compliance with these discharge limits. Permits are subject to periodic renewal. EPA's Effluent Limitations Guidelines and S tandards for Steam Electric Power Generating Point Source Category In November 2015, the EPA published its final rule setting Effluent Limitations Guidelines (ELG) for the steam electric power generating industry. The ELG rule establishes federal limits on the amount of metals and other pollutants that can be discharged in wastewater from new and existing steam electric generation plants. The rule will be applied to Wisconsin-based power plants as they renew their WPDES permits, no later than 2023. The oper ators of the Columbia and Elm Road Units have indicated that equipment upgrades may be necessary to comply with the new discharge standards. Management believes that any compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects. EPA Cooling Water Intake Rules (Section 316(b)) Section 316(b) of the Clean Water Act requires that the cooling water intake structures at electric power plants meet best available technology standards so that mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens) are reduced. The EPA finalized its Section 316(b) rule for existing facilities in 2014. Section 316(b) requirements are implemented in Wisconsin through modifications to plants' WPDES permits, which govern plant wastewater discharges. The WCCF, Blount, and Columbia plants are considered existing plants under this rule. The WCCF facility already employs a system that meets the Section 31 6(b) rule. The Blount plant's WPDES permit assumes that Blount meets best technology available (BTA) for the duration of the permit, which expires in 2023. However, MGE needs to perform an entrainment study by the end of 2021 to determine future BTA, which will be included with the next permit renewal. Section 316(b) applies to river intakes at the Columbia plant. The operator of the Columbia plant is in the process of a WPDES permit renewal. The draft permit directs the Columbia operator to conduct similar studies on their intake structures. The study requirements will not be known until the permit is final. Future BTA requirements at Blount and Columbia will be based on the results of these required intake studies and will be specified in the next permits issued in 2023 or later. MGE expects that the Section 316(b) rule will not have a material effect on its existing plants. Energy Efficiency and Renewables The Wisconsin Energy Efficiency and Renewables Act requires that 10% of the state's electricity be generated from renewable sources. MGE is in compliance with the requirement. The costs to comply with the Act and its accompanying regulations are being recovered in rates. Air Quality Federal and state air quality regulations impose rest rictions on various emissions, including emissions of particulate matter (PM), sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), and other pollutants, and require permits for operation of emission sources. These permits have been obtained by MGE and must be renewed periodically. Current EPA initiatives under the Clean Air Act, including the Cross-State Air Pollution Rule (CSAPR), and National Ambient Air Quality Standards (NAAQS), and the Affordable Clean Energy (ACE) rule have the potential to result in addi tional operating and capital expenditure costs for MGE. EPA's Greenhouse Gas (GHG) Reduction Guidelines under the Clean Air Act 111(d) Rule The EPA's Clean Power Plan (CPP) rule became effective in December 2015, setting guidelines for states to use in de veloping plans to control GHG emissions from existing fossil fuel-fired EGUs and systems. When fully implemented in 2030, the CPP was projected to reduce GHG emissions from this sector by 32% below 2005 levels. States were given up to three years to submit a plan or be subject to a federal plan to meet the reduction goals, and states were expected to meet interim goals starting in 2022 and the final goals in 2030. Implementation of the rule was expected to have a direct impact on coal and natural gas fired generating units, including possible changes in dispatch and additional operating costs. In February 2016, the U.S. Supreme Court stayed implementation of the CPP which remains in effect. In October 2017, the EPA proposed to rescind the CPP . In August 2018, the EPA proposed the ACE rule which would replace the CPP, if successfully implemented. The ACE proposal directs states to submit plans to the EPA for approval that implement standards of performance (called Best System of Emissions Reductions, or BS ER) for individual EGUs over 25 MW. ACE defines BSER as on-site, heat-rate efficiency improvements, whereas the CPP defines BSERs using carbon dioxide emission performance rates. Simple cycle units such as smaller combustion units, and combined cycle units such as the WCCF are exempt from the proposed rule. Under the ACE proposal, i f a state fails to prepare a plan, or its plan is not approved by the EPA, a federal implementation plan will be issued for that state . The proposed ACE as it is currently writte n has the potential to impact Blount , Columbia, and the Elm Road Units. Given the pending legal proceedings, and the proposed ACE rule, the nature and timing of any final requirements is subject to uncertainty. MGE is unable to determine with any certaint y the impact of the CPP and proposed ACE rule on our operations. If a n ACE rule is implemented substantially in the form of the CPP rule, it is expected to have a material impact on MGE. MGE will continue to monitor developme nts with the proposed ACE rule, the CPP rule , and related litigation. National Ambient Air Quality Standards (NAAQS) and Related Rules The EPA's NAAQS regulations have been developed to set ambient levels of six pollutants to protect sensitive human populations (primary NAAQS) and the environment (secondary NAAQS) from the negative effects of exposure to these pollutants at higher levels. The Clean Air Act requires that the EPA periodically review, and adjust as necessary, the NAAQS for these six air pollutants. The EPA's NAAQS review c an result in a lowering of the allowed ambient levels of a pollutant, a change in how the pollutant is monitored, and/or a change in which sources of that pollutant are regulated. States implement any necessary monitoring and measurement changes and recomm end areas for attainment (meets the ambient requirements) or nonattainment (does not meet these standards). The EPA makes the final attainment and nonattainment determinations. States must come up with a state implementation plan (SIP) to get nonattainment areas into attainment and maintain air quality in attainment areas. A company with facilities located in a nonattainment area will be most affected. Their facilities may be subject to additional data submissions and measurement during permitting renewals, their facilities may need to meet new emission limitations set by the SIP (which could result in significant capital expenditures), and the company may have additional expenses and/or difficulties expanding existing facilities or building new facilities. The process from determining acceptable primary and/or secondary NAAQS to executing SIPs can take years. Since the NAAQS regulations have the potential to affect both existing and new facilities in areas, MGE continuously monitors changes to these rules to evaluate whether changes could impact its operations. In addition, the EPA has adopted interstate transport rules, such as the CSAPR, to address contributions to NAAQS nonattainment from upwind sources in neighboring states. In the following paragraphs we discuss specific NAAQS and transport rule developments that may affect MGE. Ozone NAAQS In May 2018, the EPA issued a final rule which designated the northeast portion of Milwaukee County as being in nonattainment with Ozone NAAQS. The Elm Road Units are located in Milwaukee County, outside the designated nonattainment area. In August 2018, several environmental groups, the City of Chicago , and the State of Illinois filed federal lawsuits challenging several of the EPA's attainment desi gnation decisions, including the partial Milwaukee County designation as being too narrow and not sufficiently protective. MGE is monitoring the outcome of this l awsuit and how it may affect the Elm Road Units in Milwaukee County. If the entire county wher e to be considered in nonattainment as a result of this lawsuit, the State of Wisconsin would need to develop an implementation plan that addressed emissions that contribute to Ozone (NO x and Volatile Organic Compound emissions) for the County, which could affect operations and emissions control obligations of the Elm Road units. MGE is monitoring the outcome of this lawsuit and how it may affect the Elm Road Units in Milwaukee County. At this time MGE expects that the 2015 Ozone NAAQS will not have a mater ial effect on its existing plants based on final designations. EPA's Cross-State Air Pollution Rule: Proposed Ozone Season Update based on 2008 Ozone NAAQS The EPA's CSAPR is an interstate air pollution transport rule designed to reduce ozone and fine par ticulate (PM2.5) air levels in areas that the EPA has determined are being significantly impacted by pollution from neighboring and upwind states. This is accomplished in the CSAPR through a reduction in SO 2 and NO x from qualifying fossil-fuel fired power plants in upwind or "contributing" states. NO x and SO 2 contribute to fine particulate pollution and NO x contributes to ozone formation in downwind areas . Reductions are achieved through a cap and trade system. Individual plants can meet their caps through modifications and/or buying allowances on the market. In October 2016, the EPA finalized rulemaking for an update to CSAPR that incorporated 2008 Ozone NAAQS standards into the rule (the original CSAPR is based on 1997 Ozone NAAQS standards) and began fur ther reducing summertime ozone season NO x allowances in 2017. The update affects 22 states, including Wisconsin, by further limiting statewide NO x allowances in each of those states. The rule also includes revisions to CSAPR that are designed to address is sues remaining from the D.C. Circuit remand of CSAPR, including Wisconsin's inclusion in the NO x ozone season portion of the rule. The State of Wisconsin filed a legal challenge to the CSAPR update rule asserting, among other things, that the rule over-con trols NO x emissions in Wisconsin. MGE has m et our CSAPR obligations in 2018 and 2017 through a combination of reduced emissions through pollution control (e.g. SCR installation at Columbia), as well as owned, received, and purchased allowances. There rem ains uncertainty around CSAPR due to legal challenges, however, MGE expects that we will meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor developments and litigations to this rule. Clean Air Visibility Rule (CAVR) Columbia is subject to the best available retrofit technology (BART) regulations, a subsection of the EPA's CAVR, which may require pollution control retrofits. Columbia's existing pollution control upgrades, and the EPA's stance that compliance with the C SAPR equals compliance with BART, should mean that Columbia will not need to do additional work to meet BART requirements. At this time, however, the BART regulatory obligations, compliance strategies, and costs remain uncertain in Wisconsin due to the con tinued legal challeng es surrounding CSAPR and CAVR. MGE will continue to monitor developments to this rule. Solid Waste EPA's Coal Combustion Residuals Rule The EPA's Coal Combustion Residuals Rule (CCR), which regulates coal ash from burning coal for pu rpose of generating electricity as a solid waste, and defines what ash use activities would be considered generally exempt beneficial reuse of coal ash. The CCR rule also regulates existing, modified, and new landfills, ash ponds, and other surface impound ments used for coal combustion residuals by regulating their design, location, monitoring, and operation. Review of the Elm Road Units has indicated that the costs to comply with this rule are not expected to be significant. Columbia's operator has compl eted a review of their system and has determined that an onsite ash pond will need to be closed and replaced with a dry ash handling system. The dry ash handling system installation is planned for 2020-2021. In July 2018, the EPA published a final rule t hat included amendments to the CCR (which include the allowance of alternative performance standards for landfills and surface impoundments, revised risk-based groundwater protection standards, and an extension of the deadline by which certain facilities m ust cease the placement of waste in CCR units). In August 2018, the Court of Appeals for the D.C. Circuit vacated parts of the CCR for not being sufficiently protective of the environment. It is unclear how the EPA will respond to that decision. MGE will c ontinue to monitor potential rule modifications to assess potential impacts on our operations. In 2015, MGE recorded an asset retirement obligation for its share of the legal liability associated with the effect of the CCR. Actual costs of compliance may be different than the amount recorded due to potential changes in compliance strategies that will be used, as well as other potential cost estimate changes. Columbia Based upon current available information, compliance with various environmental requirements and initiatives is expected to result in significant additional operating and capital expenditures at Columbia as noted below. Columbia Clean Air Act Litigation Columbia is a coal-fired generating station operated by WPL in which WPL, WPSC, and MGE have ownership interests. In December 2009, the EPA sent a Notice of Violation (NOV) to the co-owners, including MGE. The NOV alleged that WPL, which is the plant operator, and the Columbia co-owners failed to comply with appropriate pre-constructi on review and permitting requirements and, as a result, violated the Prevention of Significant Deterioration program requirements, Title V Operating Permit requirements of the CAA, and the Wisconsin SIP. In June 2013, the court approved and entered a conse nt decree entered by the EPA, Sierra Club, and the co-owners of Columbia. One of the requirements of the consent decree requires installation of an SCR system at Columbia Unit 2 by December 31, 2018. Installation of the SCR was approved by the PSCW, which was placed in service in 2018 . d. Legal Matters - MGE Energy and MGE. MGE is involved in various legal matters that are being defended and handled in the normal course of business. MGE maintains accruals for such costs that are probable of being incurred and subject to reasonable estimation. The accrued amount for these matters is not material to the financial statements. MGE does not expect the resolution of these matters to have a material adverse effect on its consolidated results of operations, financial condition, or cash flow s. e . Other Commitments. MGE Energy holds investment s in nonpublic venture funds . From time to time, these entities require additional capital infusions from their investors. MGE Energy has committed to contribute $ 11.4 million in capital for such infusions. The timing of these infusions is dependent on the needs of the investee and is therefore uncertain at this time. In addition, MGE Energy has a three year agreement with a venture debt fund expiring in December 201 9 . MGE Ene rgy has committed to invest up to a t otal of $ 1.5 million into this fund. As of December 31, 2018 , MGE Energy has $ 0.6 million remaining in commitments. The timing of infusions is dependent on the need s of the fund and is therefore uncertain at this time. MGE has several other commitments related to various projects. Payments for these commitments are expected to be as follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Other commitments $ 333 $ 333 $ 333 $ 333 $ 333 $ 3,665

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations - MGE Energy and MGE. MGE recorded an obligation for the fair value of its legal liability for asset retirement obligations (AROs) associated with removal of the West Campus Cogeneration Facility and the Elm Road Units, electric substation s, combustion turbine generating unit s , wind generating facilities, and photovoltaic generating facilities, all of which are located on property not owned by MGE Energy and MGE and would need to be removed upon the ultimate end of the a ssociated lease s . The significant conditional AROs identified by MGE included the costs of abandoning in place gas services and mains, the abatement and disposal of equipment and buildings contaminated with asbestos and PCB s, and the proper disposal and re moval of tanks , batteries, and underground cable . Changes in management ' s assumptions regarding settlement dates, settlement methods, or assig ned probabilities could have a material effect on the liabilities and the associated regulatory asset recorded as of December 31, 2018 . MGE also may have AROs relating to the removal of various assets, such as certain electric and gas distribution facilities. These facilities are generally located on property owned by third parties, on which MGE is permitte d to operate by lease, permit, easement, license, or service agreement. The asset retirement obligations associated with these facilities cannot be reasonably determined due to the indeterminate life of the related agreements. The following table summariz es the change in AROs . Amounts include conditional AROs. (In thousands) 2018 2017 Balance as of January 1, $ 26,738 $ 26,886 Liabilities incurred (a) 1,943 145 Accretion expense 1,415 1,359 Liabilities settled (b) (175) (1,789) Revisions in estimated cash flows 59 137 Balance as of December 31, $ 29,980 $ 26,738 (a) In 2018 , MGE recorded an obligation of $1.6 million for the fair value of its legal liability for AROs associated with Forward Wind. See Footnote 5 for additional information on the purchase of Forward Wind. (b) In 2017 , MGE removed asbestos at Blount for $1.6 million .

Revenue

Revenue	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer	Revenue - MGE Energy and MGE. Revenues disaggregated by revenue source were as follows: (In thousands) Year Ended December 31, Electric revenues 2018 2017 2016 Residential $ 138,566 $ 136,168 $ 136,792 Commercial (a) 204,683 216,461 213,101 Industrial 13,878 16,176 17,589 Other-retail/municipal 34,023 38,010 35,559 Total retail 391,150 406,815 403,041 Sales to the market 7,438 4,067 6,135 Other revenues 1,870 2,323 1,483 Adjustments to revenues 424 721 (1,653) Total electric revenues 400,882 413,926 409,006 Gas revenues Residential 94,017 88,695 81,014 Commercial/Industrial (a) 59,060 55,151 48,497 Total retail 153,077 143,846 129,511 Gas transportation 4,283 4,561 4,635 Other revenues 407 418 397 Total gas revenues 157,767 148,825 134,543 Non-regulated energy revenues 1,119 348 1,196 Total Operating Revenue (a) $ 559,768 $ 563,099 $ 544,745 (a) In 2017 and 2016, MGE had less than $0.1 million of revenues related to CNG vehicle fuel servicing. No revenue was recognized for fuel servicing by MGE Energy in 2017 and 2016. Performance Obligations A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account. A contract's transaction price is allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The majority of MGE Energy's and MGE's contracts have a single performance obligation. Retail Revenue (Residential, Commercial, Industrial, and Other Retail/Municipal) Retail revenue of electric and gas utility service represent MGE's core business activi ties. Tariffs are approved by the PSCW through a rate order and provide MGE's customers with the standard terms and conditions, including pricing terms. The performance obligation to deliver electricity or gas is satisfied over time as the customer simulta neously receives and consumes the commodities provided by MGE. MGE recognizes revenues as the commodity is delivered to customers. Meters are read on a systematic basis throughout the month based on established meter-reading schedules and the customer is s ubsequently billed for their services. At the end of the month, MGE accrues an estimate for the unbilled amount of commodities delivered to customers. The unbilled revenue estimate is based on daily system demand volumes, weather factors, estimated line lo sses, estimated customer usage by class, and applicable customer rates. Utility Cost Recovery Mechanisms MGE's tariff rates include a provision for fuel cost recovery. The PSCW allows Wisconsin utilities to defer electric fuel-related costs, less excess revenues, that fall outside a symmetrical cost tolerance band. Any over/under recovery of the actual costs in a given year is determined in the following year and is then reflected in future billings to electric retail customers. Over-collection of fuel-re lated costs that are outside the approved range will be recognized as a reduction of revenue. Prior to adoption of the new revenue recognition guidance, effective January 1, 2018, over-collected fuel-related costs were reflected in "Purchased power" expens e. Under-collection of these costs will continue to be recognized in "Purchased power" expense in the consolidated statements of income. The cumulative effects of these deferred amounts will be recorded in "Regulatory assets" or "Regulatory liabilities" on the consolidated balance sheets until they are reflected in future billings to customers. See Footnote 8.b. for further information. MGE received a PSCW order in January 2018 to defer the over-collection of income tax expense collected in customer rates as a result of the Tax Cuts and Jobs Act (the Tax Act) reduction in the income tax rate to 21 percent. See Footnote 12 for further information. MGE has other cost recovery mechanisms. For example, any over-collection of the difference between actual cost s incurred and the amount of costs collected from customers is recorded as a reduction of revenue in the period incurred. Sales to the Market Sales to the market include energy charges, capacity or demand charges, and ancillary charges represented by who lesale sales of electricity made to third parties who are not ultimate users of the electricity. Most of these sales are spot market transactions on the markets operated by MISO. Each transaction is considered a performance obligation and revenue is recogn ized in the period in which energy charges, capacity or demand charges, and ancillary services are sold into MISO. MGE reports, on a net basis, transactions on the MISO markets in which it buys and sells power within the same hour to meet electric energy d elivery requirements. Transportation of Gas MGE has contracts under which MGE provides gas transportation services to customers who have elected to purchase gas from a third party and have the gas delivered via pipelines within MGE's service territory. R evenue is recognized as service is rendered or gas is delivered to customers. Tariffs are approved by the PSCW through a rate order and provide gas transportation customers with the standard terms and conditions, including pricing terms.

Noncontrolling Interest

Noncontrolling Interest	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Noncontrolling Interest	Noncontrolling Interest - MGE. The noncontrolling interest on MGE ' s consolidated balance sheets as of December 31 was as follows: (In thousands) 2018 2017 MGE Power Elm Road (a) $ 97,519 $ 97,635 MGE Power West Campus (a) 43,935 43,267 Total Noncontrolling Interest $ 141,454 $ 140,902 The net income attributable to noncontrolling interest , net of tax, for the years ended December 31, 2018 , 2017 , and 2016 was as follows : (In thousands) 2018 2017 2016 MGE Power Elm Road (a) $ 15,384 $ 29,274 $ 14,748 MGE Power West Campus (a) 7,168 13,963 7,200 MGE Transco (b) - - 1,410 Net Income Attributable to Noncontrolling Interest, Net of Tax $ 22,552 $ 43,237 $ 23,358 (a) MGE Power Elm Road and MGE Power West Campus are not su bsidiaries of MGE; however, they have been consolidated in the consolidated financial s tatements of MGE (see Footnote 3 ). MGE Power Elm Road and MGE Power West Campus are 100 % owned by MGE Power, and MGE Power is 100 % o wned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE consolidated financial statements as noncontrolling interest . In 2017, there was a $14.8 million and $6.8 million one-time tax impact as a result of the Tax Act for MGE Power Elm Road and MGE Power West Campus, respectively. The Tax Act reduced the f ederal tax rate from 35% to 21%. See Footnote 12 for further information . (b ) A s of December 31, 2018 , MGE Energy is the owner of MGE Transco. In July 2016, MGE's ownership interest in MGE Transco declined below a majority as a result of continued funding of ATC capital contributions by MGE Energy. As a result of the change in majority owner ship in MGE Transco , MGE deconsolidated MGE Energy's proportionate share of the equity in MGE Transco. The change in co nsolidation was applied prospectively by reducing its investment and noncontrolling interest on MGE's consolidated financial statements. The change had no effect on MGE Energy's consolidated financial statements; however, MGE Energy's proportionate share o f the equity and net income of MGE Transco classified as noncontrolling interest was deconsolidated from MGE ' s financial statements. No gain or loss was recognized in July 2016 due to MGE ceasing to have a controlling financial interest .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information - MGE Energy and MGE. The electric utility business purchases, generates and distributes electricity, and contracts for transmission service. The gas utility business purchases and distributes natural gas and contracts for the transportation of natural gas. Both the electric and gas segments operate through MGE Energy ' s principal subsidiary, MGE. The nonregulated energy operations are conducted through MGE Energy ' s subsidiaries: MGE Power, MGE Power Elm Road, and MGE Power West Campus . These subsidiaries own and lease electric generating capacity to assist MGE . MGE Power Elm Road has an ownership interest in two coal-fired generating units in Oak Creek, Wisconsin , which are leased to MGE, and MGE Power West Campus owns a control ling interest in the electric generation plant of a natural gas-fired cogeneration facility on the UW campus . MGE Power West Campus's portion is also leased to MGE . The transmission investment segment invests in ATC, a company that provides electric trans mission services primarily in Wisconsin , and ATC Holdco, a company formed to pursue electric transmission development and investments outside of Wisconsin . These investments are held in MGE Transco and MGEE Transco, respectively. See Footnote 6 for further discussion . The "All O ther s" segment includes: corporate, CWDC, MAGAEL, MGE State Energy Services, MGE Services, NGV Fueling Services (dissolved in 2018), and North Mendota . These entities ' operations consist of investing in companies and property which relate to the regulated operations, financing the regulated operations, or owning and operating natural gas compression equipment . General corporate expenses include the cost of executive management, corporate accounting and finance, information technolog y, risk management, human resources and legal functions, and employee benefits that are allocated to electric and gas segments based on formulas prescribed by the PSCW. Identifiable assets are those used in MGE 's operations in each segment. Sales between our electric and gas segments are based on PSCW approved tariffed rates. Additionally, intersegment operations related to the leasing arrangement between our el ectric segment and MGE Power Elm Road /MGE Power West Campus are based on terms previously approved by the PSCW. Consistent with internal reporting, management has presented the direct financing capital leas e s between MGE and MGE Power Elm Road /MGE Power West Campus based on actual lease payments included in rates. Lease payments made by MGE to MGE Power Elm Road and MGE Power West Campus are shown as operating expenses. The lease payments received by MGE Power Elm Road and MGE Power West Campus from MGE are shown as lease income in interdepartmental revenues. The depreciation expense associated with the Elm Road Units and WCCF is reflected in the nonregulated energy segment. The following table shows segment information for MGE Energy ' s and MGE ' s operations: (In thousands) MGE Energy Electric Gas Non-Regulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Consolidated Total Year Ended December 31, 2018 Operating revenues $ 400,882 $ 157,767 $ 1,119 $ - $ - $ - $ 559,768 Interdepartmental revenues (289) 16,076 39,526 - - (55,313) - Total operating revenues 400,593 173,843 40,645 - - (55,313) 559,768 Depreciation and amortization (38,925) (10,060) (7,427) - - - (56,412) Other operating expenses (297,374) (145,883) (144) (16) (1,045) 55,313 (389,149) Operating income (loss) 64,294 17,900 33,074 (16) (1,045) - 114,207 Other income (deductions), net 7,294 3,132 - 8,602 (1,973) - 17,055 Interest (expense) income, net (12,198) (3,692) (5,307) - 1,588 - (19,609) Income (loss) before taxes 59,390 17,340 27,767 8,586 (1,430) - 111,653 Income tax (provision) benefit (13,453) (4,474) (7,534) (2,345) 372 - (27,434) Net income (loss) $ 45,937 $ 12,866 $ 20,233 $ 6,241 $ (1,058) $ - $ 84,219 Year Ended December 31, 2017 Operating revenues $ 413,926 $ 148,825 $ 348 $ - $ - $ - $ 563,099 Interdepartmental revenues (510) 14,974 44,468 - - (58,932) - Total operating revenues 413,416 163,799 44,816 - - (58,932) 563,099 Depreciation and amortization (36,660) (9,000) (7,417) - - - (53,077) Other operating expenses (a) (308,100) (135,029) (190) (9) (1,001) 58,932 (385,397) Operating income (loss) 68,656 19,770 37,209 (9) (1,001) - 124,625 Other income (deductions), net (a) 4,539 1,912 - 9,844 (1,896) - 14,399 Interest (expense) income, net (11,257) (3,234) (5,533) - 700 - (19,324) Income (loss) before taxes 61,938 18,448 31,676 9,835 (2,197) - 119,700 Income tax (provision) benefit (b) (20,547) (7,303) 8,860 (3,954) 850 - (22,094) Net income (loss) $ 41,391 $ 11,145 $ 40,536 $ 5,881 $ (1,347) $ - $ 97,606 Year Ended December 31, 2016 Operating revenues $ 409,006 $ 134,543 $ 1,196 $ - $ - $ - $ 544,745 Interdepartmental revenues 1,912 21,378 43,930 - - (67,220) - Total operating revenues 410,918 155,921 45,126 - - (67,220) 544,745 Depreciation and amortization (29,122) (8,128) (7,372) - (24) - (44,646) Other operating expenses (a) (313,649) (128,721) (155) (17) (895) 67,220 (376,217) Operating income (loss) 68,147 19,072 37,599 (17) (919) - 123,882 Other income, net (a) 3,668 1,668 - 8,429 292 - 14,057 Interest (expense) income, net (11,147) (3,223) (5,768) - 272 - (19,866) Income (loss) before taxes 60,668 17,517 31,831 8,412 (355) - 118,073 Income tax (provision) benefit (20,115) (6,894) (12,775) (2,836) 107 - (42,513) Net income (loss) $ 40,553 $ 10,623 $ 19,056 $ 5,576 $ (248) $ - $ 75,560 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for further information. (b) In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information. (In thousands) MGE Electric Gas Non-Regulated Energy Transmission Investment (d) Consolidation/ Elimination Entries Consolidated Total Year Ended December 31, 2018 Operating revenues $ 400,882 $ 157,767 $ 1,119 $ - $ - $ 559,768 Interdepartmental revenues (289) 16,076 39,526 - (55,313) - Total operating revenues 400,593 173,843 40,645 - (55,313) 559,768 Depreciation and amortization (38,925) (10,060) (7,427) - - (56,412) Other operating (expenses) income (c) (310,626) (150,195) (7,678) - 55,313 (413,186) Operating income (c) 51,042 13,588 25,540 - - 90,170 Other income, net (c) 7,093 2,970 - - - 10,063 Interest expense, net (12,198) (3,692) (5,307) - - (21,197) Net income 45,937 12,866 20,233 - - 79,036 Less: Net income attributable to noncontrolling interest, net of tax - - - - (22,552) (22,552) Net income attributable to MGE $ 45,937 $ 12,866 $ 20,233 $ - $ (22,552) $ 56,484 Year Ended December 31, 2017 Operating revenues $ 413,929 $ 148,834 $ 348 $ - $ - $ 563,111 Interdepartmental revenues (513) 14,965 44,468 - (58,920) - Total operating revenues 413,416 163,799 44,816 - (58,920) 563,111 Depreciation and amortization (36,660) (9,000) (7,417) - - (53,077) Other operating (expenses) income (a)(b)(c) (328,093) (142,175) 8,670 - 58,920 (402,678) Operating income (c) 48,663 12,624 46,069 - - 107,356 Other income, net (a)(c) 3,985 1,755 - - - 5,740 Interest expense, net (11,257) (3,234) (5,533) - - (20,024) Net income 41,391 11,145 40,536 - - 93,072 Less: net income attributable to noncontrolling interest, net of tax - - - - (43,237) (43,237) Net income attributable to MGE $ 41,391 $ 11,145 $ 40,536 $ - $ (43,237) $ 49,835 Year Ended December 31, 2016 Operating revenues $ 409,030 $ 134,572 $ 1,196 $ - $ - $ 544,798 Interdepartmental revenues 1,888 21,349 43,930 - (67,167) - Total operating revenues 410,918 155,921 45,126 - (67,167) 544,798 Depreciation and amortization (29,122) (8,128) (7,372) - - (44,622) Other operating expenses (a)(c) (333,632) (135,578) (12,930) - 67,167 (414,973) Operating income (loss) (c) 48,164 12,215 24,824 - - 85,203 Other income (deductions), net (a)(c) 3,536 1,631 - 4,360 - 9,527 Interest expense, net (11,147) (3,223) (5,768) - - (20,138) Net income 40,553 10,623 19,056 4,360 - 74,592 Less: Net income attributable to noncontrolling interest, net of tax - - - - (23,358) (23,358) Net income attributable to MGE $ 40,553 $ 10,623 $ 19,056 $ 4,360 $ (23,358) $ 51,234 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for further information. (b) In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information. (c) Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income. (d) As of July 31, 2016, MGE no longer consolidates MGE Energy's proportionate share of equity earnings in MGE Transco. See Footnote 6 for further information. The following table shows segment information for MGE Energy's and MGE's assets and capital expenditures: Utility Consolidated (In thousands) MGE Energy Electric Gas Non-regulated Energy Transmission Investment (e) All Others Consolidation/ Elimination Entries Total Assets: December 31, 2018 $ 1,193,083 $ 377,005 $ 265,301 $ 66,366 $ 465,661 $ (378,798) $ 1,988,618 December 31, 2017 1,058,988 354,875 270,384 61,783 485,548 (376,396) 1,855,182 December 31, 2016 1,038,308 329,538 271,277 74,535 465,202 (377,800) 1,801,060 Capital Expenditures: Year ended Dec. 31, 2018 $ 176,399 $ 30,497 $ 5,301 $ - $ - $ - $ 212,197 Year ended Dec. 31, 2017 77,353 26,847 3,931 - - - 108,131 Year ended Dec. 31, 2016 50,699 29,136 3,824 - - - 83,659 Utility Consolidated (In thousands) MGE Electric Gas Non-regulated Energy Consolidation/ Elimination Entries Total Assets: December 31, 2018 $ 1,193,083 $ 377,005 $ 265,251 $ (448) $ 1,834,891 December 31, 2017 1,058,988 354,875 270,334 (156) 1,684,041 December 31, 2016 1,038,308 329,538 271,227 (221) 1,638,852 Capital Expenditures: Year ended Dec. 31, 2018 $ 176,399 $ 30,497 $ 5,301 $ - $ 212,197 Year ended Dec. 31, 2017 77,353 26,847 3,931 - 108,131 Year ended Dec. 31, 2016 50,699 29,136 3,824 - 83,659 (e) In December 2017, there was a $20.4 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.

Quarterly Summary of Operations

Quarterly Summary of Operations	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Summary of Operations	Quarterly Summary of Operations - MGE Energy (unaudited). (In thousands, except per share amounts) Quarters Ended 2018 March 31 June 30 September 30 December 31 Operating revenues: Electric revenues $ 94,867 $ 99,282 $ 119,388 $ 88,464 Gas revenues 62,765 24,980 18,407 51,615 Total Operating Revenues 157,632 124,262 137,795 140,079 Operating expenses 131,444 100,031 97,997 116,089 Operating income 26,188 24,231 39,798 23,990 Interest and other income, net 180 (52) (695) (1,987) Income tax provision (6,367) (5,828) (9,597) (5,642) Earnings on common stock $ 20,001 $ 18,351 $ 29,506 $ 16,361 Earnings per common share $ 0.58 $ 0.53 $ 0.85 $ 0.47 Dividends per share $ 0.323 $ 0.323 $ 0.338 $ 0.338 2017 Operating revenues: Electric revenues $ 98,397 $ 102,382 $ 120,761 $ 92,734 Gas revenues 58,426 24,081 18,778 47,540 Total Operating Revenues 156,823 126,463 139,539 140,274 Operating expenses (a) 124,987 100,868 97,542 115,077 Operating income 31,836 25,595 41,997 25,197 Interest and other income, net (a) (1,369) (1,316) 216 (2,456) Income tax provision (b) (11,167) (8,736) (15,584) 13,393 Earnings on common stock $ 19,300 $ 15,543 $ 26,629 $ 36,134 Earnings per common share $ 0.56 $ 0.45 $ 0.77 $ 1.04 Dividends per share $ 0.308 $ 0.308 $ 0.323 $ 0.323 (a ) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for more information. ( b) In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information. Notes: • The quarterly results of operations within a year may not be comparable because of seasonal and other factors. • The sum of earnings per share of common stock for any four quarters may vary slightly from the earnings per share of common stock for the equivalent twelve-month period due to rounding. • MGE Energy's operations are based primarily on its utility subsidiary MGE.

Condensed Parent Company Financ

Condensed Parent Company Financial Statements	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Parent Company Financial Statements	Schedule I Condensed Parent Company Financial Statements MGE Energy, Inc. Statements of Comprehensive Income (Parent Company Only) (In thousands) For the Years Ended December 31, 2018 2017 2016 Operating Expenses: Other operations and maintenance $ 913 $ 880 $ 720 Total Operating Expenses 913 880 720 Operating Loss (913) (880) (720) Equity in earnings of investments 85,220 99,246 75,581 Other (loss) income, net (1,966) (2,165) 435 Interest income, net 1,489 605 176 Income before income taxes 83,830 96,806 75,472 Income tax provision 389 800 88 Net Income 84,219 97,606 75,560 Other Comprehensive Income, Net of Tax: Unrealized gain (loss) on available-for-sale securities, net of tax ($-, $(117), and $104) - 175 (155) Comprehensive Income $ 84,219 $ 97,781 $ 75,405 The accompanying notes are an integral part of the above consolidated financial statements. MGE Energy, Inc. Statements of Cash Flows (Parent Company Only) (In thousands) For the Years Ended December 31, 2018 2017 2016 Net Cash Flows Provided by Operating Activities $ 27,211 $ 70,268 $ 74,994 Investing Activities: Contributions to affiliates (3,200) (6,522) (2,789) Contributions to other investments (2,626) (4,534) (360) Other 873 843 385 Cash Used for Investing Activities (4,953) (10,213) (2,764) Financing Activities: Cash dividends paid on common stock (45,762) (43,682) (41,775) Other - (58) (11) Cash Used for Financing Activities (45,762) (43,740) (41,786) Change in cash, cash equivalents, and restricted cash (23,504) 16,315 30,444 Cash, cash equivalents, and restricted cash at beginning of period 98,540 82,225 51,781 Cash, cash equivalents, and restricted cash at end of period $ 75,036 $ 98,540 $ 82,225 The accompanying notes are an integral part of the above consolidated financial statements. Schedule I Condensed Parent Company Financial Statements (continued) MGE Energy, Inc. Balance Sheets (Parent Company Only) (In thousands) As of December 31, ASSETS 2018 2017 Current Assets: Cash and cash equivalents $ 75,036 $ 98,540 Other current assets 3,646 1,601 Total Current Assets 78,682 100,141 Other deferred assets and other 110 171 Investments: Investments in affiliates 763,625 702,134 Other investments 7,672 5,640 Total Investments 771,297 707,774 Total Assets $ 850,089 $ 808,086 LIABILITIES AND SHAREHOLDERS' EQUITY Current Liabilities: Accounts payable to affiliates $ 617 $ 665 Other current liabilities 2,500 2,047 Total Current Liabilities 3,117 2,712 Other Credits: Deferred income taxes 27,151 23,480 Accounts payable to affiliates 3,177 3,707 Total Other Credits 30,328 27,187 Shareholders' Equity: Common shareholders' equity 350,936 350,936 Retained earnings 465,708 426,874 Accumulated other comprehensive income, net of tax - 377 Total Shareholders' Equity 816,644 778,187 Commitments and contingencies (see Footnote 3) Total Liabilities and Shareholders' Equity $ 850,089 $ 808,086 The accompanying notes are an integral part of the above consolidated financial statements. Schedule I Condensed Parent Company Financial Statements (continued) Notes to Condensed Financial Statements (Parent Company Only) 1. Basis of Presentation. MGE Energy is a holding company and conducts substantially all of its business operations through its subsidiaries. For Parent Company only presentation, investment in subsidiaries are accounted for using the equity method. These condensed Parent Company financial statements and related notes have been prepared in accordance with Rule 12-04, Sc hedule I of Regulation S-X. These statements should be read in conjunction with the financial statements and the notes in Item 8. Financial Statements and Supplementary Data of the Annual Report on Form 10-K for the year ended December 31, 2018 . 2 . Credit Agreements. As of December 31, 2018 , MGE Energy had access to an unsecured , committed credit facility with ag gregate bank commitments of $ 50.0 million . As of December 31, 2018 , no borrowings were outstanding under this facility. See Footnote 1 1 of the Notes to Consolidated Financial Statements in this Report for further information regarding MGE Energy's credit agreements. 3 . Commitments and Contingencies. See Footnote 1 7 of the Notes to Consolidated Financial Statements in this Report for commitments and contingencies. 4 . Dividend s from Affiliates. Dividends from Affiliates (In thousands) 2018 2017 2016 MGE (a) $ - $ 45,000 $ 50,000 MGE Power Elm Road 15,500 12,000 13,500 MGE Power West Campus 6,500 6,000 9,500 MGE Transco 4,625 4,669 1,107 MGEE Transco 60 112 - NGV Fueling Services 50 - - Total $ 26,735 $ 67,781 $ 74,107 (a ) Excludes $15.8 million dividend in kind to MGE Energy from MGE in 2016 . Dividend Restrictions Dividend payments by MGE to MGE Energy are subject to restrictions arising under a PSCW rate order and, to a lesser degree, MGE's first mortgage bonds. The PSCW order restricts any dividen ds , above the PSCW authorized amount of $70.8 million , that MGE may pay MGE Energy if its common equity ratio, calculated in the manner used in the rate proceeding, is less than 55 % . MGE's thirteen month rollin g average common equity ratio as of December 31, 2018 , is 56.3 % as det ermined under the calculation used in the rate proceeding. MGE was not restricted from paying cash dividends in 2018 . Cash dividends of $ 45.0 million were paid by MGE to MGE Energy in 2017 . MGE paid no dividends to MGE Energy during 2018 . The rate proceeding calculation includes as indebtedness imputed amounts for MGE's outstanding purchase power capacity payments and other PSCW adjustments, but does not include the indebtedness associated with MGE Power Elm Road or MGE Power West Campus, which are consolidated into MGE's financial statements but are not direct obligations of MGE. MGE has covenanted with the holders of its first mortgage bonds not to declare or pay any dividend or make any other distribution on or purchase an y shares of its common stock unless, after giving effect thereto, the aggregate amount of all such dividends and distributions and all amounts applied to such purchases, after December 31, 1945, shall not exceed the earned surplus (retained earnings) accum ulated subsequent to December 31, 1945. As of December 31, 2018 , approximately $ 400.0 million was available for the payment of dividends under this covenant. See Footnotes 10 and 11 of the Notes to Consolid ated Financial Statements in this Report for long-term debt and lines of credit dividend restrictions.

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
Valuation and Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	Schedule II MGE Energy, Inc. and Madison Gas and Electric Company Valuation and Qualifying Accounts Additions Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Net Accounts Written Off (a) Balance at End of Period Fiscal Year 2016: Accumulated provision for uncollectibles $ 3,694,080 1,195,500 19,500 (1,465,784) $ 3,443,296 Fiscal Year 2017: Accumulated provision for uncollectibles $ 3,443,296 1,015,970 20,400 (1,304,721) $ 3,174,945 Fiscal Year 2018: Accumulated provision for uncollectibles $ 3,174,945 1,065,970 320,400 (1,407,653) $ 3,153,662 (a) Net of recovery of amounts previously written off.

Significant Accounting Policies

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation - MGE Energy and MGE. MGE, a wholly owned subsidiary of MGE Energy, is a regulated electric and gas utility headquartered in Madison, Wisconsin. MGE Energy and MGE consolidate all majority owned subsidiaries in which they have a controlling influence. Additional wholly owned subsidiaries of MGE Energy include CWDC, MAGAEL, MGE Power, MGE State Energy Services, MGE Services, MGE Transco, and MGEE Transco . CWDC owns 100% of North Mendota, a subsidiary created to serve as a d evel opment entity for property. MGE Power owns 100 % o f MGE Power Elm Road and MGE Power West Campus. MGE Power and its subsidiaries are part of MGE Energy' s nonregulated energy operations, which were formed to own and lease electric generation projects to assist MGE. MGE Transco and MGEE Transco are nonregul ated entities formed to manage the investments in ATC and ATC Holdco, respectively. On December 1, 2016, MGE ' s ownership interest in MGE Transco was transferred to MGE Energy. See Footnote 6 for further discussion of the transfer of MGE ' s investment in MGE Transco. MGE Energy and MGE consolidate variable interest entities (VIEs) for which it is the primary beneficiary. Variable interest entities are legal entities that possess any of the following characteristics: equity investors who have an insufficient amount of equity at risk to finance their activities, equity owners who do not have the power to direct the significant activities of the entity (or have voting rights that are disproportionate to their ownership interest), or equity holders who do not rec eive expected losses or returns significant to the VIE. If MGE Energy or MGE is not the primary beneficiary and an ownership interest is held, the VIE is accounted for under the equity method of accounting. When assessing the determination of the primary b eneficiary, all relevant facts and circumstances are considered, including: the power, through voting or similar rights, to direct the activities of the VIE that most significantly impact the VIE's economic performance and the obligation to absorb the expe cted losses and/or the right to receive the expected returns of the VIE. Ongoing reassessments of all VIEs are performed to determine if the primary beneficiary status has changed. MGE has consolidated MGE Power Elm Road and MGE Power West Campus. Both ent ities are VIEs. MGE is considered the primary beneficiary of these entities as a result of contractual agreements. See Footnote 3 for more discussion of these entities. Prior to December 1, 2016, MGE Transco was jointly owned by MGE Energy and MGE. MGE's ownership interest in MGE Transco declined below a majority in July 2016. As a result of the change in majority ownership, MGE deconsolidated MGE Energy's proportionate share of the equity in MGE Transco. See Footnote 20 for further discussion regarding th e deconsolidation of noncontrolling interest . The consolidated financial statements reflect the application of certain accounting policies described in this note. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates - MGE Energy and MGE. In order to prepare consolidated financial statements in conformity with GAAP, management must make estimates and assumptions. These estimates could affect reported amounts of assets, liabilities, and disclosures at the date of the financial statements, as well as the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from management's estimates.
Cash and Cash Equivalents	Cash Equivalents MGE Energy and MGE consider all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.
Restricted Cash	Restricted Cash MGE has certain cash accounts that are restricted to uses other than current operations and designated for a specific purpose. MGE's restricted cash accounts include cash held by trustees for certain employee benefits and cash deposits held by third parties. These are included in "Other current assets" on the consolidated balance s heets.
Receivable Margin Account	Receivable – Margin Account Cash amounts held by counterparties as margin collateral for certain financial transactions are recorded as Receivable – margin account in "Other current assets" on the consolidated balance sheets. The costs being hedged are fuel for electric generation, purchased power, and cost of gas sold.
Trade Receivables, Allowance for Doubtful Accounts, and Concentration Risk	Trade Receivables, Allowance for Doubtful Accounts, and Concentration Risk - MGE Energy and MGE. Trade accounts receivable are recorded at the invoiced amount and do not bear interest. However, a 1 % late payment charge is recorded on all receivables unpaid after the due date. The allowance for doubtful accounts associated with these receivables represents our best estimate of the amount of probable credit losses in our existing accounts receivable. We determine our allowance for doubtful accounts based on historical write-off experience, regional economic data, and review of the accounts receivable aging . MGE manages this concentration and the related credit risk through its credit and collection pol icies, which are consistent with state regulatory requirements.
Inventories	Inventories - MGE Energy and MGE. Inventories consist of natural gas in storage, fuel for electric generation, materials and supplies, and renewable energy credits (R ECs). MGE values natural gas in storage, fuel for electric generation , and materials and supplies using average cost. REC allowances are included in "Materials and supplies" on the consolidated balance sheets and are recorded based on specific identification. These allo wances are charged to purchase power expense as they are used in operations.
Chattel Paper Agreement	Chattel Paper Agreements - MGE Energy and MGE. MGE makes available to qualifying customers a financing program for the purchase and installation of energy-related equipment that will provide more efficient use of utility service at the customer's property. The energy-related equipment installed at the customer sites is used to secure the customer loans. MGE is a party to a chattel paper purchase agreement with a financial institution under which MGE can sell, transfer, and assign to the financial i nstitution an undivided interest with recourse, in up to $ 10.0 million of the financing program receivables, until July 31, 2019. The length of the MGE guarantee to the financial institution varies from one to ten years depending on the term of the underlying customer loan. The loan balances outstanding as of December 31, 2018 , approximates the fair value of the energy-related equipment acting as collateral. MGE accounts for these agreements as secured borrowings.
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities - MGE Energy and MGE. Regulatory assets and regulatory liabilities are recorded consistent with regulatory treatment. Regulatory assets represent costs which are deferred due to the probable future recovery from customers through regulated rates. Regulatory liabilities represent the excess recovery of costs or accrued credits which were deferred because MGE believes it is probable such amounts will be returned to customers through future regulated rates. Regulator y assets and liabilities are amortized in the consolidated statements of income consistent with the recovery or refund included in customer rates. MGE believes that it is probable that its recorded regulatory assets and liabilities will be recovered and re funded, respectively, in future rates.
Debt Issuance Costs	Debt Issuance Costs - MGE Energy and MGE. Premiums, discounts, and expenses incurred with the issuance of outstanding long-term debt are amortized over the life of the debt issue. Any call premiums or unamortized expenses associated with refinancing higher-cost debt obligations used to finance utility-regulated assets and operations are amortized consistent with regulatory treatment of those items. These costs are included as a direct r eduction to the related debt liability on the consolidated balance sheets.
Property, Plant, and Equipment	Property, Plant, and Equipment - MGE Energy and MGE. Property, plant, and equipment is recorded at original cost. Cost includes indirect costs consisting of payroll taxes, pensions, postretirement benefits, other fringe benefits, and administrative and general costs. Also, included in the cost is AFUDC for utility property and capitalized interest for nonregulated property. Additions for significant replacements of property are charged to property, plant, and equipment at cost; and minor items are ch arged to maintenance expense. Depreciation rates on utility property are approved by the PSCW, based on the estimated economic lives of property, and include estimates for salvage value and removal costs. Removal costs of utility property, less any salvage value, are adjusted through regulatory liabilities. Depreciation rates on nonregulated property are based on the estimated economic lives of the property. Provisions at composite straight-line depreciation rates ap proximate the following percentages for the cost of depreciable property: 2018 2017 2016 Electric (a)(b) 2.9 % 3.0 % 2.5 % Gas (a) 2.1 % 2.1 % 2.1 % Nonregulated 2.3 % 2.3 % 2.3 % (a ) In December 2015, the PSCW approved new depreciation rates, which were implemented and became effective as of January 1, 2016. (b) In September 2016, the PSCW approved new depreciation rates for Columbia effective January 1, 2017.
Asset Retirement Obligations Policy	Asset Retirement Obligations - MGE Energy and MGE. A liability is recorded for the fair value of an asset retirement o bligation (ARO) to be recognized in the period in which it is incurred if it can be reasonably estimated. The offsetting associated asset retirement costs are capitalized as a long-lived asset and depreciated over the asset ' s useful life. The expected present value technique used to calculate the fair value of ARO liabilities includes assumptions about costs, probabilities, settlement dates, interest accretion, and inflation. Revisions to the assumptions, including the timing or amount of expected asset retirement costs, could result in increases or decreases to the AROs. All asset retirement obligations are recorded as "O ther long-term liabilities " on the consolidated balance sheets. MGE has regulatory treatment and recognizes regulatory assets or liabilities for the timing differences between when it recover s legal AROs in rates and when it would recognize these costs.
Repairs and Maintenance Expense	Repairs and Maintenance Expense - MGE Energy and MGE. MGE utilizes the direct expensing method for planned major maintenance projects. Under this method, MGE expenses all costs associated with major planned maintenance activities as incurred.
Purchased Gas Adjustment Clause	Purchased Gas Adjustment Clause - MGE Energy and MGE. MGE's natural gas rates are subject to a fuel adjustment clause designed to recover or refund the difference between the actual cost of purchased gas and the amount included in rates. Differences between the amounts billed to customers and the actual costs recoverable are deferred and recovered or refunded in future periods by means of prospective monthly adjustments to rates. These amounts are included in "Regulatory liabilities – current " on the consolidated balance sheets.
Revenue Recognition	Revenue Recognition - MGE Energy and MGE. Operating revenues are recorded as service is rendered or energy is delivered to customers. Meters are read on a systematic basis throughout the month based on established meter-reading schedules. At the end of the month, MGE accrues an estimate for the unbilled amount of energy delivered to customers. The unbilled revenue estimate is based on daily system demand volumes, weather factors, estimated line losses, estimated customer usage by class, and applicable customer rates. Performance Obligations A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account. A contract's transaction price is allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The majority of MGE Energy's and MGE's contracts have a single performance obligation. Retail Revenue (Residential, Commercial, Industrial, and Other Retail/Municipal) Retail revenue of electric and gas utility service represent MGE's core business activi ties. Tariffs are approved by the PSCW through a rate order and provide MGE's customers with the standard terms and conditions, including pricing terms. The performance obligation to deliver electricity or gas is satisfied over time as the customer simulta neously receives and consumes the commodities provided by MGE. MGE recognizes revenues as the commodity is delivered to customers. Meters are read on a systematic basis throughout the month based on established meter-reading schedules and the customer is s ubsequently billed for their services. At the end of the month, MGE accrues an estimate for the unbilled amount of commodities delivered to customers. The unbilled revenue estimate is based on daily system demand volumes, weather factors, estimated line lo sses, estimated customer usage by class, and applicable customer rates. Utility Cost Recovery Mechanisms MGE's tariff rates include a provision for fuel cost recovery. The PSCW allows Wisconsin utilities to defer electric fuel-related costs, less excess revenues, that fall outside a symmetrical cost tolerance band. Any over/under recovery of the actual costs in a given year is determined in the following year and is then reflected in future billings to electric retail customers. Over-collection of fuel-re lated costs that are outside the approved range will be recognized as a reduction of revenue. Prior to adoption of the new revenue recognition guidance, effective January 1, 2018, over-collected fuel-related costs were reflected in "Purchased power" expens e. Under-collection of these costs will continue to be recognized in "Purchased power" expense in the consolidated statements of income. The cumulative effects of these deferred amounts will be recorded in "Regulatory assets" or "Regulatory liabilities" on the consolidated balance sheets until they are reflected in future billings to customers. See Footnote 8.b. for further information. MGE received a PSCW order in January 2018 to defer the over-collection of income tax expense collected in customer rates as a result of the Tax Cuts and Jobs Act (the Tax Act) reduction in the income tax rate to 21 percent. See Footnote 12 for further information. MGE has other cost recovery mechanisms. For example, any over-collection of the difference between actual cost s incurred and the amount of costs collected from customers is recorded as a reduction of revenue in the period incurred. Sales to the Market Sales to the market include energy charges, capacity or demand charges, and ancillary charges represented by who lesale sales of electricity made to third parties who are not ultimate users of the electricity. Most of these sales are spot market transactions on the markets operated by MISO. Each transaction is considered a performance obligation and revenue is recogn ized in the period in which energy charges, capacity or demand charges, and ancillary services are sold into MISO. MGE reports, on a net basis, transactions on the MISO markets in which it buys and sells power within the same hour to meet electric energy d elivery requirements. Transportation of Gas MGE has contracts under which MGE provides gas transportation services to customers who have elected to purchase gas from a third party and have the gas delivered via pipelines within MGE's service territory. R evenue is recognized as service is rendered or gas is delivered to customers. Tariffs are approved by the PSCW through a rate order and provide gas transportation customers with the standard terms and conditions, including pricing terms.
Utility Cost Recovery	Utility Cost Recovery - MGE Energy and MGE. MGE's tariff rates include a provision for fuel cost recovery. The PSCW allows Wisconsin utilities to defer electric fuel-related costs, less excess revenues, that fall outside a symmetrical cost tolerance band. Any over/under recovery of the actual costs in a given year is determined in the following year and is then reflected in future billings to electric retail customers. Over-collection of fuel-related costs that are outside the approved range will be r ecognized as a reduction of revenue. Prior to adoption of the new revenue recognition guidance, effective January 1, 2018, over-collected fuel-related costs were reflected in "Purchased power" expense. Under-collection of these costs will continue to be re cognized in "Purchased power" expense in the consolidated statements of income of MGE Energy and MGE. The cumulative effects of these deferred amounts will be recorded in "Regulatory assets" or "Regulatory liabilities" on the consolidated balance sheets of MGE Energy and MGE until they are reflected in future billings to customers. See Footnote 8.b. for further information.
Allowance for Funds Used During Construction Policy	Allowance for Funds Used During Construction - MGE Energy and MGE. Allowance for funds used during construction is included in utility plant accounts and represents the cost of borrowed funds used during plant construction and a return on shareholder' s capital used for construction purposes. In the consolidated income statements, the cost of borrowed funds (AFUDC-debt) is presented as an offset to "Interest expense" and the return on shareholder's capital (AFUDC-equity funds) is shown as an item within "Other income." For both 2018 and 2017 , as approved by the PSCW, MGE capitalized AFUDC-debt and equity on 50 % of applicable average construction work in progress at 7.87 % . For 2016 , as app roved by the PSCW, MGE capitalized AFUDC-debt and equity on 50 % of applicable average construction work in progress at 7.93 %. For 2018 , 2017 , and 2016 , MGE received specific approval to recover 100 % AFUDC on certain environmental costs for Columbia. For 2018 and 2017 , MGE received specific approval to recover 100 % AFUDC on certain costs for the Saratoga Wind Farm project. These amounts are recovered under t he ratemaking process over the service lives of the related properties.
Investments	Investments - MGE Energy and MGE. Investments in limited liability companies that have specific ownership accounts in which MGE Energy or MGE's ownership interest is more than minor and are considered to have significant influence are accounted for using the equity method. All other investments are carried at fair value, with changes in fair value recognized through net income .
Capitalized Software Costs	Capitalized Software Costs - MGE Energy and MGE. Property, plant, and equipment includes the net book value of capitalized costs of internal use software totaling $ 15.1 million and $ 11.1 million as of December 31, 2018 and 2017 , respectively. During 2018 , 2017 , and 2016 , MGE recorded $ 4.7 million, $ 3.3 million, and $ 3.0 million, respectively, of amortization expense related to these costs. These costs are amortized on a straight-line basis over the estimated useful lives of the assets. For internal use software, the useful lives range from five to fifteen years.
Capitalized Software Assets Hosting Arrangements	Capitalized Software Assets – Hosting Arrangements – MGE Energy and MGE. The FASB issued authoritative guidance of accounting for software in a hosted arrangement. MGE Energy and MGE adopted the authoritative guidance as of September 30, 2018. See Footnote 2 for further information. T he net book value of capitalized costs of internal use software incurred in a hosting arrangement was $ 9.2 million and $ 0.5 million as of December 31, 2018 and 2017 , respectively. During 2018, MGE implemented an enterprise resource planning platform which was placed in service as of January 1, 2019. As of December 31, 2018 , accumulated a mortization expense was $ 0.1 million. There was no accumulated amortization expense a s of December 31, 2017 . Capitalized software assets for hosted arrangements and the related accumulated amortization expense are recorded in " Other deferred assets and other " on the consolidated balance sheets . During 2018 , MGE recorded $ 0.1 million of amortization expense related to software assets for hosted arrangements. During 2017 and 2016 , no amortization expense was recorded. These costs are recognized in " Other operations and maintenance " expense in the consolidated statements of income and are amortized on a straight-line basis over the estimated useful lives of the assets. Software ass ets for hosted arrangements have useful lives ranging from five to ten years.
Impairment of Long-Lived Assets Policy	Impairment of Long-Lived Assets - MGE Energy and MGE. MGE reviews plant and equipment and other property for impairment when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. MGE's policy for determining when long-lived assets are impaired is to recognize an impairment loss if the sum of the expected future cash flows (undiscounted and without interest charges) from an asset are less than the carrying amount of that asset. If an impairment loss is recognized, the amount that will be recorded will be measured as the amount by which the carrying amount of the asset exceeds the fair value of the asset.
Income Taxes and Excise Taxes	Income Taxes and Excise Taxes - MGE Energy and MGE. Income taxes Under the liability method, income taxes are deferred for all temporary differences between pretax financial and taxable income and between the book and tax basis of assets and liabilities using the tax rates scheduled by law to be in effect when the temporary differences reverse. Future tax benefits are recognized to the extent that realization of suc h benefits is more likely than not. A valuation allowance is recorded for those benefits that do not meet this criterion. Accounting for uncertainty in income taxes applies to all tax positions and requires a recognition threshold and measurement standard for the financial statement recognition and measurement of a tax position taken, or expected to be taken, in an income tax return. The threshold is defined for recognizing tax return positions in the financial statements as "more likely than not" that the position is sustainable, based on its merits. Subsequent recognition, derecognition, and measurement is based on management's best judgment given the facts, circumstances, and information available at the reporting date. Regulatory and accounting princip les have resulted in a regulatory liability related to income taxes. Excess deferred income taxes result from past taxes provided at rates higher than current rates. The income tax regulatory liability and deferred investment tax credit reflect the revenue requirement associated with the return of these tax benefits to customers. Investment tax credits from regulated operations are amortized over related property service lives. Excise taxes MGE Energy, through its utility operations, pays a state license fee tax in lieu of property taxes on prope rty used in utility operations. License fee tax is calculated as a percentage of adjusted operating revenues of the prior year. The electric tax rate is 3.19 % for retail sales and 1.59 % for sales of electricity for resale by the purchaser. The tax rate on sales of natural gas is 0.97 % . The tax is required to be estimated and prepaid in the year prior to its computation and expensing. License fee tax expense, included in "Other general taxes ," was $ 14.4 million, $ 14.1 million, and $ 14.5 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively. Operating income taxes, including tax credits and license fee tax, are included in rates for utility related items.
Share-based Compensation	Share-Based Compensation - MGE Energy and MGE. Under two separate incentive plans, eligible participants, including employees and non-employee directors, may receive performance units that entitle the holder to receive a cash payment equal to the value of a designated number of shares of MGE Energy's common stock, plus dividend equivalent payments thereon, at the end of the set performance period set in th e award. Under the plans, these awards are subject to a prescribed vesting schedule and must be settled in cash. Accordingly, no new shares of common stock are issued in connection with the plans. On the grant, date the cost of the employee or director se rvices received in exchange for a performance unit award is measured based on the current market value of MGE Energy common stock. The fair value of the awards is re-measured quarterly through the settlement date. Changes in fair value as well as the origi nal grant are recognized as compensation cost.
Derivative and Hedging Instruments	Derivative and Hedging Instruments - MGE Energy and MGE. As part of regular operations, MGE enters into contracts, including options, swaps, futures, forwards, and other contractual commitments, to manage its exposure to commodity prices. MGE recognizes all derivatives in the consolidated balance sheets at fair value, with changes in the fair value of derivative instruments to be recorded in current earnings or deferred in accumulated other comprehensive income (loss), depending on whether a de rivative is designated as, and is effective as, a hedge and on the type of hedge transaction. Derivative activities are in accordance with the company's risk management policy. If the derivative qualifies for regulatory deferral, the derivatives are mark ed to fair value and are offset with a corresponding regulatory asset or liability. Cash flows from such derivative instruments are classified on a basis consistent with the nature of the underlying hedged item.
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements
New Accounting Pronouncements	Adoption of Accounting Principles and Recently Issued Accounting Pronouncements - MGE Energy and MGE. a. Recently Adopted R evenue from Contracts with Customers. The FASB issued authoritative guidance within the codification's Revenue Recognition topic that provides guidance on the recognition, measurement, and disclosure of revenue from contracts with customers. The new standard establishes a five-step model for recognizing and measuring revenue from contracts with customers and replaces existing guidance on revenue recognition. The underlying principle is that an entity will recognize revenue to present the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. Th is authoritative guidance became effective January 1, 2018, and MGE Energy and MGE adopted the standard upon the effective date. Adoption of this standard was permitted under one of two methods: the full retrospective method or the modified retrospective m ethod. MGE Energy and MGE implemented the standard using the modified retrospective method. The cumulative impact of this guidance on our financial statements is not material, except for additional footnote disclosures. See Footnote 19 for further informat ion. Financial Instruments. In January 2016, the FASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018, and required equity investments to be measured at fair value with changes in fair value recognized in net income rather than in other comprehensive income. As a result of this guidance, MGE Energy and MGE will no longer have other comprehensive income rela ted to equity investments. This standard was applied using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the fiscal year of adoption. As of January 1, 2018, MGE Energy re corded a $0.4 million increase in retained earnings and a corresponding decrease in accumulated other comprehensive income related to equity investments within the scope of this standard. As of January 1, 2018, MGE recorded less than a $0.1 million decreas e in retained earnings and a corresponding increase in accumulated other comprehensive income related to equity investments within the scope of this standard. Restricted Cash. In November 2016, the FASB issued authoritative guidance within the codificati on's Statement of Cash Flows topic that provides guidance on the classification and presentation of changes in restricted cash within the statement of cash flows. Under the new guidance, reporting entities are required to explain the changes in the total o f restricted and unrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, i nvesting, or financing activities within the statement of cash flows based on the nature of the restriction. Reporting entities are now also required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restrictions of cash. This authoritative guidance became effective January 1, 2018. Upon the effective date, MGE Energy and MGE changed the presentation of restricted cash on the consolidated statements of cash flows to reflect the new accounting gu idance retrospectively for all periods presented. See Footnote 1.d. for further information. Pension and Other Postretirement Benefits. In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net benefit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be pre sented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense " increased and "Other income, net" increas ed $4.1 million and $4.3 million for the years ended December 31, 2017 and 2016 , respectively . The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronouncement (wh ereas under previous GAAP all components of net benefit cost were eligible for capitalization). See Footnote 13 for further information. Internal-Use Software – Hosting Arrangements . In August 2018, the FASB issued amended authoritative guidance within t he codification's Intangibles – Goodwill and Other – Internal-Use Software topic. The amended authoritative guidance aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement (hosting arrangement) that is a ser vice contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangement that include an internal-use software license). Costs for implementation activities in the development st age are capitalized depending on the nature of the costs and presented in the same line item on the balance sheet as amounts prepaid for the hosted service. Costs incurred during the preliminary and postimplementation stages are expensed as the activities are performed. The costs capitalized as part of implementation stage should be expensed over the term of the hosting contract, which includes any renewable option periods, and presented in the same line on the income statement as the fees for the associate d hosted service. This amended authoritative guidance will become effective January 1, 2020. Early adoption of the amendment is permitted, including adoption in any interim period. Entities can choose to adopt the new guidance either prospectively, for eligible costs incurred on or after the date this guidance is first applied, or retrospectively. MGE Energy and MGE early adopted these amendments retrospectively as of September 30, 2018 . The cumulative impact of this guidance on our financial statement w as not material, except for additional footnote disclosures. See Footnote 1.t. for disclosures required under this standard. b. Recently Issued Leases. In February 2016, the FASB issued authoritative guidance within the codification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liability. Prior to the authoritativ e guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance, as applied by lessors, is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optio nal practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE adopted this practical expedient. Management has completed a bottoms-up app roach to analyze the impact of the standard on our lease portfolio. MGE Energy and MGE have reviewed current accounting policies and procedures to identify potential differences in accounting treatment that would result from applying the requirements of th e new standard to our existing lease portfolio. In addition, we identified appropriate changes to our business processes, systems, and controls to support recognition and disclosure requirements under the new standard. This authoritative guidance became ef fective January 1, 2019. MGE Energy and MGE adopted the standard upon the effective date. In compliance with authorized transition guidance, MGE Energy and MGE began applying the new standard on January 1, 2019, but will continue to present periods prior t o that date according to the previous authoritative standard. MGE Energy and MGE expec t to recognize approximately $15-$17 million additional lease assets and liabilities under the new standard. We do not expect that it will have a material impact on our c onsolidated net income or cash flows.
Common Equity
Common Stock	MGE Energy sells shares of its common stock through its Stock Plan. Those shares may be newly issued shares or shares that MGE Energy has purchased in the open market for resale to participants in the Stock Plan. All sales under the Stock Plan are covered by a shelf registration statement that MGE Energy filed with the SEC. MGE Energy's transfer agent purchases shares on the open market to provide shares to meet obligations to participants in the Stock Plan. The shares are purchased on the open market through their securities broker-dealer and then are reissued under the Stock Plan as needed to meet share delivery requirements. The volume and timing of share repurchases in the open market depends upon the level of dividend reinvestment and optional share purchases being made from time to time by plan participants. As a result, there is no specific maximum number of shares to be repurchased and no specified termination date for the repurchases.
Income Taxes
Uncertainty in Income Taxes	T he difference between the tax benefit amount taken on prior year tax returns, or expected to be taken on a current year tax return, and the tax benefit amount recognized in the financial statements is accounted for as an unrecognized tax benefit. Unrecognized tax benefits ar e classified with " Other deferred l iabilities " on the consolidated balance sheets. The interest component recoverable in rates is offset by a regulatory asset. As of December 31, 2018 , 2017 , and 2016 , unrecognized tax benefits primarily related to temporary tax differences associated with the change in income tax method of accounting for electric generation and electric and gas distr ibution repairs. In addition, as of December 31, 2018 , unrecognized tax benefits relatin g to permanent differen ces and tax credits was $ 0.3 million . As of December 31, 2017 and 2016 , unrecognized tax benefits relating to permanent differen ces and tax credits was less than $ 0.1 million . The unrecognized tax benefits as of December 31, 2018 , a re not expected to significantly increase or decrease within the next twelve months. In add ition, statutes of limitations will expire for MGE Energy and MGE tax returns. The impact of the statutes of limitations expiring is not anticipated to be material.
Pension Plans and Other Postretirement Benefits
Fair Value of Pension and Other Postretirement Benefit Plan Assets	Pension and other postretirement benefit plan investments are recorded at fair value. See Foo tnote 15 for more information regarding the fair value hierarchy. The following descriptions are the categories of underlying plan assets held within the pension and other postretirement benefit plans as of December 31, 2018 : Cash and Cash Equivalents – This category includes highly liquid investments with maturities of less than three months which are traded in active markets. Equity Securities – These securities consist of U.S. and international stock funds. The U.S. stock funds are primarily invest ed in domestic equities. Securities in these funds are typically priced using the closing price from the applicable exchange, NYSE, Nasdaq, etc. The international funds are composed of international equities. Securities are priced using the closing price f rom the appropriate local stock exchange. Fixed Income Securities – These securities consist of U.S. bond funds and short-term funds. U.S. bond funds are priced by a pricing agent using inputs such as benchmark yields, reported trades, broker/dealer quotes, and issuer spreads. The short-term funds are valued initially a t cost and adjusted for amortization of any discount or premium. Real Estate – Real estate funds are funds with a direct investment in pools of real estate properties. These funds are valued by investment managers on a periodic basis using pricing models that use independent appraisals. The fair value of real estate investments is determined using net asset value. Insurance Continuance Fund (ICF) – The ICF is a supplemental retirement plan that includes assets that have been segregated and restricted to pay retiree term life insurance premiums. Fixed Rate Fund – The Fixed Rate fund is supported by an underlying portfolio of fixed income securities, including public bonds, commercial mortgages, and private placement bonds . Public market data and GAAP repo rted market values are used when available to determine fair value. All of the fair values of MGE's plan assets are measured using net asset value, except for cash and cash equivalents which are considered level 1 investments.
Derivative and Hedging Instruments
Derivative Hedging	As part of its regular operations, MGE enters into contracts, including options, swaps, futures, forwards, and other contractual commitments, to manage its exposure to commodity prices. To the extent that these contracts are derivatives, MGE assesses whether or not the normal purchases or normal sales exclusion applies. For contracts to which this exclusion cannot be applied, the derivatives are recognized in the consolidated bala nce sheets at fair value . MGE's financial commodity derivative activities are conducted in accordance with its electric and gas risk management program, which is approved by the PSCW and limits the volume MGE can hedge with specific risk management strateg ies. The maximum length of time over which cash flows related to energy commodities can be hedged is four years. If the derivative qualifies for regulatory deferral, the derivatives are marked to fair value and are offset with a corresponding regulatory as set or liability depending on whether the derivative is in a net loss or net gain position, respectively . The deferred gain or loss is recognized in earnings in the delivery month applicable to the instrument. Gains and losses related to hedges qualifying for regulatory treatment are recoverable in gas rates through the PGA or in electric rates as a component of the fuel rules mechanism.
Derivative Netting	All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreement as well a s the netting of collateral. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as we ll as the netting of collateral .
Fair Value of Financial Instruments
Recurring Fair Value Measurements	Fair value is defined as the price that would be received to sell an asset or would be paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. The accounting standard clarifies that fair value should be based on the assumptions market participants would use when pricing the asset or liability including ass umptions about risk. The standard also establishes a three level fair value hierarchy based upon the observability of the assumptions used and requires the use of observable market data when available. The levels are: Level 1 - Pricing inputs are quoted p rices within active markets for identical assets or liabilities. Level 2 - Pricing inputs are quoted prices within active markets for similar assets or liabilities; quoted prices for identical or similar instruments in markets that are not active; and mod el-derived valuations that are correlated with or otherwise verifiable by observable market data. Level 3 - Pricing inputs are unobservable and reflect management's best estimate of what market participants would use in pricing the asset or liability. T he carrying amount of cash, cash equivalents, and outstanding commercial paper approximates fair market value due to the short maturity of those investments and obligations. The estimated fair market value of long-term debt is based on quoted market prices for similar financial instruments a s of December 31 . Since long-term debt i s not traded in an active market, it is classified as Level 2. No transfers were made in or out of Level 1 or Level 2 for the year ended December 31 , 2018 . I nvestments include exchange-traded investment securities valued using quoted prices on active exchanges and are therefore classified as Level 1. Derivatives include exchange-traded derivative c ontracts, over-the-counter transactions, a purchased power agreement, and FTRs. Most exchange-traded derivative contracts are valued based on unadjusted quoted prices in active markets and are therefore classified as Le vel 1. A small number of exchange-traded derivative contracts are valued using quoted market pricing in markets with insufficient volumes and are therefore considered unobservable and classified as Level 3. Transactions done with an over-the-counter party are on inactive markets and are therefore classified as Level 3. These transactions are valued based on quoted prices from markets with similar exchange- traded transactions . FTRs are priced based upon monthly auction results for identical or similar instru ments in a closed market with limited data available and are therefore classified as Level 3 . The purchased power agreement (see Footnote 1 4 ) was valued using an internally-developed pricing model and therefore is classified as Level 3. The model project s future market energy prices and compares those prices to the projected power costs to be incurred under the contract . Inputs to the model require significant management judgment and estimation. Future energy prices are based on a forward power pricing cu rve using exchange-traded contracts in the electric futures market . A basis adjustment is applied to the market energy price to reflect the price differential between the market price delivery point and the counterparty delivery point. The historical relat ionship between the delivery points is reviewed and a discount (below 100%) or premium (above 100%) is derived. This comparison is done for both peak times when demand is high and off peak times when demand is low. If the basis adjustment is lowered, the f air value measurement will decrease , and if the basis adjustment is increased, the fair value measurement will increase. The projected power costs anticipated to be incurred under the purchased power agreement are determined using many factors, including historical generating costs, future prices, and expected fuel mix of the counterparty. An increase in the projected fuel costs would result in a decrease in the fair value measurement of the purchased power agreement. A significant input that MGE estimates is the counterparty's fuel mix in determining the projected power cost. MGE also considers the assumptions that market participants would use in valuing the asset or liability. This consideration includes assumptions about market risk such as liquidity, v olatility , and contract duration. The fair value model uses a discount rate that incorporates discounting, credit, and model risks. The following table presents the significant unobservable inputs used in the pricing model as of December 31: Model Input Significant Unobservable Inputs 2018 2017 Basis adjustment: On peak 92.1 % 92.3 % Off peak 92.8 % 94.1 % Counterparty fuel mix: Internal generation 50%-75% 55%-75% Purchased power 50%-25% 45%-25% The deferred compensation plan allows participants to defer certain cash compensation into a notional investment account. These amounts are included within other deferred liabilities in the consolidated balance sheets of MGE Energy and MGE. The notional investments earn interest based upon the semiannual rate of U.S. Treasury Bills having a 26 week maturity increased by 1 % compounded monthly with a minimu m annual rate of 7 %, compounded monthly . The notional investments are based upon observable market data, however, since the deferred compensation obligations themselves are not exchanged in an active market, they are classified as L evel 2 .
Regional Transmission Organizations	Regional Transmission Organizations - MGE Energy and MGE. MGE reports on a net basis transactions on the MISO markets in which it buys and sells power within the same hour to meet electric energy delivery requirements.
Segment Information
Segment Information	Segment Information - MGE Energy and MGE. The electric utility business purchases, generates and distributes electricity, and contracts for transmission service. The gas utility business purchases and distributes natural gas and contracts for the transportation of natural gas. Both the electric and gas segments operate through MGE Energy ' s principal subsidiary, MGE. The nonregulated energy operations are conducted through MGE Energy ' s subsidiaries: MGE Power, MGE Power Elm Road, and MGE Power West Campus . These subsidiaries own and lease electric generating capacity to assist MGE . MGE Power Elm Road has an ownership interest in two coal-fired generating units in Oak Creek, Wisconsin , which are leased to MGE, and MGE Power West Campus owns a control ling interest in the electric generation plant of a natural gas-fired cogeneration facility on the UW campus . MGE Power West Campus's portion is also leased to MGE . The transmission investment segment invests in ATC, a company that provides electric trans mission services primarily in Wisconsin , and ATC Holdco, a company formed to pursue electric transmission development and investments outside of Wisconsin . These investments are held in MGE Transco and MGEE Transco, respectively. See Footnote 6 for further discussion . The "All O ther s" segment includes: corporate, CWDC, MAGAEL, MGE State Energy Services, MGE Services, NGV Fueling Services (dissolved in 2018), and North Mendota . These entities ' operations consist of investing in companies and property which relate to the regulated operations, financing the regulated operations, or owning and operating natural gas compression equipment . General corporate expenses include the cost of executive management, corporate accounting and finance, information technolog y, risk management, human resources and legal functions, and employee benefits that are allocated to electric and gas segments based on formulas prescribed by the PSCW. Identifiable assets are those used in MGE 's operations in each segment. Sales between our electric and gas segments are based on PSCW approved tariffed rates. Additionally, intersegment operations related to the leasing arrangement between our el ectric segment and MGE Power Elm Road /MGE Power West Campus are based on terms previously approved by the PSCW. Consistent with internal reporting, management has presented the direct financing capital leas e s between MGE and MGE Power Elm Road /MGE Power West Campus based on actual lease payments included in rates. Lease payments made by MGE to MGE Power Elm Road and MGE Power West Campus are shown as operating expenses. The lease payments received by MGE Power Elm Road and MGE Power West Campus from MGE are shown as lease income in interdepartmental revenues. The depreciation expense associated with the Elm Road Units and WCCF is reflected in the nonregulated energy segment.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Cash, Cash Equivalents, and Restricted Cash	The following table presents the components of total cash, cash equivalents, and restricted cash on the consolidated balance sheets. (In thousands) MGE Energy MGE As of December 31, 2018 2017 2018 2017 Cash and cash equivalents $ 83,102 $ 107,952 $ 4,843 $ 5,951 Restricted cash 634 1,635 634 1,635 Receivable - margin account 1,193 2,507 1,193 2,507 Cash, cash equivalents, and restricted cash $ 84,929 $ 112,094 $ 6,670 $ 10,093
Retrospective Adjustments to Cash Flows	Retrospective adjustments to cash flow amounts on MGE Energy's and MGE's consolidated statements of cash flows in accordance with the adoption of ASU 2016-18, Restricted Cash for th e years ended December 31, were as follows: (In thousands) 2017 2016 Cash provided by operating activities $ (1,618) $ 351 Cash used for investing activities 86 13 Change in cash, cash equivalents, and restricted cash (1,532) 364 Cash, cash equivalents, and restricted cash at beginning of period 5,674 5,310 Cash, cash equivalents, and restricted cash at end of period $ 4,142 $ 5,674
Schedule of Remaining Contractual Maturities for Chattel Paper Agreements	As of December 31, 2018 , the remaining contractual maturities of the chattel paper agreements were as follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Repurchase-to-Maturity Transactions: Loans $ 396 $ 407 $ 392 $ 354 $ 510 $ 122
Straight-Line Depreciation Rates	Provisions at composite straight-line depreciation rates ap proximate the following percentages for the cost of depreciable property: 2018 2017 2016 Electric (a)(b) 2.9 % 3.0 % 2.5 % Gas (a) 2.1 % 2.1 % 2.1 % Nonregulated 2.3 % 2.3 % 2.3 % (a ) In December 2015, the PSCW approved new depreciation rates, which were implemented and became effective as of January 1, 2016. (b) In September 2016, the PSCW approved new depreciation rates for Columbia effective January 1, 2017.

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2018
Variable Interest Entity [Line Items]
Variable interest entities significant balance sheet accounts	As of December 31, MGE has included the following significant accounts on its consolidated b alance sheets related to its interest in these VIEs: MGE Power Elm Road MGE Power West Campus (In thousands) 2018 2017 2018 2017 Property, plant, and equipment, net $ 173,464 $ 176,002 $ 81,273 $ 80,282 Construction work in progress 530 1,225 478 610 Affiliate receivables - - 3,707 4,236 Deferred income taxes 30,595 29,256 14,222 13,795 Long-term debt (a) 56,806 59,416 41,496 43,262 Noncontrolling interest 97,519 97,635 43,935 43,267 (a) MGE Power Elm Road ' s long-term debt includes debt issuance costs of $ 0.5 million and $ 0.6 million as of December 31, 2018 and 2017 , respectively. The debt is secured by a collateral assignment of lease payments that MGE makes to MGE Power Elm Road for use of the Elm Road Units pursuant to the related long-term leases. MGE Power West Campus ' s long-term debt includes debt issuance cos ts of $ 0.1 million as of December 31, 2018 and 2017 . The debt is secured by a collateral assignment of lease payments that MGE makes to MGE Power West Campus for use of the cogeneration facility pursuant to the long-term lease. See Footnote 10 for further information on the long-term debt securities.

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant, and Equipment	Property, plant, and equipm ent consisted of the following as of December 31: MGE Energy MGE (In thousands) 2018 2017 2018 2017 Utility: Electric (a)(b) $ 1,310,421 $ 1,209,336 $ 1,310,438 $ 1,209,353 Gas 442,581 415,542 442,593 415,553 Total utility plant 1,753,002 1,624,878 1,753,031 1,624,906 Less: Accumulated depreciation and amortization (a)(b) 639,486 599,469 639,486 599,469 In-service utility plant, net 1,113,516 1,025,409 1,113,545 1,025,437 Nonregulated: Nonregulated 322,855 319,611 322,855 319,611 Less: Accumulated depreciation and amortization 66,605 61,707 66,605 61,707 In-service nonregulated plant, net 256,250 257,904 256,250 257,904 Construction work in progress: Utility construction work in progress (a)(c) 138,663 56,208 138,663 56,208 Nonregulated construction work in progress 1,008 1,836 1,008 1,836 Total property, plant, and equipment $ 1,509,437 $ 1,341,357 $ 1,509,466 $ 1,341,385 (a ) As of December 31, 2018 and 2017 , MGE has classified $ 3.1 million and $ 8.8 million, respectively, of Columbia assets as held-for-sale on the consolidated balance sheets related to the partial sale of plant assets to WPL. See Footnote 5.a. for further discussion. (b) In April 2018, MGE, along with two other utilities, purchased the Forward Wind Energy Center (Forward Wind), which consists of 86 wind turbines located in Wisconsin. The aggregate purchase price was approximately $ 174 million, of which MGE's proportionate share is 12.8 %, or approximately $ 23 million. (c) In December 2017, the PSCW authorized construction of a 66 MW wind farm, consisting of 33 turbines, located near Saratoga, Iowa. MGE received specific approval to recover 100 % AFUDC on the project. As of December 31, 2018 , MG E has incurred $ 95.8 million of capital expenditures. After tax, MGE has recognized $ 2.5 million in AFUDC equity related to this project for the year ended December 31, 2018 . Construction of the project was completed in February 2019 .

Joint Plant Ownership (Tables)

Joint Plant Ownership (Tables)	12 Months Ended
	Dec. 31, 2018
Columbia Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Schedule of Joint Plant Ownership	MGE's interest in Columbia' s gross utility plant in servic e, and the related accumulated depreciation reserves a s of December 31 were as follows: (In thousands) 2018 2017 Utility plant $ 292,157 $ 274,450 Accumulated depreciation (94,766) (87,144) Property, plant, and equipment, net 197,391 187,306 Construction work in progress 2,021 20,382 Total property, plant, and equipment $ 199,412 $ 207,688
Elm Road Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Schedule of Joint Plant Ownership	MGE Power Elm Road ' s interest in the portion of the Elm Road Units in-service and the related accumulated depreciation reserves a s of December 31 were as follows: (In thousands) 2018 2017 Nonregulated plant $ 207,361 $ 206,063 Accumulated depreciation (33,897) (30,061) Property, plant, and equipment, net 173,464 176,002 Construction work in progress 530 1,225 Total property, plant, and equipment $ 173,994 $ 177,227
Forward Wind [Member]
Jointly Owned Utility Plant Interests [Line Items]
Schedule of Joint Plant Ownership	MGE's interest in the portion of Forward Wind ' s utility plant in service and the related accumulated depreciation reserves as of December 31 were as follows: (In thousands) 2018 Nonregulated plant $ 33,929 Accumulated depreciation (12,530) Property, plant, and equipment, net 21,399 Construction work in progress 67 Total property, plant, and equipment $ 21,466
West Campus [Member]
Jointly Owned Utility Plant Interests [Line Items]
Schedule of Joint Plant Ownership	MGE Power West Campus' interest in WCCF and the related a ccu mulated depreciation reserves as of December 31 were as follows: (In thousands) 2018 2017 Nonregulated plant $ 113,328 $ 111,386 Accumulated depreciation (32,055) (31,104) Property, plant, and equipment, net 81,273 80,282 Construction work in progress 478 610 Total property, plant, and equipment $ 81,751 $ 80,892

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments Disclosure [Abstract]
Equity Method, Available for Sale Securities, and Other Investments	MGE Energy MGE (In thousands) 2018 2017 2018 2017 Equity securities (a) $ 9,363 $ 7,291 $ 388 $ 409 Equity method investments: ATC and ATC Holdco (b) 66,313 59,298 - - Other 26 1,128 - - Total equity method investments 66,339 60,426 - - Other investments 2,298 55 - - Total $ 78,000 $ 67,772 $ 388 $ 409 (a ) Reflects modified retrospective application of new authoritative guidance related to Financial Instruments as described in Footnote 2. Prior to January 1, 2018, investments were considered available for sale securities. As of December 31, 2017, MGE Energy had available for sale securities with a cost basis of $6.7 million, gross unrealized gains of $0.7 million, and gross unrealized losses of less than $0.1 million. As of December 31, 2017, MGE had available for sale securities with a cost basis of $ 0.5 million and gross unrealized losses of less than $0.1 million. (b) In December 2017, there was a $ 20.4 million one-time tax impact related to ATC as a result of the Tax Act. See Footnote 12 for further information. During the years ended December 31, 2018 , 2017 , and 2016 , certain inves tments were liquidated. As a re sult of these liquidations, MGE Energy and MGE received the following: MGE Energy MGE (In thousands) 2018 2017 2016 2018 2017 2016 Cash proceeds $ 960 $ 677 $ 408 $ 3 $ - $ 16 Gain (loss) on sale 476 522 121 3 - (8)
Equity Method Investments Summarized Financial Data	For the years ended December 31, 2018 , 2017 , and 2016 , MGE Transco recorded the following: (In thousands) 2018 2017 2016 Equity earnings from investment in ATC $ 8,821 $ 10,125 $ 8,670 Dividends received from ATC (a) 4,611 9,078 7,926 Capital contributions to ATC 2,841 3,551 2,486 (a ) MGE Transco recorded a $ 2.3 million and a $ 2.1 million dividend receivable from ATC as of December 31, 2017 and 2016 , respectively. A cash dividend was received in January of each of the proceeding years. ATC's summarized financial data is as follows: (In thousands) Income statement data for the year ended December 31, 2018 2017 2016 Operating revenues $ 690,510 $ 721,672 $ 650,806 Operating expenses (358,703) (346,308) (323,947) Other income 2,405 7,402 5,361 Interest expense, net (110,725) (110,138) (99,464) Earnings before members' income taxes $ 223,487 $ 272,628 $ 232,756 Balance sheet data as of December 31, 2018 2017 Current assets $ 87,250 $ 87,730 Noncurrent assets 4,928,793 4,598,919 Total assets $ 5,016,043 $ 4,686,649 Current liabilities $ 640,040 $ 767,248 Long-term debt 2,013,997 1,790,590 Other noncurrent liabilities 295,281 240,286 Members' equity 2,066,725 1,888,525 Total members' equity and liabilities $ 5,016,043 $ 4,686,649

Regulatory Assets and Liabili_2

Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	The following regulatory assets and liab ilities are reflected in MGE's c onsolidated b alance s heet s as of December 31: (In thousands) 2018 2017 Regulatory Assets Asset retirement obligation $ 9,199 $ 8,328 Conservation costs 81 222 Debt related costs 9,288 9,749 Derivatives 31,830 41,958 Tax recovery related to AFUDC equity 6,482 5,497 Unfunded pension and other postretirement liability 96,030 84,342 Other 1,991 359 Total Regulatory Assets $ 154,901 $ 150,455 Regulatory Liabilities Deferred fuel savings $ 9,504 $ 4,229 Elm Road 2,515 931 Income taxes 135,449 131,689 Non-ARO removal costs 19,891 18,536 Pension and other postretirement service costs 3,669 - Purchased gas adjustment 1,186 1,404 Renewable energy credits 700 454 Transmission 5,476 1,967 Other 1,074 576 Total Regulatory Liabilities $ 179,464 $ 159,786

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	December 31, (In thousands) 2018 2017 First Mortgage Bonds: (a) 7.70%, 2028 Series $ 1,200 $ 1,200 Tax Exempt Debt: 3.45%, 2027 Series, Industrial Development Revenue Bonds 19,300 19,300 Medium-Term Notes: (b) 6.12%, due 2028 20,000 20,000 7.12%, due 2032 25,000 25,000 6.247%, due 2037 25,000 25,000 Total Medium-Term Notes 70,000 70,000 Other Long-Term Debt: (d) 5.59%, due 2018 (c)(e) - 20,000 3.38%, due 2020 (e) 15,000 15,000 3.09%, due 2023 (e) 30,000 30,000 3.29%, due 2026 (e) 15,000 15,000 3.11%, due 2027 (e) 30,000 30,000 5.68%, due 2033 (f) 25,064 26,121 5.19%, due 2033 (f) 16,561 17,290 5.26%, due 2040 (e) 15,000 15,000 5.04%, due 2040 (g) 35,139 36,806 4.74%, due 2041 (g) 22,167 23,166 4.38%, due 2042 (e) 28,000 28,000 4.42%, due 2043 (e) 20,000 20,000 4.47%, due 2048 (e) 20,000 20,000 3.76%, due 2052 (e) 40,000 40,000 4.19%, due 2048 (c)(e) 60,000 - 4.24%, due 2053 (c)(e) 20,000 - 4.34%, due 2058 (c)(e) 20,000 - Total Other Long-Term Debt 411,931 336,383 Long-term debt due within one year (4,553) (24,452) Unamortized discount and debt issuance costs (4,535) (4,270) Total Long-Term Debt $ 493,343 $ 398,161 (a) MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust, under which its first mortgage bonds are issued. The Mortgage Indenture provides that dividends or any other distribution or purchase of shares may not be made if the aggregate amount thereof since December 31, 1945 , would exceed the earned surplus (retained earnings) accumulated subsequent to December 31, 1945. As of December 31, 2018 , approximately $ 400.0 m illion was available for the payment of dividends under this covenant. (b ) T he indenture under which MGE's Medium-T erm notes are issued provides that those notes will be entitled to be equally and ratably secured in the event that MGE issues any additional firs t mortgage bonds. (c ) In July 2018, MGE issued a total of $ 4 0 million of new long-term unsecured debt. In September 2018, MGE issued $60 million of new long-term unsecured debt. MGE used the net proceeds from these debt financings to assist with financing capital expenditures, such as the Saratoga Wind Farm, and to refinance $20 million of long-term debt w hich matured in September 2018. (d ) Unsecured notes issued pursuant to various Note Purchase Agreements with one or more purchasers. The notes are not i ssued under, or governed by, MGE ' s Indenture dated as of September 1, 1998, which governs MGE ' s Medium-Term Notes. (e ) Issued by MGE. Under that Note Purchase Agreement: (i) note holders have the right to require MGE to repurchase their notes at par in the event of an acquisition of beneficial ownership of 30 % or more of the outstanding vot ing stock of MGE Energy, (ii) MGE must maintain a ratio of its consolidated indebtedness to consolidated total capitalization not to exceed a maximum of 65 %, and (iii) MGE cannot issue "Priority Debt" in an amount exceeding 20 % of its consolidated assets. Priority Debt is defined as any indebtedness of MGE secured by liens other than specified liens permitted by the Note Purchase Agreement and certain unsecured indebtedness of certain subsidiaries. As of December 31, 2018 , MGE was in compliance with the covenant requirements. (f ) Issued by MGE Power West Campus. The Note Purchase Agreements require it to maintain a projected debt service coverage ratio of not less than 1.25 to 1.00 , and debt to total capitalization ratio of not more than 0.65 to 1.00 . The notes are secured by a collateral assignment of lease payments that MGE is making to MGE Power West Campus for use of its ownership interest in the WCCF pursuant to a long-term lease. As of December 31, 2018 , MGE Power West Campus was in compliance with the covenant requirements. (g) Issued by M GE Power Elm Road. The Note Purchase Agreement requires MGE Power Elm Road to maintain a projected and actual debt service coverage ratio at the end of any calendar quarter of not less than 1.25 to 1.00 for the trailing 12-month period. The notes are secured by a collateral assignment of lease payments that MGE is making to MGE Power Elm Road for use of its ownership interest in the Elm Road Units pursuant to long-term leases. As of December 31, 2018 , MGE Power Elm Road was in compliance with the covenant requirements.
Schedule of Long-Term Debt Maturities	Below is MGE Energy's and MGE's aggregate maturities for all long-term debt for years following December 31, 2018 . (In thousands) 2019 2020 2021 2022 2023 Thereafter Long-term debt maturities $ 4,553 $ 19,659 $ 4,771 $ 4,889 $ 35,014 $ 433,545

Notes Payable to Banks, Comme_2

Notes Payable to Banks, Commercial Paper, and Lines of Credit (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Short-Term Borrowings	Information concerning short-term borrowings is shown below: (In thousands) MGE Energy (a) MGE As of December 31, 2018 2017 2018 2017 Available lines of credit $ 150,000 $ 150,000 $ 100,000 $ 100,000 Short-term debt outstanding $ 13,000 $ 4,000 $ 13,000 $ 4,000 Weighted-average interest rate 2.55 % 1.55 % 2.55 % 1.55 % Year Ended December 31, Maximum short-term borrowings $ 31,500 $ 7,500 $ 31,500 $ 7,500 Average short-term borrowings $ 9,211 $ 304 $ 9,211 $ 304 Weighted-average interest rate 1.92 % 1.18 % 1.92 % 1.18 % (a) MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Tax Provision	On a consolidated and separate company basis, the income tax provision consists of the following provision (benefit) components for the years ended December 31 : MGE Energy MGE (In thousands) 2018 2017 2016 2018 2017 2016 Current payable: Federal $ 18,622 $ 21,125 $ 16,908 $ 19,926 $ 21,512 $ 17,521 State 5,163 5,129 3,287 5,704 5,316 3,497 Net-deferred: Federal 120 (8,346) 17,571 (2,563) (11,195) 16,391 State 3,629 4,264 4,850 2,494 3,435 4,485 Amortized investment tax credits (100) (78) (103) (100) (78) (103) Total income tax provision $ 27,434 $ 22,094 $ 42,513 $ 25,461 $ 18,990 $ 41,791
Effective Tax Rate Reconciliation	The consolidated income tax provision differs from the amount computed by applying the statutory federal income tax rate to income before income taxes, as follows: MGE Energy MGE 2018 2017 2016 2018 2017 2016 Statutory federal income tax rate 21.0 % 35.0 % 35.0 % 21.0 % 35.0 % 35.0 % State income taxes, net of federal benefit 6.3 % 5.1 % 5.1 % 6.2 % 5.1 % 5.1 % Amortized investment tax credits (0.1) % - % (0.1) % (0.1) % - % (0.1) % Credit for electricity from wind energy (0.3) % (1.6) % (1.6) % (0.4) % (1.7) % (1.7) % Domestic manufacturing deduction - % (1.4) % (1.3) % - % (1.5) % (1.3) % AFUDC equity, net (0.6) % (0.2) % (0.2) % (0.5) % (0.2) % (0.2) % Federal income tax rate reduction - % (18.1) % - % - % (19.3) % - % Amortization of utility excess deferred tax (a) (1.8) % - % - % (2.0) % - % - % Other, net, individually insignificant 0.1 % (0.3) % (0.9) % 0.2 % (0.4) % (0.9) % Effective income tax rate 24.6 % 18.5 % 36.0 % 24.4 % 17.0 % 35.9 % (a) Included are impacts of the Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting.
Deferred Tax Liabilities (Assets)	MGE Energy MGE (In thousands) 2018 2017 2018 2017 Deferred tax assets Investment in ATC 23,638 24,781 - - Accrued expenses 15,385 15,135 15,385 15,135 Pension and other postretirement benefits 34,914 32,196 34,914 32,196 Deferred tax regulatory account 37,121 36,124 37,121 36,124 Derivatives 8,861 11,525 8,861 11,525 Other 15,137 12,790 15,185 12,831 Gross deferred income tax assets 135,056 132,551 111,466 107,811 Less valuation allowance (86) (86) (86) (86) Net deferred income tax assets 134,970 132,465 111,380 107,725 Deferred tax liabilities Property-related $ 244,114 $ 238,437 $ 244,114 $ 238,544 Investment in ATC 50,771 48,324 - - Bond transactions 765 832 765 832 Pension and other postretirement benefits 47,644 42,919 47,644 42,919 Derivatives 8,861 11,525 8,861 11,525 Tax deductible prepayments 6,014 6,169 6,014 6,169 Other 8,753 9,389 8,598 9,222 Gross deferred income tax liabilities 366,922 357,595 315,996 309,211 Deferred income taxes $ 231,952 $ 225,130 $ 204,616 $ 201,486
Schedule Of Remeasurements Of Deferred Income Taxes Due To Tax Reform [Table Text Block]	The one-time impacts recorded to remeasure deferred income tax balances at the 21 percent corpo rate federal income tax rate as of December 31, 2017 were as follows: (In thousands) MGE Energy MGE Net Decrease in Deferred Tax Liability $ 176,871 $ 156,493 Decrease in Regulatory Asset 4,347 4,347 Increase in Regulatory Liability (b) 130,497 130,497 Decrease in Investment ATC 20,375 - Net Deferred Income Tax Benefit Recorded (c) 21,651 21,649 (b) Given that changes in income taxes are generally passed through in customer rates for the regulated utility, a regu latory liability was recorded. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, which will be subject to review by the PSCW. A portion of the regulatory liability will be returned to customers based on a mandated timeframe dictated by applicable tax laws. (c) Generated by nonregulated activities.
Unrecognized Tax Benefits and Interest	A tabular reconciliation o f unrecognized tax benefits and is as follows: (In thousands) Unrecognized Tax Benefits: 2018 2017 2016 Unrecognized tax benefits, January 1, $ 1,924 $ 2,487 $ 2,528 Additions based on tax positions related to the current year 425 552 452 Additions based on tax positions related to the prior years 272 19 39 Reductions based on tax positions related to the prior years (672) (1,134) (532) Unrecognized tax benefits, December 31, $ 1,949 $ 1,924 $ 2,487 (In thousands) Interest on Unrecognized Tax Benefits: 2018 2017 2016 Accrued interest on unrecognized tax benefits, January 1, $ 165 $ 388 $ 311 Reduction in interest expense on uncertain tax positions (136) (312) (27) Interest expense on uncertain tax positions 162 89 104 Accrued interest on unrecognized tax benefits, December 31, $ 191 $ 165 $ 388
Tax Years that Remain Subject to Examination	The following table shows tax years that remain subject to examination by major jurisdictio n: Taxpayer Open Years MGE Energy and consolidated subsidiaries in federal return 2015 through 2018 MGE Energy Wisconsin combined reporting corporation return 2013 through 2018

Pension Plans and Other Postr_2

Pension Plans and Other Postretirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2018
Compensation and Retirement Disclosure [Abstract]
Schedule of Benefit Obligations and Change in Plan Assets	(In thousands) Pension Benefits Other Postretirement Benefits Change in Benefit Obligations: 2018 2017 2018 2017 Net benefit obligation at beginning of year $ 391,269 $ 349,556 $ 82,290 $ 78,842 Service cost 5,723 5,383 1,283 1,231 Interest cost 12,859 12,625 2,612 2,666 Plan participants' contributions - - 950 894 Actuarial (gain) loss (a) (34,439) 37,689 (7,555) 2,749 Gross benefits paid (15,124) (13,984) (4,623) (4,262) Less: federal subsidy on benefits paid (b) - - 204 170 Benefit obligation at end of year $ 360,288 $ 391,269 $ 75,161 $ 82,290 Change in Plan Assets: Fair value of plan assets at beginning of year $ 361,651 $ 311,933 $ 48,470 $ 43,177 Actual return on plan assets (24,485) 56,987 (2,780) 7,104 Employer contributions 1,738 6,715 504 1,557 Plan participants' contributions - - 950 894 Gross benefits paid (15,124) (13,984) (4,623) (4,262) Fair value of plan assets at end of year $ 323,780 $ 361,651 $ 42,521 $ 48,470 Funded Status as of December 31 $ (36,508) $ (29,618) $ (32,640) $ (33,820) (a) In 2018, higher discount rates were the main driver of the actuarial gain. However, in 2017, lower discount rates were the main driver of the actuarial loss. (b) In 2003, the Medicare Prescription Drug, Improvement and Modernization Act of 2003 was signed into law authorizing Medicare to provide prescription drug benefits to retirees. For the years ended December 31, 2018 and 2017 , the subsidy due to MGE was $ 0.2 million.
Schedule of Amounts Recognized in the Consolidated Balance Sheet	The amounts recognized in the consolidated balance sheets to reflect the funded status of the plans as of December 31 are as follows: Pension Benefits Other Postretirement Benefits (In thousands) 2018 2017 2018 2017 Long-term asset $ - $ 7,336 $ - $ - Current liability (1,732) (1,726) - - Long-term liability (34,776) (35,228) (32,640) (33,820) Net liability $ (36,508) $ (29,618) $ (32,640) $ (33,820)
Amounts Recognized in Regulatory Asset	The following table shows the amounts that have not yet been recognized in our net periodic benefit cost as of December 31 and are recorded as regulatory assets in the consolidated balance sheets: Pension Benefits Other Postretirement Benefits (In thousands) 2018 2017 2018 2017 Net actuarial loss $ 92,978 $ 81,969 $ 10,569 $ 12,600 Prior service benefit (385) (429) (7,153) (9,821) Transition obligation - - 21 23 Total $ 92,593 $ 81,540 $ 3,437 $ 2,802
Scehdule of Projected Benefit Obligations in Excess of Plan Assets	The projected benefit obligation and fair value of plan assets for pension plans with a projected benefit obligation in excess of plan assets were as follows: (In thousands) Pension Benefits Projected Benefit Obligation in Excess of Plan Assets 2018 2017 Projected benefit obligation, end of year $ 360,288 $ 36,954 Fair value of plan assets, end of year 323,780 -
Schedule of Accumulated Benefit Obligations in Excess of Plan Assets	The accumulated benefit obligation and fair value of plan assets for pension plans with an accumulated benefit obligation in excess of plan assets were as follows: (In thousands) Pension Benefits Accumulated Benefit Obligation in Excess of Plan Assets 2018 2017 Accumulated benefit obligation, end of year $ 31,200 $ 32,813 Fair value of plan assets, end of year - -
Net Periodic Benefit Costs	(In thousands) Pension Benefits Other Postretirement Benefits Components of Net Periodic Benefit Cost: 2018 2017 2016 2018 2017 2016 Service cost $ 5,723 $ 5,383 $ 5,365 $ 1,283 $ 1,231 $ 1,271 Interest cost 12,859 12,625 12,393 2,612 2,666 2,681 Expected return on assets (26,241) (22,963) (22,365) (3,232) (2,887) (2,829) Amortization of: Transition obligation - - - 3 3 3 Prior service (credit) cost (44) (17) 10 (2,669) (2,669) (2,669) Actuarial loss 5,278 6,352 5,600 488 660 589 Net periodic benefit cost (credit) $ (2,425) $ 1,380 $ 1,003 $ (1,515) $ (996) $ (954)
Plan Assumptions	The weighted-average assumptions used to determine the benefit obligations were as follows for the years ended December 31: Pension Benefits Other Postretirement Benefits 2018 2017 2018 2017 Discount rate 4.32 % 3.73 % 4.24 % 3.58 % Rate of compensation increase 3.20 % 3.67 % N/A N/A Assumed health care cost trend rates: Health care cost trend rate assumed for next year N/A N/A 6.25 % 6.00 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) N/A N/A 5.00 % 5.00 % Year that the rate reaches the ultimate trend rate N/A N/A 2024 2022 The weighted-average assumptions used to determine the net periodic cost were as follows for the years ended December 31: Pension Benefits Other Postretirement Benefits 2018 2017 2016 2018 2017 2016 Discount rate 3.73 % 4.30 % 4.51 % 3.60 % 4.09 % 4.32 % Expected rate of return on plan assets 7.40 % 7.40 % 7.65 % 6.94 % 6.80 % 6.96 % Rate of compensation increase 3.72 % 3.76 % 3.76 % N/A N/A N/A
Effect of 1% Increase or Decrease in Health Care Costs	The following table shows how an assumed 1% increase or 1% decrease in health care cost trends could impact postretirement benefits in 2018 d ollars: (In thousands) 1% Increase 1% Decrease Effect on other postretirement benefit obligation $ 754 $ (980) Effect on total service and interest cost components 21 (30)
Fair Value of Plan Assets by Asset Category	The asset allocation for MGE's pension plans as of December 31, 2018 and 2017 , and the target al location for 2019 , by asset category, follows : Target Allocation Percentage of Plan Assets at Year End 2018 2017 Equity securities (a) 63.0 % 60.0 % 65.0 % Fixed income securities 30.0 % 33.0 % 29.0 % Real estate 7.0 % 7.0 % 6.0 % Total 100.0 % 100.0 % 100.0 % (a) Target allocations for equity securities are broken out as follows: 45.5 % United States equity, 17.5 % non- United States equity . All of the fair values of MGE's plan assets are measured using net asset value, except for cash and cash equivalents which are considered level 1 investments. The fair values of MGE ' s pla n assets by asset category as of December 31 are as follows: (In thousands) 2018 2017 Cash and Cash Equivalents $ 701 $ 488 Equity Securities: U.S. Large Cap 102,984 124,594 U.S. Mid Cap 23,683 29,138 U.S. Small Cap 28,573 37,782 International Blend 61,299 71,514 Fixed Income Securities: Short-Term Fund 4,053 4,641 High Yield Bond 19,437 19,400 Long Duration Bond 93,216 91,678 Real Estate 27,923 25,995 Insurance Continuance Fund 1,491 1,500 Fixed Rate Fund 2,941 3,391 Total $ 366,301 $ 410,121
Benefit Payments, Fiscal Year Maturity	The following benefit payments, which reflect expec ted future service, as appropriate, are expected to be paid as follows: Pension Other Postretirement Benefits (In thousands) Pension Benefits Gross Postretirement Benefits Expected Medicare Part D Subsidy Net Postretirement Benefits 2019 $ 16,362 $ 4,248 $ (228) $ 4,020 2020 17,087 4,585 (252) 4,333 2021 17,835 4,994 (276) 4,718 2022 18,956 5,325 (305) 5,020 2023 19,770 5,604 (334) 5,270 2024 - 2028 110,037 29,478 (2,103) 27,375

Derivative and Hedging Instru_2

Derivative and Hedging Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross Notional Volume of Open Derivatives	The gross notional volume of open derivatives is as follows: December 31, 2018 December 31, 2017 Commodity derivative contracts 386,440 MWh 552,310 MWh Commodity derivative contracts 5,260,000 Dth 5,460,000 Dth FTRs 2,252 MW 2,226 MW PPA 2,050 MW 2,650 MW
Fair Value of Derivative Instruments on the Balance Sheet	The following table summarizes the fair value of the derivative instruments on the consolidated balance sheet s . All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreement as well a s the netting of collateral. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as we ll as the netting of collateral . (In thousands) Derivative Assets Derivative Liabilities Balance Sheet Location December 31, 2018 Commodity derivative contracts (a) $ 727 $ 270 Other current assets Commodity derivative contracts (a) 74 72 Other deferred charges FTRs 241 - Other current assets PPA N/A 8,550 Derivative liability (current) PPA N/A 23,980 Derivative liability (long-term) December 31, 2017 Commodity derivative contracts (a) $ 566 $ 603 Derivative liability (current) (b) Commodity derivative contracts (a) 110 190 Derivative liability (long-term) FTRs 329 - Other current assets PPA N/A 8,180 Derivative liability (current) PPA N/A 33,990 Derivative liability (long-term) (a ) As of December 31, 2017 , collateral of $ 0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions as of December 31, 2018 . (b) As of December 31, 2017 , MGE presented $ 0.1 million as other current assets on the consolidated balance sheets.
Offsetting Assets	The following tables show the effect of netting arrangements for recognized deriva tive assets and liabilities that are subject to a master netting arrangement or similar arrangement on the consolidated balance sheets. Offsetting of Derivative Assets (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets December 31, 2018 Commodity derivative contracts $ 801 $ (342) $ - $ 459 FTRs 241 - - 241 December 31, 2017 Commodity derivative contracts $ 676 $ (654) $ - $ 22 FTRs 329 - - 329
Offsetting Liabilities	Offsetting of Derivative Liabilities (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets December 31, 2018 Commodity derivative contracts $ 342 $ (342) $ - $ - PPA 32,530 - - 32,530 December 31, 2017 Commodity derivative contracts $ 793 $ (654) $ (139) $ - PPA 42,170 - - 42,170
Derivative Gains and Losses in Balance Sheet	The following tables summarize the unrealized and realized gains/losses related to the derivative instruments on the consolidated balance sheets as of December 31, 2018 and 2017 , and the consolidated statements of income for the years ended December 31, 2018 and 2017 . 2018 2017 Current and Long-Term Regulatory Asset Other Current Assets Current and Long-Term Regulatory Asset Other Current Assets (In thousands) Balance as of January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized gain (11,094) - (2,743) - Realized gain (loss) reclassified to a deferred account 523 (523) (1,260) 1,260 Realized loss reclassified to income statement 443 94 (3,320) (684) Balance as of December 31, $ 31,830 $ 377 $ 41,958 $ 806
Derivative Gains and Losses in Income Statement	Realized Losses (Gains) 2018 2017 (In thousands) Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Year Ended December 31: Commodity derivative contracts $ (716) $ (199) $ 786 $ 634 FTRs (702) - (1,464) - PPA 1,080 - 4,048 -

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Estimated Fair Market Value of Financial Instruments	The estimated fair market value of financial instruments are as follows: December 31, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 83,102 $ 83,102 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper 13,000 13,000 4,000 4,000 Long-term debt (a) 502,431 518,811 426,883 475,282 MGE Assets: Cash and cash equivalents $ 4,843 $ 4,843 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper 13,000 13,000 4,000 4,000 Long-term debt (a) 502,431 518,811 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.5 million and $4.3 million as of December 31, 2018 and 2017, respectively.
Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table presents the balances of assets and liabilities measured at fair value on a recurring basis . Fair Value as of December 31, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,042 $ 296 $ - $ 746 Exchange-traded investments 848 848 - - Total Assets $ 1,890 $ 1,144 $ - $ 746 Liabilities: Derivatives, net $ 32,872 $ 124 $ - $ 32,748 Deferred compensation 3,078 - 3,078 - Total Liabilities $ 35,950 $ 124 $ 3,078 $ 32,748 MGE Assets: Derivatives, net $ 1,042 $ 296 $ - $ 746 Exchange-traded investments 43 43 - - Total Assets $ 1,085 $ 339 $ - $ 746 Liabilities: Derivatives, net $ 32,872 $ 124 $ - $ 32,748 Deferred compensation 3,078 - 3,078 - Total Liabilities $ 35,950 $ 124 $ 3,078 $ 32,748 Fair Value as of December 31, 2017 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 792 792 - - Total Assets $ 1,797 $ 1,070 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 MGE Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 64 64 - - Total Assets $ 1,069 $ 342 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 (b) These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of December 31, 2017.
Significant Unobservable Inputs	The following table presents the significant unobservable inputs used in the pricing model as of December 31: Model Input Significant Unobservable Inputs 2018 2017 Basis adjustment: On peak 92.1 % 92.3 % Off peak 92.8 % 94.1 % Counterparty fuel mix: Internal generation 50%-75% 55%-75% Purchased power 50%-25% 45%-25%
Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table summarizes the changes in Level 3 commodity derivative assets and liabilities measured at fair value on a recurring basis . (In thousands) 2018 2017 2016 Balance as of January 1, $ (42,026) $ (50,306) $ (53,501) Realized and unrealized gains (losses): Included in regulatory liabilities 10,024 8,281 3,195 Included in other comprehensive income - - - Included in earnings 132 (3,718) (5,347) Included in current assets (47) (9) (142) Purchases 23,643 24,181 23,346 Sales - - - Issuances - - - Settlements (23,728) (20,455) (17,857) Transfers in and/or out of Level 3 - - - Balance as of December 31, $ (32,002) $ (42,026) $ (50,306) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, (c) $ - $ - $ - ( c ) MGE's exchange-traded derivative contracts, over-the-count er party transactions, purchased power agreement, and FTRs are subject to regulatory deferral. These derivatives are therefore marked to fair value and are offset in the financial statements with a corresponding regulatory asset or liability.
Gains and Losses Included in Income for Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table presents total realized and unrealized gains (losses) included in income for Level 3 assets and liabiliti es measured at fair value on a recurring basis (c ) . (In thousands) Year Ended December 31, 2018 2017 2016 Purchased power expense $ 355 $ (3,314) $ (5,262) Cost of gas sold expense (223) (404) (85) Total $ 132 $ (3,718) $ (5,347) ( c ) MGE's exchange-traded derivative contracts, over-the-count er party transactions, purchased power agreement, and FTRs are subject to regulatory deferral. These derivatives are therefore marked to fair value and are offset in the financial statements with a corresponding regulatory asset or liability.

Share-Based Compensation (Table

Share-Based Compensation (Tables) - Performance Units [Member]	12 Months Ended
	Dec. 31, 2018
Director Incentive Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Unit Graded Vesting Schedule	Units granted un der the Director Incentive Plan are subject to a three- year vesting schedule. The most recent three years of units granted under this plan are as follows: Grant Date MGE Energy Units Granted January 18, 2019 5,175 March 1, 2018 1,106 January 19, 2018 4,704 January 20, 2017 4,608
Performance Unit Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Unit Graded Vesting Schedule	Units granted under the Performance Unit Plan are subject to a five-year vesting schedule. The most recent units granted under this plan are as follows: Grant Date MGE Energy Units Granted February 15, 2019 17,022 February 16, 2018 17,830 March 1, 2017 14,704 February 19, 2016 19,055 February 20, 2015 18,948

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule	Management expects to recover these costs in future customer rates. As of December 31, 2018 , the future minimum commitments related to these purchase cont racts were as follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Coal (a) $ 25,167 $ 8,213 $ 828 $ - $ - $ - Natural gas Transportation and storage (b) 21,051 20,853 20,853 20,853 20,853 53,361 Supply (c) 15,423 - - - - - Purchase power (d) 27,577 28,082 28,675 15,533 5,641 21,751 Other 6,261 3,007 2,980 2,894 2,825 7 $ 95,479 $ 60,155 $ 53,336 $ 39,280 $ 29,319 $ 75,119 (a) Total coal commitments for the Columbia and Elm Road Units , including transportation . Fuel procurement for MGE's jointly owned Columbia and Elm Road Units is handled by WPL and WEPCO, respectively, who are the operators of those facilities . (b) MGE's natural gas transportation and storage contracts require fixed monthly payments for firm supply pipeline transportation and storage capacity. The pricing components of the fixed monthly payments for the transportation and storage contracts are established by FERC but may be subject to change. (c) These commitments include market-based pricing. (d) MGE has several purchase power agreements to help meet futu re electric supply requirements .
Operating Leases, Future Minimum Rental Payments	Future minimum rental payments as of December 31, 2018 , u nder agreements classified as operating leases with noncancelable terms in excess of one year are a s follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Minimum lease payments $ 1,646 $ 1,371 $ 1,095 $ 989 $ 975 $ 22,707
Other Commitments	MGE has several other commitments related to various projects. Payments for these commitments are expected to be as follows: (In thousands) 2019 2020 2021 2022 2023 Thereafter Other commitments $ 333 $ 333 $ 333 $ 333 $ 333 $ 3,665

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Change in Asset Retirement Obligations	The following table summariz es the change in AROs . Amounts include conditional AROs. (In thousands) 2018 2017 Balance as of January 1, $ 26,738 $ 26,886 Liabilities incurred (a) 1,943 145 Accretion expense 1,415 1,359 Liabilities settled (b) (175) (1,789) Revisions in estimated cash flows 59 137 Balance as of December 31, $ 29,980 $ 26,738 (a) In 2018 , MGE recorded an obligation of $1.6 million for the fair value of its legal liability for AROs associated with Forward Wind. See Footnote 5 for additional information on the purchase of Forward Wind. (b) In 2017 , MGE removed asbestos at Blount for $1.6 million .

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Revenues disaggregated by revenue source were as follows: (In thousands) Year Ended December 31, Electric revenues 2018 2017 2016 Residential $ 138,566 $ 136,168 $ 136,792 Commercial (a) 204,683 216,461 213,101 Industrial 13,878 16,176 17,589 Other-retail/municipal 34,023 38,010 35,559 Total retail 391,150 406,815 403,041 Sales to the market 7,438 4,067 6,135 Other revenues 1,870 2,323 1,483 Adjustments to revenues 424 721 (1,653) Total electric revenues 400,882 413,926 409,006 Gas revenues Residential 94,017 88,695 81,014 Commercial/Industrial (a) 59,060 55,151 48,497 Total retail 153,077 143,846 129,511 Gas transportation 4,283 4,561 4,635 Other revenues 407 418 397 Total gas revenues 157,767 148,825 134,543 Non-regulated energy revenues 1,119 348 1,196 Total Operating Revenue (a) $ 559,768 $ 563,099 $ 544,745 (a) In 2017 and 2016, MGE had less than $0.1 million of revenues related to CNG vehicle fuel servicing. No revenue was recognized for fuel servicing by MGE Energy in 2017 and 2016.

Noncontrolling Interest (Tables

Noncontrolling Interest (Tables) - MGE [Member]	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Balance Sheet	The noncontrolling interest on MGE ' s consolidated balance sheets as of December 31 was as follows: (In thousands) 2018 2017 MGE Power Elm Road (a) $ 97,519 $ 97,635 MGE Power West Campus (a) 43,935 43,267 Total Noncontrolling Interest $ 141,454 $ 140,902
Net Income Attributable to Noncontrolling Interest, Net of Tax	The net income attributable to noncontrolling interest , net of tax, for the years ended December 31, 2018 , 2017 , and 2016 was as follows : (In thousands) 2018 2017 2016 MGE Power Elm Road (a) $ 15,384 $ 29,274 $ 14,748 MGE Power West Campus (a) 7,168 13,963 7,200 MGE Transco (b) - - 1,410 Net Income Attributable to Noncontrolling Interest, Net of Tax $ 22,552 $ 43,237 $ 23,358 (a) MGE Power Elm Road and MGE Power West Campus are not su bsidiaries of MGE; however, they have been consolidated in the consolidated financial s tatements of MGE (see Footnote 3 ). MGE Power Elm Road and MGE Power West Campus are 100 % owned by MGE Power, and MGE Power is 100 % o wned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE consolidated financial statements as noncontrolling interest . In 2017, there was a $14.8 million and $6.8 million one-time tax impact as a result of the Tax Act for MGE Power Elm Road and MGE Power West Campus, respectively. The Tax Act reduced the f ederal tax rate from 35% to 21%. See Footnote 12 for further information . (b ) A s of December 31, 2018 , MGE Energy is the owner of MGE Transco. In July 2016, MGE's ownership interest in MGE Transco declined below a majority as a result of continued funding of ATC capital contributions by MGE Energy. As a result of the change in majority owner ship in MGE Transco , MGE deconsolidated MGE Energy's proportionate share of the equity in MGE Transco. The change in co nsolidation was applied prospectively by reducing its investment and noncontrolling interest on MGE's consolidated financial statements. The change had no effect on MGE Energy's consolidated financial statements; however, MGE Energy's proportionate share o f the equity and net income of MGE Transco classified as noncontrolling interest was deconsolidated from MGE ' s financial statements. No gain or loss was recognized in July 2016 due to MGE ceasing to have a controlling financial interest .

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Information	The following table shows segment information for MGE Energy ' s and MGE ' s operations: (In thousands) MGE Energy Electric Gas Non-Regulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Consolidated Total Year Ended December 31, 2018 Operating revenues $ 400,882 $ 157,767 $ 1,119 $ - $ - $ - $ 559,768 Interdepartmental revenues (289) 16,076 39,526 - - (55,313) - Total operating revenues 400,593 173,843 40,645 - - (55,313) 559,768 Depreciation and amortization (38,925) (10,060) (7,427) - - - (56,412) Other operating expenses (297,374) (145,883) (144) (16) (1,045) 55,313 (389,149) Operating income (loss) 64,294 17,900 33,074 (16) (1,045) - 114,207 Other income (deductions), net 7,294 3,132 - 8,602 (1,973) - 17,055 Interest (expense) income, net (12,198) (3,692) (5,307) - 1,588 - (19,609) Income (loss) before taxes 59,390 17,340 27,767 8,586 (1,430) - 111,653 Income tax (provision) benefit (13,453) (4,474) (7,534) (2,345) 372 - (27,434) Net income (loss) $ 45,937 $ 12,866 $ 20,233 $ 6,241 $ (1,058) $ - $ 84,219 Year Ended December 31, 2017 Operating revenues $ 413,926 $ 148,825 $ 348 $ - $ - $ - $ 563,099 Interdepartmental revenues (510) 14,974 44,468 - - (58,932) - Total operating revenues 413,416 163,799 44,816 - - (58,932) 563,099 Depreciation and amortization (36,660) (9,000) (7,417) - - - (53,077) Other operating expenses (a) (308,100) (135,029) (190) (9) (1,001) 58,932 (385,397) Operating income (loss) 68,656 19,770 37,209 (9) (1,001) - 124,625 Other income (deductions), net (a) 4,539 1,912 - 9,844 (1,896) - 14,399 Interest (expense) income, net (11,257) (3,234) (5,533) - 700 - (19,324) Income (loss) before taxes 61,938 18,448 31,676 9,835 (2,197) - 119,700 Income tax (provision) benefit (b) (20,547) (7,303) 8,860 (3,954) 850 - (22,094) Net income (loss) $ 41,391 $ 11,145 $ 40,536 $ 5,881 $ (1,347) $ - $ 97,606 Year Ended December 31, 2016 Operating revenues $ 409,006 $ 134,543 $ 1,196 $ - $ - $ - $ 544,745 Interdepartmental revenues 1,912 21,378 43,930 - - (67,220) - Total operating revenues 410,918 155,921 45,126 - - (67,220) 544,745 Depreciation and amortization (29,122) (8,128) (7,372) - (24) - (44,646) Other operating expenses (a) (313,649) (128,721) (155) (17) (895) 67,220 (376,217) Operating income (loss) 68,147 19,072 37,599 (17) (919) - 123,882 Other income, net (a) 3,668 1,668 - 8,429 292 - 14,057 Interest (expense) income, net (11,147) (3,223) (5,768) - 272 - (19,866) Income (loss) before taxes 60,668 17,517 31,831 8,412 (355) - 118,073 Income tax (provision) benefit (20,115) (6,894) (12,775) (2,836) 107 - (42,513) Net income (loss) $ 40,553 $ 10,623 $ 19,056 $ 5,576 $ (248) $ - $ 75,560 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for further information. (b) In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information. (In thousands) MGE Electric Gas Non-Regulated Energy Transmission Investment (d) Consolidation/ Elimination Entries Consolidated Total Year Ended December 31, 2018 Operating revenues $ 400,882 $ 157,767 $ 1,119 $ - $ - $ 559,768 Interdepartmental revenues (289) 16,076 39,526 - (55,313) - Total operating revenues 400,593 173,843 40,645 - (55,313) 559,768 Depreciation and amortization (38,925) (10,060) (7,427) - - (56,412) Other operating (expenses) income (c) (310,626) (150,195) (7,678) - 55,313 (413,186) Operating income (c) 51,042 13,588 25,540 - - 90,170 Other income, net (c) 7,093 2,970 - - - 10,063 Interest expense, net (12,198) (3,692) (5,307) - - (21,197) Net income 45,937 12,866 20,233 - - 79,036 Less: Net income attributable to noncontrolling interest, net of tax - - - - (22,552) (22,552) Net income attributable to MGE $ 45,937 $ 12,866 $ 20,233 $ - $ (22,552) $ 56,484 Year Ended December 31, 2017 Operating revenues $ 413,929 $ 148,834 $ 348 $ - $ - $ 563,111 Interdepartmental revenues (513) 14,965 44,468 - (58,920) - Total operating revenues 413,416 163,799 44,816 - (58,920) 563,111 Depreciation and amortization (36,660) (9,000) (7,417) - - (53,077) Other operating (expenses) income (a)(b)(c) (328,093) (142,175) 8,670 - 58,920 (402,678) Operating income (c) 48,663 12,624 46,069 - - 107,356 Other income, net (a)(c) 3,985 1,755 - - - 5,740 Interest expense, net (11,257) (3,234) (5,533) - - (20,024) Net income 41,391 11,145 40,536 - - 93,072 Less: net income attributable to noncontrolling interest, net of tax - - - - (43,237) (43,237) Net income attributable to MGE $ 41,391 $ 11,145 $ 40,536 $ - $ (43,237) $ 49,835 Year Ended December 31, 2016 Operating revenues $ 409,030 $ 134,572 $ 1,196 $ - $ - $ 544,798 Interdepartmental revenues 1,888 21,349 43,930 - (67,167) - Total operating revenues 410,918 155,921 45,126 - (67,167) 544,798 Depreciation and amortization (29,122) (8,128) (7,372) - - (44,622) Other operating expenses (a)(c) (333,632) (135,578) (12,930) - 67,167 (414,973) Operating income (loss) (c) 48,164 12,215 24,824 - - 85,203 Other income (deductions), net (a)(c) 3,536 1,631 - 4,360 - 9,527 Interest expense, net (11,147) (3,223) (5,768) - - (20,138) Net income 40,553 10,623 19,056 4,360 - 74,592 Less: Net income attributable to noncontrolling interest, net of tax - - - - (23,358) (23,358) Net income attributable to MGE $ 40,553 $ 10,623 $ 19,056 $ 4,360 $ (23,358) $ 51,234 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for further information. (b) In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information. (c) Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income. (d) As of July 31, 2016, MGE no longer consolidates MGE Energy's proportionate share of equity earnings in MGE Transco. See Footnote 6 for further information. The following table shows segment information for MGE Energy's and MGE's assets and capital expenditures: Utility Consolidated (In thousands) MGE Energy Electric Gas Non-regulated Energy Transmission Investment (e) All Others Consolidation/ Elimination Entries Total Assets: December 31, 2018 $ 1,193,083 $ 377,005 $ 265,301 $ 66,366 $ 465,661 $ (378,798) $ 1,988,618 December 31, 2017 1,058,988 354,875 270,384 61,783 485,548 (376,396) 1,855,182 December 31, 2016 1,038,308 329,538 271,277 74,535 465,202 (377,800) 1,801,060 Capital Expenditures: Year ended Dec. 31, 2018 $ 176,399 $ 30,497 $ 5,301 $ - $ - $ - $ 212,197 Year ended Dec. 31, 2017 77,353 26,847 3,931 - - - 108,131 Year ended Dec. 31, 2016 50,699 29,136 3,824 - - - 83,659 Utility Consolidated (In thousands) MGE Electric Gas Non-regulated Energy Consolidation/ Elimination Entries Total Assets: December 31, 2018 $ 1,193,083 $ 377,005 $ 265,251 $ (448) $ 1,834,891 December 31, 2017 1,058,988 354,875 270,334 (156) 1,684,041 December 31, 2016 1,038,308 329,538 271,227 (221) 1,638,852 Capital Expenditures: Year ended Dec. 31, 2018 $ 176,399 $ 30,497 $ 5,301 $ - $ 212,197 Year ended Dec. 31, 2017 77,353 26,847 3,931 - 108,131 Year ended Dec. 31, 2016 50,699 29,136 3,824 - 83,659 (e) In December 2017, there was a $20.4 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.

Quarterly Summary of Operatio_2

Quarterly Summary of Operations (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Summary of Operations	(In thousands, except per share amounts) Quarters Ended 2018 March 31 June 30 September 30 December 31 Operating revenues: Electric revenues $ 94,867 $ 99,282 $ 119,388 $ 88,464 Gas revenues 62,765 24,980 18,407 51,615 Total Operating Revenues 157,632 124,262 137,795 140,079 Operating expenses 131,444 100,031 97,997 116,089 Operating income 26,188 24,231 39,798 23,990 Interest and other income, net 180 (52) (695) (1,987) Income tax provision (6,367) (5,828) (9,597) (5,642) Earnings on common stock $ 20,001 $ 18,351 $ 29,506 $ 16,361 Earnings per common share $ 0.58 $ 0.53 $ 0.85 $ 0.47 Dividends per share $ 0.323 $ 0.323 $ 0.338 $ 0.338 2017 Operating revenues: Electric revenues $ 98,397 $ 102,382 $ 120,761 $ 92,734 Gas revenues 58,426 24,081 18,778 47,540 Total Operating Revenues 156,823 126,463 139,539 140,274 Operating expenses (a) 124,987 100,868 97,542 115,077 Operating income 31,836 25,595 41,997 25,197 Interest and other income, net (a) (1,369) (1,316) 216 (2,456) Income tax provision (b) (11,167) (8,736) (15,584) 13,393 Earnings on common stock $ 19,300 $ 15,543 $ 26,629 $ 36,134 Earnings per common share $ 0.56 $ 0.45 $ 0.77 $ 1.04 Dividends per share $ 0.308 $ 0.308 $ 0.323 $ 0.323 (a ) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for more information. ( b) In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information. Notes: • The quarterly results of operations within a year may not be comparable because of seasonal and other factors. • The sum of earnings per share of common stock for any four quarters may vary slightly from the earnings per share of common stock for the equivalent twelve-month period due to rounding. • MGE Energy's operations are based primarily on its utility subsidiary MGE.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details-1) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Trade Receivables, Allowance for Doubtful Accounts, and Concentration Risk
Late payment charge on upaid receivables	1.00%
Inventories
Renewable energy credit allowance included in inventory	$ 700,000	$ 500,000
Purchased Gas Adjustment Clause
Purchased gas adjustment, over (under) collected	1,200,000	1,400,000
Regional Transmission Organizations
Reduction to sales and purchased power expense from reporting RTO transactions from net basis reporting	$ 90,300,000	87,900,000		$ 77,200,000
Allowance for Funds Used During Construction
Authorized AFUDC rate	100.00%
Capitalized Software Costs
Capitalized software	$ 15,100,000	11,100,000
Capitalized software amortization	4,700,000	3,300,000		3,000,000
Capitalized Software Hosting Agreement Costs
Capitalized Computer Software Hosting Agreement Net	9,200,000	500,000
Capitalized Computer Software Hosting Agreement Amortization	100,000	0		0
Capitalized Computer Software Hosting Agreement Accumulated Amortization	100,000	0
Impairment of Long-Lived Assets
Impairment of long-lived assets	$ 0	0		0
Excise taxes
License fee tax rate, electric, retail sales	3.19%
License fee tax rate, electric, resale by purchaser	1.59%
License fee tax rate, natural gas	0.97%
License fee tax expense	$ 14,400,000	$ 14,100,000		$ 14,500,000
Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase agreement, maximum exposure	10,000,000
2019 [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase-to-Maturity Transactions, loans due	396,000
2020 [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase-to-Maturity Transactions, loans due	407,000
2021 [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase-to-Maturity Transactions, loans due	392,000
2022 [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase-to-Maturity Transactions, loans due	354,000
2023 [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase-to-Maturity Transactions, loans due	510,000
Thereafter [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase-to-Maturity Transactions, loans due	$ 122,000
Minimum [Member]
Capitalized Software Hosting Agreement Costs
Capitalized software hosting agreement, useful life	5 years
Minimum [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
MGE guarantee to the financial institution, term	1 year
Minimum [Member] | Capitalized Software [Member]
Property, Plant, and Equiptment
Property, plant, and equipment, useful life	5 years
Maximum [Member]
Capitalized Software Hosting Agreement Costs
Capitalized software hosting agreement, useful life	10 years
Maximum [Member] | Chattel Paper Agreements [Member]
Transfers and Servicing
MGE guarantee to the financial institution, term	10 years
Maximum [Member] | Capitalized Software [Member]
Property, Plant, and Equiptment
Property, plant, and equipment, useful life	15 years
PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate	50.00%	50.00%		50.00%
Rate at which AFUDC was capitalized	7.87%	7.87%		7.93%
Columbia Environmental Project, SCR [Member] | PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate	100.00%	100.00%		100.00%
Saratoga Wind [Member] | PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate	100.00%
Electric [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	2.90%	3.00%	[1]	2.50%	[2]
Gas [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	2.10%	2.10%		2.10%	[2]
Non Regulated Energy [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	2.30%	2.30%		2.30%
MGE Power Elm Road [Member]
Principles of Consolidation
Ownership percentage by parent	100.00%
MGE Power West Campus [Member]
Principles of Consolidation
Ownership percentage by parent	100.00%
[1]	In September 2016, the PSCW approved new depreciation rates for Columbia effective January 1, 2017.
[2]	In December 2015, the PSCW approved new depreciation rates, which were implemented and became effective as of January 1, 2016.

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details-2) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 83,102,000	$ 107,952,000
Restricted cash	634,000	1,635,000
Receivable - margin account	1,193,000	2,507,000
Cash, cash equivalents, and restricted cash	84,929,000	112,094,000	$ 101,633,000	$ 86,694,000
MGE [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	4,843,000	5,951,000
Restricted cash	634,000	1,635,000
Receivable - margin account	1,193,000	2,507,000
Cash, cash equivalents, and restricted cash	$ 6,670,000	$ 10,093,000	$ 16,442,000	$ 32,070,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies (Details-3) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash Provided by Operating Activities	$ 153,040,000	$ 131,373,000	$ 147,864,000
Cash Used for Investing Activities	(218,328,000)	(116,275,000)	(86,813,000)
Change in cash, cash equivalents, and restricted cash	(27,165,000)	10,461,000	14,939,000
Cash, cash equivalents, and restricted cash at beginning of period	112,094,000	101,633,000	86,694,000
Cash, cash equivalents, and restricted cash at end of period	84,929,000	112,094,000	101,633,000
Accounting Standards Update 2016-18 - Restricted Cash [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash Provided by Operating Activities		(1,618,000)	351,000
Cash Used for Investing Activities		86,000	13,000
Change in cash, cash equivalents, and restricted cash		(1,532,000)	364,000
Cash, cash equivalents, and restricted cash at beginning of period	$ 4,142,000	5,674,000	5,310,000
Cash, cash equivalents, and restricted cash at end of period		$ 4,142,000	$ 5,674,000

New Accounting Standards (Detai

New Accounting Standards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 0
Accumulated Other Comprehensive income (loss)	$ 0	377
MGE [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		0
Accumulated Other Comprehensive income (loss)	0	(28)
Accounting Standards Update 2016-01 - Financial Instruments - Overall [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	377
Accumulated Other Comprehensive income (loss)	(377)
Accounting Standards Update 2016-01 - Financial Instruments - Overall [Member] | MGE [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	(28)
Accumulated Other Comprehensive income (loss)	28
Accounting Standards Update 2017-07 - Compensation - Retirement Benefits [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 4,100	$ 4,300
Accounting Standards Update 2016-02 - Leases [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New accounting pronouncement, effect of adoption, in assets and liabilities (leases)	15,000
Accounting Standards Update 2016-02 - Leases [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New accounting pronouncement, effect of adoption, in assets and liabilities (leases)	$ 17,000

Variable Interest Entities (Det

Variable Interest Entities (Details) $ in Thousands		Dec. 31, 2018USD ($)MW	Dec. 31, 2017USD ($)MW
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net		$ 1,369,766	$ 1,283,313
Construction work in progress		139,671	58,044
Accrued interest and taxes		7,384	5,602
Deferred income taxes		231,952	225,130
Unamortized discount and debt issuance costs, net		$ 4,535	$ 4,270
Other Variable Interest Entities
Other variable interest entities, purchase power agreement, plant capacity (in MW) | MW		11	61
MGE Power Elm Road [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net		$ 173,464	$ 176,002
Construction work in progress		530	1,225
Affiliate receivables, current and noncurrent		0	0
Deferred income taxes		30,595	29,256
Long-term debt	[1]	56,806	59,416
Noncontrolling interest	[2]	97,519	97,635
Unamortized discount and debt issuance costs, net		500	600
MGE Power West Campus [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net		81,273	80,282
Construction work in progress		478	610
Affiliate receivables, current and noncurrent		3,707	4,236
Deferred income taxes		14,222	13,795
Long-term debt	[1]	41,496	43,262
Noncontrolling interest	[2]	43,935	43,267
Unamortized discount and debt issuance costs, net		$ 100	$ 100
[1]	(a) MGE Power Elm Road ' s long-term debt includes debt issuance costs of $ 0.5 million and $ 0.6 million as of December 31, 2018 and 2017 , respectively. The debt is secured by a collateral assignment of lease payments that MGE makes to MGE Power Elm Road for use of the Elm Road Units pursuant to the related long-term leases. MGE Power West Campus ' s long-term debt includes debt issuance cos ts of $ 0.1 million as of December 31, 2018 and 2017 . The debt is secured by a collateral assignment of lease payments that MGE makes to MGE Power West Campus for use of the cogeneration facility pursuant to the long-term lease. See Footnote 10 for further information on the long-term debt securities.
[2]	MGE Power Elm Road and MGE Power West Campus are not su bsidiaries of MGE; however, they have been consolidated in the consolidated financial s tatements of MGE (see Footnote 3 ). MGE Power Elm Road and MGE Power West Campus are 100 % owned by MGE Power, and MGE Power is 100 % o wned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE consolidated financial statements as noncontrolling interest . In 2017, there was a $14.8 million and $6.8 million one-time tax impact as a result of the Tax Act for MGE Power Elm Road and MGE Power West Campus, respectively. The Tax Act reduced the f ederal tax rate from 35% to 21%. See Footnote 12 for further information .

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2018USD ($)TurbinesMW	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Property, Plant and Equipment [Line Items]
In-service utility plant, net		$ 1,369,766	$ 1,283,313
Construction work in progress		139,671	58,044
Total property, plant, and equipment		1,509,437	1,341,357
Assets held for sale		$ 3,080	8,817
Forward Wind [Abstract]
Forward Wind Number Of Operating Turbines | Turbines		86
Forward Wind Proportionate Purchase Price		$ 23,000
Forward Wind Aggregate Purchase Price		$ 174,000
Jointly Owned Utility Plant Proportionate Ownership Share		12.80%
Saratoga Wind [Abstract]
Saratoga Megawatts | MW		66
Saratoga Turbines | Turbines		33
Saratoga Wind Project Costs		$ 95,800
Allowance for Funds Used During Construction
Authorized AFUDC rate		100.00%
AFUDC equity recognized		$ 2,500
First Mortgage Bonds [Member] | 7.70%, 2028 Series
Plant related debt items
Long-term debt, gross	[1]	1,200	1,200
Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,753,002	1,624,878
Less: Accumulated depreciation and amortization	[2],[3]	639,486	599,469
In-service utility plant, net		1,113,516	1,025,409
Construction work in progress	[2],[4]	138,663	56,208
Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[2],[3]	1,310,421	1,209,336
Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		442,581	415,542
Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		322,855	319,611
Less: Accumulated depreciation and amortization		66,605	61,707
In-service utility plant, net		256,250	257,904
Construction work in progress		1,008	1,836
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, net		1,369,795	1,283,341
Construction work in progress		139,671	58,044
Total property, plant, and equipment		1,509,466	1,341,385
Assets held for sale		3,080	8,817
Allowance for Funds Used During Construction
AFUDC equity recognized		3,284	1,222	$ 1,207
MGE [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,753,031	1,624,906
Less: Accumulated depreciation and amortization	[2],[3]	639,486	599,469
In-service utility plant, net		1,113,545	1,025,437
Construction work in progress	[2],[4]	138,663	56,208
MGE [Member] | Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[2],[3]	1,310,438	1,209,353
MGE [Member] | Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		442,593	415,553
MGE [Member] | Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		322,855	319,611
Less: Accumulated depreciation and amortization		66,605	61,707
In-service utility plant, net		256,250	257,904
Construction work in progress		$ 1,008	$ 1,836
[1]	MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust, under which its first mortgage bonds are issued. The Mortgage Indenture provides that dividends or any other distribution or purchase of shares may not be made if the aggregate amount thereof since December 31, 1945 , would exceed the earned surplus (retained earnings) accumulated subsequent to December 31, 1945. As of December 31, 2018 , approximately $ 400.0 m illion was available for the payment of dividends under this covenant.
[2]	(a ) As of December 31, 2018 and 2017 , MGE has classified $ 3.1 million and $ 8.8 million, respectively, of Columbia assets as held-for-sale on the consolidated balance sheets related to the partial sale of plant assets to WPL. See Footnote 5.a. for further discussion.
[3]	(b) In April 2018, MGE, along with two other utilities, purchased the Forward Wind Energy Center (Forward Wind), which consists of 86 wind turbines located in Wisconsin. The aggregate purchase price was approximately $ 174 million, of which MGE's proportionate share is 12.8 %, or approximately $ 23 million.
[4]	(c) In December 2017, the PSCW authorized construction of a 66 MW wind farm, consisting of 33 turbines, located near Saratoga, Iowa. MGE received specific approval to recover 100 % AFUDC on the project. As of December 31, 2018 , MG E has incurred $ 95.8 million of capital expenditures. After tax, MGE has recognized $ 2.5 million in AFUDC equity related to this project for the year ended December 31, 2018 . Construction of the project was completed in February 2019 .

Joint Plant Ownership (Details)

Joint Plant Ownership (Details)	12 Months Ended
	Dec. 31, 2018USD ($)MWoperatingunitTurbinesMW	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2019
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	12.80%
Assets held for sale	$ 3,080,000	$ 8,817,000
Forward Wind Turbines | Turbines	86
Forward Wind Proportionate Purchase Price	$ 23,000,000
Forward Wind Aggregate Purchase Price	174,000,000
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	3,080,000	8,817,000
Columbia Units [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	292,157,000	274,450,000
Accumulated depreciation	(94,766,000)	(87,144,000)
Property, plant, and equipment, net	197,391,000	187,306,000
Construction work in progress	2,021,000	20,382,000
Total property, plant, and equipment	$ 199,412,000	$ 207,688,000
Columbia Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, proportion of total net summer generating capability	29.00%
Jointly owned utility plant, plant capacity (in MW) | MW	219
Jointly owned utility plant, ownership interest	19.40%	20.40%
Assets held for sale	$ 3,100,000	$ 8,800,000
Jointly owned utility plant, fuel, operating, and maintenance expense	36,500,000	36,200,000	$ 39,500,000
Columbia Units [Member] | MGE [Member] | Subsequent Event [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest				19.10%
Elm Road Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, fuel, operating, and maintenance expense	$ 17,600,000	17,300,000	21,200,000
Elm Road Units [Member] | MGE Power Elm Road [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, proportion of total net summer generating capability	14.00%
Jointly owned utility plant, proportion of total net summer generating capability, plant capacity (in MW) | MW	106
Jointly owned utility plant, number of operating units | operatingunit	2
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	$ 207,361,000	206,063,000
Accumulated depreciation	(33,897,000)	(30,061,000)
Property, plant, and equipment, net	173,464,000	176,002,000
Construction work in progress	530,000	1,225,000
Total property, plant, and equipment	$ 173,994,000	177,227,000
Elm Road Unit 1 [Member] | MGE Power Elm Road [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	615
Jointly owned utility plant, ownership interest	8.33%
Elm Road Unit 2 [Member] | MGE Power Elm Road [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	615
Jointly owned utility plant, ownership interest	8.33%
Forward Wind [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	$ 33,929,000
Accumulated depreciation	(12,530,000)
Property, plant, and equipment, net	21,399,000
Construction work in progress	67,000
Total property, plant, and equipment	$ 21,466,000
Forward Wind [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	18
Jointly owned utility plant, ownership interest	12.80%
Jointly owned utility plant, fuel, operating, and maintenance expense	$ 500,000
Forward Wind Turbines | MW	86
Forward Wind Proportionate Purchase Price	$ 23,000,000
Forward Wind Purchase Power Energy Output	12.80%
Forward Wind [Member] | Joint Owners [Member]
Jointly Owned Utility Plant Interests [Line Items]
Forward Wind Aggregate Purchase Price	$ 174,000,000
West Campus [Member] | UW [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	45.00%
Jointly owned utility plant, fuel, operating, and maintenance expense	$ 6,300,000	5,300,000	$ 5,500,000
West Campus [Member] | MGE Power West Campus [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	55.00%
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	$ 113,328,000	111,386,000
Accumulated depreciation	(32,055,000)	(31,104,000)
Property, plant, and equipment, net	81,273,000	80,282,000
Construction work in progress	478,000	610,000
Total property, plant, and equipment	$ 81,751,000	$ 80,892,000

Investments (Details-1)

Investments (Details-1) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Available-for-sale securities:
Cost basis			$ 6,700
Gross unrealized gains			700
Gross unrealized losses			(100)
Equity Securities	[1]	$ 9,363	7,291
Equity method investments:
Equity method investments		66,339	60,426
Other Investments		2,298	55
Total investments		78,000	67,772
Results of Investment Liquidation [Abstract]
Proceeds from sale of investments		960	677		$ 408
Gain (loss) on sale of investments		476	522		121
Tax Cuts and Jobs Act [Member]
Equity method investments:
Equity method investments			20,375
ATC [Member] | Tax Cuts and Jobs Act [Member]
Equity method investments:
Equity method investments			(20,400)
ATC and ATC Holdco [Member]
Equity method investments:
Equity method investments		66,313	59,298	[2]
Other Equity Method Investments [Member]
Equity method investments:
Equity method investments		26	1,128
MGE [Member]
Available-for-sale securities:
Cost basis			500
Gross unrealized losses			(100)
Equity Securities	[1]	388	409
Equity method investments:
Equity method investments		0	0
Other Investments		0	0
Total investments		388	409
Results of Investment Liquidation [Abstract]
Proceeds from sale of investments		3	0		16
Gain (loss) on sale of investments		3	0		$ (8)
MGE [Member] | Tax Cuts and Jobs Act [Member]
Equity method investments:
Equity method investments			0
MGE [Member] | ATC and ATC Holdco [Member]
Equity method investments:
Equity method investments		0	0
MGE [Member] | Other Equity Method Investments [Member]
Equity method investments:
Equity method investments		$ 0	$ 0
[1]	Reflects modified retrospective application of new authoritative guidance related to Financial Instruments as described in Footnote 2. Prior to January 1, 2018, investments were considered available for sale securities. As of December 31, 2017, MGE Energy had available for sale securities with a cost basis of $6.7 million, gross unrealized gains of $0.7 million, and gross unrealized losses of less than $0.1 million. As of December 31, 2017, MGE had available for sale securities with a cost basis of $ 0.5 million and gross unrealized losses of less than $0.1 million.
[2]	In December 2017, there was a $ 20.4 million one-time tax impact related to ATC as a result of the Tax Act. See Footnote 12 for further information.

Investments (Details-2)

Investments (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	$ 8,821		$ 10,125		$ 8,428
Dividends from investment	6,958		8,803		5,854
Capital contributions to investments	5,926		11,081		2,958
MGE Energy [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	85,220		99,246		75,581
MGE Transco [Member] | ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	8,821		10,125		8,670
Dividends from investment	4,611	[1]	9,078	[1]	7,926
Capital contributions to investments	$ 2,841		$ 3,551		2,486
Ownership interest in equity-method investee	3.60%		3.60%
Dividend receivable from ATC			$ 2,300		2,100
MGEE Transco [Member] | ATC Holdco [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments	$ 300		$ 2,900
Ownership interest in equity-method investee	4.40%		4.40%
MGE [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	$ 0		$ 0		6,366
Dividends from investment	0		0		5,032
Capital contributions to investments	0		0		1,598
Dividend in kind to parent	$ 0		$ 0		$ 15,822
[1]	MGE Transco recorded a $ 2.3 million and a $ 2.1 million dividend receivable from ATC as of December 31, 2017 and 2016 , respectively. A cash dividend was received in January of each of the proceeding years.

Investments (Details-3)

Investments (Details-3) - ATC [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity method investment summarized income statement [Abstract]
Operating revenues	$ 690,510	$ 721,672	$ 650,806
Operating expenses	(358,703)	(346,308)	(323,947)
Other income, net	2,405	7,402	5,361
Interest expense, net	(110,725)	(110,138)	(99,464)
Earnings before members' income taxes	223,487	272,628	$ 232,756
Equity method investment balance sheet assets [Abstract]
Current assets	87,250	87,730
Noncurrent assets	4,928,793	4,598,919
Total assets	5,016,043	4,686,649
Equity method investment balance sheet liabilities [Abstract]
Current liabilities	640,040	767,248
Long-term debt	2,013,997	1,790,590
Other noncurrent liabilities	295,281	240,286
Members' equity	2,066,725	1,888,525
Total members' equity and liabilities	$ 5,016,043	$ 4,686,649

Investments (Details-4)

Investments (Details-4) - ATC [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related party transaction [Line Items]
Related party expenses	$ 29	$ 29.2	$ 29.1
Due from Related Parties	$ 0.1	$ 0.2

Regulatory Assets and Liabili_3

Regulatory Assets and Liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory Assets	$ 154,901,000	$ 150,455,000
Regulatory Liabilities [Line Items]
Regulatory Liabilities	179,464,000	159,786,000
Deferred Fuel Savings [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9,504,000	4,229,000
Elm Road Regulatory Liability [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,515,000	931,000
Income Taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	135,449,000	131,689,000
Non-ARO Removal Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	19,891,000	18,536,000
Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3,669,000	0
Purchased Gas Adjustment [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,186,000	1,404,000
Renewable Energy Credits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	700,000	454,000
Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5,476,000	1,967,000
Other Regulatory Liability [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,074,000	576,000
Asset Retirement Obligation [Member]
Regulatory Assets [Line Items]
Regulatory Assets	9,199,000	8,328,000
Conservation Costs Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets	81,000	222,000
Debt Related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	9,288,000	9,749,000
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory Assets	31,830,000	41,958,000
Tax Recovery AFUDC Equity [Member]
Regulatory Assets [Line Items]
Regulatory Assets	6,482,000	5,497,000
Unfunded Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	96,030,000	84,342,000
Other Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 1,991,000	$ 359,000

Rate Matters (Details)

Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($)	1 Months Ended			4 Months Ended	12 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Rate Proceedings [Abstract]
Approved equity capital structure, percentage								9.80%
Authorized return on equity, percentage								57.20%
Fuel Rules [Abstract]
Fuel rules, bandwidth							2.00%
Fuel rules, electric fuel costs, deferral, upper threshold							102.00%
Fuel rules, electric fuel costs, deferral, lower threshold							98.00%
Deferred fuel rules monitored costs							$ 9,500,000
Public Utilities Fuel Surcharge Amount							$ 500,000
Public Utilities Fuel Surcharge Percentage							0.13%
Fuel Rules Credit ($0.00256/kWh), 2015/2016 [Member]
Fuel Rules [Abstract]
Electric fuel credit (per kWh)				$ 0.00256					$ 0.00256
Return of electric fuel credit, total									$ 8,300,000
Fuel Rules Refund, 2015/2016 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total		$ 6,200,000	$ 15,500,000
Fuel Rules Refund, 2017 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total	$ 4,200,000
Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Approved equity capital structure, percentage					9.80%	9.80%
Authorized return on equity, percentage					56.10%	56.60%
Electric Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage								(0.80%)
Authorized rate increase (decrease), amount								$ (3,300,000)
Electric Rate Proceeding [Member] | Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					0.00%	(2.24%)
Authorized rate increase (decrease), amount					$ 0	$ (9,200,000)
Gas Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage								1.90%
Authorized rate increase (decrease), amount								$ 3,100,000
Gas Rate Proceeding [Member] | Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					1.46%	1.06%
Authorized rate increase (decrease), amount					$ 2,400,000	$ 1,700,000

Common Equity (Details)

Common Equity (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018$ / shares	Sep. 30, 2018$ / shares	Jun. 30, 2018$ / shares	Mar. 31, 2018$ / shares	Dec. 31, 2017$ / shares	Sep. 30, 2017$ / shares	Jun. 30, 2017$ / shares	Mar. 31, 2017$ / shares	Dec. 31, 2018USD ($)$ / shares	Dec. 31, 2017USD ($)$ / shares	Dec. 31, 2016USD ($)$ / shares
Class of Stock [Line Items]
Common stock dividends declared									$ 45,762	$ 43,682	$ 41,775
Common stock dividends declared (in dollars per share) | $ / shares	$ 0.338	$ 0.338	$ 0.323	$ 0.3225	$ 0.323	$ 0.323	$ 0.308	$ 0.308	$ 1.32	$ 1.26	$ 1.21
MGE [Member]
Class of Stock [Line Items]
Cash dividends paid to parent by MGE									$ 0	$ 45,000	$ 50,000
MGE [Member] | Minimum [Member]
Class of Stock [Line Items]
Dividend restrictions, common equity ratio									0.55

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017
Debt Instrument [Line Items]
Long-term debt due within one year		$ (4,553)		$ (24,452)
Unamortized discount and debt issuance costs		(4,535)		(4,270)
Total Long-Term Debt		493,343		398,161
Long-Term Debt Maturities [Abstract]
Long term debt maturities in 2019		4,553
Long term debt maturities in 2020		19,659
Long term debt maturities in 2021		4,771
Long term debt maturities in 2022		4,889
Long term debt maturities in 2023		35,014
Long term debt maturities in future years		433,545
First Mortgage Bonds [Member] | 7.70%, 2028 Series
Debt Instrument [Line Items]
Long-term debt, gross	[1]	$ 1,200		$ 1,200
Interest rate		7.70%		7.70%
Debt covenant, allowable amount available for payment of dividends		$ 400,000
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[1]	1,200		$ 1,200
Tax Exempt Debt [Member] | 3.45%, 2027 Series, Industrial Development Revenue Bonds
Debt Instrument [Line Items]
Long-term debt, gross		$ 19,300		$ 19,300
Interest rate		3.45%		3.45%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross		$ 19,300		$ 19,300
Medium-Term Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross		70,000		70,000
Long-Term Debt Maturities [Abstract]
Long-term debt, gross		70,000		70,000
Medium-Term Notes [Member] | 6.12%, due 2028
Debt Instrument [Line Items]
Long-term debt, gross	[2]	$ 20,000		$ 20,000
Interest rate		6.12%		6.12%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[2]	$ 20,000		$ 20,000
Medium-Term Notes [Member] | 7.12%, due 2032
Debt Instrument [Line Items]
Long-term debt, gross	[2]	$ 25,000		$ 25,000
Interest rate		7.12%		7.12%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[2]	$ 25,000		$ 25,000
Medium-Term Notes [Member] | 6.247%, due 2037
Debt Instrument [Line Items]
Long-term debt, gross	[2]	$ 25,000		$ 25,000
Interest rate		6.247%		6.247%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[2]	$ 25,000		$ 25,000
Other Long-Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross		411,931		336,383
Long-Term Debt Maturities [Abstract]
Long-term debt, gross		411,931		336,383
Other Long-Term Debt [Member] | 5.59%, due 2018
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	0	[3]	$ 20,000
Interest rate				5.59%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	0	[3]	$ 20,000
Other Long-Term Debt [Member] | 3.38%, due 2020
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 15,000		$ 15,000
Interest rate		3.38%		3.38%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 15,000		$ 15,000
Other Long-Term Debt [Member] | 3.38%, due 2020 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 3.38%, due 2020 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 3.09%, due 2023
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 30,000		$ 30,000
Interest rate		3.09%		3.09%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 30,000		$ 30,000
Other Long-Term Debt [Member] | 3.09%, due 2023 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 3.09%, due 2023 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 3.29%, due 2026
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 15,000		$ 15,000
Interest rate		3.29%		3.29%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 15,000		$ 15,000
Other Long-Term Debt [Member] | 3.29%, due 2026 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 3.29%, due 2026 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 3.11% due 2027
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 30,000		$ 30,000
Interest rate		3.11%		3.11%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 30,000		$ 30,000
Other Long-Term Debt [Member] | 3.11% due 2027 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 3.11% due 2027 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 5.68%, due 2033
Debt Instrument [Line Items]
Long-term debt, gross	[4],[6]	$ 25,064		$ 26,121
Interest rate		5.68%		5.68%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[6]	$ 25,064		$ 26,121
Other Long-Term Debt [Member] | 5.19%, due 2033
Debt Instrument [Line Items]
Long-term debt, gross	[4],[6]	$ 16,561		$ 17,290
Interest rate		5.19%		5.19%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[6]	$ 16,561		$ 17,290
Other Long-Term Debt [Member] | 5.26%, due 2040
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 15,000		$ 15,000
Interest rate		5.26%		5.26%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 15,000		$ 15,000
Other Long-Term Debt [Member] | 5.26%, due 2040 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 5.26%, due 2040 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 5.04%, due 2040
Debt Instrument [Line Items]
Long-term debt, gross	[4],[7]	$ 35,139		$ 36,806
Interest rate		5.04%		5.04%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[7]	$ 35,139		$ 36,806
Other Long-Term Debt [Member] | 4.74%, due 2041
Debt Instrument [Line Items]
Long-term debt, gross	[4],[7]	$ 22,167		$ 23,166
Interest rate		4.74%		4.74%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[7]	$ 22,167		$ 23,166
Other Long-Term Debt [Member] | 4.38%, due 2042
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 28,000		$ 28,000
Interest rate		4.38%		4.38%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 28,000		$ 28,000
Other Long-Term Debt [Member] | 4.38%, due 2042 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 4.38%, due 2042 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 4.42%, due 2043
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 20,000		$ 20,000
Interest rate		4.42%		4.42%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 20,000		$ 20,000
Other Long-Term Debt [Member] | 4.42%, due 2043 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 4.42%, due 2043 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 4.47%, due 2048
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 20,000		$ 20,000
Interest rate		4.47%		4.47%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 20,000		$ 20,000
Other Long-Term Debt [Member] | 4.47%, due 2048 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 4.47%, due 2048 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 3.76% due 2052
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 40,000		$ 40,000
Interest rate		3.76%		3.76%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 40,000		$ 40,000
Other Long-Term Debt [Member] | 3.76% due 2052 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 3.76% due 2052 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 4.19% due 2048
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 60,000	[3]	0
Interest rate		4.19%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 60,000	[3]	0
Other Long-Term Debt [Member] | 4.19% due 2048 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 4.19% due 2048 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 4.24% due 2053
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 20,000	[3]	0
Interest rate		4.24%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 20,000	[3]	0
Other Long-Term Debt [Member] | 4.24% due 2053 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 4.24% due 2053 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
Other Long-Term Debt [Member] | 4.34% due 2058
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 20,000	[3]	0
Interest rate		4.34%
Long-Term Debt Maturities [Abstract]
Long-term debt, gross	[4],[5]	$ 20,000	[3]	0
Other Long-Term Debt [Member] | 4.34% due 2058 | Minimum [Member]
Debt Instrument [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Other Long-Term Debt [Member] | 4.34% due 2058 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
Priority debt to assets ratio		0.2
MGE Power Elm Road [Member]
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs		$ (500)		(600)
MGE Power Elm Road [Member] | Other Long-Term Debt [Member] | 5.04%, due 2040 | Minimum [Member]
Debt Instrument [Line Items]
Debt service coverage ratio		1.25
MGE Power Elm Road [Member] | Other Long-Term Debt [Member] | 4.74%, due 2041 | Minimum [Member]
Debt Instrument [Line Items]
Debt service coverage ratio		1.25
MGE Power West Campus [Member]
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs		$ (100)		$ (100)
MGE Power West Campus [Member] | Other Long-Term Debt [Member] | 5.68%, due 2033 | Minimum [Member]
Debt Instrument [Line Items]
Debt service coverage ratio		1.25
MGE Power West Campus [Member] | Other Long-Term Debt [Member] | 5.68%, due 2033 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
MGE Power West Campus [Member] | Other Long-Term Debt [Member] | 5.19%, due 2033 | Minimum [Member]
Debt Instrument [Line Items]
Debt service coverage ratio		1.25
MGE Power West Campus [Member] | Other Long-Term Debt [Member] | 5.19%, due 2033 | Maximum [Member]
Debt Instrument [Line Items]
Debt to total capitalization ratio		0.65
[1]	MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust, under which its first mortgage bonds are issued. The Mortgage Indenture provides that dividends or any other distribution or purchase of shares may not be made if the aggregate amount thereof since December 31, 1945 , would exceed the earned surplus (retained earnings) accumulated subsequent to December 31, 1945. As of December 31, 2018 , approximately $ 400.0 m illion was available for the payment of dividends under this covenant.
[2]	T he indenture under which MGE's Medium-T erm notes are issued provides that those notes will be entitled to be equally and ratably secured in the event that MGE issues any additional firs t mortgage bonds.
[3]	In July 2018, MGE issued a total of $ 4 0 million of new long-term unsecured debt. In September 2018, MGE issued $60 million of new long-term unsecured debt. MGE used the net proceeds from these debt financings to assist with financing capital expenditures, such as the Saratoga Wind Farm, and to refinance $20 million of long-term debt w hich matured in September 2018.
[4]	Unsecured notes issued pursuant to various Note Purchase Agreements with one or more purchasers. The notes are not i ssued under, or governed by, MGE ' s Indenture dated as of September 1, 1998, which governs MGE ' s Medium-Term Notes.
[5]	Issued by MGE. Under that Note Purchase Agreement: (i) note holders have the right to require MGE to repurchase their notes at par in the event of an acquisition of beneficial ownership of 30 % or more of the outstanding vot ing stock of MGE Energy, (ii) MGE must maintain a ratio of its consolidated indebtedness to consolidated total capitalization not to exceed a maximum of 65 %, and (iii) MGE cannot issue "Priority Debt" in an amount exceeding 20 % of its consolidated assets. Priority Debt is defined as any indebtedness of MGE secured by liens other than specified liens permitted by the Note Purchase Agreement and certain unsecured indebtedness of certain subsidiaries. As of December 31, 2018 , MGE was in compliance with the covenant requirements.
[6]	Issued by MGE Power West Campus. The Note Purchase Agreements require it to maintain a projected debt service coverage ratio of not less than 1.25 to 1.00 , and debt to total capitalization ratio of not more than 0.65 to 1.00 . The notes are secured by a collateral assignment of lease payments that MGE is making to MGE Power West Campus for use of its ownership interest in the WCCF pursuant to a long-term lease. As of December 31, 2018 , MGE Power West Campus was in compliance with the covenant requirements.
[7]	Issued by M GE Power Elm Road. The Note Purchase Agreement requires MGE Power Elm Road to maintain a projected and actual debt service coverage ratio at the end of any calendar quarter of not less than 1.25 to 1.00 for the trailing 12-month period. The notes are secured by a collateral assignment of lease payments that MGE is making to MGE Power Elm Road for use of its ownership interest in the Elm Road Units pursuant to long-term leases. As of December 31, 2018 , MGE Power Elm Road was in compliance with the covenant requirements.

Notes Payable to Banks, Comme_3

Notes Payable to Banks, Commercial Paper, and Lines of Credit (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Short-term debt outstanding	[1]	$ 13,000	$ 4,000
Weighted-average interest rate	[1]	2.55%	1.55%
Maximum short-term borrowings	[1]	$ 31,500	$ 7,500
Average short-term borrowings	[1]	$ 9,211	$ 304
Weighted-average interest rate during the year	[1]	1.92%	1.18%
Line of Credit [Member]
Short-term Debt [Line Items]
Available lines of credit	[1]	$ 150,000	$ 150,000
Line of Credit [Member] | MGE Energy unsecured committed revolving line of credit totaling $50 million | MGE Energy [Member]
Short-term Debt [Line Items]
Available lines of credit		50,000
Line of credit, borrowings outstanding		$ 0
Debt covenant, required parent company ownership of MGE		100.00%
Line of Credit [Member] | MGE Energy unsecured committed revolving line of credit totaling $50 million | Minimum [Member] | MGE Energy [Member]
Short-term Debt [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
Line of Credit [Member] | MGE Energy unsecured committed revolving line of credit totaling $50 million | Maximum [Member] | MGE Energy [Member]
Short-term Debt [Line Items]
Debt to total capitalization ratio		0.65
MGE [Member]
Short-term Debt [Line Items]
Short-term debt outstanding		$ 13,000	$ 4,000
Weighted-average interest rate		2.55%	1.55%
Maximum short-term borrowings		$ 31,500	$ 7,500
Average short-term borrowings		$ 9,211	$ 304
Weighted-average interest rate during the year		1.92%	1.18%
MGE [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Available lines of credit		$ 100,000	$ 100,000
MGE [Member] | Line of Credit [Member] | MGE unsecured committed revolving lines of credit totaling $100 million
Short-term Debt [Line Items]
Available lines of credit		100,000
Line of credit, borrowings outstanding		$ 0
Debt covenant, required parent company ownership of MGE		100.00%
MGE [Member] | Line of Credit [Member] | MGE unsecured committed revolving lines of credit totaling $100 million | Minimum [Member]
Short-term Debt [Line Items]
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value		30.00%
MGE [Member] | Line of Credit [Member] | MGE unsecured committed revolving lines of credit totaling $100 million | Maximum [Member]
Short-term Debt [Line Items]
Debt to total capitalization ratio		0.65
[1]	MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income tax provision components [Abstract]
Current payable: Federal														$ 18,622	$ 21,125		$ 16,908
Current payable: State														5,163	5,129		3,287
Net-deferred: Federal														120	(8,346)		17,571
Net-deferred: State														3,629	4,264		4,850
Amortized investment tax credits														(100)	(78)		(103)
Total income tax provision		$ 5,642	$ 9,597	$ 5,828	$ 6,367	$ (13,393)	[1]	$ 15,584		$ 8,736		$ 11,167	[1]	$ 27,434	$ 22,094	[1]	$ 42,513
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate														21.00%	35.00%		35.00%
State income taxes, net of federal benefit														6.30%	5.10%		5.10%
Amortized investment tax credits														(0.10%)	0.00%		(0.10%)
Credit for electricity from wind energy														(0.30%)	(1.60%)		(1.60%)
Domestic manufacturing deduction														0.00%	(1.40%)		(1.30%)
AFUDC equity, net														(0.60%)	(0.20%)		(0.20%)
Federal income tax rate reduction														0.00%	(18.10%)		0.00%
Amortization of utility excess deferred tax - tax reform	[2]													(1.80%)	0.00%		0.00%
Other, net, individually significant														0.10%	(0.30%)		(0.90%)
Effective income tax rate														24.60%	18.50%		36.00%
Components Of Deferred Tax Assets [Abstract]
Investment in ATC																		$ (23,638)	$ (24,781)
Accrued expenses																		(15,385)	(15,135)
Pension and other postretirement benefits																		(34,914)	(32,196)
Deferred tax regulatory account																		(37,121)	(36,124)
Derivatives																		(8,861)	(11,525)
Other deferred tax assets																		(15,137)	(12,790)
Gross deferred income tax assets																		(135,056)	(132,551)
Less valuation allowance																		86	86
Net deferred income tax assets																		(134,970)	(132,465)
Components Of Deferred Tax Liabilities [Abstract]
Property-related																		244,114	238,437
Investment in ATC																		50,771	48,324
Bond transactions																		765	832
Pension and other postretirement benefits																		47,644	42,919
Derivatives																		8,861	11,525
Tax deductible prepayments																		6,014	6,169
Other deferred tax liabilities																		8,753	9,389
Gross deferred income tax liabilities																		366,922	357,595
Deferred income taxes																		231,952	225,130
Effects Of The Tax Cuts And Jobs Act [Abstract]
Increase in Regulatory Liability Tax Cuts and Jobs Act																		179,464	159,786
Decrease in Investment ATC Tax Cuts and Jobs Act																		66,339	60,426
Regulatory liabilities - current																		13,826	5,633
Operating loss deductions and tax credit carryforwards [Abstract]
State net tax operating loss deductions																		1,400
Unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits, beginning balance					1,924							2,487		$ 1,924	$ 2,487		$ 2,528
Additions based on tax positions related to current year														425	552		452
Additions based on tax positions related to prior year														272	19		39
Reductions based on tax positions related to prior years														(672)	(1,134)		(532)
Unrecognized tax benefits, ending balance		1,949				1,924								1,949	1,924		2,487
Interest on unrecognized tax benefits [Roll Forward]
Accrued interest on unrecognized tax benefits, beginning balance					165							388		165	388		311
Reduction in interest expense on uncertain tax positions														(136)	(312)		(27)
Interest expense on uncertain tax positions														162	89		104
Accrued interest on unrecognized tax benefits, ending balance		191				165								191	165		388
Unrecognized Tax Benefits
Unrecognized tax benefits		$ 1,949			$ 1,924	$ 1,924						$ 2,487		1,924	1,924		2,528	1,949	1,924	$ 2,487
Unrecognized tax benefits permanent differences																		300	100	$ 100
Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Decrease in Deferred Tax Liability Tax Cuts And Jobs Act																			176,871
Decrease in Regulatory Asset Tax Cuts And Jobs Act																			4,347
Increase in Regulatory Liability Tax Cuts and Jobs Act	[3]																		130,497
Decrease in Investment ATC Tax Cuts and Jobs Act																			20,375
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act	[4]														21,651
Tax Cuts and Jobs Act [Member] | ATC [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Decrease in Investment ATC Tax Cuts and Jobs Act																			(20,400)
Revenue Subject to Refund | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current																		3,100
Return of tax credit																		8,200
Revenue Subject to Refund | Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Return of tax credit, total														2,800
MGE [Member]
Income tax provision components [Abstract]
Current payable: Federal														19,926	21,512		17,521
Current payable: State														5,704	5,316		3,497
Net-deferred: Federal														(2,563)	(11,195)		16,391
Net-deferred: State														2,494	3,435		4,485
Amortized investment tax credits														(100)	(78)		(103)
Total income tax provision														$ 25,461	$ 18,990		$ 41,791
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate														21.00%	35.00%		35.00%
State income taxes, net of federal benefit														6.20%	5.10%		5.10%
Amortized investment tax credits														(0.10%)	0.00%		(0.10%)
Credit for electricity from wind energy														(0.40%)	(1.70%)		(1.70%)
Domestic manufacturing deduction														0.00%	(1.50%)		(1.30%)
AFUDC equity, net														(0.50%)	(0.20%)		(0.20%)
Federal income tax rate reduction														0.00%	(19.30%)		0.00%
Amortization of utility excess deferred tax - tax reform	[2]													(2.00%)	0.00%		0.00%
Other, net, individually significant														0.20%	(0.40%)		(0.90%)
Effective income tax rate														24.40%	17.00%		35.90%
Components Of Deferred Tax Assets [Abstract]
Investment in ATC																		0	0
Accrued expenses																		(15,385)	(15,135)
Pension and other postretirement benefits																		(34,914)	(32,196)
Deferred tax regulatory account																		(37,121)	(36,124)
Derivatives																		(8,861)	(11,525)
Other deferred tax assets																		(15,185)	(12,831)
Gross deferred income tax assets																		(111,466)	(107,811)
Less valuation allowance																		86	86
Net deferred income tax assets																		(111,380)	(107,725)
Components Of Deferred Tax Liabilities [Abstract]
Property-related																		244,114	238,544
Investment in ATC																		0	0
Bond transactions																		765	832
Pension and other postretirement benefits																		47,644	42,919
Derivatives																		8,861	11,525
Tax deductible prepayments																		6,014	6,169
Other deferred tax liabilities																		8,598	9,222
Gross deferred income tax liabilities																		315,996	309,211
Deferred income taxes																		204,616	201,486
Effects Of The Tax Cuts And Jobs Act [Abstract]
Decrease in Investment ATC Tax Cuts and Jobs Act																		0	0
Regulatory liabilities - current																		13,826	5,633
Operating loss deductions and tax credit carryforwards [Abstract]
State net tax operating loss deductions																		$ 1,400
MGE [Member] | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Decrease in Deferred Tax Liability Tax Cuts And Jobs Act																			156,493
Decrease in Regulatory Asset Tax Cuts And Jobs Act																			4,347
Increase in Regulatory Liability Tax Cuts and Jobs Act	[3]																		130,497
Decrease in Investment ATC Tax Cuts and Jobs Act																			$ 0
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act	[4]														$ 21,649
[1]	In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.
[2]	Included are impacts of the Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting.
[3]	Given that changes in income taxes are generally passed through in customer rates for the regulated utility, a regu latory liability was recorded. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, which will be subject to review by the PSCW. A portion of the regulatory liability will be returned to customers based on a mandated timeframe dictated by applicable tax laws.
[4]	Generated by nonregulated activities.

Pension Plans and Other Postr_3

Pension Plans and Other Postretirement Benefits (Details-1) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined contribution plans [Abstract]
Defined contribution costs		$ 3,900	$ 3,500	$ 3,100
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		410,121
Fair value of plan assets at end of year		366,301	410,121
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset		0	7,336
Long-term liability		(67,483)	(69,088)
Pension Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year		391,269	349,556
Service cost		5,723	5,383	5,365
Interest cost		12,859	12,625	12,393
Plan participants' contributions		0	0
Actuarial (gain) loss	[1]	(34,439)	37,689
Gross benefits paid		(15,124)	(13,984)
Less: federal subsidy on benefits paid		0	0
Benefit obligation at end of year		360,288	391,269	349,556
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		361,651	311,933
Actual return on plan assets		(24,485)	56,987
Employer contributions		1,738	6,715
Plan participants' contributions		0	0
Gross benefits paid		(15,124)	(13,984)
Fair value of plan assets at end of year		323,780	361,651	311,933
Funded Status at December 31		(36,508)	(29,618)
Accumulated benefit obligation		335,800	356,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset		0	7,336
Current liability		(1,732)	(1,726)
Long-term liability		(34,776)	(35,228)
Net liability		(36,508)	(29,618)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		92,978	81,969
Prior service (credit) cost		(385)	(429)
Transition obligation		0	0
Total		92,593	81,540
Projected benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation with projected benefit obligation in excess of plan assets, end of year		360,288	36,954
Fair value of plan assets with projected benefit obligation in excess of plan assets, end of year		323,780	0
Accumulated benefit obligation in excess of plan assets [Abstract]
Accumulated benefit obligation with accumulated benefit obligation in excess of plan assets, end of year		31,200	32,813
Fair value of plan assets with accumulated benefit obligation in excess of plan assets, end of year		0	0
Postretirement Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year		82,290	78,842
Service cost		1,283	1,231	1,271
Interest cost		2,612	2,666	2,681
Plan participants' contributions		950	894
Actuarial (gain) loss	[1]	(7,555)	2,749
Gross benefits paid		(4,623)	(4,262)
Less: federal subsidy on benefits paid	[2]	204	170
Benefit obligation at end of year		75,161	82,290	78,842
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		48,470	43,177
Actual return on plan assets		(2,780)	7,104
Employer contributions		504	1,557
Plan participants' contributions		950	894
Gross benefits paid		(4,623)	(4,262)
Fair value of plan assets at end of year		42,521	48,470	$ 43,177
Funded Status at December 31		(32,640)	(33,820)
Medicare subsidy due to MGE		200	200
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset		0	0
Current liability		0	0
Long-term liability		(32,640)	(33,820)
Net liability		(32,640)	(33,820)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		10,569	12,600
Prior service (credit) cost		(7,153)	(9,821)
Transition obligation		21	23
Total		$ 3,437	$ 2,802
[1]	In 2018, higher discount rates were the main driver of the actuarial gain. However, in 2017, lower discount rates were the main driver of the actuarial loss.
[2]	In 2003, the Medicare Prescription Drug, Improvement and Modernization Act of 2003 was signed into law authorizing Medicare to provide prescription drug benefits to retirees. For the years ended December 31, 2018 and 2017 , the subsidy due to MGE was $ 0.2 million.

Pension Plans and Other Postr_4

Pension Plans and Other Postretirement Benefits (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	$ 5,723	$ 5,383	$ 5,365
Interest cost	12,859	12,625	12,393
Expected return on assets	(26,241)	(22,963)	(22,365)
Amortization of:
Transition obligation	0	0	0
Prior service (credit) cost	(44)	(17)	10
Actuarial loss	5,278	6,352	5,600
Net periodic benefit cost (credit)	(2,425)	1,380	1,003
Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	1,283	1,231	1,271
Interest cost	2,612	2,666	2,681
Expected return on assets	(3,232)	(2,887)	(2,829)
Amortization of:
Transition obligation	3	3	3
Prior service (credit) cost	(2,669)	(2,669)	(2,669)
Actuarial loss	488	660	589
Net periodic benefit cost (credit)	$ (1,515)	$ (996)	$ (954)

Pension Plans and Other Postr_5

Pension Plans and Other Postretirement Benefits (Details-3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	4.32%	3.73%
Rate of compensation increase	3.20%	3.67%
Weighted-average assumptions used to determine net periodic cost:
Discount rate	3.73%	4.30%	4.51%
Long-term rate of return	7.40%	7.40%	7.65%
Rate of compensation increase	3.72%	3.76%	3.76%
Postretirement Benefits [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	4.24%	3.58%
Assumed health care cost trend rates:
Health care cost trend rate assumed for next year	6.25%	6.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	5.00%	5.00%
Year that the rate reaches the ultimate trend rate	2,024	2,022
Weighted-average assumptions used to determine net periodic cost:
Discount rate	3.60%	4.09%	4.32%
Long-term rate of return	6.94%	6.80%	6.96%
How assumed 1% increase or decrease in health care cost trends could impact postretirement benefits [Abstract]
Effect on other postretirement benefit obligation - 1% increase	$ 754
Effect on other postretirement benefit obligation - 1% decrease	(980)
Effect on total service and interest cost components - 1% increase	21
Effect on total service and interest cost components - 1% decrease	$ (30)

Pension Plans and Other Postr_6

Pension Plans and Other Postretirement Benefits (Details-4) $ in Thousands		12 Months Ended
		Dec. 31, 2018USD ($)concentration	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Other postretirement benefits [Abstract]
Fair value of plan assets		$ 366,301	$ 410,121
Pension Benefits [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Target Plan Asset Allocation		100.00%
Actual Plan Asset Allocation		100.00%	100.00%
Other postretirement benefits [Abstract]
Fair value of plan assets		$ 323,780	$ 361,651	$ 311,933
Pension Benefits [Member] | Plan Assets [Member]
Concentration of Credit Risk [Abstract]
Concentration risk, percentage		10.00%
Concentration risk, number of significant concentrations | concentration		0
Pension Benefits [Member] | Equity Securities [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Target Plan Asset Allocation	[1]	63.00%
Actual Plan Asset Allocation		60.00%	65.00%
Pension Benefits [Member] | United States Equity Securities [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Target Plan Asset Allocation		45.50%
Pension Benefits [Member] | Non-United States Equity Securities [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Target Plan Asset Allocation		17.50%
Pension Benefits [Member] | Fixed Income Securities [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Target Plan Asset Allocation		30.00%
Actual Plan Asset Allocation		33.00%	29.00%
Pension Benefits [Member] | Real Estate [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Target Plan Asset Allocation		7.00%
Actual Plan Asset Allocation		7.00%	6.00%
Postretirement Benefits [Member]
Other postretirement benefits [Abstract]
Fair value of plan assets		$ 42,521	$ 48,470	$ 43,177
Postretirement Benefits [Member] | Plan Assets [Member]
Concentration of Credit Risk [Abstract]
Concentration risk, percentage		10.00%
Concentration risk, number of significant concentrations | concentration		0
Master Pension Trust [Member]
Other postretirement benefits [Abstract]
Fair value of plan assets		$ 37,500	$ 43,100
[1]	Target allocations for equity securities are broken out as follows: 45.5 % United States equity, 17.5 % non- United States equity .

Pension Plans and Other Postr_7

Pension Plans and Other Postretirement Benefits (Details-5) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 366,301	$ 410,121
Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	701	488
Equity Securities [Member] | U.S. Large Cap [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	102,984	124,594
Equity Securities [Member] | U.S. Mid Cap [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,683	29,138
Equity Securities [Member] | U.S. Small Cap [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28,573	37,782
Equity Securities [Member] | International Blend [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	61,299	71,514
Fixed Income Securities [Member] | Short-Term Fund [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,053	4,641
Fixed Income Securities [Member] | High Yield Bond [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19,437	19,400
Fixed Income Securities [Member] | Long Duration Bond [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	93,216	91,678
Real Estate [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27,923	25,995
Insurance Continuance Fund [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,491	1,500
Fixed Rate Fund [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,941	$ 3,391

Pension Plans and Other Postr_8

Pension Plans and Other Postretirement Benefits (Details-6) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Expected Cash Flows
Expected employer contributions, 2019	$ 0
Expected employer contributions, 2020	0
Cash contributions to pension and other postretirement plans	5,584	$ 11,304	$ 14,452
Pension Benefits [Member]
Benefit Payments, Gross
Defined benefit plan expected gross future benefit payments, 2019	16,362
Defined benefit plan expected gross future benefit payments, 2020	17,087
Defined benefit plan expected gross future benefit payments, 2021	17,835
Defined benefit plan expected gross future benefit payments, 2022	18,956
Defined benefit plan expected gross future benefit payments, 2023	19,770
Defined benefit plan expected gross future benefit payments, 2024-2028	110,037
Postretirement Benefits [Member]
Benefit Payments, Gross
Defined benefit plan expected gross future benefit payments, 2019	4,248
Defined benefit plan expected gross future benefit payments, 2020	4,585
Defined benefit plan expected gross future benefit payments, 2021	4,994
Defined benefit plan expected gross future benefit payments, 2022	5,325
Defined benefit plan expected gross future benefit payments, 2023	5,604
Defined benefit plan expected gross future benefit payments, 2024-2028	29,478
Medicare Part D Subsidies
Expected Medicare Part D Subsidies, 2019	(228)
Expected Medicare Part D Subsidies, 2020	(252)
Expected Medicare Part D Subsidies, 2021	(276)
Expected Medicare Part D Subsidies, 2022	(305)
Expected Medicare Part D Subsidies, 2023	(334)
Expected Medicare Part D Subsidies, 2024-2028	(2,103)
Benefit Payments, Net
Defined benefit plan expected net future benefit payments, 2018	4,020
Defined benefit plan expected net future benefit payments, 2020	4,333
Defined benefit plan expected net future benefit payments, 2021	4,718
Defined benefit plan expected net future benefit payments, 2022	5,020
Defined benefit plan expected net future benefit payments, 2023	5,270
Defined benefit plan expected net future benefit payments, 2024-2028	$ 27,375

Derivative and Hedging Instru_3

Derivative and Hedging Instruments (Details-1) $ in Thousands		12 Months Ended
		Dec. 31, 2018USD ($)DthMWhMW		Dec. 31, 2017USD ($)DthMWhMW	Dec. 31, 2016USD ($)
Derivative Fair Values [Abstract]
Derivative, right to reclaim collateral (receivable)		$ 0		$ 100
Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		377		806	$ 230
Commodity Contracts and Financial Transimission Rights [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		$ 700		$ 200
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		386,440		552,310
Notional amount, decatherm measure (in Dth) | Dth		5,260,000		5,460,000
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 801		$ 676
Liability Derivatives, fair value, gross basis		342		793
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	727
Liability Derivatives, fair value, gross basis		270	[1]	100
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	74
Liability Derivatives, fair value, gross basis	[1]	$ 72
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1],[2]			566
Liability Derivatives, fair value, gross basis	[1],[2]			603
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]			110
Liability Derivatives, fair value, gross basis	[1]			$ 190
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Maximum term of derivative hedging contract		4 years
Financial Transmission Rights [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		2,252		2,226
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 241		$ 329
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		241		329
Liability Derivatives, fair value, gross basis		$ 0		$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		2,050		2,650
Derivative Fair Values [Abstract]
Derivative fair value, net		$ (32,500)		$ (42,200)
Liability Derivatives, fair value, gross basis		32,530		42,170
PPA [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		8,550		8,180
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		$ 23,980		$ 33,990
[1]	As of December 31, 2017 , collateral of $ 0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions as of December 31, 2018 .
[2]	As of December 31, 2017 , MGE presented $ 0.1 million as other current assets on the consolidated balance sheets.

Derivative and Hedging Instru_4

Derivative and Hedging Instruments (Details-2) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Commodity Derivative Contracts [Member]
Offsetting Assets [Line Items]
Gross amounts	$ 801	$ 676
Gross amounts offset in balance sheet	(342)	(654)
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	459	22
Financial Transmission Rights [Member]
Offsetting Assets [Line Items]
Gross amounts	241	329
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 241	$ 329

Derivative and Hedging Instru_5

Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	$ 342	$ 793
Gross amounts offset in balance sheet	(342)	(654)
Collateral posted against derivative positions	0	(139)
Net amount presented in the balance sheet	0	0
PPA [Member]
Offsetting Liabilities [Line Items]
Gross amounts	32,530	42,170
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in the balance sheet	$ 32,530	$ 42,170

Derivative and Hedging Instru_6

Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Current and Long-Term Regulatory Asset [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	$ 41,958	$ 49,281
Unrealized (gain) loss	(11,094)	(2,743)
Realized (loss) gain reclassified to a deferred account	523	(1,260)
Realized loss reclassified to income statement	443	(3,320)
Ending balance	31,830	41,958
Other Current Assets [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	806	230
Unrealized (gain) loss	0	0
Realized (loss) gain reclassified to a deferred account	(523)	1,260
Realized loss reclassified to income statement	94	(684)
Ending balance	$ 377	$ 806

Derivative and Hedging Instru_7

Derivative and Hedging Instruments (Details-5) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)counterparty	Dec. 31, 2017USD ($)
Counterparties in net liability position or default [Abstract]
Derivative, net liability position of counterparties	$ 0	$ 100
Number of counterparties in default | counterparty	0
Commodity Derivative Contracts [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	$ (716)	786
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	(199)	634
Financial Transmission Rights [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	(702)	(1,464)
Financial Transmission Rights [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	0	0
PPA [Member]
Derivative collateral required to be posted for ten-year PPA [Abstract]
Minimum collateral that may be required to be posted	20,000
Maximum collateral that may be required to be posted	40,000
Collateral posted	0
PPA [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	1,080	4,048
PPA [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	$ 0	$ 0

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,535	$ 4,270
Carrying Amount [Member]
Assets:
Cash and cash equivalents		83,102	107,952
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	502,431	426,883
Fair Value [Member]
Assets:
Cash and cash equivalents		83,102	107,952
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	518,811	475,282
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		4,843	5,951
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	502,431	426,883
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		4,843	5,951
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	$ 518,811	$ 475,282
[1]	Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.5 million and $4.3 million at December 31, 2018 and 2017, respectively.

Fair Value of Financial Instr_4

Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Assets:
Available-for-sale securities	[1]	$ 9,363	$ 7,291
Recurring [Member]
Assets:
Derivative assets, net		1,042	1,005
Total Assets		1,890	1,797
Liabilities:
Derivative liabilities, net		32,872	42,963	[2]
Deferred compensation		3,078	3,065
Total Liabilities		35,950	46,028
Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		848	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		296	278
Total Assets		1,144	1,070
Liabilities:
Derivative liabilities, net		124	210	[2]
Deferred compensation		0	0
Total Liabilities		124	210
Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		848	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		0	0
Liabilities:
Derivative liabilities, net		0	0	[2]
Deferred compensation		3,078	3,065
Total Liabilities		3,078	3,065
Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net		746	727
Total Assets		746	727
Liabilities:
Derivative liabilities, net		32,748	42,753	[2]
Deferred compensation		0	0
Total Liabilities		32,748	42,753
Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
MGE [Member]
Assets:
Available-for-sale securities	[1]	388	409
Liabilities:
Derivative liability, collateral offset		0	100
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net		1,042	1,005
Total Assets		1,085	1,069
Liabilities:
Derivative liabilities, net		32,872	42,963	[2]
Deferred compensation		3,078	3,065
Total Liabilities		35,950	46,028
MGE [Member] | Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		43	64
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		296	278
Total Assets		339	342
Liabilities:
Derivative liabilities, net		124	210	[2]
Deferred compensation		0	0
Total Liabilities		124	210
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		43	64
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		0	0
Liabilities:
Derivative liabilities, net		0	0	[2]
Deferred compensation		3,078	3,065
Total Liabilities		3,078	3,065
MGE [Member] | Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
MGE [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net		746	727
Total Assets		746	727
Liabilities:
Derivative liabilities, net		32,748	42,753	[2]
Deferred compensation		0	0
Total Liabilities		32,748	42,753
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		$ 0	$ 0
[1]	Reflects modified retrospective application of new authoritative guidance related to Financial Instruments as described in Footnote 2. Prior to January 1, 2018, investments were considered available for sale securities. As of December 31, 2017, MGE Energy had available for sale securities with a cost basis of $6.7 million, gross unrealized gains of $0.7 million, and gross unrealized losses of less than $0.1 million. As of December 31, 2017, MGE had available for sale securities with a cost basis of $ 0.5 million and gross unrealized losses of less than $0.1 million.
[2]	These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of December 31, 2017.

Fair Value of Financial Instr_5

Fair Value of Financial Instruments (Details-3)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Basis adjustment:
Basis adjustment - on peak	92.10%	92.30%
Basis adjustment - off peak	92.80%	94.10%
US Treasury Bills [Member]
Deferred compensation plan
Investment interest calculation, investment maturity period (26 weeks)	182 days
Investment interest calculation, monthly compounding rate	1.00%
Investment interest calculation, minimum annual rate compounded monthly	7.00%
Minimum [Member]
Counterparty fuel mix:
Internal generation	50.00%	55.00%
Purchased power	25.00%	25.00%
Maximum [Member]
Counterparty fuel mix:
Internal generation	75.00%	75.00%
Purchased power	50.00%	45.00%

Fair Value of Financial Instr_6

Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance		$ (42,026)	$ (50,306)	$ (53,501)
Realized and unrealized gains (losses):
Included in regulatory liabilities		10,024	8,281	3,195
Included in other comprehensive income		0	0	0
Included in earnings	[1]	132	(3,718)	(5,347)
Included in current assets		(47)	(9)	(142)
Purchases		23,643	24,181	23,346
Sales		0	0	0
Issuances		0	0	0
Settlements		(23,728)	(20,455)	(17,857)
Transfers in and/or out of Level 3		0	0	0
Ending balance		(32,002)	(42,026)	(50,306)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	0	0	0
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	355	(3,314)	(5,262)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ (223)	$ (404)	$ (85)
[1]	MGE's exchange-traded derivative contracts, over-the-count er party transactions, purchased power agreement, and FTRs are subject to regulatory deferral. These derivatives are therefore marked to fair value and are offset in the financial statements with a corresponding regulatory asset or liability.

Share-Based Compensation (Detai

Share-Based Compensation (Details) - USD ($) $ in Millions

Feb. 15, 2019

Jan. 18, 2019

Mar. 01, 2018

Feb. 16, 2018

Jan. 19, 2018

Mar. 01, 2017

Jan. 20, 2017

Feb. 19, 2016

Feb. 20, 2015

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation expense

$ 1.1

$ 1

$ 3.1

Cash payments distributed related to awards previously granted and now payable

1.6

Awards forfeited during period, value

$ 0

$ 0

$ 0

Awards forfeited during period, units

0

0

0

Outstanding awards vested during period

$ 5.2

Performance Unit Plan [Member] | Performance Units [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Awards granted (in units)

17,830

14,704

19,055

18,948

Performance Unit Plan [Member] | Performance Units [Member] | Subsequent Event [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Awards granted (in units)

17,022

Director Incentive Agreement [Member] | Performance Units [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

Awards granted (in units)

1,106

4,704

4,608

Director Incentive Agreement [Member] | Performance Units [Member] | Subsequent Event [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Awards granted (in units)

5,175

Commitments and Contingencies_2

Commitments and Contingencies (Details-1) $ in Thousands	Dec. 31, 2018USD ($)TurbinesMW
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	$ 95,479
Purchase obligation due in second year	60,155
Purchase obligation due in third year	53,336
Purchase obligation due in fourth year	39,280
Purchase obligation due in fifth year	29,319
Purchase obligation due thereafter	$ 75,119
Saratoga Wind
Saratoga Capacity (MW) | MW	66
Saratoga Turbines | Turbines	33
Saratoga Wind Project Costs	$ 95,800
Coal [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	25,167	[1]
Purchase obligation due in second year	8,213	[1]
Purchase obligation due in third year	828	[1]
Purchase obligation due in fourth year	0	[1]
Purchase obligation due in fifth year	0	[1]
Purchase obligation due thereafter	0	[1]
Natural Gas, Transportation and Storage [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	21,051	[2]
Purchase obligation due in second year	20,853	[2]
Purchase obligation due in third year	20,853	[2]
Purchase obligation due in fourth year	20,853	[2]
Purchase obligation due in fifth year	20,853	[2]
Purchase obligation due thereafter	53,361	[2]
Natural Gas, Supply [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	15,423	[3]
Purchase obligation due in second year	0	[3]
Purchase obligation due in third year	0	[3]
Purchase obligation due in fourth year	0	[3]
Purchase obligation due in fifth year	0	[3]
Purchase obligation due thereafter	0	[3]
Purchase Power [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	27,577	[4]
Purchase obligation due in second year	28,082	[4]
Purchase obligation due in third year	28,675	[4]
Purchase obligation due in fourth year	15,533	[4]
Purchase obligation due in fifth year	5,641	[4]
Purchase obligation due thereafter	21,751	[4]
Other [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	6,261
Purchase obligation due in second year	3,007
Purchase obligation due in third year	2,980
Purchase obligation due in fourth year	2,894
Purchase obligation due in fifth year	2,825
Purchase obligation due thereafter	$ 7
[1]	Total coal commitments for the Columbia and Elm Road Units , including transportation . Fuel procurement for MGE's jointly owned Columbia and Elm Road Units is handled by WPL and WEPCO, respectively, who are the operators of those facilities .
[2]	MGE's natural gas transportation and storage contracts require fixed monthly payments for firm supply pipeline transportation and storage capacity. The pricing components of the fixed monthly payments for the transportation and storage contracts are established by FERC but may be subject to change.
[3]	These commitments include market-based pricing.
[4]	MGE has several purchase power agreements to help meet futu re electric supply requirements .

Commitments and Contingencies_3

Commitments and Contingencies (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Leases, Future Minimum Rental Payments [Abstract]
Minimum lease payments, 2019	$ 1,646
Minimum lease payments, 2020	1,371
Minimum lease payments, 2021	1,095
Minimum lease payments, 2022	989
Minimum lease payments, 2023	975
Minimum lease payments, Thereafter	22,707
Rental expense under operating leases	$ 1,600	$ 1,700	$ 2,000
Operating leases, renewal option term (one year or less)	1 year

Commitments and Contingencies_4

Commitments and Contingencies (Details-3)	Dec. 31, 2018pollutantstateMW
Minimum [Member]
EPA Greenhouse Gas Reduction Guidlines [Abstract]
Reduction in GHG emissions, percentage	32.00%
Standard of Performance Plan for EGUs over threshold | MW	25
Wisconsin Energy Efficiency and Renewables Act [Member]
Energy Efficiency and Renewables
Minimum electricity generated from renewable resources	10.00%
EPA [Member]
EPA's National Ambient Air Quality Standards
Number of pollutants monitored by the National Ambient Air Quality Standards | pollutant	6
EPA's Cross State Air Pollution Rule
Number of states incorporating 2008 ozone NAAQS attainment levels | state	22

Commitments and Contingencies_5

Commitments and Contingencies (Details-4)	12 Months Ended
	Dec. 31, 2018USD ($)
Other Commitments [Line Items]
Other commitments, due in 2019	$ 333,000
Other commitments, due in 2020	333,000
Other commitments, due in 2021	333,000
Other commitments, due in 2022	333,000
Other commitments, due in 2023	333,000
Other commitment, due thereafter	3,665,000
Investments in Non Public Entities, Capital Infusions [Member]
Other Commitments [Line Items]
Other commitment, initial agreed upon commitment total	$ 11,400,000
Venture Debt Fund [Member]
Other Commitments [Line Items]
Other commitment, contract term, expiring in 2019	3 years
Other commitment, initial agreed upon commitment total	$ 1,500,000
Other commitments, total as of balance sheet date	$ 600,000

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017
Asset Retirement Obligations [Roll Forward]
Asset retirement obligation, beginning balance	$ 26,738		$ 26,886
Liabilities incurred	1,943	[1]	145
Accretion expense	1,415		1,359
Liabilities settled	(175)		(1,789)	[2]
Revisions in estimated cash flows	59		137
Asset retirement obligation, ending balance	29,980		26,738
Blount Asbestos Removal [Member]
Asset Retirement Obligations [Roll Forward]
Liabilities settled			$ (1,600)
Forward Wind [Member]
Asset Retirement Obligations [Roll Forward]
Liabilities incurred	$ 1,600
[1]	In 2018, MGE recorded an obligation of $1.6 million for the fair value of its legal liability for AROs associated with Forward Wind. See Footnote 5 for additional information on the purchase of Forward Wind.
[2]	In 2017, MGE removed a stack at Blount resulting in a $1.6 million settlement .

Revenue (Details-1)

Revenue (Details-1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Total Operating Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 559,768	$ 563,099	[1]	$ 544,745	[1]
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	400,882	413,926		409,006
Electric [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	138,566	136,168		136,792
Electric [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	204,683	216,461	[1]	213,101	[1]
Electric [Member] | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	13,878	16,176		17,589
Electric [Member] | Other-retail/municipal [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	34,023	38,010		35,559
Electric [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	391,150	406,815		403,041
Electric [Member] | Sales To The Market [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	7,438	4,067		6,135
Electric [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	1,870	2,323		1,483
Electric [Member] | Adjustments To Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	424	721		(1,653)
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	157,767	148,825		134,543
Gas [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	94,017	88,695		81,014
Gas [Member] | Commercial/Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	59,060	55,151	[1]	48,497	[1]
Gas [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	153,077	143,846		129,511
Gas [Member] | Gas Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	4,283	4,561		4,635
Gas [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	407	418		397
Non Regulated Energy [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 1,119	348		1,196
MGE [Member]
Disaggregation of Revenue [Line Items]
CNG Vehicle Fuel Servicing		$ 100		$ 100
[1]	In 2017 and 2016, MGE had less than $0.1 million of revenues related to CNG vehicle fuel servicing. No revenue was recognized for fuel servicing by MGE Energy in 2017 and 2016.

Noncontrolling Interest (Detail

Noncontrolling Interest (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act	[1]		$ 21,651
MGE Power [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent		100.00%
MGE [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet		$ 141,454	140,902
Net income attributable to noncontrolling interest, net of tax		22,552	43,237	$ 23,358
MGE [Member] | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act	[1]		21,649
MGE Transco [Member]
Noncontrolling Interest [Line Items]
Net income attributable to noncontrolling interest, net of tax	[2]	0	0	1,410
MGE Power West Campus [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet	[3]	43,935	43,267
Net income attributable to noncontrolling interest, net of tax	[3]	7,168	13,963	7,200
MGE Power West Campus [Member] | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act			6,800
MGE Power Elm Road [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet	[3]	97,519	97,635
Net income attributable to noncontrolling interest, net of tax	[3]	$ 15,384	29,274	$ 14,748
MGE Power Elm Road [Member] | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act			$ 14,800
[1]	Generated by nonregulated activities.
[2]	A s of December 31, 2018 , MGE Energy is the owner of MGE Transco. In July 2016, MGE's ownership interest in MGE Transco declined below a majority as a result of continued funding of ATC capital contributions by MGE Energy. As a result of the change in majority owner ship in MGE Transco , MGE deconsolidated MGE Energy's proportionate share of the equity in MGE Transco. The change in co nsolidation was applied prospectively by reducing its investment and noncontrolling interest on MGE's consolidated financial statements. The change had no effect on MGE Energy's consolidated financial statements; however, MGE Energy's proportionate share o f the equity and net income of MGE Transco classified as noncontrolling interest was deconsolidated from MGE ' s financial statements. No gain or loss was recognized in July 2016 due to MGE ceasing to have a controlling financial interest .
[3]	MGE Power Elm Road and MGE Power West Campus are not su bsidiaries of MGE; however, they have been consolidated in the consolidated financial s tatements of MGE (see Footnote 3 ). MGE Power Elm Road and MGE Power West Campus are 100 % owned by MGE Power, and MGE Power is 100 % o wned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE consolidated financial statements as noncontrolling interest . In 2017, there was a $14.8 million and $6.8 million one-time tax impact as a result of the Tax Act for MGE Power Elm Road and MGE Power West Campus, respectively. The Tax Act reduced the f ederal tax rate from 35% to 21%. See Footnote 12 for further information .

Segment Information (Details)

Segment Information (Details) - USD ($)		3 Months Ended												12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating revenues		$ 140,079,000	$ 137,795,000	$ 124,262,000	$ 157,632,000	$ 140,274,000		$ 139,539,000		$ 126,463,000		$ 156,823,000		$ 559,768,000	$ 563,099,000		$ 544,745,000
Depreciation and amortization														(56,412,000)	(53,077,000)		(44,646,000)
Other operating expenses														(389,149,000)	(385,397,000)	[1]	(376,217,000)	[1]
Operating Income (Loss)		23,990,000	39,798,000	24,231,000	26,188,000	25,197,000		41,997,000		25,595,000		31,836,000		114,207,000	124,625,000		123,882,000
Other (deductions) income, net														17,055,000	14,399,000	[1]	14,057,000	[1]
Interest (expense) income, net														(19,609,000)	(19,324,000)		(19,866,000)
Income before income taxes														111,653,000	119,700,000		118,073,000
Income tax (provision) benefit		(5,642,000)	(9,597,000)	(5,828,000)	(6,367,000)	13,393,000	[2]	(15,584,000)	[2]	(8,736,000)	[2]	(11,167,000)	[2]	(27,434,000)	(22,094,000)	[2]	(42,513,000)
Net Income		16,361,000	$ 29,506,000	$ 18,351,000	$ 20,001,000	36,134,000		$ 26,629,000		$ 15,543,000		$ 19,300,000		84,219,000	97,606,000		75,560,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,988,618,000				1,855,182,000								1,988,618,000	1,855,182,000		1,801,060,000
Capital expenditures														212,197,000	108,131,000		83,659,000
Effects Of The Tax Cuts And Jobs Act [Abstract]
Investment in ATC		66,339,000				60,426,000								66,339,000	60,426,000
Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act	[3]														21,651,000
Investment in ATC						20,375,000									20,375,000
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues														400,882,000	413,926,000		409,006,000
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues														157,767,000	148,825,000		134,543,000
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues														1,119,000	348,000		1,196,000
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues														559,768,000	563,099,000		544,745,000
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues														400,593,000	413,416,000		410,918,000
Depreciation and amortization														(38,925,000)	(36,660,000)		(29,122,000)
Other operating expenses														(297,374,000)	(308,100,000)	[1]	(313,649,000)	[1]
Operating Income (Loss)														64,294,000	68,656,000		68,147,000
Other (deductions) income, net														7,294,000	4,539,000	[1]	3,668,000	[1]
Interest (expense) income, net														(12,198,000)	(11,257,000)		(11,147,000)
Income before income taxes														59,390,000	61,938,000		60,668,000
Income tax (provision) benefit														(13,453,000)	(20,547,000)	[2]	(20,115,000)
Net Income														45,937,000	41,391,000		40,553,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,193,083,000				1,058,988,000								1,193,083,000	1,058,988,000		1,038,307,800
Capital expenditures														176,399,000	77,353,000		50,699,000
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues														173,843,000	163,799,000		155,921,000
Depreciation and amortization														(10,060,000)	(9,000,000)		(8,128,000)
Other operating expenses														(145,883,000)	(135,029,000)	[1]	(128,721,000)	[1]
Operating Income (Loss)														17,900,000	19,770,000		19,072,000
Other (deductions) income, net														3,132,000	1,912,000	[1]	1,668,000	[1]
Interest (expense) income, net														(3,692,000)	(3,234,000)		(3,223,000)
Income before income taxes														17,340,000	18,448,000		17,517,000
Income tax (provision) benefit														(4,474,000)	(7,303,000)	[2]	(6,894,000)
Net Income														12,866,000	11,145,000		10,623,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		377,005,000				354,875,000								377,005,000	354,875,000		329,538,200
Capital expenditures														30,497,000	26,847,000		29,136,000
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues														40,645,000	44,816,000		45,126,000
Depreciation and amortization														(7,427,000)	(7,417,000)		(7,372,000)
Other operating expenses														(144,000)	(190,000)	[1]	(155,000)	[1]
Operating Income (Loss)														33,074,000	37,209,000		37,599,000
Other (deductions) income, net														0	0	[1]	0	[1]
Interest (expense) income, net														(5,307,000)	(5,533,000)		(5,768,000)
Income before income taxes														27,767,000	31,676,000		31,831,000
Income tax (provision) benefit														(7,534,000)	8,860,000	[2]	(12,775,000)
Net Income														20,233,000	40,536,000		19,056,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		265,301,000				270,384,000								265,301,000	270,384,000		271,277,000
Capital expenditures														5,301,000	3,931,000		3,824,000
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0
Depreciation and amortization														0	0		0
Other operating expenses														(16,000)	(9,000)	[1]	(17,000)	[1]
Operating Income (Loss)														(16,000)	(9,000)		(17,000)
Other (deductions) income, net														8,602,000	9,844,000	[1]	8,429,000	[1]
Interest (expense) income, net														0	0		0
Income before income taxes														8,586,000	9,835,000		8,412,000
Income tax (provision) benefit														(2,345,000)	(3,954,000)	[2]	(2,836,000)
Net Income														6,241,000	5,881,000		5,576,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		66,366,000				61,783,000	[4]							66,366,000	61,783,000	[4]	74,535,000
Capital expenditures														0	0		0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0
Depreciation and amortization														0	0		(24,000)
Other operating expenses														(1,045,000)	(1,001,000)	[1]	(895,000)	[1]
Operating Income (Loss)														(1,045,000)	(1,001,000)		(919,000)
Other (deductions) income, net														(1,973,000)	(1,896,000)	[1]	292,000	[1]
Interest (expense) income, net														1,588,000	700,000		272,000
Income before income taxes														(1,430,000)	(2,197,000)		(355,000)
Income tax (provision) benefit														372,000	850,000	[2]	107,000
Net Income														(1,058,000)	(1,347,000)		(248,000)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		465,661,000				485,548,000								465,661,000	485,548,000		465,202,000
Capital expenditures														0	0		0
Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues														(55,313,000)	(58,932,000)		(67,220,000)
Depreciation and amortization														0	0		0
Other operating expenses														55,313,000	58,932,000	[1]	67,220,000	[1]
Operating Income (Loss)														0	0		0
Other (deductions) income, net														0	0	[1]	0	[1]
Interest (expense) income, net														0	0		0
Income before income taxes														0	0		0
Income tax (provision) benefit														0	0	[2]	0
Net Income														0	0		0
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		(378,798,000)				(376,396,000)								(378,798,000)	(376,396,000)		(377,800,000)
Capital expenditures														0	0		0
Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues														(289,000)	(510,000)		1,912,000
Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues														16,076,000	14,974,000		21,378,000
Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues														39,526,000	44,468,000		43,930,000
Consolidation/Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0
Consolidation/Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues														559,768,000	563,111,000		544,798,000
Depreciation and amortization														(56,412,000)	(53,077,000)		(44,622,000)
Other operating expenses	[5]													(413,186,000)	(402,678,000)	[1],[2]	(414,973,000)	[1]
Operating Income (Loss)	[5]													90,170,000	107,356,000		85,203,000
Other (deductions) income, net	[5]													10,063,000	5,740,000	[1]	9,527,000	[1]
Interest (expense) income, net														(21,197,000)	(20,024,000)		(20,138,000)
Income tax (provision) benefit														(25,461,000)	(18,990,000)		(41,791,000)
Net Income Including Noncontrolling Interest														79,036,000	93,072,000		74,592,000
Less Net Income Attributable to Noncontrolling Interest, net of tax														(22,552,000)	(43,237,000)		(23,358,000)
Net Income														56,484,000	49,835,000		51,234,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,834,891,000				1,684,041,000								1,834,891,000	1,684,041,000		1,638,852,000
Capital expenditures														212,197,000	108,131,000		83,659,000
Effects Of The Tax Cuts And Jobs Act [Abstract]
Investment in ATC		0				0								0	0
MGE [Member] | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act	[3]														21,649,000
Investment in ATC						0									0
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues														400,882,000	413,929,000		409,030,000
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues														157,767,000	148,834,000		134,572,000
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues														1,119,000	348,000		1,196,000
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0	[6]
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues														559,768,000	563,111,000		544,798,000
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues														400,593,000	413,416,000		410,918,000
Depreciation and amortization														(38,925,000)	(36,660,000)		(29,122,000)
Other operating expenses	[5]													(310,626,000)	(328,093,000)	[1],[2]	(333,632,000)	[1]
Operating Income (Loss)	[5]													51,042,000	48,663,000		48,164,000
Other (deductions) income, net	[5]													7,093,000	3,985,000	[1]	3,536,000	[1]
Interest (expense) income, net														(12,198,000)	(11,257,000)		(11,147,000)
Net Income Including Noncontrolling Interest														45,937,000	41,391,000		40,553,000
Less Net Income Attributable to Noncontrolling Interest, net of tax														0	0		0
Net Income														45,937,000	41,391,000		40,553,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,193,083,000				1,058,988,000								1,193,083,000	1,058,988,000		1,038,307,800
Capital expenditures														176,399,000	77,353,000		50,699,000
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues														173,843,000	163,799,000		155,921,000
Depreciation and amortization														(10,060,000)	(9,000,000)		(8,128,000)
Other operating expenses	[5]													(150,195,000)	(142,175,000)	[1],[2]	(135,578,000)	[1]
Operating Income (Loss)	[5]													13,588,000	12,624,000		12,215,000
Other (deductions) income, net	[5]													2,970,000	1,755,000	[1]	1,631,000	[1]
Interest (expense) income, net														(3,692,000)	(3,234,000)		(3,223,000)
Net Income Including Noncontrolling Interest														12,866,000	11,145,000		10,623,000
Less Net Income Attributable to Noncontrolling Interest, net of tax														0	0		0
Net Income														12,866,000	11,145,000		10,623,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		377,005,000				354,875,000								377,005,000	354,875,000		329,538,200
Capital expenditures														30,497,000	26,847,000		29,136,000
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues														40,645,000	44,816,000		45,126,000
Depreciation and amortization														(7,427,000)	(7,417,000)		(7,372,000)
Other operating expenses	[5]													(7,678,000)	8,670,000	[1],[2]	(12,930,000)	[1]
Operating Income (Loss)	[5]													25,540,000	46,069,000		24,824,000
Other (deductions) income, net	[5]													0	0	[1]	0	[1]
Interest (expense) income, net														(5,307,000)	(5,533,000)		(5,768,000)
Net Income Including Noncontrolling Interest														20,233,000	40,536,000		19,056,000
Less Net Income Attributable to Noncontrolling Interest, net of tax														0	0		0
Net Income														20,233,000	40,536,000		19,056,000
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		265,251,000				270,334,000								265,251,000	270,334,000		271,227,000
Capital expenditures														5,301,000	3,931,000		3,824,000
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues														0	0		0	[6]
Depreciation and amortization														0	0		0	[6]
Other operating expenses	[5]													0	0	[1],[2]	0	[1],[6]
Operating Income (Loss)	[5]													0	0		0	[6]
Other (deductions) income, net	[5]													0	0	[1]	4,360,000	[1],[6]
Interest (expense) income, net														0	0		0	[6]
Net Income Including Noncontrolling Interest														0	0		4,360,000	[6]
Less Net Income Attributable to Noncontrolling Interest, net of tax														0	0		0	[6]
Net Income														0	0		4,360,000	[6]
MGE [Member] | Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues														(55,313,000)	(58,920,000)		(67,167,000)
Depreciation and amortization														0	0		0
Other operating expenses	[5]													55,313,000	58,920,000	[1],[2]	67,167,000	[1]
Operating Income (Loss)	[5]													0	0		0
Other (deductions) income, net	[5]													0	0	[1]	0	[1]
Interest (expense) income, net														0	0		0
Net Income Including Noncontrolling Interest														0	0		0
Less Net Income Attributable to Noncontrolling Interest, net of tax														(22,552,000)	(43,237,000)		(23,358,000)
Net Income														(22,552,000)	(43,237,000)		(23,358,000)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		$ (448,000)				$ (156,000)								(448,000)	(156,000)		(221,000)
Capital expenditures														0	0		0
MGE [Member] | Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues														(289,000)	(513,000)		1,888,000
MGE [Member] | Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues														16,076,000	14,965,000		21,349,000
MGE [Member] | Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues														39,526,000	44,468,000		43,930,000
MGE [Member] | Consolidation/Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues														$ 0	$ 0		$ 0	[6]
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for further information.
[2]	In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.
[3]	Generated by nonregulated activities.
[4]	In December 2017, there was a $20.4 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.
[5]	Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.
[6]	As of July 31, 2016, MGE no longer consolidates MGE Energy's proportionate share of equity earnings in MGE Transco. See Footnote 6 for further information.

Quarterly Summary of Operatio_3

Quarterly Summary of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended												12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Operating Revenues:
Electric revenues		$ 88,464	$ 119,388	$ 99,282	$ 94,867	$ 92,734		$ 120,761		$ 102,382		$ 98,397		$ 402,001	$ 414,274		$ 410,202
Gas revenues		51,615	18,407	24,980	62,765	47,540		18,778		24,081		58,426		157,767	148,825		134,543
Total Operating Revenues		140,079	137,795	124,262	157,632	140,274		139,539		126,463		156,823		559,768	563,099		544,745
Operating expenses		116,089	97,997	100,031	131,444	115,077	[1]	97,542	[1]	100,868	[1]	124,987	[1]	445,561	438,474		420,863
Operating Income (Loss)		23,990	39,798	24,231	26,188	25,197		41,997		25,595		31,836		114,207	124,625		123,882
Interest and other income, net		(1,987)	(695)	(52)	180	(2,456)	[1]	216	[1]	(1,316)	[1]	(1,369)	[1]
Income tax provision		(5,642)	(9,597)	(5,828)	(6,367)	13,393	[2]	(15,584)	[2]	(8,736)	[2]	(11,167)	[2]	(27,434)	(22,094)	[2]	(42,513)
Net Income		$ 16,361	$ 29,506	$ 18,351	$ 20,001	$ 36,134		$ 26,629		$ 15,543		$ 19,300		$ 84,219	$ 97,606		$ 75,560
Earnings per common share		$ 0.47	$ 0.85	$ 0.53	$ 0.58	$ 1.04		$ 0.77		$ 0.45		$ 0.56		$ 2.43	$ 2.82		$ 2.18
Dividends per share		$ 0.338	$ 0.338	$ 0.323	$ 0.3225	$ 0.323		$ 0.323		$ 0.308		$ 0.308		$ 1.32	$ 1.26		$ 1.21
Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act
Net Deferred Income Tax Benefit Tax Cuts And Jobs Act	[3]														$ 21,651
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for more information.
[2]	In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.
[3]	Generated by nonregulated activities.

Schedule I - Condensed Parent C

Schedule I - Condensed Parent Company Finanical Statements (Details-Comprehensive Income Statement) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Operating Expenses:
Other operations and maintenance													$ 177,823	$ 177,740		$ 172,335
Total Operating Expenses	$ 116,089	$ 97,997	$ 100,031	$ 131,444	$ 115,077	[1]	$ 97,542	[1]	$ 100,868	[1]	$ 124,987	[1]	445,561	438,474		420,863
Operating Income (Loss)	23,990	39,798	24,231	26,188	25,197		41,997		25,595		31,836		114,207	124,625		123,882
Equity earnings of investments													8,821	10,125		8,428
Income before income taxes													111,653	119,700		118,073
Income tax provision	(5,642)	(9,597)	(5,828)	(6,367)	13,393	[2]	(15,584)	[2]	(8,736)	[2]	(11,167)	[2]	(27,434)	(22,094)	[2]	(42,513)
Net Income	$ 16,361	$ 29,506	$ 18,351	$ 20,001	$ 36,134		$ 26,629		$ 15,543		$ 19,300		84,219	97,606		75,560
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized gain (loss) on available for sale securities, net of tax													0	175		(155)
Comprehensive Income													84,219	97,781		75,405
MGE Energy [Member]
Operating Expenses:
Other operations and maintenance													913	880		720
Total Operating Expenses													913	880		720
Operating Income (Loss)													(913)	(880)		(720)
Equity earnings of investments													85,220	99,246		75,581
Other income/(loss), net													(1,966)	(2,165)		435
Interest income, net													1,489	605		176
Income before income taxes													83,830	96,806		75,472
Income tax provision													389	800		88
Net Income													84,219	97,606		75,560
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Unrealized gain (loss) on available for sale securities, net of tax													0	175		(155)
Comprehensive Income													$ 84,219	$ 97,781		$ 75,405
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits. See Footnote 2 for more information.
[2]	In December 2017, there was a $21.7 million one-time tax impact as a result of the Tax Act. See Footnote 12 for further information.

Schedule I - Condensed Parent_2

Schedule I - Condensed Parent Company Finanical Statements (Details-Comprehensive Income Statement Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Unrealized gain (loss) on available-for-sale securities, taxes expense (benefit)	$ 0	$ 117	$ (104)
MGE Energy [Member]
Condensed Income Statements, Captions [Line Items]
Unrealized gain (loss) on available-for-sale securities, taxes expense (benefit)	$ 0	$ 117	$ (104)

Schedule I - Condensed Parent_3

Schedule I - Condensed Parent Company Finanical Statements (Details-Cash Flow Statement) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	$ 153,040	$ 131,373	$ 147,864
Investing Activities:
Other	(205)	118	(196)
Cash Used for Investing Activities	(218,328)	(116,275)	(86,813)
Financing Activities:
Cash dividends paid on common stock	(45,762)	(43,682)	(41,775)
Other	(662)	(597)	(70)
Cash Provided by (Used for) Financing Activities	38,123	(4,637)	(46,112)
Change in cash, cash equivalents, and restricted cash:	(27,165)	10,461	14,939
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633	86,694
Cash, cash equivalents, and restricted cash at end of period	84,929	112,094	101,633
MGE Energy [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	27,211	70,268	74,994
Investing Activities:
Contributions to affiliates	(3,200)	(6,522)	(2,789)
Contributions to other Investments	(2,626)	(4,534)	(360)
Other	873	843	385
Cash Used for Investing Activities	(4,953)	(10,213)	(2,764)
Financing Activities:
Cash dividends paid on common stock	(45,762)	(43,682)	(41,775)
Other	0	(58)	(11)
Cash Provided by (Used for) Financing Activities	(45,762)	(43,740)	(41,786)
Change in cash, cash equivalents, and restricted cash:	(23,504)	16,315	30,444
Cash, cash equivalents, and restricted cash at beginning of period	98,540	82,225	51,781
Cash, cash equivalents, and restricted cash at end of period	$ 75,036	$ 98,540	$ 82,225

Schedule I - Condensed Parent_4

Schedule I - Condensed Parent Company Finanical Statements (Details-Balance Sheet) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Assets:
Cash and cash equivalents	$ 83,102,000	$ 107,952,000
Other current assets	8,593,000	12,507,000
Total Current Assets	240,560,000	290,631,000
Other deferred assets and other
Other deferred assets and other	12,488,000	731,000
Investments:
Other investments	2,298,000	55,000
Total investments	78,000,000	67,772,000
Total Assets	1,988,618,000	1,855,182,000	$ 1,801,060,000
Current Liabilities:
Other current liabilities	14,113,000	18,758,000
Total Current Liabilities	120,628,000	126,514,000
Other Credits:
Deferred income taxes	231,952,000	225,130,000
Total Other Credits	558,003,000	552,320,000
Shareholders' Equity:
Retained earnings	465,708,000	426,874,000
Accumulated other comprehensive income, net of tax	0	377,000
Total Common Shareholders' Equity	816,644,000	778,187,000	$ 724,088,000	$ 690,458,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	1,988,618,000	1,855,182,000
MGE Energy [Member]
Current Assets:
Cash and cash equivalents	75,036,000	98,540,000
Other current assets	3,646,000	1,601,000
Total Current Assets	78,682,000	100,141,000
Other deferred assets and other
Other deferred assets and other	110,000	171,000
Investments:
Investments in affiliates	763,625,000	702,134,000
Other investments	7,672,000	5,640,000
Total investments	771,297,000	707,774,000
Total Assets	850,089,000	808,086,000
Current Liabilities:
Accounts payable to affiliates	617,000	665,000
Other current liabilities	2,500,000	2,047,000
Total Current Liabilities	3,117,000	2,712,000
Other Credits:
Deferred income taxes	27,151,000	23,480,000
Accounts payable to affiliates	3,177,000	3,707,000
Total Other Credits	30,328,000	27,187,000
Shareholders' Equity:
Common shareholders' equity	350,936,000	350,936,000
Retained earnings	465,708,000	426,874,000
Accumulated other comprehensive income, net of tax	0	377,000
Total Common Shareholders' Equity	816,644,000	778,187,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	$ 850,089,000	$ 808,086,000

Schedule I - Condensed Parent_5

Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 1) - Line of Credit [Member] - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Credit facilities [Line Items]
Available lines of credit	[1]	$ 150,000	$ 150,000
MGE Energy unsecured committed revolving line of credit totaling $50 million | MGE Energy [Member]
Credit facilities [Line Items]
Available lines of credit		50,000
Line of credit, borrowings outstanding		$ 0
[1]	MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.

Schedule I - Condensed Parent_6

Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 2) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
MGE Energy [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 26,735	$ 67,781	$ 74,107
First Mortgage Bonds [Member] | 7.70%, 2028 Series
Dividend Restrictions
Debt covenant, allowable amount available for payment of dividends	400,000
MGE [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	0	45,000	50,000	[1]
Dividend in kind from affiliate	$ 0	0	15,822
Dividend Restrictions
Common equity ratio	0.563
Amount available for dividend payments without regulatory approval	$ 70,800
MGE [Member] | Minimum [Member]
Dividend Restrictions
Dividend restrictions, common equity ratio	0.55
MGE Power Elm Road [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 15,500	12,000	13,500
MGE Power West Campus [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	6,500	6,000	9,500
MGE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	4,625	4,669	1,107
MGEE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	60	112	0
NGV Fueling Services [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 50	$ 0	$ 0
[1]	Excludes $15.8 million dividend in kind to MGE Energy from MGE in 2016 .

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of period		$ 3,174,945	$ 3,443,296	$ 3,694,080
Charged to costs and expenses		1,065,970	1,015,970	1,195,500
Charged to other accounts		320,400	20,400	19,500
Net accounts written off	[1]	(1,407,653)	(1,304,721)	(1,465,784)
Balance at end of period		$ 3,153,662	$ 3,174,945	$ 3,443,296
[1]	Net of recovery of amounts previously written off.