MGE Energy (MGEE) 10-K 24 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2021	Jun. 30, 2020
Document and Entity Information [Line Items]
Entity Registrant Name	MGE Energy, Inc.
Entity Central Index Key	0001161728
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Amendment Flag	false
Trading Symbol	MGEE
Document Fiscal Year Focus	2020
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			$ 2,292,032,738
Entity Common Stock Shares Outstanding		36,163,370
Entity Emerging Growth Company	false
Entity Small Business	false
lCFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Security 12(b) Title	Common Stock, $1 Par Value Per Share
Entity Tax Identification Number	39-2040501
Entity File Number	000-49965
Entity Incorporation State Country Code	WI
Entity Address Address Line 1	133 S Blair Street
Entity Address City Or Town	Madison
Entity Address State Or Province	WI
Entity Address Postal Zip Code	53788
City Area Code	608
Local Phone Number	252-7000
Document Transition Report	false
Document Annual Report	true
MGE [Member]
Document and Entity Information [Line Items]
Entity Registrant Name	Madison Gas and Electric Company
Entity Central Index Key	0000061339
Entity Well known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding		17,347,894
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Interactive Data Current	Yes
Entity Tax Identification Number	39-0444025
Entity File Number	000-1125
Entity Incorporation State Country Code	WI
Entity Address Address Line 1	133 South Blair Street
Entity Address City Or Town	Madison
Entity Address State Or Province	WI
Entity Address Postal Zip Code	53788
City Area Code	608
Local Phone Number	252-7000
Document Transition Report	false
Document Annual Report	true

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Revenues:
Electric revenues	$ 394,372	$ 408,980	$ 402,001
Gas revenues	144,261	159,875	157,767
Total Operating Revenues	538,633	568,855	559,768
Operating Expenses:
Fuel for electric generation	41,684	51,954	56,141
Purchased power	42,883	41,474	50,807
Cost of gas sold	63,697	79,775	84,968
Other operations and maintenance	186,430	193,322	177,823
Depreciation and amortization	74,188	71,562	56,412
Other general taxes	19,754	19,858	19,410
Total Operating Expenses	428,636	457,945	445,561
Operating Income	109,997	110,910	114,207
Other income, net	25,365	18,811	17,055
Interest expense, net	(23,521)	(23,063)	(19,609)
Income before income taxes	111,841	106,658	111,653
Income tax provision	(19,423)	(19,784)	(27,434)
Net Income Including Noncontrolling Interest	92,418	86,874	84,219
Net Income	$ 92,418	$ 86,874	$ 84,219
Earnings Per Share of Common Stock (basic and diluted)	$ 2.60	$ 2.51	$ 2.43
Dividends per share of common stock	$ 1.45	$ 1.38	$ 1.32
Weighted Average Shares Outstanding (basic and diluted)	35,612	34,668	34,668
MGE [Member]
Operating Revenues:
Electric revenues	$ 394,372	$ 408,980	$ 402,001
Gas revenues	144,261	159,875	157,767
Total Operating Revenues	538,633	568,855	559,768
Operating Expenses:
Fuel for electric generation	41,684	51,954	56,141
Purchased power	42,883	41,474	50,807
Cost of gas sold	63,697	79,775	84,968
Other operations and maintenance	185,450	192,440	176,762
Depreciation and amortization	74,188	71,562	56,412
Other general taxes	19,750	19,858	19,410
Total Operating Expenses	427,652	457,063	444,500
Operating Income	110,981	111,792	115,268
Other income, net	15,019	10,703	10,426
Interest expense, net	(23,642)	(24,298)	(21,197)
Income before income taxes	102,358	98,197	104,497
Income tax provision	(16,835)	(17,418)	(25,461)
Net Income Including Noncontrolling Interest	85,523	80,779	79,036
Less Net Income Attributable to Noncontrolling Interest, net of tax	(22,393)	(22,349)	(22,552)
Net Income	$ 63,130	$ 58,430	$ 56,484

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net Income	$ 92,418,000	$ 86,874,000	$ 84,219,000
Items not affecting cash:
Depreciation and amortization	74,188,000	71,562,000	56,412,000
Deferred income taxes	10,363,000	7,212,000	3,749,000
Provision for doubtful receivables	1,415,000	1,615,000	1,366,000
Employee benefit plan (credit) cost	(3,716,000)	(3,813,000)	(2,002,000)
Equity earnings in investments	(10,221,000)	(9,889,000)	(8,821,000)
Other items	(2,750,000)	163,000	(814,000)
Changes in working capital items:
Trade and other receivables (change)	(3,838,000)	(1,285,000)	(2,235,000)
Inventories (change)	(842,000)	(3,420,000)	2,724,000
Unbilled revenues (change)	(1,613,000)	2,345,000	3,157,000
Prepaid taxes (change)	1,713,000	(677,000)	10,320,000
Other current assets (change)	(1,057,000)	29,000	251,000
Accounts payable (change)	14,353,000	(7,432,000)	(4,855,000)
Other current liabilities (change)	(5,635,000)	(10,264,000)	11,957,000
Dividends from investment	8,998,000	7,347,000	6,958,000
Cash contributions to pension and other postretirement plans	(6,296,000)	(5,714,000)	(5,584,000)
Other noncurrent items, net	4,963,000	(4,178,000)	(3,762,000)
Cash Provided by Operating Activities	172,443,000	130,475,000	153,040,000
Investing Activities:
Capital expenditures	(203,139,000)	(164,036,000)	(212,197,000)
Capital contributions to investments	(5,601,000)	(7,813,000)	(5,926,000)
Other	(1,672,000)	(508,000)	(205,000)
Cash Used for Investing Activities	(210,412,000)	(172,357,000)	(218,328,000)
Financing Activities:
Issuance of common stock, net	79,635,000	0	0
Cash dividends paid on common stock	(51,729,000)	(47,842,000)	(45,762,000)
Repayment of long-term debt	(38,959,000)	(4,553,000)	(24,453,000)
Issuance of long-term debt	19,300,000	50,000,000	100,000,000
Proceeds from (Repayments of) short-term debt	52,500,000	(13,000,000)	9,000,000
Other	(1,553,000)	(1,838,000)	(662,000)
Cash Provided by (Used for) Financing Activities	59,194,000	(17,233,000)	38,123,000
Change in cash, cash equivalents, and restricted cash:	21,225,000	(59,115,000)	(27,165,000)
Cash, cash equivalents, and restricted cash at beginning of period	25,814,000	84,929,000	112,094,000
Cash, cash equivalents, and restricted cash at end of period	47,039,000	25,814,000	84,929,000
Supplemental disclosures of cash flow information:
Interest paid	23,898,000	23,171,000	20,018,000
Income taxes paid	8,127,000	14,617,000	12,597,000
Income taxes received	0	(255,000)	(59,000)
Significant noncash investing activities:
Accrued capital expenditures	5,719,000	26,697,000	11,129,000
MGE [Member]
Operating Activities:
Net Income	85,523,000	80,779,000	79,036,000
Items not affecting cash:
Depreciation and amortization	74,188,000	71,562,000	56,412,000
Deferred income taxes	8,543,000	5,286,000	(69,000)
Provision for doubtful receivables	1,415,000	1,615,000	1,366,000
Employee benefit plan (credit) cost	(3,716,000)	(3,813,000)	(2,002,000)
Other items	(1,828,000)	1,256,000	(107,000)
Changes in working capital items:
Trade and other receivables (change)	(3,840,000)	(1,285,000)	(2,160,000)
Inventories (change)	(842,000)	(3,420,000)	2,724,000
Unbilled revenues (change)	(1,613,000)	2,345,000	3,157,000
Prepaid taxes (change)	616,000	327,000	9,283,000
Other current assets (change)	(1,157,000)	147,000	255,000
Accounts payable (change)	14,603,000	(7,754,000)	(4,817,000)
Accrued interest and taxes (change)	1,651,000	(1,565,000)	4,761,000
Other current liabilities (change)	(4,909,000)	(9,618,000)	9,685,000
Cash contributions to pension and other postretirement plans	(6,296,000)	(5,714,000)	(5,584,000)
Other noncurrent items, net	3,980,000	(4,278,000)	(3,946,000)
Cash Provided by Operating Activities	166,318,000	125,870,000	147,994,000
Investing Activities:
Capital expenditures	(203,139,000)	(164,036,000)	(212,197,000)
Other	(2,122,000)	(782,000)	(1,105,000)
Cash Used for Investing Activities	(205,261,000)	(164,818,000)	(213,302,000)
Financing Activities:
Distributions to parent from noncontrolling interest	(21,500,000)	(23,500,000)	(22,000,000)
Capital contributions from parent	30,000,000	30,500,000	0
Repayment of long-term debt	(38,959,000)	(4,553,000)	(24,453,000)
Issuance of long-term debt	19,300,000	50,000,000	100,000,000
Proceeds from (Repayments of) short-term debt	52,500,000	(13,000,000)	9,000,000
Other	(1,523,000)	(1,640,000)	(662,000)
Cash Provided by (Used for) Financing Activities	39,818,000	37,807,000	61,885,000
Change in cash, cash equivalents, and restricted cash:	875,000	(1,141,000)	(3,423,000)
Cash, cash equivalents, and restricted cash at beginning of period	5,529,000	6,670,000	10,093,000
Cash, cash equivalents, and restricted cash at end of period	6,404,000	5,529,000	6,670,000
Supplemental disclosures of cash flow information:
Interest paid	23,898,000	23,171,000	20,018,000
Income taxes paid	0	95,000	0
Income taxes received	0	(249,000)	(59,000)
Significant noncash investing activities:
Accrued capital expenditures	$ 5,719,000	$ 26,697,000	$ 11,129,000

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)		Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents		$ 44,738,000	$ 23,481,000
Accounts receivable, less reserves		41,384,000	40,482,000
Other accounts receivables, less reserves		7,300,000	7,940,000
Unbilled revenues		27,511,000	25,899,000
Materials and supplies, at average cost		32,513,000	26,287,000
Fuel for electric generation, at average cost		6,356,000	8,358,000
Stored natural gas, at average cost		8,396,000	10,637,000
Prepaid taxes		15,179,000	16,892,000
Regulatory assets - current		14,748,000	11,432,000
Other current assets		11,394,000	10,233,000
Total Current Assets		209,519,000	181,641,000
Other long-term receivables		1,435,000	1,811,000
Regulatory assets		142,504,000	134,314,000
Pension and other postretirement benefit asset		13,873,000	13,630,000
Other deferred assets and other		22,259,000	19,093,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,630,286,000	1,530,199,000
Construction work in progress		139,099,000	112,484,000
Total Property, Plant, and Equipment		1,769,385,000	1,642,683,000
Investments		94,676,000	88,492,000
Total Assets		2,253,651,000	2,081,664,000
Current Liabilities:
Long-term debt due within one year		4,771,000	19,659,000
Short-term debt	[1]	52,500,000	0
Accounts payable		54,642,000	55,161,000
Accrued interest and taxes		8,539,000	7,244,000
Accrued payroll related items		12,635,000	12,752,000
Regulatory liabilities - current		41,664,000	9,228,000
Derivative liabilities		10,160,000	10,100,000
Other current liabilities		6,015,000	14,676,000
Total Current Liabilities		190,926,000	128,820,000
Other Credits:
Deferred income taxes		231,471,000	243,302,000
Investment tax credit - deferred		21,821,000	763,000
Regulatory liabilities		142,239,000	164,965,000
Accrued pension and other postretirement benefits		78,168,000	68,665,000
Derivative liabilities		3,980,000	15,340,000
Finance lease liabilities		17,532,000	17,379,000
Other deferred liabilities and other		72,211,000	63,013,000
Total Other Credits		567,422,000	573,427,000
Common shareholders' equity:
Common stock		36,163,000	34,668,000
Additional paid-in capital		394,408,000	316,268,000
Retained earnings		545,429,000	504,740,000
Total Common Shareholders' Equity		976,000,000	855,676,000
Long-term debt		519,303,000	523,741,000
Total Capitalization		1,495,303,000	1,379,417,000
Commitments and contingencies (see Footnote 16)
Total Liabilities and Capitalization		2,253,651,000	2,081,664,000
MGE [Member]
Current Assets:
Cash and cash equivalents		4,103,000	3,196,000
Accounts receivable, less reserves		41,384,000	40,482,000
Affiliate receivables		532,000	530,000
Other accounts receivables, less reserves		7,295,000	7,936,000
Unbilled revenues		27,511,000	25,899,000
Materials and supplies, at average cost		32,513,000	26,287,000
Fuel for electric generation, at average cost		6,356,000	8,358,000
Stored natural gas, at average cost		8,396,000	10,637,000
Prepaid taxes		14,848,000	15,463,000
Regulatory assets - current		14,748,000	11,432,000
Other current assets		11,326,000	10,065,000
Total Current Assets		169,012,000	160,285,000
Affiliate receivable long-term		2,118,000	2,648,000
Regulatory assets		142,504,000	134,314,000
Pension and other postretirement benefit asset		13,873,000	13,630,000
Other deferred assets and other		22,448,000	19,680,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,630,314,000	1,530,227,000
Construction work in progress		139,099,000	112,484,000
Total Property, Plant, and Equipment		1,769,413,000	1,642,711,000
Investments		603,000	209,000
Total Assets		2,119,971,000	1,973,477,000
Current Liabilities:
Long-term debt due within one year		4,771,000	19,659,000
Short-term debt		52,500,000	0
Accounts payable		54,576,000	54,845,000
Accrued interest and taxes		10,405,000	8,754,000
Accrued payroll related items		12,635,000	12,752,000
Regulatory liabilities - current		41,664,000	9,228,000
Derivative liabilities		10,160,000	10,100,000
Other current liabilities		6,042,000	12,683,000
Total Current Liabilities		192,753,000	128,021,000
Other Credits:
Deferred income taxes		200,390,000	214,041,000
Investment tax credit - deferred		21,821,000	763,000
Regulatory liabilities		142,239,000	164,965,000
Accrued pension and other postretirement benefits		78,168,000	68,665,000
Derivative liabilities		3,980,000	15,340,000
Finance lease liabilities		17,532,000	17,379,000
Other deferred liabilities and other		72,173,000	62,973,000
Total Other Credits		536,303,000	544,126,000
Common shareholders' equity:
Common stock		17,348,000	17,348,000
Additional paid-in capital		252,917,000	222,917,000
Retained earnings		460,151,000	397,021,000
Total Common Shareholders' Equity		730,416,000	637,286,000
Noncontrolling interest		141,196,000	140,303,000
Total Equity		871,612,000	777,589,000
Long-term debt		519,303,000	523,741,000
Total Capitalization		1,390,915,000	1,301,330,000
Commitments and contingencies (see Footnote 16)
Total Liabilities and Capitalization		$ 2,119,971,000	$ 1,973,477,000
[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, 2020	Dec. 31, 2019
Receivables, Net
Reserve for uncollectible accounts receivable	$ 5,787	$ 2,820
Reserve for uncollectible other accounts receivable	$ 1,290	$ 438
Common shareholders' equity
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	75,000	75,000
Common stock, shares issued	36,163	34,668
Common stock, shares outstanding	36,163	34,668
MGE [Member]
Receivables, Net
Reserve for uncollectible accounts receivable	$ 5,787	$ 2,820
Reserve for uncollectible other accounts receivable	$ 1,290	$ 438
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 Sta

MGE Energy Inc Consolidated Statements of Common Equity - USD ($) $ in Thousands	Total	Cumulative Effect Period Of Adoption Adjustment [Member]	Cumulative Effect Period Of Adoption Adjusted Balance [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member]Cumulative Effect Period Of Adoption Adjustment [Member]	Retained Earnings [Member]Cumulative Effect Period Of Adoption Adjusted Balance [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]Cumulative Effect Period Of Adoption Adjustment [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]Cumulative Effect Period Of Adoption Adjusted Balance [Member]
Beginning balance, shares at Dec. 31, 2017				34,668,000
Beginning balance, value at Dec. 31, 2017	$ 778,187	$ 0	$ 778,187	$ 34,668	$ 316,268	$ 426,874	$ 377	$ 427,251	$ 377	$ (377)	$ 0
Increase (Decrease) in Equity [Roll Forward]
Net Income	84,219					84,219
Common stock dividends declared	(45,762)					(45,762)
Issuance of common stock, net	0
Ending balance, shares at Dec. 31, 2018				34,668,000
Ending balance, value at Dec. 31, 2018	816,644			$ 34,668	316,268	465,708			0
Increase (Decrease) in Equity [Roll Forward]
Net Income	86,874					86,874
Common stock dividends declared	(47,842)					(47,842)
Issuance of common stock, net	0
Ending balance, shares at Dec. 31, 2019				34,668,000
Ending balance, value at Dec. 31, 2019	855,676			$ 34,668	316,268	504,740			0
Increase (Decrease) in Equity [Roll Forward]
Net Income	92,418					92,418
Common stock dividends declared	$ (51,729)					(51,729)
Common stock issued during period	1,500,000
Common stock issued, net value				1,495
Issuance of common stock, net	$ 79,635			$ 1,495	78,140
Ending balance, shares at Dec. 31, 2020				36,163,000
Ending balance, value at Dec. 31, 2020	$ 976,000			$ 36,163	$ 394,408	$ 545,429			$ 0

Madison Gas and Electric Compan

Madison Gas and Electric Company Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	MGE [Member]	Cumulative Effect Period Of Adoption Adjustment [Member]MGE [Member]	Cumulative Effect Period Of Adoption Adjusted Balance [Member]MGE [Member]	Common Stock [Member]	Common Stock [Member]MGE [Member]	Additional Paid-In Capital [Member]MGE [Member]	Retained Earnings [Member]MGE [Member]	Retained Earnings [Member]Cumulative Effect Period Of Adoption Adjustment [Member]MGE [Member]	Retained Earnings [Member]Cumulative Effect Period Of Adoption Adjusted Balance [Member]MGE [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]MGE [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]Cumulative Effect Period Of Adoption Adjustment [Member]MGE [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member]Cumulative Effect Period Of Adoption Adjusted Balance [Member]MGE [Member]	Noncontrolling Interest [Member]MGE [Member]
Beginning balance, shares at Dec. 31, 2017					34,668	17,348
Beginning balance, value at Dec. 31, 2017		$ 632,774	$ 0	$ 632,774		$ 17,348	$ 192,417	$ 282,135	$ (28)	$ 282,107	$ (28)	$ 28	$ 0	$ 140,902
Increase (Decrease) in Equity [Roll Forward]
Net Income	$ 84,219	79,036						56,484						22,552
Capital contributions from 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
Increase (Decrease) in Equity [Roll Forward]
Net Income	86,874	80,779						58,430						22,349
Capital contributions from parent		30,500					30,500
Distributions to parent from noncontrolling interest		(23,500)												(23,500)
Ending balance, shares at Dec. 31, 2019					34,668	17,348
Ending balance, value at Dec. 31, 2019		777,589				$ 17,348	222,917	397,021			0			140,303
Increase (Decrease) in Equity [Roll Forward]
Net Income	$ 92,418	85,523						63,130						22,393
Capital contributions from parent		30,000					30,000
Distributions to parent from noncontrolling interest		(21,500)												(21,500)
Ending balance, shares at Dec. 31, 2020					36,163	17,348
Ending balance, value at Dec. 31, 2020		$ 871,612				$ 17,348	$ 252,917	$ 460,151			$ 0			$ 141,196

Consolidated Statements of Comm

Consolidated Statements of Common Equity (Parentheticals) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Dividends per share of common stock	$ 0.370	$ 0.370	$ 0.353	$ 0.353	$ 0.353	$ 0.353	$ 0.338	$ 0.338	$ 1.45	$ 1.38	$ 1.32

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
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 conformity with accounting principles generally accepted in the United 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 conform 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 development entity for property. MGE Power owns 100% of 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 nonregulated entities formed to own the investments in ATC and ATC Holdco, respectively. MGE did not own any subsidiaries as of December 31, 2020. 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 receive 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 beneficiary, 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 expected 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 entities 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. 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. With the global outbreak of the Coronavirus Disease 2019 (COVID-19) and the declaration of a pandemic by the World Health Organization on March 11, 2020, U.S. governmental authorities have deemed electric and gas utilities to be critical infrastructure. MGE Energy therefore has an obligation to keep operating and maintaining our critical electric and gas infrastructure. Since then, MGE Energy has been subject to, and is following, local, state and federal public health and safety regulations and guidance to control the pandemic. MGE Energy and MGE considered the impact of COVID-19 developments on the assumptions and estimates used in the preparation of these financial statements. 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, 2020 2019 2020 2019 Cash and cash equivalents $ 44,738 $ 23,481 $ 4,103 $ 3,196 Restricted cash 644 619 644 619 Receivable - margin account 1,657 1,714 1,657 1,714 Cash, cash equivalents, and restricted cash $ 47,039 $ 25,814 $ 6,404 $ 5,529 Cash Equivalents All highly liquid investments purchased with an original maturity of three months or less are considered 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 sheets. 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. 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. A 1% late payment charge is recorded on all receivables unpaid after the due date. In late March 2020, the 1% late payment charge was suspended in response to the PSCW's COVID-19 order. The order also suspended disconnection or refusal of services to any customer, with limited exceptions. The PSCW order was lifted on July 25, 2020; however, as permitted by regulatory action, MGE notified the PSCW of its election to continue to waive late fees until April 1, 2021. See Footnote 9.c. for further information. The allowance for credit losses associated with these receivables represents MGE's best estimate of the amount of probable credit losses for existing accounts receivable. MGE manages concentration of credit risk through its credit and collection policies, which are consistent with state regulatory requirements. The allowance for credit losses is estimated based on historical write-off experience, regional economic data, review of the accounts receivable aging, and reasonable and supportable forecasts that affect the collectability of the reported amount. MGE has considered the effects of COVID-19 developments and associated governmental regulations, including suspension of disconnections for non-payment, in its estimate of allowance for credit losses by applying data from historical recessions and other significant economic downturns. As of December 31, 2020, MGE had a reserve balance of $ 7.1 million against accounts receivable. During the year ended December 31, 2020, MGE recorded $ 1.4 million in write-offs. During the year ended December 31, 2020, MGE recorded $ 5.2 million of additional reserves, which included estimated impacts of COVID-19. The PSCW issued a deferral accounting order for deferral of incremental COVID-19-related costs. Recovery of these costs are expected to be addressed in future rate proceedings. As of December 31, 2020, MGE had deferred $ 3.8 million of incremental COVID-19-related costs as a regulatory asset. See Footnote 8 for further information. f. Inventories - MGE Energy and MGE. Inventories consist of natural gas in storage, fuel for electric generation, materials and supplies, and renewable energy credits (RECs). 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 allowances are charged to purchase power expense as they are used in operations. MGE's REC allowance balance as of December 31, 2020 and 2019, was $ 0.8 million and $ 0.6 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 institution an undivided interest with recourse, in up to $ 1.5 million of the financing program receivables, until July 31, 2021. 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, 2020, approximates the fair value of the energy-related equipment acting as collateral. MGE accounts for these agreements as secured borrowings. As of December 31, 2020, there were $ 0.7 million of loans outstanding related to this program. 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. Regulatory assets and liabilities are amortized in the consolidated statements of income consistent with the recovery or refund included in customer rates. MGE believes it is probable that its recorded regulatory assets and liabilities will be recovered and refunded, respectively, in future rates. See Footnote 8 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 reduction 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 charged 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 approximate the following percentages for the cost of depreciable property: 2020 2019 2018 Electric (a) 3.5 % 3.6 % 2.9 % Gas 2.2 % 2.1 % 2.1 % Nonregulated 2.3 % 2.3 % 2.3 % (a) In the December 2018 rate settlement, the PSCW approved new depreciation rates for Columbia effective January 1, 2019. k. Asset Retirement Obligations - MGE Energy and MGE. A liability is recorded for the fair value of an asset retirement obligation (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 "Other 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 recovers legal AROs in rates and when it would recognize these costs. See Footnote 17 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, 2020 and 2019, MGE had over collected $ 1.8 million and $ 1.9 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 20 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 around the amount approved for a utility in its annual fuel proceedings. Any over- or 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 recognized as a reduction of revenue. Under-collection of these costs will be recognized in "Purchased power" expense in the consolidated statements of income. The cumulative effects of these deferred amounts will be recorded as a regulatory asset or regulatory liability until they are reflected in future billings to customers. See Footnote 9.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 $ 61.8 million, a $ 75.6 million, and a $ 90.3 million reduction to sales to the market and purchase power expense for MISO markets for the years ended December 31, 2020, 2019, and 2018, respectively. 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 2020, 2019 and 2018, as approved by the PSCW, MGE capitalized AFUDC-debt and equity on 50% of applicable average construction work in progress at 7.03%, 7.0%, and 7.87%, respectively. MGE received specific approval to recover 100% AFUDC on certain costs for Saratoga, Two Creeks, Badger Hollow I and II, its customer information and billing project, and on certain environmental costs for Columbia. These amounts are recovered under the ratemaking process over the service lives of the related properties. During 2020, 2019, and 2018, MGE recorded $ 2.1 million, $ 0.8 million, and $ 1.1 million, respectively, of AFUDC-debt. During 2020, 2019, and 2018, MGE recorded $ 5.9 million, $ 2.3 million, and $ 3.3 million, respectively, of AFUDC-equity. 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. For equity security investments without readily determinable fair values, MGE Energy and MGE have elected to use the practicability exception to measure these investments, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. Equity security investments with readily determinable fair values are carried at fair value. Realized and unrealized gains and losses are included in earnings. See Footnote 7 for further information on investments and Footnote 19 for further information on fair value of investments. s. Capitalized Software Costs - MGE Energy and MGE. The net book value of capitalized costs of internal use software included in property, plant, and equipment was $ 20.4 million and $ 24.6 million as of December 31, 2020 and 2019, respectively. As of December 31, 2020 and 2019, accumulated amortization was $ 36.9 million and $ 31.8 million, respectively. During 2020 and 2019, MGE recorded $ 5.1 million of amortization expense. During 2018, MGE recorded $ 4.7 million of amortization expense. Capitalized software costs are amortized on a straight-line basis over the estimated useful lives of the assets. The useful lives range from five fifteen t. Capitalized Software Assets – Hosting Arrangements – MGE Energy and MGE. The net book value of capitalized costs of internal use software incurred in a hosting arrangement was $ 14.8 million and $ 13.6 million as of December 31, 2020 and 2019, respectively. As of December 31, 2020 and 2019, accumulated amortization was $ 3.2 million and $ 1.4 million, respectively. 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 2020, 2019, and 2018, MGE recorded $ 1.8 million, $ 1.4 million, and $ 0.1 million, respectively, of amortization expense related to software assets for hosted arrangements. 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 term of the hosted contract, which includes renewable option periods. Software assets for hosted arrangements have terms ranging from five ten 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 during 2020, 2019, and 2018. 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 such 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 principles have resulted in a regulatory liability related to income taxes. Excess deferred income taxes result from past taxes provided at customer 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 property 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 $ 14.1 million, $ 13.9 million, and $ 14.4 million for the years ended December 31, 2020, 2019, and 2018, 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. The 2020 Performance Unit Plan (the 2020 Plan) was adopted in February 2020 for eligible employees. Plan participants may receive awards of performance units, restricted units, or both. Prior to the adoption of the 2020 Plan, eligible employees received awards of performance units under the 2006 Performance Unit Plan. Under the 2013 Director Incentive Plan, eligible non-employee directors may receive awards of performance units. Under the incentive plans, eligible participants, including employees and non-employee directors, may receive performance or restricted 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 a performance period set in the 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 services received in exchange for a performance or restricted 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 original grant are recognized as compensation cost. See Footnote 12 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 derivatives, excluding those that qualify for the normal purchases or normal sales exclusion, 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 derivative 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 marked to fair value and are offset with a corresponding regulatory asset or liability depending on whether the derivative is in a net loss or net gain position, respectively. 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, 2020
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements	New Accounting Standards - MGE Energy and MGE. Recently Adopted Credit Losses. In June 2016, the Financial Accounting Standards Board issued authoritative guidance within the codification's Credit Losses topic, which introduced a new model for recognizing credit losses on financial instruments based on an estimate of current expected credit losses. The authoritative guidance became effective January 1, 2020. MGE adopted the standard on the effective date. The adoption of this standard did not have a material impact on MGE Energy's and MGE's financial statements. New disclosures are required under the new standard. See Footnote 1.e. for allowance for credit loss disclosures.

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2020
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 and leasing those assets to MGE. MGE Power Elm Road's sole principal asset is an undivided ownership interest in two coal-fired generating plants (the Elm Road Units) located in Oak Creek, Wisconsin, which it leases to MGE pursuant to long-term leases. MGE 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 terms of the contractual agreements, MGE is expected to absorb a majority of the expected losses or residual value associated with the ownership of the generation assets by MGE Power Elm Road and Power West Campus and therefore MGE holds a variable interest despite the absence of an equity 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 WCCF'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 balance sheets related to its interest in these VIEs: MGE Power Elm Road MGE Power West Campus (In thousands) 2020 2019 2020 2019 Property, plant, and equipment, net $ 166,883 $ 170,763 $ 79,077 $ 79,473 Construction work in progress 697 468 677 309 Affiliate receivables - - 2,803 3,600 Accrued interest and accrued (prepaid) taxes 2,701 1,364 671 ( 160) Deferred income taxes 30,646 30,621 14,521 14,363 Long-term debt (a) 51,590 54,207 37,652 39,627 Noncontrolling interest 96,856 97,172 44,340 43,131 (a) MGE Power Elm Road's long-term debt includes debt issuance costs of $ 0.4 million as of December 31, 2020 and 2019. 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 costs of $ 0.1 million as of December 31, 2020 and 2019. 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 14 for further information on the long-term debt securities. MGE is permitted by PSCW order to recover lease payments made to MGE Power Elm Road and MGE Power West Campus in customer rates. 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, 2020 and 2019, MGE had 13 megawatts 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 no 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, 2020
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant, and Equipment - MGE Energy and MGE. Property, plant, and equipment consisted of the following as of December 31: MGE Energy MGE (In thousands) 2020 2019 2020 2019 Utility: Electric (a) $ 1,608,658 $ 1,480,684 $ 1,608,675 $ 1,480,701 Gas 496,450 472,123 496,461 472,134 Total utility plant 2,105,108 1,952,807 2,105,136 1,952,835 Less: Accumulated depreciation and amortization 721,382 674,251 721,382 674,251 In-service utility plant, net 1,383,726 1,278,556 1,383,754 1,278,584 Nonregulated: Nonregulated 320,691 323,266 320,691 323,266 Less: Accumulated depreciation and amortization 74,131 71,623 74,131 71,623 In-service nonregulated plant, net 246,560 251,643 246,560 251,643 Construction work in progress: Utility construction work in progress (b) 137,725 111,707 137,725 111,707 Nonregulated construction work in progress 1,374 777 1,374 777 Total property, plant, and equipment $ 1,769,385 $ 1,642,683 $ 1,769,413 $ 1,642,711 (a) In 2019, the PSCW authorized construction of Two Creeks. The project was placed in service in November 2020. Total capital expenditures for the project were $ 62.9 million, excluding AFUDC. After tax, MGE recognized $ 2.4 million and $ 1.0 million, respectively, of AFUDC equity for the years ended December 31, 2020 and 2019. MGE received specific approval to recover 100% AFUDC on the project. (b) In 2019, the PSCW authorized construction of Badger Hollow I. Construction of the project is expected to be completed in April 2021. As of December 31, 2020, and 2019, MGE had $ 54.7 million and $ 18.7 million (excluding AFUDC), respectively, in construction work in progress. After tax, MGE recognized $ 2.0 million and $ 0.2 million, respectively, of AFUDC equity related to Badger Hollow I for the years ended December 31, 2020 and 2019. Phase II of the project was authorized by the PSCW in 2020. Construction of Badger Hollow II is expected to be completed in December 2022. As of December 31, 2020, MGE had $ 5.2 million (excluding AFUDC) in construction work in progress. After tax, MGE recognized $ 0.2 million of AFUDC equity related to Badger Hollow II for the year ended December 31, 2020. MGE received specific approval to recover % AFUDC on these projects . MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust. As of December 31, 2020 and 2019, there was $ 1.2 million of first mortgage bonds outstanding under that indenture. See Footnote 14 for further discussion of the mortgage indenture and the entitlement of certain senior notes to be equally and ratably secured if MGE issues additional first mortgage bonds.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Leases - MGE Energy and MGE. As part of its regular operations, MGE enters into various contracts related to IT equipment, substations, cell towers, land, wind easements, and other property in use for operations. A contract is or contains a lease if the contract conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Determination as to whether an arrangement is or contains a lease is completed at inception. Leases with an initial term of 12 months or less are not recorded on the consolidated balance sheets; lease expense for these leases are recognized on a straight-line basis over the lease term. Leases with initial terms in excess of 12 months are recorded as operating or financing leases on the consolidated balance sheets. Operating lease assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. For leases that do not provide an implicit rate, a collateralized incremental borrowing rate based on the information available at commencement date, including lease term, is used in determining the present value of future payments. The operating lease asset also includes any lease payments made and excludes lease incentives and initial direct costs incurred. Lease terms may include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the lease term. MGE has regulatory treatment and recognizes regulatory assets or liabilities for timing differences between when net lease costs are recorded and when costs are recognized. As of December 31, 2020, MGE had no significant leases not yet commenced that would create significant future rights and obligations. The following table shows lease expense for the years ended December 31: (In thousands) 2020 2019 Income Statement Location Finance lease expense: Amortization of leased assets $ 1,694 $ 1,524 Depreciation and amortization Interest on lease liabilities 784 792 Interest expense, net Operating lease expense 319 144 Other operations and maintenance Total lease expense $ 2,797 $ 2,460 The following table shows the lease assets and liabilities on the consolidated balance sheets as of December 31: (In thousands) 2020 2019 Balance Sheet Location Lease assets: Finance lease assets $ 15,682 $ 15,895 Property, plant, and equipment, net Operating lease assets (a) 5,988 671 Other deferred assets and other Total lease assets $ 21,670 $ 16,566 Lease liabilities: Finance lease liabilities - current $ 1,066 $ 888 Other current liabilities Finance lease liabilities - long-term 17,532 17,379 Finance lease liabilities Operating lease liabilities - current 171 203 Other current liabilities Operating lease liabilities - long-term (a) 5,840 496 Other deferred liabilities and other Total lease liabilities $ 24,609 $ 18,966 (a) Increase in operating lease assets and long-term operating lease liabilities related to land leases for new solar farms in 2020. The following table shows other lease information for the years ended December 31: (In thousands) 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Finance leases - Financing cash flows $ 1,149 $ 945 Finance leases - Operating cash flows 784 792 Operating leases - Operating cash flows 319 134 Lease assets obtained in exchange for lease liabilities: Finance leases 1,480 12,101 Operating leases 5,791 657 The following table shows the weighted average remaining lease terms and discounts as of December 31: Weighted-average remaining lease terms (in years): 2020 2019 Finance leases 37 39 Operating leases 34 15 Weighted-average discount rates: Finance leases 4.32 % 4.37 % Operating leases 2.84 % 3.32 % The following table shows maturities of lease liabilities as of December 31: (In thousands) Finance Operating 2021 $ 1,820 $ 338 2022 1,700 274 2023 1,520 203 2024 959 207 2025 774 211 Thereafter 39,787 8,636 Subtotal 46,560 9,869 Less: Present value discount ( 27,962) ( 3,858) Lease Liability $ 18,598 $ 6,011

Joint Plant Ownership

Joint Plant Ownership	12 Months Ended
	Dec. 31, 2020
Regulated Operations [Abstract]
Joint Plant Ownership	Joint Plant Ownership - MGE Energy and MGE. MGE has undivided ownership interests in jointly owned facilities. Generation and operating expenses are primarily divided between the joint owners under the same method as ownership. MGE provides its own financing and the respective portion of facilities and costs are included in the corresponding operating expenses (fuel for electric generation, purchased power, other operations and maintenance, etc.) in the consolidated statements of income. The following table shows MGE's interest in utility plant in service, and the related accumulated depreciation reserves and other information related to MGE's jointly owned facilities: (In thousands, except for percentages and MW) Columbia (a) Elm Road (b) West Campus (c) Forward Wind (d) Two Creeks (e) Badger Hollow I & II (f) Ownership interest 19 % 8.33 % 55 % 12.8 % 33 % 33 % Share of generation (MW) 211 MW 106 MW 157 MW 18 MW 50 MW 100 MW For the year ended December 31, Operating expense - 2020 $ 27,127 $ 17,259 $ (g) $ 664 $ 118 $ - Operating expense - 2019 32,604 19,661 (g) 642 - - Operating expense - 2018 36,517 17,555 (g) 600 (h) - - As of December 31, 2020 Utility plant $ 289,597 $ 203,847 $ 115,657 $ 34,028 $ 67,577 $ - Accumulated depreciation ( 118,742) ( 36,964) ( 36,580) ( 14,092) ( 225) - Construction work in progress 997 697 677 - - 63,140 As of December 31, 2019 Utility plant $ 291,997 $ 207,834 $ 113,259 $ 34,054 $ - $ - Accumulated depreciation ( 105,778) ( 37,071) ( 33,786) ( 13,413) - - Construction work in progress 1,777 468 309 45 45,286 18,953 (a) In February 2021, MGE and the other co-owners announced plans to retire Columbia, a two unit coal-fired generation facility located in Portage, Wisconsin. The co-owners intend to retire Unit 1 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates for Units 1 and 2 are subject to PSCW and regional regulatory reviews, including identification and approval of energy and capacity resources to replace Columbia. (b) Two coal-fired generating units in Oak Creek, Wisconsin. (c) MGE Power West Campus and the UW jointly own the West Campus Cogeneration Facility (WCCF) located on the UW campus in Madison, Wisconsin. The UW owns a controlling interest in the chilled-water and steam plants, which are used to meet the needs for air-conditioning and steam-heat capacity for the UW campus. MGE Power West Campus owns a controlling interest in the electric generation plant, which is leased and operated by MGE. (d) The Forward Wind Energy Center (Forward Wind) consists of 86 wind turbines located near Brownsville, Wisconsin. (e) The Two Creeks solar generation array is located in the Town of Two Creeks and the City of Two Rivers in Manitowoc and Kewaunee Counties, Wisconsin. Date of commercial operation of the solar array was November 2020. (f) The Badger Hollow I and II solar farm is located in southwestern Wisconsin in Iowa County, near the villages of Montfort and Cobb. Badger Hollow I and II estimated commercial operation dates are April 2021 and December 2022, respectively. (g) 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, 2020, 2019, and 2018, the UW's allocated share of fuel and operating costs was $ 5.2 million, $ 6.6 million, and $ 6.3 million, respectively. (h) Amount was deferred as a regulatory asset in 2018. This amount was recovered in rates and recognized as operating and maintenance expense in 2019.

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments Disclosure [Abstract]
Investments	Investments - MGE Energy and MGE. a. Equity Securities, Equity Method Investments, and Other Investments. MGE Energy MGE (In thousands) 2020 2019 2020 2019 Equity securities $ 17,906 $ 14,546 $ 603 $ 209 Equity method investments: ATC and ATC Holdco 74,423 71,609 - - Other 39 39 - - Total equity method investments 74,462 71,648 - - Other investments 2,308 2,298 - - Total $ 94,676 $ 88,492 $ 603 $ 209 Equity securities represent publicly traded securities and private equity investments in common stock of companies in various industries. During the years ended December 31, 2020, 2019, and 2018, certain investments were liquidated. As a result of these liquidations, the following was received: MGE Energy MGE (In thousands) 2020 2019 2018 2020 2019 2018 Cash proceeds $ 622 $ 216 $ 960 $ - $ 2 $ 3 Gain (loss) on sale 379 580 476 - ( 343) 3 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 outside of Wisconsin. The ownership interest in ATC Holdco is held by MGEE Transco, a wholly-owned subsidiary of MGE Energy. As of December 31, 2020 and 2019, MGE Transco held a 3.6% ownership interest in ATC. As of December 31, 2020 and 2019, MGEE Transco held a 4.4% ownership interest in ATC Holdco. MGE Transco and MGEE Transco have accounted for their investment in ATC and ATC Holdco, respectively, under the equity method of accounting. Equity earnings from investments are recorded as "Other income" on the consolidated statements of income of MGE Energy. For the years ended December 31, MGE Transco recorded the following: (In thousands) 2020 2019 2018 Equity earnings from investment in ATC $ 10,167 $ 9,889 $ 8,821 Dividends received from ATC (a) 8,633 7,347 4,611 Capital contributions to ATC 1,249 3,018 2,841 (a) MGE Transco recorded a $ 2.3 million dividend receivable from ATC as of December 31, 2017. A cash dividend was received in January of 2018. ATC Holdco was formed in December 2016. ATC Holdco's future transmission development activities have been suspended for the near term. In 2020, 2019, and 2018, MGEE Transco recorded capital contributions of $ 0.3 million, $ 0.1 million, and $ 0.3 million, respectively, to ATC Holdco. (In thousands) Income statement data for the year ended December 31, 2020 2019 2018 Operating revenues $ 758,117 $ 744,371 $ 690,510 Operating expenses ( 372,463) ( 373,527) ( 358,703) Other income 1,922 48 2,405 Interest expense, net ( 112,818) ( 110,490) ( 110,725) Earnings before members' income taxes $ 274,758 $ 260,402 $ 223,487 Balance sheet data as of December 31, 2020 2019 Current assets $ 92,735 $ 84,635 Noncurrent assets 5,400,538 5,244,220 Total assets $ 5,493,273 $ 5,328,855 Current liabilities $ 310,749 $ 502,601 Long-term debt 2,512,246 2,312,799 Other noncurrent liabilities 378,205 298,828 Members' equity 2,292,073 2,214,627 Total members' equity and liabilities $ 5,493,273 $ 5,328,855 MGE receives transmission and other services from ATC. During 2020, 2019, and 2018, MGE recorded $ 30.7 million, $ 30.4 million, and $ 29.0 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, 2020 and 2019, MGE had a receivable due from ATC of $ 2.6 million (related primarily to Badger Hollow I and II) and $ 1.6 million (related primarily to Two Creeks and Badger Hollow I and II), respectively. MGE is reimbursed for these costs after the new generation assets are placed into service.

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	12 Months Ended
	Dec. 31, 2020
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities - MGE Energy and MGE. The following regulatory assets and liabilities are reflected in MGE's consolidated balance sheets as of December 31: (In thousands) 2020 2019 Regulatory Assets Asset retirement obligation $ 11,935 $ 10,756 COVID-19 costs 3,933 - Debt related costs 8,586 8,885 Deferred pension and other postretirement costs 5,280 6,216 Derivatives 13,989 26,875 Leases 2,748 2,400 Tax recovery related to AFUDC equity 8,952 7,060 Unfunded pension and other postretirement liability 101,594 83,214 Other 235 340 Total Regulatory Assets $ 157,252 $ 145,746 Regulatory Liabilities Deferred fuel savings $ 5,047 $ 1,794 Elm Road 1,957 2,322 Income taxes 129,856 129,528 Non-ARO removal costs 28,197 26,543 Pension and other postretirement service costs 7,524 4,499 Purchased gas adjustment 1,832 1,864 Renewable energy credits 802 558 Transmission 7,669 6,019 Other 1,019 1,066 Total Regulatory Liabilities $ 183,903 $ 174,193 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 customers 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 except for COVID-19 costs. Asset Retirement Obligation See Footnote 17 for a discussion of asset retirement obligations. COVID-19 Costs In March 2020, the PSCW issued an order authorizing deferral of expenditures incurred to ensure the provision of safe, reliable, and affordable access to utility services during the COVID-19 pandemic and late payment charges. Expenditures include items such as bad debt expense and personal protective equipment. Foregone revenue from late payment charges and the potential delay in payments from customers is expected to impact the timing of cash inflows. Subject to PSCW approval of recovery, foregone late payment charges are expected to be recognized as revenue when it is collected from customers, and deferred expenditures are expected to be recognized as a regulatory asset as costs are incurred (meaning that those expenditures will affect cash flows when paid but will not affect income until recovery is permitted by the PSCW). Recovery of expenditures and late payment charges is expected to be addressed in future rate proceedings. While management believes that cost recovery is probable, the timing of collection from customers cannot be estimated at this time. Management will continue to assess the probability of recovery of deferred costs as the COVID-19 pandemic progresses. Debt Related Costs This balance includes debt issuance costs of extinguished debt and other debt related expenses, including make-whole premiums paid on redemptions of long-term debt. The PSCW has allowed rate recovery on unamortized issuance costs for extinguished debt facilities. 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. Deferred Pension and Other Postretirement Costs As a result of lower investment returns in the fourth quarter of 2018, pension and postretirement benefit costs increased in 2019. In August 2019, the PSCW approved MGE's request to defer the difference between estimated pension and other postretirement costs included in the 2019 and 2020 rate settlement and actual expense incurred. The deferred cost for employee benefit plans was factored into future rate actions starting in 2021. 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 liability 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 that began on June 1, 2012, and ends on May 31, 2022. See Footnote 18 for further discussion. Leases As part of its regular operations, MGE enters into various contracts related to IT equipment, substations, cell towers, land, wind easements, and other property in use for operations. Leases with initial terms in excess of 12 months are recorded as operating or financing leases on the consolidated balance sheets. MGE has regulatory treatment and recognizes regulatory assets or liabilities for timing differences between when net lease costs are recorded and when costs are recognized. See Footnote 5 for further information. Tax Recovery Related to AFUDC Equity AFUDC equity represents the after-tax equity cost associated with utility plant construction and results in a temporary difference 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 or funded 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 status represents future expenses that are expected to be recovered in rates. See Footnote 11 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- or under-recovery of the actual costs is determined on an annual basis and is adjusted in future billings to electric retail customers. See Footnote 9.b. for further discussion. Elm Road Costs associated with Elm Road are estimated in MGE's rates 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. The current accounting treatment for these costs allows MGE to reflect any differential between costs reflected in rates and actual costs incurred in its next rate filing. Income Taxes Excess deferred income taxes result from a decrease in tax rates subsequent to ratemaking settlements. The settlements were reached using tax rates that are higher than the currently applicable rates, and MGE is required to return these tax benefits to customers. The regulatory liability and deferred investment tax credit reflects the revenue requirement associated with the return of these tax benefits to customers. Changes in income 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 2017 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 timeframe dictated by applicable tax laws. The 2021 rate settlement includes a one-time $ 18.2 million return to customers of the portion of electric excess deferred taxes related to the 2017 Tax Act not governed by IRS normalization rules. 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 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 11 for further discussion. Purchased Gas Adjustment 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 credits 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, 2020
Regulated Operations [Abstract]
Rate Matters	Rate Matters - MGE Energy and MGE. a. Rate Proceedings. In December 2020, the PSCW approved a settlement agreement for MGE's 2021 rate case. The settlement agreement provides for a zero percent increase for electric rates and an approximately 4.0% increase for gas rates in 2021. The electric rate settlement includes an increase in rate base but the associated rate increase is primarily offset by lower fuel and purchase power costs and a one-time $ 18.2 million return to customers of the portion of excess deferred taxes related to the 2017 Tax Act not governed by IRS normalization rules. As part of the settlement, the fuel rules bandwidth will be set at plus or minus 1% for 2021. When compared to the 2020 rate case, the settlement includes lower forecasted electric sales for 2021 to reflect changes to customer usage during the COVID-19 pandemic. The gas rate increase covers infrastructure costs and technology improvements. The settlement agreement also includes escrow accounting treatment for pension and other postretirement benefit costs, bad debt expense, and customer credit card fees. Escrow accounting treatment allows MGE to defer any difference between estimated costs in rates and actual costs incurred until its next rate filing. Any difference would be recorded as a regulatory asset or regulatory liability. The return on common stock equity for 2021 is 9.8 % based on a capital structure of 55.8 % common equity in 2021. On January 27, 2021, Sierra Club and Vote Solar filed a Petition for Judicial Review of Agency Action (the Petition) in Dane County Circuit Court. The Petition challenges the final decision issued by the PSCW approving the rate settlement in MGE's 2021 rate case. The PSCW is named as the respondent in the Petition; MGE is not named as a party. The remedies sought in the Petition are unclear. The PSCW is expected to vigorously defend its final decision to approve the settlement agreement in the rate case, and MGE has intervened in the Petition in cooperation with the PSCW. In December 2018, the PSCW approved a settlement agreement between MGE and intervening parties in the then pending rate case. The settlement decreased electric rates by 2.24 %, or $ 9.2 million, in 2019. The decrease in electric rates reflected the ongoing impacts of the 2017 Tax Act. Lower fuel costs and an increase in rate base from renewable generation assets further impacted the rate change. In 2020, electric rates decreased a further 0.84 %, or $ 3.4 million, as approved by the PSCW in December 2019 in MGE's 2020 Fuel Cost Plan, which reflected lower fuel costs. The settlement agreement increased gas rates by 1.06 %, or $ 1.7 million, in 2019 and 1.46 %, or $ 2.4 million, in 2020. The gas increase covered infrastructure costs. It also reflected the impacts of the 2017 Tax Act. The return on common stock equity for 2019 and 2020 was 9.8 % based on a capital structure consisting of 56.6 % common equity in 2019 and 56.1 % common equity in 2020. b. Fuel Rules. Fuel rules require 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- or under-recovery of the actual costs is determined in the following year and is then reflected in future billings to electric retail customers. In 2020 the fuel rules bandwidth was set at plus or minus 2%. Under fuel rules, MGE deferred costs, less 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 return 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 that order. The fuel rules bandwidth is set at plus or minus 1% in 2021. These costs are subject to the PSCW's annual review of fuel costs completed in the year following the deferral. The PSCW issued final decisions in the 2018 and 2017 fuel rules proceedings for MGE to refund additional fuel savings realized to its retail electric customers over a one-month period. MGE returned $ 9.5 million and $ 4.2 million of electric fuel-related savings in October 2019 and 2018, respectively. There was no change to the refund in the fuel rules proceedings from the amount MGE deferred in the previous year. The PSCW issued a final decision in the 2019 fuel rules proceedings regarding $ 1.5 million of deferred savings giving MGE the option either to use the $ 1.5 million as part of the settlement to MGE's 2021 rate case or to refund the balance to customers in October 2020. MGE elected to include the savings as part of the 2021 rate change settlement as described above, reducing electric retail rates as opposed to a one-time credit back to retail customers. There was no change to the refund in the fuel rules proceedings from the amount MGE deferred in the previous year. As of December 31, 2020, MGE has deferred $ 3.2 million of 2020 fuel-related savings. These costs will be subject to the PSCW's annual review of 2020 fuel costs, expected to be completed in 2021 . c. COVID-19. On March 24, 2020, the PSCW ordered changes to the tariff provisions of all public utilities in Wisconsin in response to the COVID-19 pandemic. The order prohibited late payment charges, service disconnections, service refusals, and cash deposits as a condition of service. The order also required utilities to offer deferred payment arrangements to customers. The order resulted in increased bad debt expense and foregone revenue from late payment charges. This order, as it pertained to the prohibitions on service disconnections for residential customers, was in effect until November 1, 2020, at which time the annual winter disconnection moratorium began and continues until April 15, 2021. All other restrictions were lifted in July 2020. As permitted by regulatory action, MGE notified the PSCW of its election to continue to waive late fees until April 1, 2021 for all customer classes and seek recovery in a future period. On March 24, 2020, the PSCW issued a further order authorizing deferral of expenditures incurred to ensure the provision of safe, reliable, and affordable access to utility services during the COVID-19 pandemic and late payment charges. See Footnote 8 for further discussion of the COVID-19 deferral expenditures. d. 2018 Tax Reform. Customer rates approved for 2018 reflected an income tax rate of 35 percent. In January 2018, the PSCW issued an order directing Wisconsin investor-owned utilities to defer the over-collection of income tax expense as a result of the decrease in tax rate to 21 percent. The PSCW issued an order in May 2018 to return to customers the estimated 2018 over-collection of income tax expense. The decision included a one-time credit on customer bills to reflect the estimate of the over-collection for January through June 2018, along with a volumetric credit which began in July 2018 and continued through the remainder of 2018 for the estimated remaining annual amount. MGE returned $ 8.2 million to customers through bill credits as of December 31, 2018. In August 2019, the PSCW issued a decision on the 2018 tax reform proceedings for MGE to refund the remaining 2018 overcollection of income tax expense to its retail customers as a one-time bill credit. MGE returned $ 3.2 million in September 2019. There was no change to the refund order from the amount MGE deferred as of December 31, 2018.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
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) 2020 2019 2018 2020 2019 2018 Current payable: Federal $ 4,179 $ 8,017 $ 18,622 $ 3,716 $ 7,616 $ 19,926 State 5,095 4,647 5,163 4,790 4,608 5,704 Net-deferred: Federal 6,181 3,510 120 4,756 2,242 ( 2,563) State 4,182 3,702 3,629 3,787 3,044 2,494 Amortized investment tax credits ( 214) ( 92) ( 100) ( 214) ( 92) ( 100) Total income tax provision $ 19,423 $ 19,784 $ 27,434 $ 16,835 $ 17,418 $ 25,461 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 2020 2019 2018 2020 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefit 6.3 6.2 6.3 6.3 6.1 6.2 Amortized investment tax credits ( 0.2) ( 0.1) ( 0.1) ( 0.2) ( 0.1) ( 0.1) Credit for electricity from wind energy (a) ( 6.2) ( 5.7) ( 0.3) ( 6.8) ( 6.2) ( 0.4) AFUDC equity, net ( 1.2) ( 0.3) ( 0.6) ( 1.4) ( 0.3) ( 0.5) Amortization of utility excess deferred tax (b) ( 2.0) ( 2.4) ( 1.8) ( 2.2) ( 2.7) ( 2.0) Other, net, individually insignificant ( 0.3) ( 0.1) 0.1 ( 0.3) ( 0.1) 0.2 Effective income tax rate 17.4 % 18.6 % 24.6 % 16.4 % 17.7 % 24.4 % (a) Saratoga became operational in February 2019. (b) Included are impacts of the Tax Cuts and Jobs Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting. For the years ended December 31, 2020, 2019, and 2018, MGE recognized $ 2.2 million, $ 2.6 million, and $ 2.1 million, respectively. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, as determined by the PSCW. The significant components of deferred tax assets and liabilities that appear on the consolidated balance sheets as of December 31 are as follows: MGE Energy MGE (In thousands) 2020 2019 2020 2019 Deferred tax assets Investment in ATC $ 21,688 $ 22,576 $ - $ - Federal tax credits 19,199 - 20,080 - Accrued expenses 11,115 15,901 11,105 15,890 Pension and other postretirement benefits 35,446 30,968 35,446 30,968 Deferred tax regulatory account 41,318 35,493 41,318 35,493 Derivatives 3,852 7,351 3,852 7,351 Leases 6,704 5,167 6,704 5,167 Other 14,073 12,540 14,125 12,593 Gross deferred income tax assets 153,395 129,996 132,630 107,462 Less valuation allowance ( 38) ( 86) ( 38) ( 86) Net deferred income tax assets $ 153,357 $ 129,910 $ 132,592 $ 107,376 Deferred tax liabilities Property-related $ 257,397 $ 245,083 $ 257,397 $ 245,083 Investment in ATC 51,518 51,569 - - Bond transactions 595 657 595 657 Pension and other postretirement benefits 45,658 45,683 45,658 45,683 Derivatives 3,852 7,351 3,852 7,351 Tax deductible prepayments 9,059 9,078 9,059 9,051 Leases 6,704 5,167 6,704 5,167 Other 10,045 8,624 9,717 8,425 Gross deferred income tax liabilities 384,828 373,212 332,982 321,417 Deferred income taxes $ 231,471 $ 243,302 $ 200,390 $ 214,041 The components of federal and state tax benefit carryovers as of December 31, are as follows: MGE Energy MGE (In thousands) 2020 2019 2020 2019 Federal tax credits $ 19,199 $ - $ 20,080 $ - State net operating losses 621 1,406 621 1,406 Valuation allowances for state net operating losses ( 621) ( 1,406) ( 621) ( 1,406) Federal tax credit carryovers expire in 2040 and state net operating loss carryforwards expire between 2021 and 2023. Federal tax credits represent the deferred tax asset and net operating loss amounts represent the tax loss that is carried forward. The state valuation allowance reduces MGE Energy’s and MGE’s state carryforward losses to estimated realizable value due to the uncertainty of future income in various state tax jurisdictions. b. Accounting for Uncertainty in Income Taxes - MGE Energy and MGE . The 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 of unrecognized tax benefits and interest is as follows: (In thousands) Unrecognized Tax Benefits: 2020 2019 2018 Unrecognized tax benefits, January 1, $ 2,093 $ 1,949 $ 1,924 Additions based on tax positions related to the current year 796 741 425 Additions based on tax positions related to the prior years - 84 272 Reductions based on tax positions related to the prior years ( 608) ( 681) ( 672) Unrecognized tax benefits, December 31, $ 2,281 $ 2,093 $ 1,949 (In thousands) Interest on Unrecognized Tax Benefits: 2020 2019 2018 Accrued interest on unrecognized tax benefits, January 1, $ 176 $ 191 $ 165 Reduction in interest expense on uncertain tax positions ( 124) ( 137) ( 136) Interest expense on uncertain tax positions 102 122 162 Accrued interest on unrecognized tax benefits, December 31, $ 154 $ 176 $ 191 Unrecognized tax benefits are classified with "Other deferred liabilities" on the consolidated balance sheets. The interest component recoverable in rates is offset by a regulatory asset. As of December 31, 2020, 2019, and 2018, 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 distribution repairs. In addition, as of December 31, 2019 and 2018, unrecognized tax benefits relating to permanent differences and tax credits was less than $ 0.1 million and $ 0.3 million, respectively. As of December 31, 2020, there were no unrecognized tax benefits relating to permanent differences and tax credits. The unrecognized tax benefits as of December 31, 2020, are not expected to significantly increase or decrease within the next twelve months. In addition, 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 jurisdiction: Taxpayer Open Years MGE Energy and consolidated subsidiaries in federal return 2017 through 2020 MGE Energy Wisconsin combined reporting corporation return 2017 through 2020

Pension Plans and Other Postret

Pension Plans and Other Postretirement Benefits	12 Months Ended
	Dec. 31, 2020
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 $ 4.7 million, $ 4.4 million, and $ 3.9 million for the years ended December 31, 2020, 2019, and 2018, 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 benefit pension plan previously in place. a. Benefit Obligations and Plan Assets. (In thousands) Pension Benefits Other Postretirement Benefits Change in Benefit Obligations: 2020 2019 2020 2019 Net benefit obligation as of January 1, $ 410,651 $ 360,288 $ 80,901 $ 75,161 Service cost 5,296 4,692 1,264 1,110 Interest cost 12,210 14,302 2,278 2,893 Plan participants' contributions - - 1,009 969 Actuarial loss (a) 50,325 47,671 5,907 5,045 Gross benefits paid ( 17,267) ( 16,302) ( 5,245) ( 4,497) Less: federal subsidy on benefits paid (b) - - 246 220 Benefit obligation as of December 31, $ 461,215 $ 410,651 $ 86,360 $ 80,901 Change in Plan Assets: Fair value of plan assets as of January 1, $ 386,033 $ 323,780 $ 48,889 $ 42,521 Actual return on plan assets 58,935 76,766 6,514 9,277 Employer contributions 1,837 1,789 568 619 Plan participants' contributions - - 1,009 969 Gross benefits paid ( 17,267) ( 16,302) ( 5,245) ( 4,497) Fair value of plan assets at end of year 429,538 386,033 51,735 48,889 Funded Status as of December 31, $ ( 31,677) $ ( 24,618) $ ( 34,625) $ ( 32,012) (a) In 2020 and 2019, lower discount rates were the primary 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, 2020 and 2019, the subsidy due to MGE was $ 0.2 million. The accumulated benefit obligation for the defined benefit pension plans as of December 31, 2020 and 2019, was $ 430.3 million and $ 383.0 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) 2020 2019 2020 2019 Long-term asset $ 13,873 $ 13,630 $ - $ - Current liability ( 2,139) ( 1,688) - - Long-term liability ( 43,411) ( 36,560) ( 34,625) ( 32,012) Net liability $ ( 31,677) $ ( 24,618) $ ( 34,625) $ ( 32,012) 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) 2020 2019 2020 2019 Net actuarial loss $ 92,553 $ 79,290 $ 10,986 $ 8,659 Prior service benefit ( 144) ( 268) ( 1,816) ( 4,484) Transition obligation - - 15 17 Total $ 92,409 $ 79,022 $ 9,185 $ 4,192 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 2020 2019 Projected benefit obligation, end of year $ 45,550 $ 38,247 Fair value of plan assets, end of year - - The accumulated benefit obligation and fair value of plan assets with an accumulated benefit obligation in excess of plan assets were as follows: (In thousands) Pension Benefits Other Postretirement Benefits Accumulated Benefit Obligation in Excess of Plan Assets 2020 2019 2020 2019 Accumulated benefit obligation, end of year $ 43,384 $ 35,798 $ 86,360 $ 80,901 Fair value of plan assets, end of year - - 51,735 48,889 b. Net Periodic Benefit Cost. (In thousands) Pension Benefits Other Postretirement Benefits Components of Net Periodic Benefit Cost: 2020 (a) 2019 (a) 2018 2020 (a) 2019 (a) 2018 Service cost $ 5,296 $ 4,692 $ 5,723 $ 1,264 $ 1,110 $ 1,283 Interest cost 12,210 14,302 12,859 2,278 2,893 2,612 Expected return on assets ( 27,229) ( 22,786) ( 26,241) ( 3,154) ( 2,723) ( 3,232) Amortization of: Transition obligation - - - 3 3 3 Prior service (credit) cost ( 114) ( 117) ( 44) ( 2,669) ( 2,669) ( 2,669) Actuarial loss 5,357 7,379 5,278 217 401 488 Net periodic benefit cost (credit) $ ( 4,480) $ 3,470 $ ( 2,425) $ ( 2,061) $ ( 985) $ ( 1,515) (a) During 2019, MGE deferred approximately $ 6.2 million of pension and other postretirement costs. During 2020, MGE collected approximately $ 0.9 million of pension and other postretirement costs, which reduced the amount deferred in 2019. The impact of the deferral has not been reflected in the table above. See Footnote 8 for further information. 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. 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 2020 2019 2020 2019 Discount rate 2.70 % 3.42 % 2.52 % 3.30 % Rate of compensation increase 3.22 % 3.21 % N/A N/A Assumed health care cost trend rates: Health care cost trend rate assumed for next year N/A N/A 5.75 % 6.00 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) N/A N/A 4.75 % 5.00 % Year that the rate reaches the ultimate trend rate N/A N/A 2027 2024 MGE uses individual spot rates, instead of a weighted average of the yield curve spot rates, for measuring the service cost and interest cost components of net periodic benefit cost. 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 2020 2019 2018 2020 2019 2018 Discount rate 3.42 % 4.32 % 3.73 % 3.30 % 4.24 % 3.60 % Expected rate of return on plan assets 7.20 % 7.20 % 7.40 % 6.75 % 6.72 % 6.94 % Rate of compensation increase 3.26 % 3.25 % 3.72 % N/A N/A N/A 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 expected 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 historical 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 assets 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 real 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, 2020 and 2019, and the target allocation for 2021, by asset category, follows: Target Allocation Percentage of Plan Assets at Year End 2020 2019 Equity securities (a) 63.0 % 69.0 % 64.0 % Fixed income securities 30.0 % 25.0 % 29.0 % Real estate 7.0 % 6.0 % 7.0 % Total 100.0 % 100.0 % 100.0 % (a) Target allocations for equity securities are broken out as follows: 45.5% United States equity and 17.5% non-United States equity. The fair value of plan assets for the postretirement benefit plans is $ 51.7 million and $ 48.9 million as of December 31, 2020 and 2019, respectively. Of this amount, $ 45.6 million and $ 42.8 million as of December 31, 2020 and 2019, 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 explained 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 liquidity 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, 2020. 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, 2020, 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 Footnote 19 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, 2020: 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 invested 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 from 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 at 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 reported 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 plan assets by asset category as of December 31 are as follows: (In thousands) 2020 2019 Cash and Cash Equivalents $ 1,180 $ 964 Equity Securities: U.S. Large Cap 151,218 134,458 U.S. Mid Cap 37,389 31,288 U.S. Small Cap 50,456 36,495 International Blend 87,461 76,293 Fixed Income Securities: Short-Term Fund 4,215 7,449 High Yield Bond 22,683 21,276 Long Duration Bond 92,657 92,642 Real Estate 30,005 29,671 Insurance Continuance Fund 1,506 1,530 Fixed Rate Fund 2,503 2,856 Total $ 481,273 $ 434,922 g. Expected Cash Flows. MGE does not expect to need to make any required contributions to the qualified plans for 2021. The contributions for years after 2021 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 2020, MGE made $ 6.3 h. Benefit Payments. The following benefit payments, which reflect expected 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 2021 $ 18,493 $ 4,696 $ ( 250) $ 4,446 2022 19,508 4,859 ( 277) 4,582 2023 20,353 5,145 ( 302) 4,843 2024 21,007 5,443 ( 327) 5,116 2025 21,678 5,529 ( 354) 5,175 2026 - 2030 114,762 27,163 ( 2,148) 25,015

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation - MGE Energy and MGE. In 2020, MGE Energy shareholders approved the 2021 Long-Term Incentive Plan (the 2021 Incentive Plan). It provides for the issuance of up to 500,000 shares of MGE Energy common stock in connection with awards made under the 2021 Incentive Plan. The 2021 Incentive Plan authorizes awards of restricted stock, restricted stock units, performance units, and dividend equivalents, or any combination of the foregoing. As of December 31, 2020, no awards were issued under the 2021 Incentive Plan. In February 2021, 16,267 restricted stock units and 10,187 performance units were issued under the 2021 Incentive Plan. The 2020 Performance Unit Plan (the 2020 Plan) was adopted in February 2020 for eligible employees. Plan participants may receive awards of performance units, restricted units, or both. Prior to the adoption of the 2020 plan, eligible employees could receive awards of performance units under the 2006 Performance Unit Plan. Under the 2013 Director Incentive Plan, eligible non-employee directors could receive awards of performance units. During the years ended December 31, 2020, 2019 and 2018, MGE recorded $ 1.3 million, $ 3.0 million, and $ 1.1 million, respectively, in compensation expense as a result of awards under the 2006 Performance Unit Plan, the 2020 Plan, and the 2013 Director Incentive Plan in "Other operations and maintenance" on the consolidated statements of income. a. 2013 Director Incentive Plan and 2006 Performance Unit Plan Under MGE Energy's 2013 Director Incentive Plan and its 2006 Performance Unit Plan, non-employee directors and eligible employees, respectively, could receive performance units that entitled 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 performance period set in the award. In accordance with the plans' provisions, these awards are subject to prescribed vesting schedules and must be settled in cash. Accordingly, no shares of common stock will be issued in connection with the plans. On the grant date, 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 remeasured quarterly, including as of December 31, 2020, 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 remeasured throughout the vesting period, the compensation cost is subject to variability. For nonretirement eligible employees under the 2006 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. Payouts under the 2013 Director Incentive Plan are subject to a three five The following activity occurred during 2020: 2020 Director Incentive Plan Performance Unit Plan Nonvested awards January 1, 4,611 26,468 Granted 5,048 - Vested ( 5,373) ( 9,048) Nonvested awards December 31, 4,286 17,420 No cash settlements have occurred on the awards shown in the table above as cash payments are only made at the end of the period covered by the awards. In January 2020, cash payments of $ 2.0 million were distributed relating to awards that were granted under the plans in 2017, for the 2013 Director Incentive Plan, and in 2015, for the 2006 Performance Unit Plan. b. 2020 Performance Unit Plan Performance units under the 2020 Performance Unit Plan (the 2020 Plan) 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, based upon achievement of specified performance goals during a performance period set by the Compensation Committee of MGE Energy's Board of Directors. Restricted units 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 a defined time period. Awards are subject to vesting provisions providing for 100% vesting at the end of the performance period, in the case of performance units, and at the end of the defined time period in the case of restricted units. The performance units and restricted units will be paid out in cash and are accounted for as a liability award. No shares of common stock will be issued in connection with the 2020 Plan. 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. The 2020 performance units contain market and performance conditions. The market condition is based on total shareowner return relative to an investor-owned utility peer group. The performance condition is based on achievement of targets specified in the award agreement (such as an earnings growth target). The fair value of each performance unit is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market and performance conditions contained in the award agreement during the three zero to 200% of the granted number of performance units. The 2020 restricted units will vest based on a three The following activity occurred during 2020: 2020 Performance Restricted Nonvested awards January 1, - - Granted 9,822 9,822 Vested ( 2,666) ( 2,666) Forfeited ( 153) ( 153) Nonvested awards December 31, 7,003 7,003 Fair Value of each nonvested award $ 89.13 N/A Estimated payout % based on performance criteria 100 % N/A

Notes Payable to Banks, Commerc

Notes Payable to Banks, Commercial Paper, and Lines of Credit	12 Months Ended
	Dec. 31, 2020
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. As of December 31, 2020, MGE Energy had an unsecured, committed revolving line of credit of $ 50 million expiring February 7, 2024. As of December 31, 2020, no borrowings were outstanding under this facility. The credit agreement requires MGE Energy to maintain a ratio of its consolidated indebtedness to consolidated total capitalization 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 failure 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, 2020, MGE Energy was in compliance with the covenant requirements of the credit agreement. b. MGE. For short-term borrowings, MGE generally issues commercial paper (issued at the prevailing discount rate at the time of issuance), which is supported by unused committed bank lines of credit. As of December 31, 2020, MGE had two unsecured, committed revolving lines of credit for a total of $ 100 million expiring February 7, 2024. As of December 31, 2020, no borrowings were outstanding under these facilities; however, there was $ 52.5 million in commercial paper outstanding. The credit agreements 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 change 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 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, 2020, MGE was in compliance with the covenant requirements of the credit agreements. 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, 2020 2019 2020 2019 Available capacity under line of credit $ 96,815 $ 150,000 $ 46,815 $ 100,000 Short-term debt outstanding $ 52,500 $ - $ 52,500 $ - Letters of credit issued inside credit facilities $ 685 $ - $ 685 $ - Weighted-average interest rate 0.15 % - % 0.15 % - % Year Ended December 31, Maximum short-term borrowings $ 52,500 $ 56,000 $ 52,500 $ 56,000 Average short-term borrowings $ 6,393 $ 18,364 $ 6,393 $ 18,364 Weighted-average interest rate 0.43 % 2.16 % 0.43 % 2.16 % (a) MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt - MGE Energy and MGE. a. Long-Term Debt. December 31, (In thousands) 2020 2019 First Mortgage Bonds: (a) 7.70%, 2028 Series $ 1,200 $ 1,200 Tax Exempt Debt: 3.45%, 2027 Series, Industrial Development Revenue Bonds(b) - 19,300 2.05%, 2023 Series, Industrial Development Revenue Bonds (b) 19,300 - Medium-Term Notes: (c) 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) 3.38%, retired 2020(e) - 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 2.94%, due 2029(e) 50,000 50,000 5.68%, due 2033(f) 22,762 23,946 5.19%, due 2033(f) 14,985 15,794 5.26%, due 2040(e) 15,000 15,000 5.04%, due 2040(g) 31,806 33,472 4.74%, due 2041(g) 20,167 21,167 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(e) 60,000 60,000 4.24%, due 2053(e) 20,000 20,000 4.34%, due 2058(e) 20,000 20,000 Total Other Long-Term Debt 437,720 457,379 Long-term debt due within one year ( 4,771) ( 19,659) Unamortized discount and debt issuance costs ( 4,146) ( 4,479) Total Long-Term Debt $ 519,303 $ 523,741 (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 MGE 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, 2020, approximately $ 529.9 (b) In April 2020, MGE borrowed $19.3 million from the City of Madison, Wisconsin's issuance of Industrial Development Revenue Refunding Bonds (Madison Gas and Electric Company Project), Series 2020A. The bonds carry an interest rate of 2.05% per annum with interest payable semi-annually on April 1 and October 1 of each year, which commenced on October1, 2020. The bonds require their holder to tender them on April 30, 2023, at which time the bonds will either be repriced and remarketed or redeemed and retired. MGE used the proceeds to redeem at par $19.3 million of existing Industrial Development Revenue Refunding Bonds (Madison Gas and Electric Company Project), Series 2002B due October 1, 2027. (c) The indenture under which MGE's Medium-Term notes are issued provides that those notes will be entitled to be equally and ratably secured in the event that MGE issues any additional first mortgage bonds. (d) Unsecured notes issued pursuant to various Note Purchase Agreements with one or more purchasers. The notes are not issued 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 voting 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, 2020 , MGE was in compliance with the covenant requirements. (f) Issued by MGE Power West Campus. The Note Purchase Agreements require MGE Power West Campus 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 the WCCF pursuant to a long-term lease. As of December 31, 2020, MGE Power West Campus was in compliance with the covenant requirements. (g) Issued by MGE 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 the Elm Road Units pursuant to long-term leases. As of December 31, 2020, 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, 2020. (In thousands) 2021 2022 2023 2024 2025 Thereafter Long-term debt maturities $ 4,771 $ 4,889 $ 54,314 $ 5,146 $ 5,285 $ 453,815 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 regarding these VIEs).

Common Equity

Common Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Common Equity	Common Equity. a. Common Stock - MGE Energy and MGE. MGE Energy sells shares of its common stock through its Direct Stock Purchase and Dividend Reinvestment Plan (the Stock Plan). Those shares may be newly issued shares or shares that are purchased in the open market by an independent agent for participants in the Stock Plan. The volume and timing of share repurchases in the open market depends upon the level of dividend reinvestment and optional share purchases made 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. 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, 2020 and 2019, MGE Energy issued no new shares of common stock under the Stock Plan. In May 2020, MGE Energy issued 1.5 million shares of its common stock in an underwritten offering. MGE Energy received proceeds, net of underwriter fees and issuance costs, of $ 79.6 During the years ended December 31, 2020 and 2019, MGE Energy paid $ 51.7 million (or $ 1.45 per share) and $ 47.8 million (or $ 1.38 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 order 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 MGE's common equity ratio, calculated in the manner used in the rate proceeding, is less than 55%. This restriction did not restrict MGE's payment of dividends in 2020. See Footnote 14 for further discussion of the mortgage indenture covenants regarding the payment of dividends. During the years ended December 31, 2020 and 2019, MGE paid no dividends to MGE Energy. b. Dilutive Shares Calculation - MGE Energy. MGE Energy has no dilutive securities issued.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies. a. Environmental - MGE Energy and MGE. Columbia In February 2021, MGE and the other co-owners of Columbia announced plans to retire that facility. The co-owners intend to retire Unit 1 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates for Units 1 and 2 are subject to PSCW and regional regulatory reviews, including identification and approval of energy and capacity resources to replace Columbia. Effects of environmental compliance discussed below will depend upon the final retirement dates approved and compliance requirement dates. Water Quality Water quality regulations promulgated by the EPA and WDNR in accordance with the Federal Water Pollution Control Act, 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, chemical concentrations, intake structures, and wetlands filling. The CWA also includes discharge standards, which require 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, by establishing discharge limits via water discharge permits. 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 Standards for Steam Electric Power Generating Point Source Category In August 2020, the EPA finalized rule modifications to the 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, but no later than December 31, 2023. The operators of the Columbia and Elm Road Units have indicated that equipment upgrades may be necessary to comply with the current discharge standards. In February 2021, MGE and the other owners of Columbia filed a Certificate of Authority (CA) application with the PSCW. The CA application commits to close Columbia's wet pond system to comply with the Coal Combustions Residuals (CCR) Rule as described in further detail in the solid waste section below. By committing to close the wet pond system, Columbia will be in compliance with ELG requirements. The operator of the Elm Road Units has been evaluating the rule impacts and has conducted an analysis of compliance obligations, pollution prevention technologies, and their associated costs. In February 2021, MGE and its co-owner filed a CA application with the PSCW. If approved, MGE's share of the estimated costs to comply with the rule is estimated to be approximately $ 4 million. Pending approval from the PSCW, construction is expected to begin in 2022. MGE will continue to work with the Elm Road operator to determine the final costs and timing of compliance. 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 to reduce mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens). 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. WCCF, Blount, and Columbia are considered existing plants under this rule. WCCF employs a system that meets the Section 316(b) rule. Blount's WPDES permit assumes that the plant meets best technology available (BTA) for the duration of the permit, which expires in 2023. However, MGE must 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. Columbia's operator received a permit in 2019 requiring studies of intake structures to help determine BTA. BTA improvements may not be required given that Columbia could be fully retired before the issuance of the next permit, which is expected to be issued in 2023 or later. MGE will continue to work with Columbia’s operator to evaluate all regulatory requirements applicable to the planned retirements. Management believes that the Section 316(b) rule will not have a material effect on its existing plants and that any compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects. Air Quality Federal and state air quality regulations impose restrictions on various emissions, including emissions of particulate matter (PM), sulfur dioxide (SO 2 x EPA's Greenhouse Gas (GHG) Reduction Guidelines under the Clean Air Act 111(d) Rule In January 2021, the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) vacated and remanded to the EPA the Affordable Clean Energy Rule (ACE Rule) and the repeal of the predecessor Clean Power Plan Rule (CPP Rule), both of which regulated greenhouse gas emissions from existing electric generation units pursuant to Section 111(d) of the Clean Air Act. MGE is still evaluating this D.C. Circuit decision for what impacts it may have on MGE operations. MGE will continue to evaluate the rule development and monitor ongoing and potential legal proceedings. 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 can 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 recommend areas for attainment (meets the ambient requirements) or nonattainment (does not meet these standards). The EPA makes 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. Its facilities may be subject to additional data submission and measurement requirements during permitting renewals, its facilities may need to meet new emission limitations set by the SIP (which could result in significant capital expenditures), and it may have additional expenses and/or difficulties expanding existing facilities or building new facilities. The process, which starts with determining acceptable primary and/or secondary NAAQS and ends with executing SIPs can take years. Since the NAAQS regulations have the potential to affect both existing and new facilities, 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 designating 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 designation decisions, including the partial Milwaukee County designation as being too narrow and not sufficiently protective. In July 2020, the U.S. District Court of the District of Columbia remanded the partial Milwaukee County attainment designation back to the EPA for further explanation. If the entire county were to be considered in nonattainment, the State of Wisconsin would need to develop an implementation plan that addressed emissions that contribute to Ozone (NO x EPA's Cross-State Air Pollution Rule The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and fine particulate (PM2.5) air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. This is accomplished in the CSAPR through a reduction in SO 2 x x 2 x In 2016 the EPA finalized a CSAPR Update Rule to address pollution transport related to an updated ozone NAAQS. In September 2019, the D.C. Circuit remanded the rule to the EPA holding that the rule improperly provided only a partial remedy for addressing interstate transport of pollutants from upwind to downwind states. In October 2020 the EPA published a proposed CSAPR Update Rule to address the remand which explicitly excludes Wisconsin. The EPA is under court order to finalize this update by March 2021. If the proposed rule is finalized as written, Wisconsin will not be subject to the emissions reductions included in the CSAPR Update Rule but will remain subject to the reductions required by the original CSAPR. MGE has met its current obligations through a combination of reduced emissions through pollution control (e.g., SCR installation at Columbia), as well as owned, received, and purchased allowances. While uncertainty remains around CSAPR due to legal challenges, MGE expects to meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor developments 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 CSAPR 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 continued legal challenges surrounding CSAPR and CAVR. MGE will continue to monitor developments to this rule. Columbia Clean Air Act Litigation Columbia is a coal-fired generating station operated by WPL and 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 and the Columbia co-owners failed to comply with appropriate pre-construction 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 consent decree entered by the EPA, Sierra Club, and the co-owners of Columbia. One of the requirements of the consent decree required installation of an SCR system at Columbia Unit 2 by December 31, 2018. Installation of the SCR was approved by the PSCW and the SCR was placed in service in 2018. The consent decree remains open for compliance monitoring, but significant additional operating and capital expenditures are not expected. Solid Waste EPA's Coal Combustion Residuals Rule The EPA's 2015 Coal Combustion Residuals Rule (CCR) regulates coal ash from burning coal for the purpose 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 landfills, ash ponds, and other surface impoundments used for coal combustion residuals by regulating their design, location, monitoring, and operation. In July 2018, the EPA published a final rule that included amendments to the CCR. The amendments 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 must cease the placement of waste in CCR units. In August 2018, the D.C. Circuit vacated parts of the 2015 CCR for not being sufficiently protective of the environment. In August 2020, the EPA revised the CCR rule to require owners or operators of coal-fired power plants to stop transporting CCR and non-CCR wastewater (a process known as "sluicing") to unlined surface impoundments. In addition, regulated entities must initiate impoundment closure as soon as feasible and in no event later than April 2021, unless the EPA grants an extension. Columbia requested an extension to comply by October 2022. The EPA will address the remaining issues on remand in a subsequent action. Review of the Elm Road Units has indicated that the costs to comply with the CRR rule are not expected to be significant. Columbia's operator has completed a review of its system and has developed a compliance plan. In February 2021, a CA application was filed with the PSCW for approval to install technology required to cease bottom ash transport water discharges rather than extend the longevity of the ash ponds. If approved, MGE's share of the estimated costs of the project would be approximately $ 4 million. Construction is expected to be completed by the end of 2022. In 2015, MGE recorded an asset retirement obligation for its share of the legal liability associated with the effect of the CCR rule. 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. MGE will continue to monitor final rule modifications to assess potential impacts on our operations. b. 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 flows. In January 2021, certain environmental groups filed a petition against the PSCW regarding MGE's 2021 rate settlement. MGE has intervened in the petition in cooperation with the PSCW. See Footnote 9.a. for more information regarding this matter. c. 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, 2020, the future minimum commitments related to these purchase contracts were as follows: (In thousands) 2021 2022 2023 2024 2025 Thereafter Coal (a) $ 11,399 $ 5,249 $ 1,515 $ - $ - $ - Natural gas Transportation and storage (b) 21,851 22,120 22,553 22,553 22,553 18,316 Supply (c) 9,527 - - - - - Purchase power (d) 27,017 15,399 5,856 5,458 5,567 11,717 Renewable energy (e) 6,663 2,862 1,245 759 776 30,939 Other 2,833 2,044 1,711 776 104 892 $ 79,290 $ 47,674 $ 32,880 $ 29,546 $ 29,000 $ 61,864 (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 approved 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 future electric supply requirements. (e) Operational commitments for solar and wind facilities. d. Other Commitments. MGE Energy holds investments in nonpublic venture capital funds. From time to time, these entities require additional capital infusions from their investors. MGE Energy has committed to contribute $ 13.6 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 1.5 million into this fund. As of December 31, 2020, MGE Energy has $ 0.4 million remaining in commitments. The timing of infusions is dependent on the needs 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) 2021 2022 2023 2024 2025 Thereafter Other commitments $ 333 $ 333 $ 333 $ 333 $ 333 $ 2,999

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2020
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 substations, combustion turbine generating units, 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 associated leases. 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 PCBs, and the proper disposal and removal of tanks, batteries, and underground cable. Changes in management's assumptions regarding settlement dates, settlement methods, or assigned probabilities could have a material effect on the liabilities and the associated regulatory asset recorded as of December 31, 2020. 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 permitted 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 summarizes the change in AROs. Amounts include conditional AROs . (In thousands) 2020 2019 Balance as of January 1, $ 28,355 $ 29,980 Liabilities incurred (a) 3,503 1,586 Accretion expense 1,366 1,574 Liabilities settled ( 372) ( 323) Revisions in estimated cash flows (b) ( 1,656) ( 4,462) Balance as of December 31, $ 31,196 $ 28,355 (a) In 2020, MGE recorded an obligation of $ 3.2 million for the fair value of its legal liability for AROs associated with Two Creeks. See Footnote 6 for additional information on Two Creeks. In 2019, MGE recorded an obligation of $ 1.5 million for the fair value of its legal liability for AROs associated with Saratoga. Construction of Saratoga was completed in February 2019. (b) In 2019, MGE revised the AROs associated with certain wind farms based on updated estimated decommissioning costs.

Derivative and Hedging Instrume

Derivative and Hedging Instruments	12 Months Ended
	Dec. 31, 2020
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 balance 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 strategies. The maximum length of time over which cash flows related to energy commodities can be hedged is four b. Notional Amounts. The gross notional volume of open derivatives is as follows: December 31, 2020 December 31, 2019 Commodity derivative contracts 259,080 MWh 417,840 MWh Commodity derivative contracts 6,030,000 Dth 6,605,000 Dth FTRs 2,869 MW 2,750 MW PPA 850 MW 1,450 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 corresponding 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, 2020, the fair value of exchange traded derivatives and FTRs exceeded their cost basis by $ 0.2 million. As of December 31, 2019, the cost basis of exchange traded derivatives and FTRs exceeded their fair value by $ 1.4 million. 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 after the base term. The agreement is accounted for as a derivative contract and is recognized at its fair value on the consolidated balance sheets. 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 as of December 31, 2020 and 2019, reflected a loss position of $ 14.1 million and $ 25.4 million, respectively. The actual cost will be recognized in purchased power expense in the month of purchase. The following table summarizes the fair value of the derivative instruments on the consolidated balance sheets. 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 as the netting of collateral. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as well as the netting of collateral. (In thousands) Derivative Assets Derivative Liabilities Balance Sheet Location December 31, 2020 Commodity derivative contracts (a) $ 617 $ 593 Other current assets Commodity derivative contracts (a) 189 39 Other deferred charges FTRs - 23 Other current liabilities PPA N/A 10,160 Derivative liability (current) PPA N/A 3,980 Derivative liability (long-term) December 31, 2019 Commodity derivative contracts (a) $ 157 $ 1,521 Derivative liability (current) (b) Commodity derivative contracts (a) 73 217 Derivative liability (long-term) FTRs 73 - Other current assets PPA N/A 10,100 Derivative liability (current) PPA N/A 15,340 Derivative liability (long-term) (a) As of December 31, 2019, collateral of $ 1.5 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, 2020. (b) As of December 31, 2019, MGE posted $ 0.1 million as other current assets on the consolidated balance sheets. The following tables show the effect of netting arrangements for recognized derivative 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, 2020 Commodity derivative contracts $ 806 $ ( 632) $ - $ 174 December 31, 2019 Commodity derivative contracts $ 230 $ ( 192) $ - $ 38 FTRs 73 - - 73 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, 2020 Commodity derivative contracts $ 632 $ ( 632) $ - $ - FTRs 23 - - 23 PPA 14,140 - - 14,140 December 31, 2019 Commodity derivative contracts $ 1,738 $ ( 192) $ ( 1,546) $ - PPA 25,440 - - 25,440 The following tables summarize the unrealized and realized gains/losses related to the derivative instruments on the consolidated balance sheets and the consolidated statements of income. 2020 2019 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, $ 26,875 $ 1,100 $ 31,830 $ 377 Unrealized gain ( 4,895) - ( 5,493) - Realized (loss) gain reclassified to a deferred account ( 2,232) 2,232 ( 1,896) 1,896 Realized (loss) gain reclassified to income statement ( 5,759) ( 2,170) 2,434 ( 1,173) Balance as of December 31, $ 13,989 $ 1,162 $ 26,875 $ 1,100 Realized Losses (Gains) 2020 2019 (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 $ 2,566 $ 1,729 $ 1,258 $ 863 FTRs 63 - ( 574) - PPA 3,571 - ( 2,808) - 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 sheets 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, 2020, 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 posted. As of December 31, 2020 and 2019, 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 portfolio. As of December 31, 2020, no counterparties had defaulted.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2020
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 assumptions 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 prices 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 model-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. The 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. Since long-term debt is 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, 2020 December 31, 2019 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 44,738 $ 44,738 $ 23,481 $ 23,481 Liabilities: Short-term debt - commercial paper 52,500 52,500 - - Long-term debt (a) 528,220 639,271 547,879 611,909 MGE Assets: Cash and cash equivalents $ 4,103 $ 4,103 $ 3,196 $ 3,196 Liabilities: Short-term debt - commercial paper 52,500 52,500 - - Long-term debt (a) 528,220 639,271 547,879 611,909 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $ 4.1 4.5 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, 2020 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 806 $ 436 $ - $ 370 Exchange-traded investments 1,750 1,750 - - Total Assets $ 2,556 $ 2,186 $ - $ 370 Liabilities: Derivatives, net (b) $ 14,795 $ 370 $ - $ 14,425 Deferred compensation 3,509 - 3,509 - Total Liabilities $ 18,304 $ 370 $ 3,509 $ 14,425 MGE Assets: Derivatives, net $ 806 $ 436 $ - $ 370 Exchange-traded investments 603 603 - - Total Assets $ 1,409 $ 1,039 $ - $ 370 Liabilities: Derivatives, net (b) $ 14,795 $ 370 $ - $ 14,425 Deferred compensation 3,509 - 3,509 - Total Liabilities $ 18,304 $ 370 $ 3,509 $ 14,425 Fair Value as of December 31, 2019 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 303 $ 189 $ - $ 114 Exchange-traded investments 1,271 1,271 - - Total Assets $ 1,574 $ 1,460 $ - $ 114 Liabilities: Derivatives, net (c) $ 27,178 $ 608 $ - $ 26,570 Deferred compensation 3,157 - 3,157 - Total Liabilities $ 30,335 $ 608 $ 3,157 $ 26,570 MGE Assets: Derivatives, net $ 303 $ 189 $ - $ 114 Exchange-traded investments 209 209 - - Total Assets $ 512 $ 398 $ - $ 114 Liabilities: Derivatives, net (c) $ 27,178 $ 608 $ - $ 26,570 Deferred compensation 3,157 - 3,157 - Total Liabilities $ 30,335 $ 608 $ 3,157 $ 26,570 (b) These amounts are shown gross. No collateral was posted against derivative positions with counterparties as of December 31, 2020. (c) These amounts are shown gross and exclude $ 1.5 million of collateral that was posted against derivative positions with counterparties as of December 31, 2019. Investments include exchange-traded investment securities valued using quoted prices on active exchanges and are therefore classified as Level 1. 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. The notional investments earn interest based upon the semiannual rate of U.S. Treasury Bills having a 26 1% compounded monthly with a minimum 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 Level 2. Derivatives include exchange-traded derivative contracts, 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 Level 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 instruments in a closed market with limited data available and are therefore classified as Level 3. The purchased power agreement (see Footnote 18) was valued using an internal pricing model and therefore is classified as Level 3. The model projects 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 curve 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 relationship 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 fair 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, volatility, 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: Model Input Significant Unobservable Inputs 2020 2019 Basis adjustment: On peak 94.2 % 92.1 % Off peak 94.5 % 92.7 % Counterparty fuel mix: Internal generation - range 46%-65 % 40%-60 % Internal generation - weighted average 56.5 % 52.2 % Purchased power - range 54%-35 % 60%-40 % Purchased power - weighted average 43.5 % 47.8 % The following table summarizes the changes in Level 3 commodity derivative assets and liabilities measured at fair value on a recurring basis. (In thousands) 2020 2019 2018 Balance as of January 1, $ ( 26,456) $ ( 32,002) $ ( 42,026) Realized and unrealized gains (losses): Included in regulatory assets 12,402 5,545 10,024 Included in other comprehensive income - - - Included in earnings ( 6,439) ( 3,765) 132 Included in current assets ( 87) ( 70) ( 47) Purchases 22,232 22,974 23,643 Sales - - - Issuances - - - Settlements ( 15,707) ( 19,138) ( 23,728) Transfers in and/or out of Level 3 - - - Balance as of December 31, $ ( 14,055) $ ( 26,456) $ ( 32,002) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, (d) $ - $ - $ - The following table presents total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis (d). (In thousands) Year Ended December 31, 2020 2019 2018 Purchased power expense $ ( 5,888) $ ( 3,334) $ 355 Cost of gas sold expense ( 551) ( 431) ( 223) Total $ ( 6,439) $ ( 3,765) $ 132 (d) MGE's exchange-traded derivative contracts, over-the-counter 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.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2020
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 2020 2019 2018 Residential $ 146,431 $ 140,006 $ 138,566 Commercial 198,043 213,265 204,683 Industrial 11,514 12,772 13,878 Other-retail/municipal 32,915 35,174 34,023 Total retail 388,903 401,217 391,150 Sales to the market 4,015 5,664 7,438 Other revenues 774 1,404 2,294 Total electric revenues 393,692 408,285 400,882 Gas revenues Residential 88,765 95,146 94,017 Commercial/Industrial 49,682 59,051 59,060 Total retail 138,447 154,197 153,077 Gas transportation 5,713 5,293 4,283 Other revenues 101 385 407 Total gas revenues 144,261 159,875 157,767 Non-regulated energy revenues 680 695 1,119 Total Operating Revenue $ 538,633 $ 568,855 $ 559,768 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 contracts have a single performance obligation. Retail Revenue (Residential, Commercial, Industrial, and Other Retail/Municipal) Providing electric and gas utility service to retail customers represents MGE's core business activity. 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 simultaneously 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 customers are subsequently billed for services received. At the end of the month, MGE accrues an estimate for unbilled commodities 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. 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- or 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 recognized as a reduction of revenue. Under-collection of these costs will 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 9.b. for further information. MGE also has other cost recovery mechanisms. For example, any over-collection of the difference between actual costs 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 wholesale 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 recognized 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 delivery requirements. Transportation of Gas MGE has contracts under which it provides gas transportation services to customers who have elected to purchase gas from a third party MGE delivers this gas via pipelines within its service territory. Revenue 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 standard terms and conditions, including pricing terms.

Noncontrolling Interest

Noncontrolling Interest	12 Months Ended
	Dec. 31, 2020
MGE [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest	Noncontrolling Interest - MGE. The noncontrolling interest on MGE's consolidated balance sheets was as follows: As of December 31, (In thousands) 2020 2019 MGE Power Elm Road (a) $ 96,856 $ 97,172 MGE Power West Campus (a) 44,340 43,131 Total Noncontrolling Interest $ 141,196 $ 140,303 The net income attributable to noncontrolling interest, net of tax, was as follows: Years ending December 31, (In thousands) 2020 2019 2018 MGE Power Elm Road (a) $ 15,184 $ 15,153 $ 15,384 MGE Power West Campus (a) 7,209 7,196 7,168 Net Income Attributable to Noncontrolling Interest, Net of Tax $ 22,393 $ 22,349 $ 22,552 (a) MGE Power Elm Road and MGE Power West Campus are not subsidiaries of MGE; however, they have been consolidated in the consolidated financial statements 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% owned 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.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2020
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 electric generating capacity that they lease to MGE 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 controlling 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 transmission 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 7 for further discussion. The "All Others" 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, in the case of NGV Fueling Services, owning and operating natural gas compression equipment. General corporate expenses include the cost of executive management, corporate accounting and finance, information technology, 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 electric 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 leases 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, 2020 Operating revenues $ 393,692 $ 144,261 $ 680 $ - $ - $ - $ 538,633 Interdepartmental revenues 765 12,157 40,402 - - ( 53,324) - Total operating revenues 394,457 156,418 41,082 - - ( 53,324) 538,633 Depreciation and amortization ( 54,658) ( 12,049) ( 7,481) - - - ( 74,188) Operating income (loss) 57,847 19,674 33,460 ( 1) ( 983) - 109,997 Interest (expense) income, net ( 14,446) ( 4,370) ( 4,826) - 121 - ( 23,521) Income tax (provision) benefit ( 4,230) ( 4,805) ( 7,800) ( 2,786) 198 - ( 19,423) Equity in earnings of investments - - - 10,221 - - 10,221 Net income (loss) 50,522 14,167 20,834 7,434 ( 539) - 92,418 Year Ended December 31, 2019 Operating revenues $ 408,285 $ 159,875 $ 695 $ - $ - $ - $ 568,855 Interdepartmental revenues 806 16,070 40,020 - - ( 56,896) - Total operating revenues 409,091 175,945 40,715 - - ( 56,896) 568,855 Depreciation and amortization ( 52,755) ( 11,320) ( 7,487) - - - ( 71,562) Operating income (loss) 59,180 19,528 33,084 - ( 882) - 110,910 Interest (expense) income, net ( 14,978) ( 4,237) ( 5,083) - 1,235 - ( 23,063) Income tax (provision) benefit ( 5,037) ( 4,753) ( 7,628) ( 2,602) 236 - ( 19,784) Equity in earnings of investments - - - 9,547 - - 9,547 Net income (loss) 46,318 14,088 20,373 6,945 ( 850) - 86,874 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) Operating income (loss) 64,294 17,900 33,074 ( 16) ( 1,045) - 114,207 Interest (expense) income, net ( 12,198) ( 3,692) ( 5,307) - 1,588 - ( 19,609) Income tax (provision) benefit ( 13,453) ( 4,474) ( 7,534) ( 2,345) 372 - ( 27,434) Equity in earnings of investments - - - 8,602 - - 8,602 Net income (loss) 45,937 12,866 20,233 6,241 ( 1,058) - 84,219 (In thousands) MGE Electric Gas Non-Regulated Energy Consolidation/ Elimination Entries Consolidated Total Year Ended December 31, 2020 Operating revenues $ 393,692 $ 144,261 $ 680 $ - $ 538,633 Interdepartmental revenues 765 12,157 40,402 ( 53,324) - Total operating revenues 394,457 156,418 41,082 ( 53,324) 538,633 Depreciation and amortization ( 54,658) ( 12,049) ( 7,481) - ( 74,188) Operating income 57,847 19,674 33,460 - 110,981 Interest expense, net ( 14,446) ( 4,370) ( 4,826) - ( 23,642) Income tax provision ( 4,230) ( 4,805) ( 7,800) - ( 16,835) Net income attributable to MGE 50,522 14,167 20,834 ( 22,393) 63,130 Year Ended December 31, 2019 Operating revenues $ 408,285 $ 159,875 $ 695 $ - $ 568,855 Interdepartmental revenues 806 16,070 40,020 ( 56,896) - Total operating revenues 409,091 175,945 40,715 ( 56,896) 568,855 Depreciation and amortization ( 52,755) ( 11,320) ( 7,487) - ( 71,562) Operating income 59,180 19,528 33,084 - 111,792 Interest expense, net ( 14,978) ( 4,237) ( 5,083) - ( 24,298) Income tax provision ( 5,037) ( 4,753) ( 7,628) - ( 17,418) Net income attributable to MGE 46,318 14,088 20,373 ( 22,349) 58,430 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) Operating income 64,294 17,900 33,074 - 115,268 Interest expense, net ( 12,198) ( 3,692) ( 5,307) - ( 21,197) Income tax provision ( 13,453) ( 4,474) ( 7,534) - ( 25,461) Net income attributable to MGE 45,937 12,866 20,233 ( 22,552) 56,484 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 (a) All Others Consolidation/ Elimination Entries Total Assets: December 31, 2020 $ 1,421,302 $ 444,702 $ 254,298 $ 74,480 $ 495,483 $ ( 436,614) $ 2,253,651 December 31, 2019 1,308,277 408,001 258,004 71,668 443,278 ( 407,564) 2,081,664 December 31, 2018 1,193,083 377,005 265,301 66,366 465,661 ( 378,798) 1,988,618 Capital Expenditures: Year ended Dec. 31, 2020 $ 162,210 $ 36,906 $ 4,023 $ - $ - $ - $ 203,139 Year ended Dec. 31, 2019 125,086 36,193 2,757 - - - 164,036 Year ended Dec. 31, 2018 176,399 30,497 5,301 - - - 212,197 Utility Consolidated (In thousands) MGE Electric Gas Non-regulated Energy Consolidation/ Elimination Entries Total Assets: December 31, 2020 $ 1,421,302 $ 444,702 $ 254,248 $ ( 281) $ 2,119,971 December 31, 2019 1,308,277 408,001 257,954 ( 755) 1,973,477 December 31, 2018 1,193,083 377,005 265,251 ( 448) 1,834,891 Capital Expenditures: Year ended Dec. 31, 2020 $ 162,210 $ 36,906 $ 4,023 $ - $ 203,139 Year ended Dec. 31, 2019 125,086 36,193 2,757 - 164,036 Year ended Dec. 31, 2018 176,399 30,497 5,301 - 212,197 (a) The Transmission Investment segment represents MGE Energy's investment in equity method investees.

Quarterly Summary of Operations

Quarterly Summary of Operations	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Summary of Operations	Quarterly Summary of Operations - MGE Energy (unaudited). (In thousands, except per share amounts) Quarters Ended 2020 March 31 June 30 September 30 December 31 Operating revenues: Electric revenues $ 93,028 $ 93,961 $ 116,568 $ 90,815 Gas revenues 56,845 23,079 18,643 45,694 Total Operating Revenues 149,873 117,040 135,211 136,509 Operating expenses 118,433 95,520 96,886 117,797 Operating income 31,440 21,520 38,325 18,712 Interest and other income, net ( 390) 1,011 769 454 Income tax provision ( 5,013) ( 3,740) ( 7,300) ( 3,370) Earnings on common stock $ 26,037 $ 18,791 $ 31,794 $ 15,796 Earnings per common share $ 0.75 $ 0.53 $ 0.88 $ 0.44 Dividends per share $ 0.353 $ 0.353 $ 0.370 $ 0.370 2019 Operating revenues: Electric revenues $ 97,469 $ 97,077 $ 120,821 $ 93,613 Gas revenues 70,100 25,070 17,377 47,328 Total Operating Revenues 167,569 122,147 138,198 140,941 Operating expenses 137,057 102,364 99,460 119,064 Operating income 30,512 19,783 38,738 21,877 Interest and other income, net ( 796) ( 730) ( 627) ( 2,099) Income tax provision ( 5,709) ( 3,505) ( 7,454) ( 3,116) Earnings on common stock $ 24,007 $ 15,548 $ 30,657 $ 16,662 Earnings per common share $ 0.69 $ 0.45 $ 0.88 $ 0.48 Dividends per share $ 0.338 $ 0.338 $ 0.353 $ 0.353 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, 2020
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 Income (Parent Company Only) (In thousands) For the Years Ended December 31, 2020 2019 2018 Operating Expenses: Other operations and maintenance $ 882 $ 815 $ 913 Total Operating Expenses 882 815 913 Operating Loss ( 882) ( 815) ( 913) Equity in earnings of investments 92,922 87,728 85,220 Other income (loss), net 94 ( 1,500) ( 1,966) Interest income, net 78 1,224 1,489 Income before income taxes 92,212 86,637 83,830 Income tax provision 206 237 389 Net Income $ 92,418 $ 86,874 $ 84,219 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, 2020 2019 2018 Net Cash Flows Provided by Operating Activities $ 27,631 $ 27,901 $ 27,211 Investing Activities: Contributions to affiliates ( 32,157) ( 33,631) ( 3,200) Contributions to other investments ( 3,809) ( 4,496) ( 2,626) Other 622 214 873 Cash Used for Investing Activities ( 35,344) ( 37,913) ( 4,953) Financing Activities: Issuance of common stock, net 79,635 - - Cash dividends paid on common stock ( 51,729) ( 47,842) ( 45,762) Cash Provided by (Used for) Financing Activities 27,906 ( 47,842) ( 45,762) Change in cash, cash equivalents, and restricted cash 20,193 ( 57,854) ( 23,504) Cash, cash equivalents, and restricted cash at beginning of period 17,182 75,036 98,540 Cash, cash equivalents, and restricted cash at end of period $ 37,375 $ 17,182 $ 75,036 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 2020 2019 Current Assets: Cash and cash equivalents $ 37,375 $ 17,182 Other current assets 1,494 3,180 Total Current Assets 38,869 20,362 Other deferred assets and other 364 498 Investments: Investments in affiliates 953,810 856,444 Other investments 15,634 12,910 Total Investments 969,444 869,354 Total Assets $ 1,008,677 $ 890,214 LIABILITIES AND SHAREHOLDERS' EQUITY Current Liabilities: Accounts payable to affiliates $ 530 $ 530 Other current liabilities 66 2,314 Total Current Liabilities 596 2,844 Other Credits: Deferred income taxes 29,926 29,006 Accounts payable to affiliates 2,118 2,647 Other deferred liabilities 37 41 Total Other Credits 32,081 31,694 Shareholders' Equity: Common shareholders' equity 430,571 350,936 Retained earnings 545,429 504,740 Total Shareholders' Equity 976,000 855,676 Commitments and contingencies (see Footnote 3) Total Liabilities and Shareholders' Equity $ 1,008,677 $ 890,214 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, Schedule 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, 2020. 2. Credit Agreements. As of December 31, 2020, MGE Energy had access to an unsecured, committed credit facility with aggregate bank commitments of $ 50.0 million. As of December 31, 2020, no borrowings were outstanding under this facility. See Footnote 13 of the Notes to Consolidated Financial Statements in this Report for further information regarding MGE Energy's credit agreement. 3. Commitments and Contingencies. See Footnote 16 of the Notes to Consolidated Financial Statements in this Report for information regarding commitments and contingencies. 4. Dividends from Affiliates. Dividends from Affiliates (In thousands) 2020 2019 2018 MGE Power Elm Road $ 15,500 $ 15,500 $ 15,500 MGE Power West Campus 6,000 8,000 6,500 MGE Transco 5,864 4,653 4,625 MGEE Transco 350 93 60 NGV Fueling Services - - 50 Total $ 27,714 $ 28,246 $ 26,735 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 dividends 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 rolling average common equity ratio as of December 31, 2020, is 60.2% as determined under the calculation used in the rate proceeding. This restriction did not impact MGE's payment of dividends in 2020. No cash dividends were paid by MGE to MGE Energy in 2020 or 2019. 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 any 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) accumulated subsequent to December 31, 1945. As of December 31, 2020, approximately $ 529.9 million was available for the payment of dividends under this covenant. See Footnotes 13 and 14 of the Notes to Consolidated Financial Statements in this Report for more information on dividend restrictions appearing in credit agreements and long-term debt, respectively.

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2020
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 2018: Accumulated provision for uncollectibles $ 3,174,945 1,065,970 320,400 ( 1,407,653) $ 3,153,662 Fiscal Year 2019: Accumulated provision for uncollectibles $ 3,153,662 1,614,943 20,160 ( 1,530,496) $ 3,258,269 Fiscal Year 2020: Accumulated provision for uncollectibles $ 3,258,269 5,164,943 (b) 26,400 ( 1,373,047) $ 7,076,565 (a) Net of recovery of amounts previously written off (b) As of December 31, 2020, MGE had deferred $ 3.8 million of incremental COVID-19-related costs as a regulatory asset. See Footnote 8 of the Notes to Consolidated Financial Statements in this Report for further information.

Significant Accounting Policies

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
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 development entity for property. MGE Power owns 100% of 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 nonregulated entities formed to own the investments in ATC and ATC Holdco, respectively. MGE did not own any subsidiaries as of December 31, 2020. 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 receive 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 beneficiary, 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 expected 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 entities 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. 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. With the global outbreak of the Coronavirus Disease 2019 (COVID-19) and the declaration of a pandemic by the World Health Organization on March 11, 2020, U.S. governmental authorities have deemed electric and gas utilities to be critical infrastructure. MGE Energy therefore has an obligation to keep operating and maintaining our critical electric and gas infrastructure. Since then, MGE Energy has been subject to, and is following, local, state and federal public health and safety regulations and guidance to control the pandemic. MGE Energy and MGE considered the impact of COVID-19 developments on the assumptions and estimates used in the preparation of these financial statements.
Cash and Cash Equivalents	Cash Equivalents All highly liquid investments purchased with an original maturity of three months or less are considered 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 sheets.
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. A 1% late payment charge is recorded on all receivables unpaid after the due date. In late March 2020, the 1% late payment charge was suspended in response to the PSCW's COVID-19 order. The order also suspended disconnection or refusal of services to any customer, with limited exceptions. The PSCW order was lifted on July 25, 2020; however, as permitted by regulatory action, MGE notified the PSCW of its election to continue to waive late fees until April 1, 2021. See Footnote 9.c. for further information. The allowance for credit losses associated with these receivables represents MGE's best estimate of the amount of probable credit losses for existing accounts receivable. MGE manages concentration of credit risk through its credit and collection policies, which are consistent with state regulatory requirements. The allowance for credit losses is estimated based on historical write-off experience, regional economic data, review of the accounts receivable aging, and reasonable and supportable forecasts that affect the collectability of the reported amount. MGE has considered the effects of COVID-19 developments and associated governmental regulations, including suspension of disconnections for non-payment, in its estimate of allowance for credit losses by applying data from historical recessions and other significant economic downturns.
Inventories	Inventories - MGE Energy and MGE. Inventories consist of natural gas in storage, fuel for electric generation, materials and supplies, and renewable energy credits (RECs). 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 allowances 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 institution an undivided interest with recourse, in up to $ 1.5 million of the financing program receivables, until July 31, 2021. 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, 2020, 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. Regulatory assets and liabilities are amortized in the consolidated statements of income consistent with the recovery or refund included in customer rates. MGE believes it is probable that its recorded regulatory assets and liabilities will be recovered and refunded, 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 reduction 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 charged 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 approximate the following percentages for the cost of depreciable property: 2020 2019 2018 Electric (a) 3.5 % 3.6 % 2.9 % Gas 2.2 % 2.1 % 2.1 % Nonregulated 2.3 % 2.3 % 2.3 % (a) In the December 2018 rate settlement, the PSCW approved new depreciation rates for Columbia effective January 1, 2019.
Asset Retirement Obligations Policy	Asset Retirement Obligations - MGE Energy and MGE. A liability is recorded for the fair value of an asset retirement obligation (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 "Other 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 recovers 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 contracts have a single performance obligation. Retail Revenue (Residential, Commercial, Industrial, and Other Retail/Municipal) Providing electric and gas utility service to retail customers represents MGE's core business activity. 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 simultaneously 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 customers are subsequently billed for services received. At the end of the month, MGE accrues an estimate for unbilled commodities 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. 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- or 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 recognized as a reduction of revenue. Under-collection of these costs will 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 9.b. for further information. MGE also has other cost recovery mechanisms. For example, any over-collection of the difference between actual costs 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 wholesale 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 recognized 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 delivery requirements. Transportation of Gas MGE has contracts under which it provides gas transportation services to customers who have elected to purchase gas from a third party MGE delivers this gas via pipelines within its service territory. Revenue 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 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 around the amount approved for a utility in its annual fuel proceedings. Any over- or 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 recognized as a reduction of revenue. Under-collection of these costs will be recognized in "Purchased power" expense in the consolidated statements of income. The cumulative effects of these deferred amounts will be recorded as a regulatory asset or regulatory liability until they are reflected in future billings to customers. See Footnote 9.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 2020, 2019 and 2018, as approved by the PSCW, MGE capitalized AFUDC-debt and equity on 50% of applicable average construction work in progress at 7.03%, 7.0%, and 7.87%, respectively. MGE received specific approval to recover 100% AFUDC on certain costs for Saratoga, Two Creeks, Badger Hollow I and II, its customer information and billing project, and on certain environmental costs for Columbia. These amounts are recovered under the ratemaking process over the service lives of the related properties. During 2020, 2019, and 2018, MGE recorded $ 2.1 million, $ 0.8 million, and $ 1.1 million, respectively, of AFUDC-debt. During 2020, 2019, and 2018, MGE recorded $ 5.9 million, $ 2.3 million, and $ 3.3 million, respectively, of AFUDC-equity.
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. For equity security investments without readily determinable fair values, MGE Energy and MGE have elected to use the practicability exception to measure these investments, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. Equity security investments with readily determinable fair values are carried at fair value. Realized and unrealized gains and losses are included in earnings.
Capitalized Software Costs	Capitalized Software Costs - MGE Energy and MGE. The net book value of capitalized costs of internal use software included in property, plant, and equipment was $ 20.4 million and $ 24.6 million as of December 31, 2020 and 2019, respectively. As of December 31, 2020 and 2019, accumulated amortization was $ 36.9 million and $ 31.8 million, respectively. During 2020 and 2019, MGE recorded $ 5.1 million of amortization expense. During 2018, MGE recorded $ 4.7 million of amortization expense. Capitalized software costs are amortized on a straight-line basis over the estimated useful lives of the assets. The useful lives range from five fifteen
Capitalized Software Assets Hosting Agreements	Capitalized Software Assets – Hosting Arrangements – MGE Energy and MGE. The net book value of capitalized costs of internal use software incurred in a hosting arrangement was $ 14.8 million and $ 13.6 million as of December 31, 2020 and 2019, respectively. As of December 31, 2020 and 2019, accumulated amortization was $ 3.2 million and $ 1.4 million, respectively. 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 2020, 2019, and 2018, MGE recorded $ 1.8 million, $ 1.4 million, and $ 0.1 million, respectively, of amortization expense related to software assets for hosted arrangements. 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 term of the hosted contract, which includes renewable option periods. Software assets for hosted arrangements have terms ranging from five ten
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 such 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 principles have resulted in a regulatory liability related to income taxes. Excess deferred income taxes result from past taxes provided at customer 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 property 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 $ 14.1 million, $ 13.9 million, and $ 14.4 million for the years ended December 31, 2020, 2019, and 2018, respectively. Operating income taxes, including tax credits and license fee tax, are included in rates for utility related items.
Share-based Compensation	The 2020 Performance Unit Plan (the 2020 Plan) was adopted in February 2020 for eligible employees. Plan participants may receive awards of performance units, restricted units, or both. Prior to the adoption of the 2020 Plan, eligible employees received awards of performance units under the 2006 Performance Unit Plan. Under the 2013 Director Incentive Plan, eligible non-employee directors may receive awards of performance units. Under the incentive plans, eligible participants, including employees and non-employee directors, may receive performance or restricted 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 a performance period set in the 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 services received in exchange for a performance or restricted 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 original 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 derivatives, excluding those that qualify for the normal purchases or normal sales exclusion, 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 derivative 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 marked to fair value and are offset with a corresponding regulatory asset or liability depending on whether the derivative is in a net loss or net gain position, respectively. 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	New Accounting Standards - MGE Energy and MGE. Recently Adopted Credit Losses. In June 2016, the Financial Accounting Standards Board issued authoritative guidance within the codification's Credit Losses topic, which introduced a new model for recognizing credit losses on financial instruments based on an estimate of current expected credit losses. The authoritative guidance became effective January 1, 2020. MGE adopted the standard on the effective date. The adoption of this standard did not have a material impact on MGE Energy's and MGE's financial statements. New disclosures are required under the new standard. See Footnote 1.e. for allowance for credit loss disclosures.
Leases	As part of its regular operations, MGE enters into various contracts related to IT equipment, substations, cell towers, land, wind easements, and other property in use for operations. A contract is or contains a lease if the contract conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Determination as to whether an arrangement is or contains a lease is completed at inception. Leases with an initial term of 12 months or less are not recorded on the consolidated balance sheets; lease expense for these leases are recognized on a straight-line basis over the lease term. Leases with initial terms in excess of 12 months are recorded as operating or financing leases on the consolidated balance sheets. Operating lease assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. For leases that do not provide an implicit rate, a collateralized incremental borrowing rate based on the information available at commencement date, including lease term, is used in determining the present value of future payments. The operating lease asset also includes any lease payments made and excludes lease incentives and initial direct costs incurred. Lease terms may include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the lease term. MGE has regulatory treatment and recognizes regulatory assets or liabilities for timing differences between when net lease costs are recorded and when costs are recognized. As of December 31, 2020, MGE had no significant leases not yet commenced that would create significant future rights and obligations.
Income Taxes
Uncertainty in Income Taxes	The 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 are classified with "Other deferred liabilities" on the consolidated balance sheets. The interest component recoverable in rates is offset by a regulatory asset. As of December 31, 2020, 2019, and 2018, 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 distribution repairs. In addition, as of December 31, 2019 and 2018, unrecognized tax benefits relating to permanent differences and tax credits was less than $ 0.1 million and $ 0.3 million, respectively. As of December 31, 2020, there were no unrecognized tax benefits relating to permanent differences and tax credits. The unrecognized tax benefits as of December 31, 2020, are not expected to significantly increase or decrease within the next twelve months. In addition, 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 Footnote 19 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, 2020: 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 invested 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 from 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 at 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 reported 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.
Common Equity
Common Stock	MGE Energy sells shares of its common stock through its Direct Stock Purchase and Dividend Reinvestment Plan (the Stock Plan). Those shares may be newly issued shares or shares that are purchased in the open market by an independent agent for participants in the Stock Plan. The volume and timing of share repurchases in the open market depends upon the level of dividend reinvestment and optional share purchases made 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. All sales under the Stock Plan are covered by a shelf registration statement that MGE Energy filed with the SEC.
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 balance 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 strategies. The maximum length of time over which cash flows related to energy commodities can be hedged is four
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 as the netting of collateral. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as well 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 assumptions 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 prices 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 model-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. The 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. Since long-term debt is not traded in an active market, it is classified as Level 2. Investments include exchange-traded investment securities valued using quoted prices on active exchanges and are therefore classified as Level 1. 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. The notional investments earn interest based upon the semiannual rate of U.S. Treasury Bills having a 26 1% compounded monthly with a minimum 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 Level 2. Derivatives include exchange-traded derivative contracts, 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 Level 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 instruments in a closed market with limited data available and are therefore classified as Level 3. The purchased power agreement (see Footnote 18) was valued using an internal pricing model and therefore is classified as Level 3. The model projects 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 curve 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 relationship 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 fair 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, volatility, 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: Model Input Significant Unobservable Inputs 2020 2019 Basis adjustment: On peak 94.2 % 92.1 % Off peak 94.5 % 92.7 % Counterparty fuel mix: Internal generation - range 46%-65 % 40%-60 % Internal generation - weighted average 56.5 % 52.2 % Purchased power - range 54%-35 % 60%-40 % Purchased power - weighted average 43.5 % 47.8 %
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. This treatment resulted in a $ 61.8 million, a $ 75.6 million, and a $ 90.3 million reduction to sales to the market and purchase power expense for MISO markets for the years ended December 31, 2020, 2019, and 2018, respectively.
Segment Information
Segment Information	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 electric generating capacity that they lease to MGE 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 controlling 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 transmission 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 7 for further discussion. The "All Others" 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, in the case of NGV Fueling Services, owning and operating natural gas compression equipment. General corporate expenses include the cost of executive management, corporate accounting and finance, information technology, 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 electric 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 leases 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, 2020
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, 2020 2019 2020 2019 Cash and cash equivalents $ 44,738 $ 23,481 $ 4,103 $ 3,196 Restricted cash 644 619 644 619 Receivable - margin account 1,657 1,714 1,657 1,714 Cash, cash equivalents, and restricted cash $ 47,039 $ 25,814 $ 6,404 $ 5,529
Straight-Line Depreciation Rates	Provisions at composite straight-line depreciation rates approximate the following percentages for the cost of depreciable property: 2020 2019 2018 Electric (a) 3.5 % 3.6 % 2.9 % Gas 2.2 % 2.1 % 2.1 % Nonregulated 2.3 % 2.3 % 2.3 % (a) In the December 2018 rate settlement, the PSCW approved new depreciation rates for Columbia effective January 1, 2019.

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2020
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 balance sheets related to its interest in these VIEs: MGE Power Elm Road MGE Power West Campus (In thousands) 2020 2019 2020 2019 Property, plant, and equipment, net $ 166,883 $ 170,763 $ 79,077 $ 79,473 Construction work in progress 697 468 677 309 Affiliate receivables - - 2,803 3,600 Accrued interest and accrued (prepaid) taxes 2,701 1,364 671 ( 160) Deferred income taxes 30,646 30,621 14,521 14,363 Long-term debt (a) 51,590 54,207 37,652 39,627 Noncontrolling interest 96,856 97,172 44,340 43,131 (a) MGE Power Elm Road's long-term debt includes debt issuance costs of $ 0.4 million as of December 31, 2020 and 2019. 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 costs of $ 0.1 million as of December 31, 2020 and 2019. 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 14 for further information on the long-term debt securities.

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant, and Equipment	Property, plant, and equipment consisted of the following as of December 31: MGE Energy MGE (In thousands) 2020 2019 2020 2019 Utility: Electric (a) $ 1,608,658 $ 1,480,684 $ 1,608,675 $ 1,480,701 Gas 496,450 472,123 496,461 472,134 Total utility plant 2,105,108 1,952,807 2,105,136 1,952,835 Less: Accumulated depreciation and amortization 721,382 674,251 721,382 674,251 In-service utility plant, net 1,383,726 1,278,556 1,383,754 1,278,584 Nonregulated: Nonregulated 320,691 323,266 320,691 323,266 Less: Accumulated depreciation and amortization 74,131 71,623 74,131 71,623 In-service nonregulated plant, net 246,560 251,643 246,560 251,643 Construction work in progress: Utility construction work in progress (b) 137,725 111,707 137,725 111,707 Nonregulated construction work in progress 1,374 777 1,374 777 Total property, plant, and equipment $ 1,769,385 $ 1,642,683 $ 1,769,413 $ 1,642,711 (a) In 2019, the PSCW authorized construction of Two Creeks. The project was placed in service in November 2020. Total capital expenditures for the project were $ 62.9 million, excluding AFUDC. After tax, MGE recognized $ 2.4 million and $ 1.0 million, respectively, of AFUDC equity for the years ended December 31, 2020 and 2019. MGE received specific approval to recover 100% AFUDC on the project. (b) In 2019, the PSCW authorized construction of Badger Hollow I. Construction of the project is expected to be completed in April 2021. As of December 31, 2020, and 2019, MGE had $ 54.7 million and $ 18.7 million (excluding AFUDC), respectively, in construction work in progress. After tax, MGE recognized $ 2.0 million and $ 0.2 million, respectively, of AFUDC equity related to Badger Hollow I for the years ended December 31, 2020 and 2019. Phase II of the project was authorized by the PSCW in 2020. Construction of Badger Hollow II is expected to be completed in December 2022. As of December 31, 2020, MGE had $ 5.2 million (excluding AFUDC) in construction work in progress. After tax, MGE recognized $ 0.2 million of AFUDC equity related to Badger Hollow II for the year ended December 31, 2020. MGE received specific approval to recover % AFUDC on these projects .

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Lease Cost	The following table shows lease expense for the years ended December 31: (In thousands) 2020 2019 Income Statement Location Finance lease expense: Amortization of leased assets $ 1,694 $ 1,524 Depreciation and amortization Interest on lease liabilities 784 792 Interest expense, net Operating lease expense 319 144 Other operations and maintenance Total lease expense $ 2,797 $ 2,460
Lease Balance Sheet	The following table shows the lease assets and liabilities on the consolidated balance sheets as of December 31: (In thousands) 2020 2019 Balance Sheet Location Lease assets: Finance lease assets $ 15,682 $ 15,895 Property, plant, and equipment, net Operating lease assets (a) 5,988 671 Other deferred assets and other Total lease assets $ 21,670 $ 16,566 Lease liabilities: Finance lease liabilities - current $ 1,066 $ 888 Other current liabilities Finance lease liabilities - long-term 17,532 17,379 Finance lease liabilities Operating lease liabilities - current 171 203 Other current liabilities Operating lease liabilities - long-term (a) 5,840 496 Other deferred liabilities and other Total lease liabilities $ 24,609 $ 18,966 (a) Increase in operating lease assets and long-term operating lease liabilities related to land leases for new solar farms in 2020.
Other Financial Information	The following table shows other lease information for the years ended December 31: (In thousands) 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Finance leases - Financing cash flows $ 1,149 $ 945 Finance leases - Operating cash flows 784 792 Operating leases - Operating cash flows 319 134 Lease assets obtained in exchange for lease liabilities: Finance leases 1,480 12,101 Operating leases 5,791 657
Weighted Average And Discount Rate	The following table shows the weighted average remaining lease terms and discounts as of December 31: Weighted-average remaining lease terms (in years): 2020 2019 Finance leases 37 39 Operating leases 34 15 Weighted-average discount rates: Finance leases 4.32 % 4.37 % Operating leases 2.84 % 3.32 %
Lessee Operating Lease Liability Maturity	The following table shows maturities of lease liabilities as of December 31: (In thousands) Finance Operating 2021 $ 1,820 $ 338 2022 1,700 274 2023 1,520 203 2024 959 207 2025 774 211 Thereafter 39,787 8,636 Subtotal 46,560 9,869 Less: Present value discount ( 27,962) ( 3,858) Lease Liability $ 18,598 $ 6,011
Lessee Finance Lease Liability Maturity	The following table shows maturities of lease liabilities as of December 31: (In thousands) Finance Operating 2021 $ 1,820 $ 338 2022 1,700 274 2023 1,520 203 2024 959 207 2025 774 211 Thereafter 39,787 8,636 Subtotal 46,560 9,869 Less: Present value discount ( 27,962) ( 3,858) Lease Liability $ 18,598 $ 6,011

Joint Plant Ownership (Tables)

Joint Plant Ownership (Tables)	12 Months Ended
	Dec. 31, 2020
Regulated Operations [Abstract]
Schedule of Joint Plant Ownership	The following table shows MGE's interest in utility plant in service, and the related accumulated depreciation reserves and other information related to MGE's jointly owned facilities: (In thousands, except for percentages and MW) Columbia (a) Elm Road (b) West Campus (c) Forward Wind (d) Two Creeks (e) Badger Hollow I & II (f) Ownership interest 19 % 8.33 % 55 % 12.8 % 33 % 33 % Share of generation (MW) 211 MW 106 MW 157 MW 18 MW 50 MW 100 MW For the year ended December 31, Operating expense - 2020 $ 27,127 $ 17,259 $ (g) $ 664 $ 118 $ - Operating expense - 2019 32,604 19,661 (g) 642 - - Operating expense - 2018 36,517 17,555 (g) 600 (h) - - As of December 31, 2020 Utility plant $ 289,597 $ 203,847 $ 115,657 $ 34,028 $ 67,577 $ - Accumulated depreciation ( 118,742) ( 36,964) ( 36,580) ( 14,092) ( 225) - Construction work in progress 997 697 677 - - 63,140 As of December 31, 2019 Utility plant $ 291,997 $ 207,834 $ 113,259 $ 34,054 $ - $ - Accumulated depreciation ( 105,778) ( 37,071) ( 33,786) ( 13,413) - - Construction work in progress 1,777 468 309 45 45,286 18,953 (a) In February 2021, MGE and the other co-owners announced plans to retire Columbia, a two unit coal-fired generation facility located in Portage, Wisconsin. The co-owners intend to retire Unit 1 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates for Units 1 and 2 are subject to PSCW and regional regulatory reviews, including identification and approval of energy and capacity resources to replace Columbia. (b) Two coal-fired generating units in Oak Creek, Wisconsin. (c) MGE Power West Campus and the UW jointly own the West Campus Cogeneration Facility (WCCF) located on the UW campus in Madison, Wisconsin. The UW owns a controlling interest in the chilled-water and steam plants, which are used to meet the needs for air-conditioning and steam-heat capacity for the UW campus. MGE Power West Campus owns a controlling interest in the electric generation plant, which is leased and operated by MGE. (d) The Forward Wind Energy Center (Forward Wind) consists of 86 wind turbines located near Brownsville, Wisconsin. (e) The Two Creeks solar generation array is located in the Town of Two Creeks and the City of Two Rivers in Manitowoc and Kewaunee Counties, Wisconsin. Date of commercial operation of the solar array was November 2020. (f) The Badger Hollow I and II solar farm is located in southwestern Wisconsin in Iowa County, near the villages of Montfort and Cobb. Badger Hollow I and II estimated commercial operation dates are April 2021 and December 2022, respectively. (g) 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, 2020, 2019, and 2018, the UW's allocated share of fuel and operating costs was $ 5.2 million, $ 6.6 million, and $ 6.3 million, respectively. (h) Amount was deferred as a regulatory asset in 2018. This amount was recovered in rates and recognized as operating and maintenance expense in 2019.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Investments Disclosure [Abstract]
Equity Method and Other Investments	MGE Energy MGE (In thousands) 2020 2019 2020 2019 Equity securities $ 17,906 $ 14,546 $ 603 $ 209 Equity method investments: ATC and ATC Holdco 74,423 71,609 - - Other 39 39 - - Total equity method investments 74,462 71,648 - - Other investments 2,308 2,298 - - Total $ 94,676 $ 88,492 $ 603 $ 209 During the years ended December 31, 2020, 2019, and 2018, certain investments were liquidated. As a result of these liquidations, the following was received: MGE Energy MGE (In thousands) 2020 2019 2018 2020 2019 2018 Cash proceeds $ 622 $ 216 $ 960 $ - $ 2 $ 3 Gain (loss) on sale 379 580 476 - ( 343) 3
Equity Method Investments Summarized Financial Data	Equity earnings from investments are recorded as "Other income" on the consolidated statements of income of MGE Energy. For the years ended December 31, MGE Transco recorded the following: (In thousands) 2020 2019 2018 Equity earnings from investment in ATC $ 10,167 $ 9,889 $ 8,821 Dividends received from ATC (a) 8,633 7,347 4,611 Capital contributions to ATC 1,249 3,018 2,841 (a) MGE Transco recorded a $ 2.3 million dividend receivable from ATC as of December 31, 2017. A cash dividend was received in January of 2018. (In thousands) Income statement data for the year ended December 31, 2020 2019 2018 Operating revenues $ 758,117 $ 744,371 $ 690,510 Operating expenses ( 372,463) ( 373,527) ( 358,703) Other income 1,922 48 2,405 Interest expense, net ( 112,818) ( 110,490) ( 110,725) Earnings before members' income taxes $ 274,758 $ 260,402 $ 223,487 Balance sheet data as of December 31, 2020 2019 Current assets $ 92,735 $ 84,635 Noncurrent assets 5,400,538 5,244,220 Total assets $ 5,493,273 $ 5,328,855 Current liabilities $ 310,749 $ 502,601 Long-term debt 2,512,246 2,312,799 Other noncurrent liabilities 378,205 298,828 Members' equity 2,292,073 2,214,627 Total members' equity and liabilities $ 5,493,273 $ 5,328,855

Regulatory Assets and Liabili_2

Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	The following regulatory assets and liabilities are reflected in MGE's consolidated balance sheets as of December 31: (In thousands) 2020 2019 Regulatory Assets Asset retirement obligation $ 11,935 $ 10,756 COVID-19 costs 3,933 - Debt related costs 8,586 8,885 Deferred pension and other postretirement costs 5,280 6,216 Derivatives 13,989 26,875 Leases 2,748 2,400 Tax recovery related to AFUDC equity 8,952 7,060 Unfunded pension and other postretirement liability 101,594 83,214 Other 235 340 Total Regulatory Assets $ 157,252 $ 145,746 Regulatory Liabilities Deferred fuel savings $ 5,047 $ 1,794 Elm Road 1,957 2,322 Income taxes 129,856 129,528 Non-ARO removal costs 28,197 26,543 Pension and other postretirement service costs 7,524 4,499 Purchased gas adjustment 1,832 1,864 Renewable energy credits 802 558 Transmission 7,669 6,019 Other 1,019 1,066 Total Regulatory Liabilities $ 183,903 $ 174,193

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
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) 2020 2019 2018 2020 2019 2018 Current payable: Federal $ 4,179 $ 8,017 $ 18,622 $ 3,716 $ 7,616 $ 19,926 State 5,095 4,647 5,163 4,790 4,608 5,704 Net-deferred: Federal 6,181 3,510 120 4,756 2,242 ( 2,563) State 4,182 3,702 3,629 3,787 3,044 2,494 Amortized investment tax credits ( 214) ( 92) ( 100) ( 214) ( 92) ( 100) Total income tax provision $ 19,423 $ 19,784 $ 27,434 $ 16,835 $ 17,418 $ 25,461
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 2020 2019 2018 2020 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % State income taxes, net of federal benefit 6.3 6.2 6.3 6.3 6.1 6.2 Amortized investment tax credits ( 0.2) ( 0.1) ( 0.1) ( 0.2) ( 0.1) ( 0.1) Credit for electricity from wind energy (a) ( 6.2) ( 5.7) ( 0.3) ( 6.8) ( 6.2) ( 0.4) AFUDC equity, net ( 1.2) ( 0.3) ( 0.6) ( 1.4) ( 0.3) ( 0.5) Amortization of utility excess deferred tax (b) ( 2.0) ( 2.4) ( 1.8) ( 2.2) ( 2.7) ( 2.0) Other, net, individually insignificant ( 0.3) ( 0.1) 0.1 ( 0.3) ( 0.1) 0.2 Effective income tax rate 17.4 % 18.6 % 24.6 % 16.4 % 17.7 % 24.4 % (a) Saratoga became operational in February 2019. (b) Included are impacts of the Tax Cuts and Jobs Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting. For the years ended December 31, 2020, 2019, and 2018, MGE recognized $ 2.2 million, $ 2.6 million, and $ 2.1 million, respectively. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, as determined by the PSCW.
Deferred Tax Liabilities (Assets)	The significant components of deferred tax assets and liabilities that appear on the consolidated balance sheets as of December 31 are as follows: MGE Energy MGE (In thousands) 2020 2019 2020 2019 Deferred tax assets Investment in ATC $ 21,688 $ 22,576 $ - $ - Federal tax credits 19,199 - 20,080 - Accrued expenses 11,115 15,901 11,105 15,890 Pension and other postretirement benefits 35,446 30,968 35,446 30,968 Deferred tax regulatory account 41,318 35,493 41,318 35,493 Derivatives 3,852 7,351 3,852 7,351 Leases 6,704 5,167 6,704 5,167 Other 14,073 12,540 14,125 12,593 Gross deferred income tax assets 153,395 129,996 132,630 107,462 Less valuation allowance ( 38) ( 86) ( 38) ( 86) Net deferred income tax assets $ 153,357 $ 129,910 $ 132,592 $ 107,376 Deferred tax liabilities Property-related $ 257,397 $ 245,083 $ 257,397 $ 245,083 Investment in ATC 51,518 51,569 - - Bond transactions 595 657 595 657 Pension and other postretirement benefits 45,658 45,683 45,658 45,683 Derivatives 3,852 7,351 3,852 7,351 Tax deductible prepayments 9,059 9,078 9,059 9,051 Leases 6,704 5,167 6,704 5,167 Other 10,045 8,624 9,717 8,425 Gross deferred income tax liabilities 384,828 373,212 332,982 321,417 Deferred income taxes $ 231,471 $ 243,302 $ 200,390 $ 214,041
Summary Of Tax Credit Carryforwards	The components of federal and state tax benefit carryovers as of December 31, are as follows: MGE Energy MGE (In thousands) 2020 2019 2020 2019 Federal tax credits $ 19,199 $ - $ 20,080 $ - State net operating losses 621 1,406 621 1,406 Valuation allowances for state net operating losses ( 621) ( 1,406) ( 621) ( 1,406)
Unrecognized Tax Benefits and Interest	A tabular reconciliation of unrecognized tax benefits and interest is as follows: (In thousands) Unrecognized Tax Benefits: 2020 2019 2018 Unrecognized tax benefits, January 1, $ 2,093 $ 1,949 $ 1,924 Additions based on tax positions related to the current year 796 741 425 Additions based on tax positions related to the prior years - 84 272 Reductions based on tax positions related to the prior years ( 608) ( 681) ( 672) Unrecognized tax benefits, December 31, $ 2,281 $ 2,093 $ 1,949 (In thousands) Interest on Unrecognized Tax Benefits: 2020 2019 2018 Accrued interest on unrecognized tax benefits, January 1, $ 176 $ 191 $ 165 Reduction in interest expense on uncertain tax positions ( 124) ( 137) ( 136) Interest expense on uncertain tax positions 102 122 162 Accrued interest on unrecognized tax benefits, December 31, $ 154 $ 176 $ 191
Tax Years that Remain Subject to Examination	The following table shows tax years that remain subject to examination by major jurisdiction: Taxpayer Open Years MGE Energy and consolidated subsidiaries in federal return 2017 through 2020 MGE Energy Wisconsin combined reporting corporation return 2017 through 2020

Pension Plans and Other Postr_2

Pension Plans and Other Postretirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2020
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: 2020 2019 2020 2019 Net benefit obligation as of January 1, $ 410,651 $ 360,288 $ 80,901 $ 75,161 Service cost 5,296 4,692 1,264 1,110 Interest cost 12,210 14,302 2,278 2,893 Plan participants' contributions - - 1,009 969 Actuarial loss (a) 50,325 47,671 5,907 5,045 Gross benefits paid ( 17,267) ( 16,302) ( 5,245) ( 4,497) Less: federal subsidy on benefits paid (b) - - 246 220 Benefit obligation as of December 31, $ 461,215 $ 410,651 $ 86,360 $ 80,901 Change in Plan Assets: Fair value of plan assets as of January 1, $ 386,033 $ 323,780 $ 48,889 $ 42,521 Actual return on plan assets 58,935 76,766 6,514 9,277 Employer contributions 1,837 1,789 568 619 Plan participants' contributions - - 1,009 969 Gross benefits paid ( 17,267) ( 16,302) ( 5,245) ( 4,497) Fair value of plan assets at end of year 429,538 386,033 51,735 48,889 Funded Status as of December 31, $ ( 31,677) $ ( 24,618) $ ( 34,625) $ ( 32,012) (a) In 2020 and 2019, lower discount rates were the primary 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, 2020 and 2019, 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) 2020 2019 2020 2019 Long-term asset $ 13,873 $ 13,630 $ - $ - Current liability ( 2,139) ( 1,688) - - Long-term liability ( 43,411) ( 36,560) ( 34,625) ( 32,012) Net liability $ ( 31,677) $ ( 24,618) $ ( 34,625) $ ( 32,012)
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) 2020 2019 2020 2019 Net actuarial loss $ 92,553 $ 79,290 $ 10,986 $ 8,659 Prior service benefit ( 144) ( 268) ( 1,816) ( 4,484) Transition obligation - - 15 17 Total $ 92,409 $ 79,022 $ 9,185 $ 4,192
Schedule 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 2020 2019 Projected benefit obligation, end of year $ 45,550 $ 38,247 Fair value of plan assets, end of year - -
Schedule of Accumulated Benefit Obligations in Excess of Plan Assets	The accumulated benefit obligation and fair value of plan assets with an accumulated benefit obligation in excess of plan assets were as follows: (In thousands) Pension Benefits Other Postretirement Benefits Accumulated Benefit Obligation in Excess of Plan Assets 2020 2019 2020 2019 Accumulated benefit obligation, end of year $ 43,384 $ 35,798 $ 86,360 $ 80,901 Fair value of plan assets, end of year - - 51,735 48,889
Net Periodic Benefit Costs	(In thousands) Pension Benefits Other Postretirement Benefits Components of Net Periodic Benefit Cost: 2020 (a) 2019 (a) 2018 2020 (a) 2019 (a) 2018 Service cost $ 5,296 $ 4,692 $ 5,723 $ 1,264 $ 1,110 $ 1,283 Interest cost 12,210 14,302 12,859 2,278 2,893 2,612 Expected return on assets ( 27,229) ( 22,786) ( 26,241) ( 3,154) ( 2,723) ( 3,232) Amortization of: Transition obligation - - - 3 3 3 Prior service (credit) cost ( 114) ( 117) ( 44) ( 2,669) ( 2,669) ( 2,669) Actuarial loss 5,357 7,379 5,278 217 401 488 Net periodic benefit cost (credit) $ ( 4,480) $ 3,470 $ ( 2,425) $ ( 2,061) $ ( 985) $ ( 1,515) (a) During 2019, MGE deferred approximately $ 6.2 million of pension and other postretirement costs. During 2020, MGE collected approximately $ 0.9 million of pension and other postretirement costs, which reduced the amount deferred in 2019. The impact of the deferral has not been reflected in the table above. See Footnote 8 for further information.
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 2020 2019 2020 2019 Discount rate 2.70 % 3.42 % 2.52 % 3.30 % Rate of compensation increase 3.22 % 3.21 % N/A N/A Assumed health care cost trend rates: Health care cost trend rate assumed for next year N/A N/A 5.75 % 6.00 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) N/A N/A 4.75 % 5.00 % Year that the rate reaches the ultimate trend rate N/A N/A 2027 2024 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 2020 2019 2018 2020 2019 2018 Discount rate 3.42 % 4.32 % 3.73 % 3.30 % 4.24 % 3.60 % Expected rate of return on plan assets 7.20 % 7.20 % 7.40 % 6.75 % 6.72 % 6.94 % Rate of compensation increase 3.26 % 3.25 % 3.72 % N/A N/A N/A
Fair Value of Plan Assets by Asset Category	The asset allocation for MGE's pension plans as of December 31, 2020 and 2019, and the target allocation for 2021, by asset category, follows: Target Allocation Percentage of Plan Assets at Year End 2020 2019 Equity securities (a) 63.0 % 69.0 % 64.0 % Fixed income securities 30.0 % 25.0 % 29.0 % Real estate 7.0 % 6.0 % 7.0 % Total 100.0 % 100.0 % 100.0 % (a) Target allocations for equity securities are broken out as follows: 45.5% United States equity and 17.5% non-United States equity. The fair values of MGE's plan assets by asset category as of December 31 are as follows: (In thousands) 2020 2019 Cash and Cash Equivalents $ 1,180 $ 964 Equity Securities: U.S. Large Cap 151,218 134,458 U.S. Mid Cap 37,389 31,288 U.S. Small Cap 50,456 36,495 International Blend 87,461 76,293 Fixed Income Securities: Short-Term Fund 4,215 7,449 High Yield Bond 22,683 21,276 Long Duration Bond 92,657 92,642 Real Estate 30,005 29,671 Insurance Continuance Fund 1,506 1,530 Fixed Rate Fund 2,503 2,856 Total $ 481,273 $ 434,922
Benefit Payments, Fiscal Year Maturity	The following benefit payments, which reflect expected 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 2021 $ 18,493 $ 4,696 $ ( 250) $ 4,446 2022 19,508 4,859 ( 277) 4,582 2023 20,353 5,145 ( 302) 4,843 2024 21,007 5,443 ( 327) 5,116 2025 21,678 5,529 ( 354) 5,175 2026 - 2030 114,762 27,163 ( 2,148) 25,015

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
2013 Director Incentive Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Unit Graded Vesting Schedule	The following activity occurred during 2020: 2020 Director Incentive Plan Performance Unit Plan Nonvested awards January 1, 4,611 26,468 Granted 5,048 - Vested ( 5,373) ( 9,048) Nonvested awards December 31, 4,286 17,420
2006 Performance Unit Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Unit Graded Vesting Schedule	The following activity occurred during 2020: 2020 Director Incentive Plan Performance Unit Plan Nonvested awards January 1, 4,611 26,468 Granted 5,048 - Vested ( 5,373) ( 9,048) Nonvested awards December 31, 4,286 17,420
2020 Performance Unit Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Unit Graded Vesting Schedule	The following activity occurred during 2020: 2020 Performance Restricted Nonvested awards January 1, - - Granted 9,822 9,822 Vested ( 2,666) ( 2,666) Forfeited ( 153) ( 153) Nonvested awards December 31, 7,003 7,003 Fair Value of each nonvested award $ 89.13 N/A Estimated payout % based on performance criteria 100 % N/A

Notes Payable to Banks, Comme_2

Notes Payable to Banks, Commercial Paper, and Lines of Credit (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 2020 2019 Available capacity under line of credit $ 96,815 $ 150,000 $ 46,815 $ 100,000 Short-term debt outstanding $ 52,500 $ - $ 52,500 $ - Letters of credit issued inside credit facilities $ 685 $ - $ 685 $ - Weighted-average interest rate 0.15 % - % 0.15 % - % Year Ended December 31, Maximum short-term borrowings $ 52,500 $ 56,000 $ 52,500 $ 56,000 Average short-term borrowings $ 6,393 $ 18,364 $ 6,393 $ 18,364 Weighted-average interest rate 0.43 % 2.16 % 0.43 % 2.16 % (a) MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	December 31, (In thousands) 2020 2019 First Mortgage Bonds: (a) 7.70%, 2028 Series $ 1,200 $ 1,200 Tax Exempt Debt: 3.45%, 2027 Series, Industrial Development Revenue Bonds(b) - 19,300 2.05%, 2023 Series, Industrial Development Revenue Bonds (b) 19,300 - Medium-Term Notes: (c) 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) 3.38%, retired 2020(e) - 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 2.94%, due 2029(e) 50,000 50,000 5.68%, due 2033(f) 22,762 23,946 5.19%, due 2033(f) 14,985 15,794 5.26%, due 2040(e) 15,000 15,000 5.04%, due 2040(g) 31,806 33,472 4.74%, due 2041(g) 20,167 21,167 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(e) 60,000 60,000 4.24%, due 2053(e) 20,000 20,000 4.34%, due 2058(e) 20,000 20,000 Total Other Long-Term Debt 437,720 457,379 Long-term debt due within one year ( 4,771) ( 19,659) Unamortized discount and debt issuance costs ( 4,146) ( 4,479) Total Long-Term Debt $ 519,303 $ 523,741 (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 MGE 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, 2020, approximately $ 529.9 (b) In April 2020, MGE borrowed $19.3 million from the City of Madison, Wisconsin's issuance of Industrial Development Revenue Refunding Bonds (Madison Gas and Electric Company Project), Series 2020A. The bonds carry an interest rate of 2.05% per annum with interest payable semi-annually on April 1 and October 1 of each year, which commenced on October1, 2020. The bonds require their holder to tender them on April 30, 2023, at which time the bonds will either be repriced and remarketed or redeemed and retired. MGE used the proceeds to redeem at par $19.3 million of existing Industrial Development Revenue Refunding Bonds (Madison Gas and Electric Company Project), Series 2002B due October 1, 2027. (c) The indenture under which MGE's Medium-Term notes are issued provides that those notes will be entitled to be equally and ratably secured in the event that MGE issues any additional first mortgage bonds. (d) Unsecured notes issued pursuant to various Note Purchase Agreements with one or more purchasers. The notes are not issued 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 voting 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, 2020 , MGE was in compliance with the covenant requirements. (f) Issued by MGE Power West Campus. The Note Purchase Agreements require MGE Power West Campus 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 the WCCF pursuant to a long-term lease. As of December 31, 2020, MGE Power West Campus was in compliance with the covenant requirements. (g) Issued by MGE 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 the Elm Road Units pursuant to long-term leases. As of December 31, 2020, 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, 2020. (In thousands) 2021 2022 2023 2024 2025 Thereafter Long-term debt maturities $ 4,771 $ 4,889 $ 54,314 $ 5,146 $ 5,285 $ 453,815

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule	As of December 31, 2020, the future minimum commitments related to these purchase contracts were as follows: (In thousands) 2021 2022 2023 2024 2025 Thereafter Coal (a) $ 11,399 $ 5,249 $ 1,515 $ - $ - $ - Natural gas Transportation and storage (b) 21,851 22,120 22,553 22,553 22,553 18,316 Supply (c) 9,527 - - - - - Purchase power (d) 27,017 15,399 5,856 5,458 5,567 11,717 Renewable energy (e) 6,663 2,862 1,245 759 776 30,939 Other 2,833 2,044 1,711 776 104 892 $ 79,290 $ 47,674 $ 32,880 $ 29,546 $ 29,000 $ 61,864 (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 approved 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 future electric supply requirements. (e) Operational commitments for solar and wind facilities.
Other Commitments	MGE has several other commitments related to various projects. Payments for these commitments are expected to be as follows: (In thousands) 2021 2022 2023 2024 2025 Thereafter Other commitments $ 333 $ 333 $ 333 $ 333 $ 333 $ 2,999

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]
Change in Asset Retirement Obligations	The following table summarizes the change in AROs. Amounts include conditional AROs (In thousands) 2020 2019 Balance as of January 1, $ 28,355 $ 29,980 Liabilities incurred (a) 3,503 1,586 Accretion expense 1,366 1,574 Liabilities settled ( 372) ( 323) Revisions in estimated cash flows (b) ( 1,656) ( 4,462) Balance as of December 31, $ 31,196 $ 28,355 (a) In 2020, MGE recorded an obligation of $ 3.2 million for the fair value of its legal liability for AROs associated with Two Creeks. See Footnote 6 for additional information on Two Creeks. In 2019, MGE recorded an obligation of $ 1.5 million for the fair value of its legal liability for AROs associated with Saratoga. Construction of Saratoga was completed in February 2019. (b) In 2019, MGE revised the AROs associated with certain wind farms based on updated estimated decommissioning costs.

Derivative and Hedging Instru_2

Derivative and Hedging Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 December 31, 2019 Commodity derivative contracts 259,080 MWh 417,840 MWh Commodity derivative contracts 6,030,000 Dth 6,605,000 Dth FTRs 2,869 MW 2,750 MW PPA 850 MW 1,450 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 sheets. 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 as the netting of collateral. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as well as the netting of collateral. (In thousands) Derivative Assets Derivative Liabilities Balance Sheet Location December 31, 2020 Commodity derivative contracts (a) $ 617 $ 593 Other current assets Commodity derivative contracts (a) 189 39 Other deferred charges FTRs - 23 Other current liabilities PPA N/A 10,160 Derivative liability (current) PPA N/A 3,980 Derivative liability (long-term) December 31, 2019 Commodity derivative contracts (a) $ 157 $ 1,521 Derivative liability (current) (b) Commodity derivative contracts (a) 73 217 Derivative liability (long-term) FTRs 73 - Other current assets PPA N/A 10,100 Derivative liability (current) PPA N/A 15,340 Derivative liability (long-term) (a) As of December 31, 2019, collateral of $ 1.5 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, 2020. (b) As of December 31, 2019, MGE posted $ 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 derivative 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, 2020 Commodity derivative contracts $ 806 $ ( 632) $ - $ 174 December 31, 2019 Commodity derivative contracts $ 230 $ ( 192) $ - $ 38 FTRs 73 - - 73
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, 2020 Commodity derivative contracts $ 632 $ ( 632) $ - $ - FTRs 23 - - 23 PPA 14,140 - - 14,140 December 31, 2019 Commodity derivative contracts $ 1,738 $ ( 192) $ ( 1,546) $ - PPA 25,440 - - 25,440
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 and the consolidated statements of income. 2020 2019 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, $ 26,875 $ 1,100 $ 31,830 $ 377 Unrealized gain ( 4,895) - ( 5,493) - Realized (loss) gain reclassified to a deferred account ( 2,232) 2,232 ( 1,896) 1,896 Realized (loss) gain reclassified to income statement ( 5,759) ( 2,170) 2,434 ( 1,173) Balance as of December 31, $ 13,989 $ 1,162 $ 26,875 $ 1,100
Derivative Gains and Losses in Income Statement	Realized Losses (Gains) 2020 2019 (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 $ 2,566 $ 1,729 $ 1,258 $ 863 FTRs 63 - ( 574) - PPA 3,571 - ( 2,808) -

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Estimated Fair Market Value of Financial Instruments	The estimated fair market value of financial instruments are as follows: December 31, 2020 December 31, 2019 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 44,738 $ 44,738 $ 23,481 $ 23,481 Liabilities: Short-term debt - commercial paper 52,500 52,500 - - Long-term debt (a) 528,220 639,271 547,879 611,909 MGE Assets: Cash and cash equivalents $ 4,103 $ 4,103 $ 3,196 $ 3,196 Liabilities: Short-term debt - commercial paper 52,500 52,500 - - Long-term debt (a) 528,220 639,271 547,879 611,909 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $ 4.1 4.5
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, 2020 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 806 $ 436 $ - $ 370 Exchange-traded investments 1,750 1,750 - - Total Assets $ 2,556 $ 2,186 $ - $ 370 Liabilities: Derivatives, net (b) $ 14,795 $ 370 $ - $ 14,425 Deferred compensation 3,509 - 3,509 - Total Liabilities $ 18,304 $ 370 $ 3,509 $ 14,425 MGE Assets: Derivatives, net $ 806 $ 436 $ - $ 370 Exchange-traded investments 603 603 - - Total Assets $ 1,409 $ 1,039 $ - $ 370 Liabilities: Derivatives, net (b) $ 14,795 $ 370 $ - $ 14,425 Deferred compensation 3,509 - 3,509 - Total Liabilities $ 18,304 $ 370 $ 3,509 $ 14,425 Fair Value as of December 31, 2019 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 303 $ 189 $ - $ 114 Exchange-traded investments 1,271 1,271 - - Total Assets $ 1,574 $ 1,460 $ - $ 114 Liabilities: Derivatives, net (c) $ 27,178 $ 608 $ - $ 26,570 Deferred compensation 3,157 - 3,157 - Total Liabilities $ 30,335 $ 608 $ 3,157 $ 26,570 MGE Assets: Derivatives, net $ 303 $ 189 $ - $ 114 Exchange-traded investments 209 209 - - Total Assets $ 512 $ 398 $ - $ 114 Liabilities: Derivatives, net (c) $ 27,178 $ 608 $ - $ 26,570 Deferred compensation 3,157 - 3,157 - Total Liabilities $ 30,335 $ 608 $ 3,157 $ 26,570 (b) These amounts are shown gross. No collateral was posted against derivative positions with counterparties as of December 31, 2020. (c) These amounts are shown gross and exclude $ 1.5 million of collateral that was posted against derivative positions with counterparties as of December 31, 2019.
Significant Unobservable Inputs	The following table presents the significant unobservable inputs used in the pricing model: Model Input Significant Unobservable Inputs 2020 2019 Basis adjustment: On peak 94.2 % 92.1 % Off peak 94.5 % 92.7 % Counterparty fuel mix: Internal generation - range 46%-65 % 40%-60 % Internal generation - weighted average 56.5 % 52.2 % Purchased power - range 54%-35 % 60%-40 % Purchased power - weighted average 43.5 % 47.8 %
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) 2020 2019 2018 Balance as of January 1, $ ( 26,456) $ ( 32,002) $ ( 42,026) Realized and unrealized gains (losses): Included in regulatory assets 12,402 5,545 10,024 Included in other comprehensive income - - - Included in earnings ( 6,439) ( 3,765) 132 Included in current assets ( 87) ( 70) ( 47) Purchases 22,232 22,974 23,643 Sales - - - Issuances - - - Settlements ( 15,707) ( 19,138) ( 23,728) Transfers in and/or out of Level 3 - - - Balance as of December 31, $ ( 14,055) $ ( 26,456) $ ( 32,002) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, (d) $ - $ - $ - (d) MGE's exchange-traded derivative contracts, over-the-counter 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 liabilities measured at fair value on a recurring basis (d). (In thousands) Year Ended December 31, 2020 2019 2018 Purchased power expense $ ( 5,888) $ ( 3,334) $ 355 Cost of gas sold expense ( 551) ( 431) ( 223) Total $ ( 6,439) $ ( 3,765) $ 132 (d) MGE's exchange-traded derivative contracts, over-the-counter 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.

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2020
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 2020 2019 2018 Residential $ 146,431 $ 140,006 $ 138,566 Commercial 198,043 213,265 204,683 Industrial 11,514 12,772 13,878 Other-retail/municipal 32,915 35,174 34,023 Total retail 388,903 401,217 391,150 Sales to the market 4,015 5,664 7,438 Other revenues 774 1,404 2,294 Total electric revenues 393,692 408,285 400,882 Gas revenues Residential 88,765 95,146 94,017 Commercial/Industrial 49,682 59,051 59,060 Total retail 138,447 154,197 153,077 Gas transportation 5,713 5,293 4,283 Other revenues 101 385 407 Total gas revenues 144,261 159,875 157,767 Non-regulated energy revenues 680 695 1,119 Total Operating Revenue $ 538,633 $ 568,855 $ 559,768

Noncontrolling Interest (Tables

Noncontrolling Interest (Tables) - MGE [Member]	12 Months Ended
	Dec. 31, 2020
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Balance Sheet	The noncontrolling interest on MGE's consolidated balance sheets was as follows: As of December 31, (In thousands) 2020 2019 MGE Power Elm Road (a) $ 96,856 $ 97,172 MGE Power West Campus (a) 44,340 43,131 Total Noncontrolling Interest $ 141,196 $ 140,303
Net Income Attributable to Noncontrolling Interest, Net of Tax	The net income attributable to noncontrolling interest, net of tax, was as follows: Years ending December 31, (In thousands) 2020 2019 2018 MGE Power Elm Road (a) $ 15,184 $ 15,153 $ 15,384 MGE Power West Campus (a) 7,209 7,196 7,168 Net Income Attributable to Noncontrolling Interest, Net of Tax $ 22,393 $ 22,349 $ 22,552 (a) MGE Power Elm Road and MGE Power West Campus are not subsidiaries of MGE; however, they have been consolidated in the consolidated financial statements 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% owned 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.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 Operating revenues $ 393,692 $ 144,261 $ 680 $ - $ - $ - $ 538,633 Interdepartmental revenues 765 12,157 40,402 - - ( 53,324) - Total operating revenues 394,457 156,418 41,082 - - ( 53,324) 538,633 Depreciation and amortization ( 54,658) ( 12,049) ( 7,481) - - - ( 74,188) Operating income (loss) 57,847 19,674 33,460 ( 1) ( 983) - 109,997 Interest (expense) income, net ( 14,446) ( 4,370) ( 4,826) - 121 - ( 23,521) Income tax (provision) benefit ( 4,230) ( 4,805) ( 7,800) ( 2,786) 198 - ( 19,423) Equity in earnings of investments - - - 10,221 - - 10,221 Net income (loss) 50,522 14,167 20,834 7,434 ( 539) - 92,418 Year Ended December 31, 2019 Operating revenues $ 408,285 $ 159,875 $ 695 $ - $ - $ - $ 568,855 Interdepartmental revenues 806 16,070 40,020 - - ( 56,896) - Total operating revenues 409,091 175,945 40,715 - - ( 56,896) 568,855 Depreciation and amortization ( 52,755) ( 11,320) ( 7,487) - - - ( 71,562) Operating income (loss) 59,180 19,528 33,084 - ( 882) - 110,910 Interest (expense) income, net ( 14,978) ( 4,237) ( 5,083) - 1,235 - ( 23,063) Income tax (provision) benefit ( 5,037) ( 4,753) ( 7,628) ( 2,602) 236 - ( 19,784) Equity in earnings of investments - - - 9,547 - - 9,547 Net income (loss) 46,318 14,088 20,373 6,945 ( 850) - 86,874 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) Operating income (loss) 64,294 17,900 33,074 ( 16) ( 1,045) - 114,207 Interest (expense) income, net ( 12,198) ( 3,692) ( 5,307) - 1,588 - ( 19,609) Income tax (provision) benefit ( 13,453) ( 4,474) ( 7,534) ( 2,345) 372 - ( 27,434) Equity in earnings of investments - - - 8,602 - - 8,602 Net income (loss) 45,937 12,866 20,233 6,241 ( 1,058) - 84,219 (In thousands) MGE Electric Gas Non-Regulated Energy Consolidation/ Elimination Entries Consolidated Total Year Ended December 31, 2020 Operating revenues $ 393,692 $ 144,261 $ 680 $ - $ 538,633 Interdepartmental revenues 765 12,157 40,402 ( 53,324) - Total operating revenues 394,457 156,418 41,082 ( 53,324) 538,633 Depreciation and amortization ( 54,658) ( 12,049) ( 7,481) - ( 74,188) Operating income 57,847 19,674 33,460 - 110,981 Interest expense, net ( 14,446) ( 4,370) ( 4,826) - ( 23,642) Income tax provision ( 4,230) ( 4,805) ( 7,800) - ( 16,835) Net income attributable to MGE 50,522 14,167 20,834 ( 22,393) 63,130 Year Ended December 31, 2019 Operating revenues $ 408,285 $ 159,875 $ 695 $ - $ 568,855 Interdepartmental revenues 806 16,070 40,020 ( 56,896) - Total operating revenues 409,091 175,945 40,715 ( 56,896) 568,855 Depreciation and amortization ( 52,755) ( 11,320) ( 7,487) - ( 71,562) Operating income 59,180 19,528 33,084 - 111,792 Interest expense, net ( 14,978) ( 4,237) ( 5,083) - ( 24,298) Income tax provision ( 5,037) ( 4,753) ( 7,628) - ( 17,418) Net income attributable to MGE 46,318 14,088 20,373 ( 22,349) 58,430 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) Operating income 64,294 17,900 33,074 - 115,268 Interest expense, net ( 12,198) ( 3,692) ( 5,307) - ( 21,197) Income tax provision ( 13,453) ( 4,474) ( 7,534) - ( 25,461) Net income attributable to MGE 45,937 12,866 20,233 ( 22,552) 56,484 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 (a) All Others Consolidation/ Elimination Entries Total Assets: December 31, 2020 $ 1,421,302 $ 444,702 $ 254,298 $ 74,480 $ 495,483 $ ( 436,614) $ 2,253,651 December 31, 2019 1,308,277 408,001 258,004 71,668 443,278 ( 407,564) 2,081,664 December 31, 2018 1,193,083 377,005 265,301 66,366 465,661 ( 378,798) 1,988,618 Capital Expenditures: Year ended Dec. 31, 2020 $ 162,210 $ 36,906 $ 4,023 $ - $ - $ - $ 203,139 Year ended Dec. 31, 2019 125,086 36,193 2,757 - - - 164,036 Year ended Dec. 31, 2018 176,399 30,497 5,301 - - - 212,197 Utility Consolidated (In thousands) MGE Electric Gas Non-regulated Energy Consolidation/ Elimination Entries Total Assets: December 31, 2020 $ 1,421,302 $ 444,702 $ 254,248 $ ( 281) $ 2,119,971 December 31, 2019 1,308,277 408,001 257,954 ( 755) 1,973,477 December 31, 2018 1,193,083 377,005 265,251 ( 448) 1,834,891 Capital Expenditures: Year ended Dec. 31, 2020 $ 162,210 $ 36,906 $ 4,023 $ - $ 203,139 Year ended Dec. 31, 2019 125,086 36,193 2,757 - 164,036 Year ended Dec. 31, 2018 176,399 30,497 5,301 - 212,197 (a) The Transmission Investment segment represents MGE Energy's investment in equity method investees.

Quarterly Summary of Operatio_2

Quarterly Summary of Operations (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Summary of Operations	(In thousands, except per share amounts) Quarters Ended 2020 March 31 June 30 September 30 December 31 Operating revenues: Electric revenues $ 93,028 $ 93,961 $ 116,568 $ 90,815 Gas revenues 56,845 23,079 18,643 45,694 Total Operating Revenues 149,873 117,040 135,211 136,509 Operating expenses 118,433 95,520 96,886 117,797 Operating income 31,440 21,520 38,325 18,712 Interest and other income, net ( 390) 1,011 769 454 Income tax provision ( 5,013) ( 3,740) ( 7,300) ( 3,370) Earnings on common stock $ 26,037 $ 18,791 $ 31,794 $ 15,796 Earnings per common share $ 0.75 $ 0.53 $ 0.88 $ 0.44 Dividends per share $ 0.353 $ 0.353 $ 0.370 $ 0.370 2019 Operating revenues: Electric revenues $ 97,469 $ 97,077 $ 120,821 $ 93,613 Gas revenues 70,100 25,070 17,377 47,328 Total Operating Revenues 167,569 122,147 138,198 140,941 Operating expenses 137,057 102,364 99,460 119,064 Operating income 30,512 19,783 38,738 21,877 Interest and other income, net ( 796) ( 730) ( 627) ( 2,099) Income tax provision ( 5,709) ( 3,505) ( 7,454) ( 3,116) Earnings on common stock $ 24,007 $ 15,548 $ 30,657 $ 16,662 Earnings per common share $ 0.69 $ 0.45 $ 0.88 $ 0.48 Dividends per share $ 0.338 $ 0.338 $ 0.353 $ 0.353 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, 2020	Dec. 31, 2019		Dec. 31, 2018
Trade Receivables, Allowance for Doubtful Accounts, and Concentration Risk
Late payment charge on upaid receivables	1.00%
Late payment charge on unpaid receivables - suspended	1.00%
Accounts receivable, allowance for credit loss, writeoff	$ 1,400,000
Accounts receivable, allowance for credit loss, period increase	5,200,000
Accounts receivable, allowance for credit loss	7,100,000
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	157,252,000	$ 145,746,000
Inventories
Renewable energy credit allowance included in inventory	800,000	600,000
Purchased Gas Adjustment Clause
Purchased gas adjustment, over (under) collected	1,800,000	1,900,000
Regional Transmission Organizations
Reduction to sales and purchased power expense from reporting RTO transactions from net basis reporting	61,800,000	75,600,000		$ 90,300,000
Allowance for Funds Used During Construction
AFUDC - equity funds	5,900,000	2,300,000		3,300,000
AFUDC - borrowed funds	2,100,000	800,000		1,100,000
Capitalized Software Costs
Capitalized software	20,400,000	24,600,000
Capitalized software - accumulated amortization	36,900,000	31,800,000
Capitalized software amortization	5,100,000	5,100,000		4,700,000
Capitalized Software Hosting Agreement Costs
Capitalized Computer Software Hosting Agreement Net	14,800,000	13,600,000
Capitalized Computer Software Hosting Agreement Amortization	1,800,000	1,400,000		100,000
Capitalized Computer Software Hosting Agreement Accumulated Amortization	3,200,000	1,400,000
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	$ 14,100,000	$ 13,900,000		$ 14,400,000
Deferred COVID Allowance For Credit Loss [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	3,800,000
Chattel Paper Agreements [Member]
Transfers and Servicing
Repurchase agreement, maximum exposure	1,500,000
Repurchase-to-Maturity Transactions, loans due	$ 700,000
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%
Authorized AFUDC rate - Signficiant projects (100%)	100.00%	100.00%		100.00%
Rate at which AFUDC was capitalized	7.03%	7.00%		7.87%
Electric [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	3.50%	3.60%	[1]	2.90%
Gas [Member]
Property, Plant, and Equiptment
Composite straight-line depreciation rates	2.20%	2.10%		2.10%
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 the December 2018 rate settlement, the PSCW approved new depreciation rates for Columbia effective January 1, 2019.

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details-2) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 44,738,000	$ 23,481,000
Restricted cash	644,000	619,000
Receivable - margin account	1,657,000	1,714,000
Cash, cash equivalents, and restricted cash	47,039,000	25,814,000	$ 84,929,000	$ 112,094,000
MGE [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	4,103,000	3,196,000
Restricted cash	644,000	619,000
Receivable - margin account	1,657,000	1,714,000
Cash, cash equivalents, and restricted cash	$ 6,404,000	$ 5,529,000	$ 6,670,000	$ 10,093,000

Variable Interest Entities (Det

Variable Interest Entities (Details)		Dec. 31, 2020USD ($)MW	Dec. 31, 2019USD ($)MW
Variable Interest Entity [Line Items]
Property, plant, and equipment, net		$ 1,630,286,000	$ 1,530,199,000
Construction work in progress		139,099,000	112,484,000
Accrued interest and accrued (prepaid) taxes		8,539,000	7,244,000
Deferred income taxes		231,471,000	243,302,000
Unamortized discount and debt issuance costs, net		$ 4,146,000	$ 4,479,000
Other Variable Interest Entities
Other variable interest entities, purchase power agreement, plant capacity (in MW) | MW		13	13
MGE Power Elm Road [Member]
Variable Interest Entity [Line Items]
Property, plant, and equipment, net		$ 166,883,000	$ 170,763,000
Construction work in progress		697,000	468,000
Affiliate receivables, current and noncurrent		0	0
Accrued interest and accrued (prepaid) taxes		2,701,000	1,364,000
Deferred income taxes		30,646,000	30,621,000
Long-term debt	[1]	51,590,000	54,207,000
Noncontrolling interest	[2]	96,856,000	97,172,000
Unamortized discount and debt issuance costs, net		400,000	400,000
MGE Power West Campus [Member]
Variable Interest Entity [Line Items]
Property, plant, and equipment, net		79,077,000	79,473,000
Construction work in progress		677,000	309,000
Affiliate receivables, current and noncurrent		2,803,000	3,600,000
Accrued interest and accrued (prepaid) taxes		671,000	(160,000)
Deferred income taxes		14,521,000	14,363,000
Long-term debt	[1]	37,652,000	39,627,000
Noncontrolling interest	[2]	44,340,000	43,131,000
Unamortized discount and debt issuance costs, net		$ 100,000	$ 100,000
[1]	MGE Power Elm Road's long-term debt includes debt issuance costs of $ 0.4 million as of December 31, 2020 and 2019. 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 costs of $ 0.1 million as of December 31, 2020 and 2019. 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 14 for further information on the long-term debt securities.
[2]	MGE Power Elm Road and MGE Power West Campus are not subsidiaries of MGE; however, they have been consolidated in the consolidated financial statements 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% owned 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.

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
In-service utility plant, net		$ 1,630,286	$ 1,530,199
Construction work in progress		139,099	112,484
Total property, plant, and equipment		1,769,385	1,642,683
Allowance for Funds Used During Construction
AFUDC equity recognized		5,900	2,300	$ 3,300
Two Creeks Units [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross (excluding AFUDC)		62,900
Allowance for Funds Used During Construction
AFUDC equity recognized		2,400	1,000
Badger Hollow I Units [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		54,700	18,700
Allowance for Funds Used During Construction
AFUDC equity recognized		2,000	$ 200
Badger Hollow II Units [Member]
Property, Plant and Equipment [Line Items]
Construction work in progress		5,200
Allowance for Funds Used During Construction
AFUDC equity recognized		$ 200
PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate		50.00%	50.00%	50.00%
Authorized AFUDC rate - Signficiant projects (100%)		100.00%	100.00%	100.00%
PSCW [Member] | Two Creeks Units [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)		100.00%
PSCW [Member] | Badger Hollow I Units [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)		100.00%
PSCW [Member] | Badger Hollow II Units [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)		100.00%
First Mortgage Bonds [Member] | 7.70%, 2028 Series [Member]
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		2,105,108	1,952,807
Less: Accumulated depreciation and amortization		721,382	674,251
In-service utility plant, net		1,383,726	1,278,556
Construction work in progress	[2]	137,725	111,707
Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,608,658	1,480,684
Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		496,450	472,123
Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		320,691	323,266
Less: Accumulated depreciation and amortization		74,131	71,623
In-service utility plant, net		246,560	251,643
Construction work in progress		1,374	777
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, net		1,630,314	1,530,227
Construction work in progress		139,099	112,484
Total property, plant, and equipment		1,769,413	1,642,711
MGE [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		2,105,136	1,952,835
Less: Accumulated depreciation and amortization		721,382	674,251
In-service utility plant, net		1,383,754	1,278,584
Construction work in progress	[2]	137,725	111,707
MGE [Member] | Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,608,675	1,480,701
MGE [Member] | Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		496,461	472,134
MGE [Member] | Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		320,691	323,266
Less: Accumulated depreciation and amortization		74,131	71,623
In-service utility plant, net		246,560	251,643
Construction work in progress		$ 1,374	$ 777
[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 MGE 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, 2020, approximately $ 529.9
[2]	In 2019, the PSCW authorized construction of Badger Hollow I. Construction of the project is expected to be completed in April 2021. As of December 31, 2020, and 2019, MGE had $ 54.7 million and $ 18.7 million (excluding AFUDC), respectively, in construction work in progress. After tax, MGE recognized $ 2.0 million and $ 0.2 million, respectively, of AFUDC equity related to Badger Hollow I for the years ended December 31, 2020 and 2019. Phase II of the project was authorized by the PSCW in 2020. Construction of Badger Hollow II is expected to be completed in December 2022. As of December 31, 2020, MGE had $ 5.2 million (excluding AFUDC) in construction work in progress. After tax, MGE recognized $ 0.2 million of AFUDC equity related to Badger Hollow II for the year ended December 31, 2020. MGE received specific approval to recover % AFUDC on these projects .

Leases (Details-1)

Leases (Details-1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease Cost [Abstract]
Amortization of leased assets, Depreciation and amortization	$ 1,694	$ 1,524
Interest on lease liabilities, Interest expense, net	784	792
Operating lease expense, Other operations and maintenance	319	144
Total lease expense	$ 2,797	$ 2,460

Leases (Details-2)

Leases (Details-2) - USD ($)	Dec. 31, 2020		Dec. 31, 2019
Lessee Disclosure [Line Items]
Total lease assets	$ 21,670,000		$ 16,566,000
Finance lease liabilities - long term	17,532,000		17,379,000
Property, plant, and equipment, net [Member]
Lessee Disclosure [Line Items]
Finance lease assets, net	15,682,000		15,895,000
Other deferred assets and other [Member]
Lessee Disclosure [Line Items]
Operating lease assets	5,988,000		671,000
Other Current Liabilities [Member]
Lessee Disclosure [Line Items]
Finance lease liabilities - current	1,066,000		888,000
Operating lease liabilities - current	171,000		203,000
Other deferred liabilities and other [Member]
Lessee Disclosure [Line Items]
Operating lease liabilities - long term	5,840,000	[1]	496,000
Other Liabilities [Member]
Lessee Disclosure [Line Items]
Total lease liabilities	$ 24,609,000		$ 18,966,000
[1]	Increase in operating lease assets and long-term operating lease liabilities related to land leases for new solar farms in 2020.

Leases (Details-3)

Leases (Details-3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee Disclosure [Abstract]
Finance leases - Financing cash flows	$ 1,149	$ 945
Finance leases - Operating cash flows	784	792
Operating leases - operating cash flows	319	134
Lease assets obtained in exchange for lease liabilities - finance leases	1,480	12,101
Lease assets obtained in exchange for lease liabilities - operating leases	$ 5,791	$ 657

Leases (Details-4)

Leases (Details-4)	Dec. 31, 2020	Dec. 31, 2019
Lessee Disclosure [Abstract]
Weighted average remaining lease term (years) finance leases	37 years	39 years
Weighted average remaining lease term (years) operating leases	34 years	15 years
Weighted average disocunt rate finance leases	4.32%	4.37%
Weighted average disocunt rate operating leases	2.84%	3.32%

Leases (Details-5)

Leases (Details-5) $ in Thousands	Dec. 31, 2020USD ($)
Finance Lease Liabilities Payments Due [Abstract]
2021	$ 1,820
2022	1,700
2023	1,520
2024	959
2025	774
Thereafter	39,787
Undiscounted finance lease liability	46,560
Less: Present value discount	(27,962)
Finance lease liability	18,598
Operating Lease Liabilities Payments Due [Abstract]
2021	338
2022	274
2023	203
2024	207
2025	211
Thereafter	8,636
Undiscounted operating lease liability	9,869
Less: Present value discount	(3,858)
Operating Lease Liability	$ 6,011

Joint Plant Ownership (Details)

Joint Plant Ownership (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2020USD ($)MW	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets		$ 157,252	$ 145,746
Other Regulatory Asset [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets		235	340
Columbia Units [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	[1]	289,597	291,997
Accumulated depreciation	[1]	(118,742)	(105,778)
Construction work in progress	[1]	$ 997	1,777
Columbia Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[1]	211
Jointly owned utility plant, ownership interest	[1]	19.00%
Jointly owned utility plant, fuel, operating, and maintenance expense	[1]	$ 27,127	32,604	$ 36,517
Elm Road Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, fuel, operating, and maintenance expense	[2]	$ 17,259	19,661	17,555
Elm Road Units [Member] | MGE Power Elm Road [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[2]	106
Jointly owned utility plant, ownership interest	[2]	8.33%
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	[2]	$ 203,847	207,834
Accumulated depreciation	[2]	(36,964)	(37,071)
Construction work in progress	[2]	697	468
Forward Wind [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	[3]	34,028	34,054
Accumulated depreciation	[3]	(14,092)	(13,413)
Construction work in progress	[3]	$ 0	45
Forward Wind [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[3]	18
Jointly owned utility plant, ownership interest	[3]	12.80%
Jointly owned utility plant, fuel, operating, and maintenance expense	[3]	$ 664	642
Forward Wind [Member] | MGE [Member] | Other Regulatory Asset [Member]
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	[3],[4]			600
West Campus [Member] | UW [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, fuel, operating, and maintenance expense	[5]	$ 5,200	6,600	6,300
West Campus [Member] | MGE Power West Campus [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[6]	157
Jointly owned utility plant, ownership interest	[6]	55.00%
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	[6]	$ 115,657	113,259
Accumulated depreciation	[6]	(36,580)	(33,786)
Construction work in progress	[6]	677	309
Two Creeks [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	[7]	67,577	0
Accumulated depreciation	[7]	(225)	0
Construction work in progress	[7]	$ 0	45,286
Two Creeks [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[7]	50
Jointly owned utility plant, ownership interest	[7]	33.00%
Jointly owned utility plant, fuel, operating, and maintenance expense	[7]	$ 118	0	0
Badger Hollow I and II [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	[8]	0	0
Accumulated depreciation	[8]	0	0
Construction work in progress	[8]	$ 63,140	18,953
Badger Hollow I and II [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW) | MW	[8]	100
Jointly owned utility plant, ownership interest	[8]	33.00%
Jointly owned utility plant, fuel, operating, and maintenance expense	[8]	$ 0	$ 0	$ 0
[1]	In February 2021, MGE and the other co-owners announced plans to retire Columbia, a two unit coal-fired generation facility located in Portage, Wisconsin. The co-owners intend to retire Unit 1 by the end of 2023 and Unit 2 by the end of 2024. Final timing and retirement dates for Units 1 and 2 are subject to PSCW and regional regulatory reviews, including identification and approval of energy and capacity resources to replace Columbia.
[2]	Two coal-fired generating units in Oak Creek, Wisconsin.
[3]	The Forward Wind Energy Center (Forward Wind) consists of 86 wind turbines located near Brownsville, Wisconsin.
[4]	Amount was deferred as a regulatory asset in 2018. This amount was recovered in rates and recognized as operating and maintenance expense in 2019.
[5]	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, 2020, 2019, and 2018, the UW's allocated share of fuel and operating costs was $ 5.2 million, $ 6.6 million, and $ 6.3 million, respectively.
[6]	MGE Power West Campus and the UW jointly own the West Campus Cogeneration Facility (WCCF) located on the UW campus in Madison, Wisconsin. The UW owns a controlling interest in the chilled-water and steam plants, which are used to meet the needs for air-conditioning and steam-heat capacity for the UW campus. MGE Power West Campus owns a controlling interest in the electric generation plant, which is leased and operated by MGE.
[7]	The Two Creeks solar generation array is located in the Town of Two Creeks and the City of Two Rivers in Manitowoc and Kewaunee Counties, Wisconsin. Date of commercial operation of the solar array was November 2020.
[8]	The Badger Hollow I and II solar farm is located in southwestern Wisconsin in Iowa County, near the villages of Montfort and Cobb. Badger Hollow I and II estimated commercial operation dates are April 2021 and December 2022, respectively.

Investments (Details-1)

Investments (Details-1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Securities [Abstract]
Equity Securities	$ 17,906	$ 14,546
Equity method investments: [Abstract]
Equity method investments	74,462	71,648
Other Investments	2,308	2,298
Total investments	94,676	88,492
Results of Investment Liquidation [Abstract]
Proceeds from sale of investments	622	216	$ 960
Gain (loss) on sale of investments	379	580	476
ATC and ATC Holdco [Member]
Equity method investments: [Abstract]
Equity method investments	74,423	71,609
Other Equity Method Investments [Member]
Equity method investments: [Abstract]
Equity method investments	39	39
MGE [Member]
Equity Securities [Abstract]
Equity Securities	603	209
Equity method investments: [Abstract]
Equity method investments	0	0
Other Investments	0	0
Total investments	603	209
Results of Investment Liquidation [Abstract]
Proceeds from sale of investments	0	2	3
Gain (loss) on sale of investments	0	(343)	$ 3
MGE [Member] | ATC and ATC Holdco [Member]
Equity method investments: [Abstract]
Equity method investments	0	0
MGE [Member] | Other Equity Method Investments [Member]
Equity method investments: [Abstract]
Equity method investments	$ 0	$ 0

Investments (Details-2)

Investments (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	$ 10,221	$ 9,889	$ 8,821
Dividends from investment	8,998	7,347	6,958
Capital contributions to investments	5,601	7,813	5,926
MGE Energy [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	92,922	87,728	85,220
MGE Transco [Member] | ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	10,167	9,889	8,821
Dividends from investment	8,633	7,347	4,611	[1]
Capital contributions to investments	$ 1,249	$ 3,018	2,841
Ownership interest in equity-method investee	3.60%	3.60%
Dividend receivable from ATC					$ 2,300
MGEE Transco [Member] | ATC Holdco [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments	$ 300	$ 100	$ 300
Ownership interest in equity-method investee	4.40%	4.40%
[1]	MGE Transco recorded a $ 2.3 million dividend receivable from ATC as of December 31, 2017. A cash dividend was received in January of 2018.

Investments (Details-3)

Investments (Details-3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity method investment summarized assets [Abstract]
Total Current Assets	$ 209,519	$ 181,641
Total Assets	2,253,651	2,081,664	$ 1,988,618
Equity method investment summarized liabilities and equity [Abstract]
Total Current Liabilities	190,926	128,820
Total Other Credits	567,422	573,427
Total Liabilities and Capitalization	2,253,651	2,081,664
ATC [Member]
Equity method investment summarized income statement [Abstract]
Operating revenues	758,117	744,371	690,510
Operating expenses	(372,463)	(373,527)	(358,703)
Other income, net	1,922	48	2,405
Interest expense, net	(112,818)	(110,490)	(110,725)
Earnings before members' income taxes	274,758	260,402	$ 223,487
Equity method investment summarized assets [Abstract]
Total Current Assets	92,735	84,635
Total Noncurrent Assets	5,400,538	5,244,220
Total Assets	5,493,273	5,328,855
Equity method investment summarized liabilities and equity [Abstract]
Total Current Liabilities	310,749	502,601
Long-term debt	2,512,246	2,312,799
Total Other Credits	378,205	298,828
Total Equity	2,292,073	2,214,627
Total Liabilities and Capitalization	$ 5,493,273	$ 5,328,855

Investments (Details-4)

Investments (Details-4) - ATC [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related party transaction [Line Items]
Related party expenses	$ 30.7	$ 30.4	$ 29
Due from Related Parties	$ 2.6	$ 1.6

Regulatory Assets and Liabili_3

Regulatory Assets and Liabilities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory Assets		$ 157,252,000	$ 145,746,000
Regulatory Liabilities [Line Items]
Regulatory Liabilities		183,903,000	174,193,000
MGE [Member] | PSCW [Member] | Electric Rate Proceeding [Member] | Scenario, Forecast [Member]
Regulatory Liabilities [Line Items]
Return of unprotected excess deferred taxes	$ 18,200,000
Deferred Fuel Savings [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		5,047,000	1,794,000
Elm Road Regulatory Liability [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,957,000	2,322,000
Income Taxes [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		129,856,000	129,528,000
Non-ARO Removal Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		28,197,000	26,543,000
Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		7,524,000	4,499,000
Purchased Gas Adjustment [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,832,000	1,864,000
Renewable Energy Credits [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		802,000	558,000
Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		7,669,000	6,019,000
Other Regulatory Liability [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,019,000	1,066,000
Asset Retirement Obligation [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11,935,000	10,756,000
COVID-19 Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3,933,000	0
Debt Related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		8,586,000	8,885,000
Deferred Pension And Other Postretirement Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5,280,000	6,216,000
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory Assets		13,989,000	26,875,000
Leases [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2,748,000	2,400,000
Tax Recovery AFUDC Equity [Member]
Regulatory Assets [Line Items]
Regulatory Assets		8,952,000	7,060,000
Unfunded Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		101,594,000	83,214,000
Other Regulatory Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 235,000	$ 340,000

Rate Matters (Details)

Rate Matters (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fuel Rules [Abstract]
Deferred fuel rules monitored costs				$ 3.2	$ 1.5
Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Return of tax credit					$ 3.2	$ 8.2
PSCW [Member] | MGE [Member]
Rate Proceedings [Abstract]
Approved equity capital structure, percentage				56.10%	56.60%
Authorized return on equity, percentage				9.80%	9.80%
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%
PSCW [Member] | Fuel Rules Refund, 2017 [Member] | MGE [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total		$ 4.2
PSCW [Member] | Fuel Rules Refund, 2018 [Member] | MGE [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total	$ 9.5
PSCW [Member] | Approved Future Rate Matters [Member] | MGE [Member]
Rate Proceedings [Abstract]
Approved equity capital structure, percentage			55.80%
Authorized return on equity, percentage			9.80%
Fuel Rules [Abstract]
Fuel rules, bandwidth			1.00%
Electric Rate Proceeding [Member] | PSCW [Member] | MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage				(0.84%)	(2.24%)
Authorized rate increase (decrease), amount				$ (3.4)	$ (9.2)
Electric Rate Proceeding [Member] | PSCW [Member] | Approved Future Rate Matters [Member] | MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage			0.00%
Effects Of The Tax Cuts And Jobs Act [Abstract]
Return of unprotected excess deferred taxes			$ 18.2
Gas Rate Proceeding [Member] | PSCW [Member] | MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage				1.46%	1.06%
Authorized rate increase (decrease), amount				$ 2.4	$ 1.7
Gas Rate Proceeding [Member] | PSCW [Member] | Approved Future Rate Matters [Member] | MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage			4.00%

Income Taxes (Details)

Income Taxes (Details) - USD ($)		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Income tax provision components [Abstract]
Current payable: Federal										$ 4,179,000		$ 8,017,000		$ 18,622,000
Current payable: State										5,095,000		4,647,000		5,163,000
Net-deferred: Federal										6,181,000		3,510,000		120,000
Net-deferred: State										4,182,000		3,702,000		3,629,000
Amortized investment tax credits										(214,000)		(92,000)		(100,000)
Total income tax provision		$ 3,370,000	$ 7,300,000	$ 3,740,000	$ 5,013,000	$ 3,116,000	$ 7,454,000	$ 3,505,000	$ 5,709,000	$ 19,423,000		$ 19,784,000		$ 27,434,000
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate										21.00%		21.00%		21.00%
State income taxes, net of federal benefit										6.30%		6.20%		6.30%
Amortized investment tax credits										(0.20%)		(0.10%)		(0.10%)
Credit for electricity from wind energy										(6.20%)	[1]	(5.70%)	[1]	(0.30%)
AFUDC equity, net										(1.20%)		(0.30%)		(0.60%)
Amortization of utility excess deferred tax	[2]									(2.00%)		(2.40%)		(1.80%)
Other, net, individually significant										(0.30%)		(0.10%)		0.10%
Effective income tax rate										17.40%		18.60%		24.60%
Components Of Deferred Tax Assets [Abstract]
Investment in ATC		21,688,000				22,576,000				$ 21,688,000		$ 22,576,000
Federal tax credits		19,199,000				0				19,199,000		0
Accrued expenses		11,115,000				15,901,000				11,115,000		15,901,000
Pension and other postretirement benefits		35,446,000				30,968,000				35,446,000		30,968,000
Deferred tax regulatory account		41,318,000				35,493,000				41,318,000		35,493,000
Derivatives		3,852,000				7,351,000				3,852,000		7,351,000
Leases		6,704,000				5,167,000				6,704,000		5,167,000
Other deferred tax assets		14,073,000				12,540,000				14,073,000		12,540,000
Gross deferred income tax assets		153,395,000				129,996,000				153,395,000		129,996,000
Less valuation allowance		(38,000)				(86,000)				(38,000)		(86,000)
Net deferred income tax assets		153,357,000				129,910,000				153,357,000		129,910,000
Components Of Deferred Tax Liabilities [Abstract]
Property-related		257,397,000				245,083,000				257,397,000		245,083,000
Investment in ATC		51,518,000				51,569,000				51,518,000		51,569,000
Bond transactions		595,000				657,000				595,000		657,000
Pension and other postretirement benefits		45,658,000				45,683,000				45,658,000		45,683,000
Derivatives		3,852,000				7,351,000				3,852,000		7,351,000
Tax deductible prepayments		9,059,000				9,078,000				9,059,000		9,078,000
Leases		6,704,000				5,167,000				6,704,000		5,167,000
Other deferred tax liabilities		10,045,000				8,624,000				10,045,000		8,624,000
Gross deferred income tax liabilities		384,828,000				373,212,000				384,828,000		373,212,000
Deferred income taxes		231,471,000				243,302,000				231,471,000		243,302,000
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		19,199,000				0				19,199,000		0
Unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits, beginning balance					2,093,000				1,949,000	2,093,000		1,949,000		$ 1,924,000
Additions based on tax positions related to current year										796,000		741,000		425,000
Additions based on tax positions related to prior year										0		84,000		272,000
Reductions based on tax positions related to prior years										(608,000)		(681,000)		(672,000)
Unrecognized tax benefits, ending balance		2,281,000				2,093,000				2,281,000		2,093,000		1,949,000
Interest on unrecognized tax benefits [Roll Forward]
Accrued interest on unrecognized tax benefits, beginning balance					$ 176,000				$ 191,000	176,000		191,000		165,000
Reduction in interest expense on uncertain tax positions										(124,000)		(137,000)		(136,000)
Interest expense on uncertain tax positions										102,000		122,000		162,000
Accrued interest on unrecognized tax benefits, ending balance		154,000				176,000				154,000		176,000		191,000
Unrecognized Tax Benefits
Unrecognized tax benefits permanent differences		0				100,000				0		100,000		300,000
State [Member]
Operating loss deductions and tax credit carryforwards [Abstract]
State net operating losses		621,000				1,406,000				621,000		1,406,000
Valuation allowances for state net operating losses		(621,000)				(1,406,000)				(621,000)		(1,406,000)
Federal [Member]
Components Of Deferred Tax Assets [Abstract]
Federal tax credits		19,199,000				0				19,199,000		0
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		19,199,000				0				19,199,000		0
Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Excess Deferred Tax Income Statement Effect										2,200,000		2,600,000		2,100,000
MGE [Member]
Income tax provision components [Abstract]
Current payable: Federal										3,716,000		7,616,000		19,926,000
Current payable: State										4,790,000		4,608,000		5,704,000
Net-deferred: Federal										4,756,000		2,242,000		(2,563,000)
Net-deferred: State										3,787,000		3,044,000		2,494,000
Amortized investment tax credits										(214,000)		(92,000)		(100,000)
Total income tax provision										$ 16,835,000		$ 17,418,000		$ 25,461,000
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate										21.00%		21.00%		21.00%
State income taxes, net of federal benefit										6.30%		6.10%		6.20%
Amortized investment tax credits										(0.20%)		(0.10%)		(0.10%)
Credit for electricity from wind energy										(6.80%)	[1]	(6.20%)	[1]	(0.40%)
AFUDC equity, net										(1.40%)		(0.30%)		(0.50%)
Amortization of utility excess deferred tax	[2]									(2.20%)		(2.70%)		(2.00%)
Other, net, individually significant										(0.30%)		(0.10%)		0.20%
Effective income tax rate										16.40%		17.70%		24.40%
Components Of Deferred Tax Assets [Abstract]
Investment in ATC		0				0				$ 0		$ 0
Federal tax credits		20,080,000				0				20,080,000		0
Accrued expenses		11,105,000				15,890,000				11,105,000		15,890,000
Pension and other postretirement benefits		35,446,000				30,968,000				35,446,000		30,968,000
Deferred tax regulatory account		41,318,000				35,493,000				41,318,000		35,493,000
Derivatives		3,852,000				7,351,000				3,852,000		7,351,000
Leases		6,704,000				5,167,000				6,704,000		5,167,000
Other deferred tax assets		14,125,000				12,593,000				14,125,000		12,593,000
Gross deferred income tax assets		132,630,000				107,462,000				132,630,000		107,462,000
Less valuation allowance		(38,000)				(86,000)				(38,000)		(86,000)
Net deferred income tax assets		132,592,000				107,376,000				132,592,000		107,376,000
Components Of Deferred Tax Liabilities [Abstract]
Property-related		257,397,000				245,083,000				257,397,000		245,083,000
Investment in ATC		0				0				0		0
Bond transactions		595,000				657,000				595,000		657,000
Pension and other postretirement benefits		45,658,000				45,683,000				45,658,000		45,683,000
Derivatives		3,852,000				7,351,000				3,852,000		7,351,000
Tax deductible prepayments		9,059,000				9,051,000				9,059,000		9,051,000
Leases		6,704,000				5,167,000				6,704,000		5,167,000
Other deferred tax liabilities		9,717,000				8,425,000				9,717,000		8,425,000
Gross deferred income tax liabilities		332,982,000				321,417,000				332,982,000		321,417,000
Deferred income taxes		200,390,000				214,041,000				200,390,000		214,041,000
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		20,080,000				0				20,080,000		0
State net tax operating loss deductions		600,000								600,000
MGE [Member] | State [Member]
Operating loss deductions and tax credit carryforwards [Abstract]
State net operating losses		621,000				1,406,000				621,000		1,406,000
Valuation allowances for state net operating losses		(621,000)				(1,406,000)				(621,000)		(1,406,000)
MGE [Member] | Federal [Member]
Components Of Deferred Tax Assets [Abstract]
Federal tax credits		20,080,000				0				20,080,000		0
Operating loss deductions and tax credit carryforwards [Abstract]
Federal tax credits		$ 20,080,000				$ 0				20,080,000		0
MGE [Member] | Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Excess Deferred Tax Income Statement Effect										$ 2,200,000		$ 2,600,000
[1]	Saratoga became operational in February 2019.
[2]	Included are impacts of the Tax Cuts and Jobs Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting. For the years ended December 31, 2020, 2019, and 2018, MGE recognized $ 2.2 million, $ 2.6 million, and $ 2.1 million, respectively. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, as determined by the PSCW.

Pension Plans and Other Postr_3

Pension Plans and Other Postretirement Benefits (Details-1) - USD ($)		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan, Deferred Pension and Other Postretirement Benefit Plan Costs Recovered [Abstract]
Defined contribution costs		$ 4,700,000		$ 4,400,000		$ 3,900,000
Change in plan assets [Roll Forward]
Fair value of plan assets as of January 1		434,922,000
Fair value of plan assets as of December 31		481,273,000		434,922,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset		13,873,000		13,630,000
Long-term liability		(78,168,000)		(68,665,000)
Pension Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation as of January 1		410,651,000		360,288,000
Service cost		5,296,000	[1]	4,692,000	[1]	5,723,000
Interest cost		12,210,000	[1]	14,302,000	[1]	12,859,000
Plan participants' contributions		0		0
Actuarial loss	[2]	50,325,000		47,671,000
Gross benefits paid		(17,267,000)		(16,302,000)
Less: federal subsidy on benefits paid	[3]	0		0
Benefit obligation as of December 31		461,215,000		410,651,000		360,288,000
Change in plan assets [Roll Forward]
Fair value of plan assets as of January 1		386,033,000		323,780,000
Actual return on plan assets		58,935,000		76,766,000
Employer contributions		1,837,000		1,789,000
Plan participants' contributions		0		0
Gross benefits paid		(17,267,000)		(16,302,000)
Fair value of plan assets as of December 31		429,538,000		386,033,000		323,780,000
Funded Status as of December 31		(31,677,000)		(24,618,000)
Accumulated benefit obligation		430,300,000		383,000,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset		13,873,000		13,630,000
Current liability		(2,139,000)		(1,688,000)
Long-term liability		(43,411,000)		(36,560,000)
Net liability		(31,677,000)		(24,618,000)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		92,553,000		79,290,000
Prior service (credit) cost		(144,000)		(268,000)
Transition obligation		0		0
Total		92,409,000		79,022,000
Projected benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation with projected benefit obligation in excess of plan assets, end of year		45,550,000		38,247,000
Fair value of plan assets with projected benefit obligation in excess of plan assets, end of year		0		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		43,384,000		35,798,000
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 as of January 1		80,901,000		75,161,000
Service cost		1,264,000	[1]	1,110,000	[1]	1,283,000
Interest cost		2,278,000	[1]	2,893,000	[1]	2,612,000
Plan participants' contributions		1,009,000		969,000
Actuarial loss	[2]	5,907,000		5,045,000
Gross benefits paid		(5,245,000)		(4,497,000)
Less: federal subsidy on benefits paid	[3]	246,000		220,000
Benefit obligation as of December 31		86,360,000		80,901,000		75,161,000
Change in plan assets [Roll Forward]
Fair value of plan assets as of January 1		48,889,000		42,521,000
Actual return on plan assets		6,514,000		9,277,000
Employer contributions		568,000		619,000
Plan participants' contributions		1,009,000		969,000
Gross benefits paid		(5,245,000)		(4,497,000)
Fair value of plan assets as of December 31		51,735,000		48,889,000		$ 42,521,000
Funded Status as of December 31		(34,625,000)		(32,012,000)
Medicare subsidy due to MGE		200,000		200,000
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		(34,625,000)		(32,012,000)
Net liability		(34,625,000)		(32,012,000)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		10,986,000		8,659,000
Prior service (credit) cost		(1,816,000)		(4,484,000)
Transition obligation		15,000		17,000
Total		9,185,000		4,192,000
Accumulated benefit obligation in excess of plan assets [Abstract]
Accumulated benefit obligation with accumulated benefit obligation in excess of plan assets, end of year		86,360,000		80,901,000
Fair value of plan assets with accumulated benefit obligation in excess of plan assets, end of year		$ 51,735,000		$ 48,889,000
[1]	During 2019, MGE deferred approximately $ 6.2 million of pension and other postretirement costs. During 2020, MGE collected approximately $ 0.9 million of pension and other postretirement costs, which reduced the amount deferred in 2019. The impact of the deferral has not been reflected in the table above. See Footnote 8 for further information.
[2]	In 2020 and 2019, lower discount rates were the primary driver of the actuarial loss.
[3]	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, 2020 and 2019, 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, 2020		Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan, Deferred Pension and Other Postretirement Benefit Plan Costs Recovered [Abstract]
Deferred (recognized) pension and OPEB costs	$ (900)		$ 6,200
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	5,296	[1]	4,692	[1]	$ 5,723
Interest cost	12,210	[1]	14,302	[1]	12,859
Expected return on assets	(27,229)	[1]	(22,786)	[1]	(26,241)
Amortization of:
Transition obligation	0	[1]	0	[1]	0
Prior service (credit) cost	(114)	[1]	(117)	[1]	(44)
Actuarial loss	5,357	[1]	7,379	[1]	5,278
Net periodic benefit cost (credit)	(4,480)	[1]	3,470	[1]	(2,425)
Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	1,264	[1]	1,110	[1]	1,283
Interest cost	2,278	[1]	2,893	[1]	2,612
Expected return on assets	(3,154)	[1]	(2,723)	[1]	(3,232)
Amortization of:
Transition obligation	3	[1]	3	[1]	3
Prior service (credit) cost	(2,669)	[1]	(2,669)	[1]	(2,669)
Actuarial loss	217	[1]	401	[1]	488
Net periodic benefit cost (credit)	$ (2,061)	[1]	$ (985)	[1]	$ (1,515)
[1]	During 2019, MGE deferred approximately $ 6.2 million of pension and other postretirement costs. During 2020, MGE collected approximately $ 0.9 million of pension and other postretirement costs, which reduced the amount deferred in 2019. The impact of the deferral has not been reflected in the table above. See Footnote 8 for further information.

Pension Plans and Other Postr_5

Pension Plans and Other Postretirement Benefits (Details-3)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	2.70%	3.42%
Rate of compensation increase	3.22%	3.21%
Weighted-average assumptions used to determine net periodic cost:
Discount rate	3.42%	4.32%	3.73%
Long-term rate of return	7.20%	7.20%	7.40%
Rate of compensation increase	3.26%	3.25%	3.72%
Postretirement Benefits [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	2.52%	3.30%
Assumed health care cost trend rates:
Health care cost trend rate assumed for next year	5.75%	6.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.75%	5.00%
Year that the rate reaches the ultimate trend rate	2027	2024
Weighted-average assumptions used to determine net periodic cost:
Discount rate	3.30%	4.24%	3.60%
Long-term rate of return	6.75%	6.72%	6.94%

Pension Plans and Other Postr_6

Pension Plans and Other Postretirement Benefits (Details-4) $ in Thousands		12 Months Ended
		Dec. 31, 2020USD ($)concentration	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Other postretirement benefits [Abstract]
Fair value of plan assets		$ 481,273	$ 434,922
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		$ 429,538	$ 386,033	$ 323,780
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		69.00%	64.00%
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		25.00%	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		6.00%	7.00%
Postretirement Benefits [Member]
Other postretirement benefits [Abstract]
Fair value of plan assets		$ 51,735	$ 48,889	$ 42,521
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		$ 45,600	$ 42,800
[1]	Target allocations for equity securities are broken out as follows: 45.5% United States equity and 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, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 481,273	$ 434,922
Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,180	964
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	151,218	134,458
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	37,389	31,288
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	50,456	36,495
Equity Securities [Member] | International Blend [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	87,461	76,293
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	4,215	7,449
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	22,683	21,276
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	92,657	92,642
Real Estate [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30,005	29,671
Insurance Continuance Fund [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,506	1,530
Fixed Rate Fund [Member] | Fair Value Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,503	$ 2,856

Pension Plans and Other Postr_8

Pension Plans and Other Postretirement Benefits (Details-6) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Expected Cash Flows
Expected employer contributions, 2021	$ 0
Cash contributions to pension and other postretirement plans	6,296,000	$ 5,714,000	$ 5,584,000
Pension Benefits [Member]
Benefit Payments, Gross
Defined benefit plan expected future benefit payments, 2021	18,493,000
Defined benefit plan expected future benefit payments, 2022	19,508,000
Defined benefit plan expected future benefit payments, 2023	20,353,000
Defined benefit plan expected future benefit payments, 2024	21,007,000
Defined benefit plan expected future benefit payments, 2025	21,678,000
Defined benefit plan expected future benefit payments, 2026-2030	114,762,000
Postretirement Benefits [Member]
Benefit Payments, Gross
Defined benefit plan expected future benefit payments, 2021	4,696,000
Defined benefit plan expected future benefit payments, 2022	4,859,000
Defined benefit plan expected future benefit payments, 2023	5,145,000
Defined benefit plan expected future benefit payments, 2024	5,443,000
Defined benefit plan expected future benefit payments, 2025	5,529,000
Defined benefit plan expected future benefit payments, 2026-2030	27,163,000
Medicare Part D Subsidies
Expected Medicare Part D Subsidies, 2021	(250,000)
Expected Medicare Part D Subsidies, 2022	(277,000)
Expected Medicare Part D Subsidies, 2023	(302,000)
Expected Medicare Part D Subsidies, 2024	(327,000)
Expected Medicare Part D Subsidies, 2025	(354,000)
Expected Medicare Part D Subsidies, 2026-2030	(2,148,000)
Benefit Payments, Net
Defined benefit plan expected net future benefit payments, 2021	4,446,000
Defined benefit plan expected net future benefit payments, 2022	4,582,000
Defined benefit plan expected net future benefit payments, 2023	4,843,000
Defined benefit plan expected net future benefit payments, 2024	5,116,000
Defined benefit plan expected net future benefit payments, 2025	5,175,000
Defined benefit plan expected net future benefit payments, 2026-2030	$ 25,015,000

Share-Based Compensation (Detai

Share-Based Compensation (Details) - USD ($)	Feb. 19, 2021	Jan. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense			$ 1,300,000	$ 3,000,000	$ 1,100,000
2006 Performance Unit Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock to be issued with plan			0
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Nonvested awards January 1,		26,468	26,468
Awards granted (in units)			0
Vested			(9,048)
Nonvested awards December 31,			17,420	26,468
2006 Performance Unit Plan [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			5 years
2013 Director Incentive Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock to be issued with plan			0
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Nonvested awards January 1,		4,611	4,611
Awards granted (in units)			5,048
Vested			(5,373)
Nonvested awards December 31,			4,286	4,611
2013 Director Incentive Agreement [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
2006 Performance Unit Plan and 2013 Director Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash payments distributed related to awards previously granted and now payable		$ 2,000,000
2020 Performance Unit Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock to be issued with plan			0
2020 Performance Unit Plan [Member] | Performance Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Estimated payout % based on performance criteria			100.00%
Fair Value of each nonvested award			$ 89.13
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Nonvested awards January 1,		0	0
Awards granted (in units)			9,822
Vested			(2,666)
Forfeited			(153)
Nonvested awards December 31,			7,003	0
2020 Performance Unit Plan [Member] | Performance Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards to be granted as percentage of target units			200.00%
2020 Performance Unit Plan [Member] | Performance Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards to be granted as percentage of target units			0.00%
2020 Performance Unit Plan [Member] | Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Nonvested awards January 1,		0	0
Awards granted (in units)			9,822
Vested			(2,666)
Forfeited			(153)
Nonvested awards December 31,			7,003	0
2021 Long Term Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Awards granted (in units)			0
2021 Long Term Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock to be issued with plan			500,000
2021 Long Term Incentive Plan [Member] | Performance Units [Member] | Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Awards granted (in units)	10,187
2021 Long Term Incentive Plan [Member] | Restricted Stock Units [Member] | Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward
Awards granted (in units)	16,267

Notes Payable to Banks, Comme_3

Notes Payable to Banks, Commercial Paper, and Lines of Credit (Details)		12 Months Ended
		Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Short-term Debt [Line Items]
Short-term debt outstanding	[1]	$ 52,500,000	$ 0
Letters of credit issued inside credit facilities	[1]	$ 685,000	$ 0
Weighted-average interest rate	[1]	0.15%	0.00%
Maximum short-term borrowings	[1]	$ 52,500,000	$ 56,000,000
Average short-term borrowings	[1]	$ 6,393,000	$ 18,364,000
Weighted-average interest rate during the year	[1]	0.43%	2.16%
Line of Credit [Member]
Short-term Debt [Line Items]
Available capacity under line of credit	[1]	$ 96,815,000	$ 150,000,000
Line of Credit [Member] | MGE Energy unsecured committed revolving line of credit totaling $50 million [Member] | MGE Energy [Member]
Short-term Debt [Line Items]
Line of credit		50,000,000
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 [Member] | 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 [Member] | 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		$ 52,500,000	0
Letters of credit issued inside credit facilities		$ 685,000	$ 0
Weighted-average interest rate		0.15%	0.00%
Maximum short-term borrowings		$ 52,500,000	$ 56,000,000
Average short-term borrowings		$ 6,393,000	$ 18,364,000
Weighted-average interest rate during the year		0.43%	2.16%
MGE [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Available capacity under line of credit		$ 46,815,000	$ 100,000,000
MGE [Member] | Line of Credit [Member] | MGE unsecured committed revolving lines of credit totaling $100 million [Member]
Short-term Debt [Line Items]
Line of credit		100,000,000
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 [Member] | 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 [Member] | 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.

Long-Term Debt (Details-1)

Long-Term Debt (Details-1) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt due within one year		$ (4,771)	$ (19,659)
Unamortized discount and debt issuance costs		(4,146)	(4,479)
Total Long-Term Debt		519,303	523,741
First Mortgage Bonds [Member] | 7.70%, 2028 Series [Member]
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		$ 529,900
Tax Exempt Debt [Member] | 3.45%, 2027 Series, Industrial Development Revenue Bonds
Debt Instrument [Line Items]
Long-term debt, gross	[2]	$ 0	$ 19,300
Interest rate		3.45%	3.45%
Tax Exempt Debt [Member] | 2.05%, 2023 Series, Industrial Development Revenue Bonds
Debt Instrument [Line Items]
Long-term debt, gross	[2]	$ 19,300	$ 0
Interest rate		2.05%
Medium-Term Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 70,000	70,000
Medium-Term Notes [Member] | 6.12%, due 2028
Debt Instrument [Line Items]
Long-term debt, gross	[3]	$ 20,000	$ 20,000
Interest rate		6.12%	6.12%
Medium-Term Notes [Member] | 7.12%, due 2032
Debt Instrument [Line Items]
Long-term debt, gross	[3]	$ 25,000	$ 25,000
Interest rate		7.12%	7.12%
Medium-Term Notes [Member] | 6.247%, due 2037
Debt Instrument [Line Items]
Long-term debt, gross	[3]	$ 25,000	$ 25,000
Interest rate		6.247%	6.247%
Other Long-Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 437,720	$ 457,379
Other Long-Term Debt [Member] | 3.38%, retired 2020
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 0	$ 15,000
Interest rate		3.38%	3.38%
Other Long-Term Debt [Member] | 3.38%, retired 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%, retired 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%
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%
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%
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] | 2.94% due 2029
Debt Instrument [Line Items]
Long-term debt, gross	[4],[5]	$ 50,000	$ 50,000
Interest rate		2.94%	2.94%
Other Long-Term Debt [Member] | 2.94% due 2029 | 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] | 2.94% due 2029 | 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	[5],[6]	$ 22,762	$ 23,946
Interest rate		5.68%	5.68%
Other Long-Term Debt [Member] | 5.19%, due 2033
Debt Instrument [Line Items]
Long-term debt, gross	[5],[6]	$ 14,985	$ 15,794
Interest rate		5.19%	5.19%
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%
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	[5],[7]	$ 31,806	$ 33,472
Interest rate		5.04%	5.04%
Other Long-Term Debt [Member] | 4.74%, due 2041
Debt Instrument [Line Items]
Long-term debt, gross	[5],[7]	$ 20,167	$ 21,167
Interest rate		4.74%	4.74%
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%
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%
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%
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%
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	$ 60,000
Interest rate		4.19%	4.19%
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	$ 20,000
Interest rate		4.24%	4.24%
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	$ 20,000
Interest rate		4.34%	4.34%
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		$ (400)	$ (400)
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 MGE 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, 2020, approximately $ 529.9
[2]	In April 2020, MGE borrowed $19.3 million from the City of Madison, Wisconsin's issuance of Industrial Development Revenue Refunding Bonds (Madison Gas and Electric Company Project), Series 2020A. The bonds carry an interest rate of 2.05% per annum with interest payable semi-annually on April 1 and October 1 of each year, which commenced on October1, 2020. The bonds require their holder to tender them on April 30, 2023, at which time the bonds will either be repriced and remarketed or redeemed and retired. MGE used the proceeds to redeem at par $19.3 million of existing Industrial Development Revenue Refunding Bonds (Madison Gas and Electric Company Project), Series 2002B due October 1, 2027.
[3]	The indenture under which MGE's Medium-Term notes are issued provides that those notes will be entitled to be equally and ratably secured in the event that MGE issues any additional first mortgage bonds.
[4]	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 voting 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, 2020 , MGE was in compliance with the covenant requirements.
[5]	Unsecured notes issued pursuant to various Note Purchase Agreements with one or more purchasers. The notes are not issued under, or governed by, MGE's Indenture dated as of September 1, 1998, which governs MGE's Medium-Term Notes.
[6]	Issued by MGE Power West Campus. The Note Purchase Agreements require MGE Power West Campus 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 the WCCF pursuant to a long-term lease. As of December 31, 2020, MGE Power West Campus was in compliance with the covenant requirements.
[7]	Issued by MGE 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 the Elm Road Units pursuant to long-term leases. As of December 31, 2020, MGE Power Elm Road was in compliance with the covenant requirements.

Long-Term Debt (Details-2)

Long-Term Debt (Details-2) $ in Thousands	Dec. 31, 2020USD ($)
Long-Term Debt Maturities [Abstract]
Long term debt maturities in 2021	$ 4,771
Long term debt maturities in 2022	4,889
Long term debt maturities in 2023	54,314
Long term debt maturities in 2024	5,146
Long term debt maturities in 2025	5,285
Long term debt maturities in future years	$ 453,815

Common Equity (Details)

Common Equity (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2020$ / shares	Sep. 30, 2020$ / shares	Jun. 30, 2020$ / shares	Mar. 31, 2020$ / shares	Dec. 31, 2019$ / shares	Sep. 30, 2019$ / shares	Jun. 30, 2019$ / shares	Mar. 31, 2019$ / shares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / shares
Class of Stock [Line Items]
Common stock dividends declared									$ 51,729,000	$ 47,842,000	$ 45,762,000
Common stock dividends declared (in dollars per share) | $ / shares	$ 0.370	$ 0.370	$ 0.353	$ 0.353	$ 0.353	$ 0.353	$ 0.338	$ 0.338	$ 1.45	$ 1.38	$ 1.32
Common stock issued during period | shares									1,500,000
Common stock issued during period under the stock plan | shares									0	0
Proceeds From Issuance Of Common Stock									$ 79,635,000	$ 0	$ 0
Dilutive Securities									0
MGE Energy [Member]
Class of Stock [Line Items]
Proceeds From Issuance Of Common Stock									79,635,000	0	$ 0
MGE [Member]
Class of Stock [Line Items]
Cash dividends paid to parent by MGE									$ 0	$ 0
MGE [Member] | Minimum [Member]
Class of Stock [Line Items]
Dividend restrictions, common equity ratio									0.55

Commitments and Contingencies_2

Commitments and Contingencies (Details-1) $ in Millions	Dec. 31, 2020USD ($)
Columbia Units [Member]
Public Utilities, General Disclosures [Line Items]
Projected costs for enviornmental regulations	$ 4
Elm Road Units [Member]
Public Utilities, General Disclosures [Line Items]
Projected costs for enviornmental regulations	$ 4

Commitments and Contingencies_3

Commitments and Contingencies (Details-2) $ in Thousands	Dec. 31, 2020USD ($)
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	$ 79,290
Purchase obligation due in second year	47,674
Purchase obligation due in third year	32,880
Purchase obligation due in fourth year	29,546
Purchase obligation due in fifth year	29,000
Purchase obligation due thereafter	61,864
Coal [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	11,399	[1]
Purchase obligation due in second year	5,249	[1]
Purchase obligation due in third year	1,515	[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	21,851	[2]
Purchase obligation due in second year	22,120	[2]
Purchase obligation due in third year	22,553	[2]
Purchase obligation due in fourth year	22,553	[2]
Purchase obligation due in fifth year	22,553	[2]
Purchase obligation due thereafter	18,316	[2]
Natural Gas, Supply [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	9,527	[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	27,017	[4]
Purchase obligation due in second year	15,399	[4]
Purchase obligation due in third year	5,856	[4]
Purchase obligation due in fourth year	5,458	[4]
Purchase obligation due in fifth year	5,567	[4]
Purchase obligation due thereafter	11,717	[4]
Renewable energy
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	6,663	[5]
Purchase obligation due in second year	2,862	[5]
Purchase obligation due in third year	1,245	[5]
Purchase obligation due in fourth year	759	[5]
Purchase obligation due in fifth year	776	[5]
Purchase obligation due thereafter	30,939	[5]
Other [Member]
Purchase Obligation, Fiscal Year Maturity [Abstract]
Purchase obligation due in next twelve months	2,833
Purchase obligation due in second year	2,044
Purchase obligation due in third year	1,711
Purchase obligation due in fourth year	776
Purchase obligation due in fifth year	104
Purchase obligation due thereafter	$ 892
[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 approved 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 future electric supply requirements.
[5]	Operational commitments for solar and wind facilities.

Commitments and Contingencies_4

Commitments and Contingencies (Details-3)	12 Months Ended
	Dec. 31, 2020USD ($)
Other Commitments [Line Items]
Other commitments, due in 2021	$ 333,000
Other commitments, due in 2022	333,000
Other commitments, due in 2023	333,000
Other commitments, due in 2024	333,000
Other commitments, due in 2025	333,000
Other commitment, due thereafter	2,999,000
Investments in Non Public Entities, Capital Infusions [Member]
Other Commitments [Line Items]
Other commitment, initial agreed upon commitment total	$ 13,600,000
Venture Debt Fund [Member]
Other Commitments [Line Items]
Other commitment, contract term, expiring in 2022	3 years
Other commitment, initial agreed upon commitment total	$ 1,500,000
Other commitments, total as of balance sheet date	$ 400,000

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligations [Roll Forward]
Asset retirement obligation, beginning balance		$ 28,355	$ 29,980
Liabilities incurred	[1]	3,503	1,586
Accretion expense		1,366	1,574
Liabilities settled		(372)	(323)
Revisions in estimated cash flows	[2]	(1,656)	(4,462)
Asset retirement obligation, ending balance		31,196	28,355
Two Creeks [Member]
Asset Retirement Obligations [Roll Forward]
Liabilities incurred		$ 3,200
Saratoga Wind Farm [Member]
Asset Retirement Obligations [Roll Forward]
Liabilities incurred			$ 1,500
[1]	In 2020, MGE recorded an obligation of $ 3.2 million for the fair value of its legal liability for AROs associated with Two Creeks. See Footnote 6 for additional information on Two Creeks. In 2019, MGE recorded an obligation of $ 1.5 million for the fair value of its legal liability for AROs associated with Saratoga. Construction of Saratoga was completed in February 2019.
[2]	In 2019, MGE revised the AROs associated with certain wind farms based on updated estimated decommissioning costs.

Derivative and Hedging Instru_3

Derivative and Hedging Instruments (Details-1)		12 Months Ended
		Dec. 31, 2020USD ($)DthMWhMW		Dec. 31, 2019USD ($)DthMWhMW	Dec. 31, 2018USD ($)
Derivative Fair Values [Abstract]
Collateral posted against derivative positions		$ 0		$ 1,500,000
Other Current Assets [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		1,162,000		1,100,000	$ 377,000
Commodity Contracts and Financial Transimission Rights [Member]
Derivative Fair Values [Abstract]
Derivative fair value, net		$ 200,000		$ (1,400,000)
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		259,080		417,840
Notional amount, decatherm measure (in Dth) | Dth		6,030,000		6,605,000
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		$ 806,000		$ 230,000
Liability Derivatives, fair value, gross basis		632,000		1,738,000
Collateral posted against derivative positions		0		1,546,000
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		617,000	[1]	100,000
Liability Derivatives, fair value, gross basis	[1]	593,000
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	189,000
Liability Derivatives, fair value, gross basis	[1]	39,000
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1],[2]			157,000
Liability Derivatives, fair value, gross basis	[1],[2]			1,521,000
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis	[1]			73,000
Liability Derivatives, fair value, gross basis	[1]			217,000
Commodity Derivative Contracts [Member] | Cash Flow Hedging [Member]
Derivative Fair Values [Abstract]
Collateral posted against derivative positions		$ 0		$ 1,500,000
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		2,869		2,750
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis				$ 73,000
Liability Derivatives, fair value, gross basis		$ 23,000
Collateral posted against derivative positions		0
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis				73,000
Liability Derivatives, fair value, gross basis				$ 0
Financial Transmission Rights [Member] | Other Current Liabilities [Member]
Derivative Fair Values [Abstract]
Asset Derivatives, fair value, gross basis		0
Liability Derivatives, fair value, gross basis		$ 23,000
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		850		1,450
Derivative Fair Values [Abstract]
Derivative fair value, net		$ 14,100,000		$ 25,400,000
Liability Derivatives, fair value, gross basis		14,140,000		25,440,000
Collateral posted against derivative positions		0		0
PPA [Member] | Derivative Liability (Current) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		10,160,000		10,100,000
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative Fair Values [Abstract]
Liability Derivatives, fair value, gross basis		$ 3,980,000		$ 15,340,000
[1]	As of December 31, 2019, collateral of $ 1.5 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, 2020.
[2]	As of December 31, 2019, MGE posted $ 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, 2020	Dec. 31, 2019
Commodity Derivative Contracts [Member]
Offsetting Assets [Line Items]
Gross amounts	$ 806	$ 230
Gross amounts offset in balance sheet	(632)	(192)
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 174	38
Financial Transmission Rights [Member]
Offsetting Assets [Line Items]
Gross amounts		73
Gross amounts offset in balance sheet		0
Collateral posted against derivative positions		0
Net amount presented in balance sheet		$ 73

Derivative and Hedging Instru_5

Derivative and Hedging Instruments (Details-3) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Offsetting Liabilities [Line Items]
Collateral posted against derivative positions	$ 0	$ (1,500,000)
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	632,000	1,738,000
Gross amounts offset in balance sheet	(632,000)	(192,000)
Collateral posted against derivative positions	0	(1,546,000)
Net amount presented in the balance sheet	0	0
Financial Transmission Rights [Member]
Offsetting Liabilities [Line Items]
Gross amounts	23,000
Gross amounts offset in balance sheet	0
Collateral posted against derivative positions	0
Net amount presented in the balance sheet	23,000
PPA [Member]
Offsetting Liabilities [Line Items]
Gross amounts	14,140,000	25,440,000
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in the balance sheet	$ 14,140,000	$ 25,440,000

Derivative and Hedging Instru_6

Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Current and Long-Term Regulatory Asset [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	$ 26,875	$ 31,830
Unrealized gain	(4,895)	(5,493)
Realized (loss) gain reclassified to a deferred account	(2,232)	(1,896)
Realized (loss) gain reclassified to income statement	(5,759)	2,434
Ending balance	13,989	26,875
Other Current Assets [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	1,100	377
Unrealized gain	0	0
Realized (loss) gain reclassified to a deferred account	2,232	1,896
Realized (loss) gain reclassified to income statement	(2,170)	(1,173)
Ending balance	$ 1,162	$ 1,100

Derivative and Hedging Instru_7

Derivative and Hedging Instruments (Details-5)	12 Months Ended
	Dec. 31, 2020USD ($)counterparty	Dec. 31, 2019USD ($)
Counterparties in net liability position or default [Abstract]
Derivative, net liability position of counterparties	$ 0	$ 0.1
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	$ 2,566,000	1,258,000
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	1,729,000	863,000
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	63,000	(574,000)
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	20,000,000
Maximum collateral that may be required to be posted	40,000,000
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	3,571,000	(2,808,000)
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, 2020	Dec. 31, 2019
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,146	$ 4,479
Carrying Amount [Member]
Assets:
Cash and cash equivalents		44,738	23,481
Liabilities:
Short-term debt - commercial paper		52,500	0
Long-Term debt	[1]	528,220	547,879
Fair Value [Member]
Assets:
Cash and cash equivalents		44,738	23,481
Liabilities:
Short-term debt - commercial paper		52,500	0
Long-Term debt	[1]	639,271	611,909
MGE [Member] | Fair Value Disclosure Item Amounts [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		4,146	4,479
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		4,103	3,196
Liabilities:
Short-term debt - commercial paper		52,500	0
Long-Term debt	[1]	528,220	547,879
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		4,103	3,196
Liabilities:
Short-term debt - commercial paper		52,500	0
Long-Term debt	[1]	$ 639,271	$ 611,909
[1]	Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $ 4.1 4.5

Fair Value of Financial Instr_4

Fair Value of Financial Instruments (Details-2) - USD ($)	Dec. 31, 2020		Dec. 31, 2019
Assets:
Available-for-sale securities	$ 17,906,000		$ 14,546,000
Liabilities:
Collateral posted against derivative positions	0		1,500,000
Recurring [Member]
Assets:
Derivative assets, net	806,000		303,000
Total Assets	2,556,000		1,574,000
Liabilities:
Derivative liabilities, net	14,795,000	[1]	27,178,000	[2]
Deferred compensation	3,509,000		3,157,000
Total Liabilities	18,304,000		30,335,000
Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	1,750,000		1,271,000
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	436,000		189,000
Total Assets	2,186,000		1,460,000
Liabilities:
Derivative liabilities, net	370,000	[1]	608,000	[2]
Deferred compensation	0		0
Total Liabilities	370,000		608,000
Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	1,750,000		1,271,000
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0		0
Total Assets	0		0
Liabilities:
Derivative liabilities, net	0	[1]	0	[2]
Deferred compensation	3,509,000		3,157,000
Total Liabilities	3,509,000		3,157,000
Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	0		0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net	370,000		114,000
Total Assets	370,000		114,000
Liabilities:
Derivative liabilities, net	14,425,000	[1]	26,570,000	[2]
Deferred compensation	0		0
Total Liabilities	14,425,000		26,570,000
Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	0		0
MGE [Member]
Assets:
Available-for-sale securities	603,000		209,000
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net	806,000		303,000
Total Assets	1,409,000		512,000
Liabilities:
Derivative liabilities, net	14,795,000	[1]	27,178,000	[2]
Deferred compensation	3,509,000		3,157,000
Total Liabilities	18,304,000		30,335,000
MGE [Member] | Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	603,000		209,000
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	436,000		189,000
Total Assets	1,039,000		398,000
Liabilities:
Derivative liabilities, net	370,000	[1]	608,000	[2]
Deferred compensation	0		0
Total Liabilities	370,000		608,000
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	603,000		209,000
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0		0
Total Assets	0		0
Liabilities:
Derivative liabilities, net	0	[1]	0	[2]
Deferred compensation	3,509,000		3,157,000
Total Liabilities	3,509,000		3,157,000
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	370,000		114,000
Total Assets	370,000		114,000
Liabilities:
Derivative liabilities, net	14,425,000	[1]	26,570,000	[2]
Deferred compensation	0		0
Total Liabilities	14,425,000		26,570,000
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	$ 0		$ 0
[1]	These amounts are shown gross. No collateral was posted against derivative positions with counterparties as of December 31, 2020.
[2]	These amounts are shown gross and exclude $ 1.5 million of collateral that was posted against derivative positions with counterparties as of December 31, 2019.

Fair Value of Financial Instr_5

Fair Value of Financial Instruments (Details-3)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Basis adjustment:
Basis adjustment - on peak	94.20%	92.10%
Basis adjustment - off peak	94.50%	92.70%
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	46.00%	40.00%
Purchased power	35.00%	40.00%
Maximum [Member]
Counterparty fuel mix:
Internal generation	65.00%	60.00%
Purchased power	54.00%	60.00%
Weighted Average [Member]
Counterparty fuel mix:
Internal generation	56.50%	52.20%
Purchased power	43.50%	47.80%

Fair Value of Financial Instr_6

Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance		$ (26,456)	$ (32,002)	$ (42,026)
Realized and unrealized gains (losses):
Included in regulatory asset		12,402	5,545	10,024
Included in other comprehensive income		0	0	0
Included in earnings	[1]	(6,439)	(3,765)	132
Included in current assets		(87)	(70)	(47)
Purchases		22,232	22,974	23,643
Sales		0	0	0
Issuances		0	0	0
Settlements		(15,707)	(19,138)	(23,728)
Transfers in and/or out of Level 3		0	0	0
Ending balance		$ (14,055)	$ (26,456)	$ (32,002)
[1]	MGE's exchange-traded derivative contracts, over-the-counter 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.

Fair Value of Financial Instr_7

Fair Value of Financial Instruments (Details-5) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	$ 0	$ 0	$ 0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings	[1]	(6,439)	(3,765)	132
Purchased Power Expense [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings	[1]	(5,888)	(3,334)	355
Cost Of Gas Sold Expense [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in earnings	[1]	$ (551)	$ (431)	$ (223)
[1]	MGE's exchange-traded derivative contracts, over-the-counter 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.

Revenue (Details-1)

Revenue (Details-1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total Operating Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 538,633	$ 568,855	$ 559,768
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	393,692	408,285	400,882
Electric [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	146,431	140,006	138,566
Electric [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	198,043	213,265	204,683
Electric [Member] | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	11,514	12,772	13,878
Electric [Member] | Other-retail/municipal [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	32,915	35,174	34,023
Electric [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	388,903	401,217	391,150
Electric [Member] | Sales To The Market [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	4,015	5,664	7,438
Electric [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	774	1,404	2,294
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	144,261	159,875	157,767
Gas [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	88,765	95,146	94,017
Gas [Member] | Commercial/Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	49,682	59,051	59,060
Gas [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	138,447	154,197	153,077
Gas [Member] | Gas Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	5,713	5,293	4,283
Gas [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	101	385	407
Non Regulated Energy [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 680	$ 695	$ 1,119

Noncontrolling Interest (Detail

Noncontrolling Interest (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
MGE Power [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent		100.00%
MGE [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet		$ 141,196,000	$ 140,303,000
Net income attributable to noncontrolling interest, net of tax		22,393,000	22,349,000	$ 22,552,000
MGE Power West Campus [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet	[1]	44,340,000	43,131,000
Net income attributable to noncontrolling interest, net of tax	[1]	7,209,000	7,196,000	7,168,000
MGE Power Elm Road [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet	[1]	96,856,000	97,172,000
Net income attributable to noncontrolling interest, net of tax	[1]	$ 15,184,000	$ 15,153,000	$ 15,384,000
[1]	MGE Power Elm Road and MGE Power West Campus are not subsidiaries of MGE; however, they have been consolidated in the consolidated financial statements 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% owned 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.

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Operating revenues		$ 136,509	$ 135,211	$ 117,040	$ 149,873	$ 140,941	$ 138,198	$ 122,147	$ 167,569	$ 538,633	$ 568,855	$ 559,768
Depreciation and amortization										(74,188)	(71,562)	(56,412)
Operating Income (Loss)		18,712	38,325	21,520	31,440	21,877	38,738	19,783	30,512	109,997	110,910	114,207
Interest (expense) income, net										(23,521)	(23,063)	(19,609)
Income before income taxes										111,841	106,658	111,653
Income tax (provision) benefit		(3,370)	(7,300)	(3,740)	(5,013)	(3,116)	(7,454)	(3,505)	(5,709)	(19,423)	(19,784)	(27,434)
Equity earnings of investments										10,221	9,889	8,821
Net Income		15,796	$ 31,794	$ 18,791	$ 26,037	16,662	$ 30,657	$ 15,548	$ 24,007	92,418	86,874	84,219
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		2,253,651				2,081,664				2,253,651	2,081,664	1,988,618
Capital expenditures										203,139	164,036	212,197
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues										393,692	408,285	400,882
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues										144,261	159,875	157,767
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues										680	695	1,119
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										538,633	568,855	559,768
Depreciation and amortization										(74,188)	(71,562)	(56,412)
Operating Income (Loss)										109,997	110,910	114,207
Interest (expense) income, net										(23,521)	(23,063)	(19,609)
Income tax (provision) benefit										(19,423)	(19,784)	(27,434)
Equity earnings of investments										10,221	9,547	8,602
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues										394,457	409,091	400,593
Depreciation and amortization										(54,658)	(52,755)	(38,925)
Operating Income (Loss)										57,847	59,180	64,294
Interest (expense) income, net										(14,446)	(14,978)	(12,198)
Income tax (provision) benefit										(4,230)	(5,037)	(13,453)
Equity earnings of investments										0	0	0
Net Income										50,522	46,318	45,937
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,421,302				1,308,277				1,421,302	1,308,277	1,193,083
Capital expenditures										162,210	125,086	176,399
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues										156,418	175,945	173,843
Depreciation and amortization										(12,049)	(11,320)	(10,060)
Operating Income (Loss)										19,674	19,528	17,900
Interest (expense) income, net										(4,370)	(4,237)	(3,692)
Income tax (provision) benefit										(4,805)	(4,753)	(4,474)
Equity earnings of investments										0	0	0
Net Income										14,167	14,088	12,866
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		444,702				408,001				444,702	408,001	377,005
Capital expenditures										36,906	36,193	30,497
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues										41,082	40,715	40,645
Depreciation and amortization										(7,481)	(7,487)	(7,427)
Operating Income (Loss)										33,460	33,084	33,074
Interest (expense) income, net										(4,826)	(5,083)	(5,307)
Income tax (provision) benefit										(7,800)	(7,628)	(7,534)
Equity earnings of investments										0	0	0
Net Income										20,834	20,373	20,233
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		254,298				258,004				254,298	258,004	265,301
Capital expenditures										4,023	2,757	5,301
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues										0	0	0
Depreciation and amortization										0	0	0
Operating Income (Loss)										(1)	0	(16)
Interest (expense) income, net										0	0	0
Income tax (provision) benefit										(2,786)	(2,602)	(2,345)
Equity earnings of investments										10,221	9,547	8,602
Net Income										7,434	6,945	6,241
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	[1]	74,480				71,668				74,480	71,668	66,366
Capital expenditures	[1]									0	0	0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues										0	0	0
Depreciation and amortization										0	0	0
Operating Income (Loss)										(983)	(882)	(1,045)
Interest (expense) income, net										121	1,235	1,588
Income tax (provision) benefit										(198)	(236)	(372)
Equity earnings of investments										0	0	0
Net Income										(539)	(850)	(1,058)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		495,483				443,278				495,483	443,278	465,661
Capital expenditures										0	0	0
Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues										(53,324)	(56,896)	(55,313)
Depreciation and amortization										0	0	0
Operating Income (Loss)										0	0	0
Interest (expense) income, net										0	0	0
Income tax (provision) benefit										0	0	0
Equity earnings of investments										0	0	0
Net Income										0	0	0
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		(436,614)				(407,564)				(436,614)	(407,564)	(378,798)
Capital expenditures										0	0	0
Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues										765	806	(289)
Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues										12,157	16,070	16,076
Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues										40,402	40,020	39,526
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										538,633	568,855	559,768
Depreciation and amortization										(74,188)	(71,562)	(56,412)
Operating Income (Loss)										110,981	111,792	115,268
Interest (expense) income, net										(23,642)	(24,298)	(21,197)
Income before income taxes										102,358	98,197	104,497
Income tax (provision) benefit										(16,835)	(17,418)	(25,461)
Net Income										63,130	58,430	56,484
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		2,119,971				1,973,477				2,119,971	1,973,477	1,834,891
Capital expenditures										203,139	164,036	212,197
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues										393,692	408,285	400,882
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues										144,261	159,875	157,767
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues										680	695	1,119
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues										538,633	568,855	559,768
Depreciation and amortization										(74,188)	(71,562)	(56,412)
Operating Income (Loss)										110,981	111,792	115,268
Interest (expense) income, net										(23,642)	(24,298)	(21,197)
Income tax (provision) benefit										(16,835)	(17,418)	(25,461)
Net Income										63,130	58,430	56,484
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues										394,457	409,091	400,593
Depreciation and amortization										(54,658)	(52,755)	(38,925)
Operating Income (Loss)										57,847	59,180	64,294
Interest (expense) income, net										(14,446)	(14,978)	(12,198)
Income tax (provision) benefit										(4,230)	(5,037)	(13,453)
Net Income										50,522	46,318	45,937
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,421,302				1,308,277				1,421,302	1,308,277	1,193,083
Capital expenditures										162,210	125,086	176,399
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues										156,418	175,945	173,843
Depreciation and amortization										(12,049)	(11,320)	(10,060)
Operating Income (Loss)										19,674	19,528	17,900
Interest (expense) income, net										(4,370)	(4,237)	(3,692)
Income tax (provision) benefit										(4,805)	(4,753)	(4,474)
Net Income										14,167	14,088	12,866
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		444,702				408,001				444,702	408,001	377,005
Capital expenditures										36,906	36,193	30,497
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues										41,082	40,715	40,645
Depreciation and amortization										(7,481)	(7,487)	(7,427)
Operating Income (Loss)										33,460	33,084	33,074
Interest (expense) income, net										(4,826)	(5,083)	(5,307)
Income tax (provision) benefit										(7,800)	(7,628)	(7,534)
Net Income										20,834	20,373	20,233
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		254,248				257,954				254,248	257,954	265,251
Capital expenditures										4,023	2,757	5,301
MGE [Member] | Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues										(53,324)	(56,896)	(55,313)
Depreciation and amortization										0	0	0
Operating Income (Loss)										0	0	0
Interest (expense) income, net										0	0	0
Income tax (provision) benefit										0	0	0
Net Income										(22,393)	(22,349)	(22,552)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		$ (281)				$ (755)				(281)	(755)	(448)
Capital expenditures										0	0	0
MGE [Member] | Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues										765	806	(289)
MGE [Member] | Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues										12,157	16,070	16,076
MGE [Member] | Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues										$ 40,402	$ 40,020	$ 39,526
[1]	The Transmission Investment segment represents MGE Energy's investment in equity method investees.

Quarterly Summary of Operatio_3

Quarterly Summary of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Revenues:
Electric revenues	$ 90,815	$ 116,568	$ 93,961	$ 93,028	$ 93,613	$ 120,821	$ 97,077	$ 97,469	$ 394,372	$ 408,980	$ 402,001
Gas revenues	45,694	18,643	23,079	56,845	47,328	17,377	25,070	70,100	144,261	159,875	157,767
Total Operating Revenues	136,509	135,211	117,040	149,873	140,941	138,198	122,147	167,569	538,633	568,855	559,768
Operating expenses	117,797	96,886	95,520	118,433	119,064	99,460	102,364	137,057	428,636	457,945	445,561
Operating Income	18,712	38,325	21,520	31,440	21,877	38,738	19,783	30,512	109,997	110,910	114,207
Interest and other income, net	454	769	1,011	(390)	(2,099)	(627)	(730)	(796)
Income tax provision	(3,370)	(7,300)	(3,740)	(5,013)	(3,116)	(7,454)	(3,505)	(5,709)	(19,423)	(19,784)	(27,434)
Net Income	$ 15,796	$ 31,794	$ 18,791	$ 26,037	$ 16,662	$ 30,657	$ 15,548	$ 24,007	$ 92,418	$ 86,874	$ 84,219
Earnings per common share	$ 0.44	$ 0.88	$ 0.53	$ 0.75	$ 0.48	$ 0.88	$ 0.45	$ 0.69	$ 2.60	$ 2.51	$ 2.43
Dividends per share	$ 0.370	$ 0.370	$ 0.353	$ 0.353	$ 0.353	$ 0.353	$ 0.338	$ 0.338	$ 1.45	$ 1.38	$ 1.32

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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Expenses:
Other operations and maintenance									$ 186,430	$ 193,322	$ 177,823
Total Operating Expenses	$ 117,797	$ 96,886	$ 95,520	$ 118,433	$ 119,064	$ 99,460	$ 102,364	$ 137,057	428,636	457,945	445,561
Operating Income	18,712	38,325	21,520	31,440	21,877	38,738	19,783	30,512	109,997	110,910	114,207
Equity earnings of investments									10,221	9,889	8,821
Income before income taxes									111,841	106,658	111,653
Income tax provision	(3,370)	(7,300)	(3,740)	(5,013)	(3,116)	(7,454)	(3,505)	(5,709)	(19,423)	(19,784)	(27,434)
Net Income	$ 15,796	$ 31,794	$ 18,791	$ 26,037	$ 16,662	$ 30,657	$ 15,548	$ 24,007	92,418	86,874	84,219
MGE Energy [Member]
Operating Expenses:
Other operations and maintenance									882	815	913
Total Operating Expenses									882	815	913
Operating Income									(882)	(815)	(913)
Equity earnings of investments									92,922	87,728	85,220
Other income/(loss), net									94	(1,500)	(1,966)
Interest income, net									78	1,224	1,489
Income before income taxes									92,212	86,637	83,830
Income tax provision									206	237	389
Net Income									$ 92,418	$ 86,874	$ 84,219

Schedule I - Condensed Parent_2

Schedule I - Condensed Parent Company Finanical Statements (Details-Cash Flow Statement) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	$ 172,443,000	$ 130,475,000	$ 153,040,000
Investing Activities:
Other	(1,672,000)	(508,000)	(205,000)
Cash Used for Investing Activities	(210,412,000)	(172,357,000)	(218,328,000)
Financing Activities:
Proceeds From Issuance Of Common Stock	79,635,000	0	0
Cash dividends paid on common stock	(51,729,000)	(47,842,000)	(45,762,000)
Other	(1,553,000)	(1,838,000)	(662,000)
Cash Provided by (Used for) Financing Activities	59,194,000	(17,233,000)	38,123,000
Change in cash, cash equivalents, and restricted cash:	21,225,000	(59,115,000)	(27,165,000)
Cash, cash equivalents, and restricted cash at beginning of period	25,814,000	84,929,000	112,094,000
Cash, cash equivalents, and restricted cash at end of period	47,039,000	25,814,000	84,929,000
MGE Energy [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	27,631,000	27,901,000	27,211,000
Investing Activities:
Contributions to affiliates	(32,157,000)	(33,631,000)	(3,200,000)
Contributions to other Investments	(3,809,000)	(4,496,000)	(2,626,000)
Other	622,000	214,000	873,000
Cash Used for Investing Activities	(35,344,000)	(37,913,000)	(4,953,000)
Financing Activities:
Proceeds From Issuance Of Common Stock	79,635,000	0	0
Cash dividends paid on common stock	(51,729,000)	(47,842,000)	(45,762,000)
Cash Provided by (Used for) Financing Activities	27,906,000	(47,842,000)	(45,762,000)
Change in cash, cash equivalents, and restricted cash:	20,193,000	(57,854,000)	(23,504,000)
Cash, cash equivalents, and restricted cash at beginning of period	17,182,000	75,036,000	98,540,000
Cash, cash equivalents, and restricted cash at end of period	$ 37,375,000	$ 17,182,000	$ 75,036,000

Schedule I - Condensed Parent_3

Schedule I - Condensed Parent Company Finanical Statements (Details-Balance Sheet) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 44,738,000	$ 23,481,000
Other current assets	11,394,000	10,233,000
Total Current Assets	209,519,000	181,641,000
Other deferred assets and other
Other deferred assets and other	22,259,000	19,093,000
Investments:
Other investments	2,308,000	2,298,000
Total investments	94,676,000	88,492,000
Total Assets	2,253,651,000	2,081,664,000	$ 1,988,618,000
Current Liabilities:
Other current liabilities	6,015,000	14,676,000
Total Current Liabilities	190,926,000	128,820,000
Other Credits:
Deferred income taxes	231,471,000	243,302,000
Other deferred liabilities and other	72,211,000	63,013,000
Total Other Credits	567,422,000	573,427,000
Shareholders' Equity:
Retained earnings	545,429,000	504,740,000
Total Common Shareholders' Equity	976,000,000	855,676,000	$ 816,644,000	$ 778,187,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	2,253,651,000	2,081,664,000
MGE Energy [Member]
Current Assets:
Cash and cash equivalents	37,375,000	17,182,000
Other current assets	1,494,000	3,180,000
Total Current Assets	38,869,000	20,362,000
Other deferred assets and other
Other deferred assets and other	364,000	498,000
Investments:
Investments in affiliates	953,810,000	856,444,000
Other investments	15,634,000	12,910,000
Total investments	969,444,000	869,354,000
Total Assets	1,008,677,000	890,214,000
Current Liabilities:
Accounts payable to affiliates	530,000	530,000
Other current liabilities	66,000	2,314,000
Total Current Liabilities	596,000	2,844,000
Other Credits:
Deferred income taxes	29,926,000	29,006,000
Accounts payable to affiliates	2,118,000	2,647,000
Other deferred liabilities and other	37,000	41,000
Total Other Credits	32,081,000	31,694,000
Shareholders' Equity:
Common shareholders' equity	430,571,000	350,936,000
Retained earnings	545,429,000	504,740,000
Total Common Shareholders' Equity	976,000,000	855,676,000
Commitments and contingencies (see Footnote 3)
Total Liabilities and Capitalization	$ 1,008,677,000	$ 890,214,000

Schedule I - Condensed Parent_4

Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 1) - Line of Credit [Member] - USD ($)		Dec. 31, 2020	Dec. 31, 2019
Credit facilities [Line Items]
Line Of Credit Facility Current Borrowing Capacity	[1]	$ 96,815,000	$ 150,000,000
MGE Energy unsecured committed revolving line of credit totaling $50 million [Member] | MGE Energy [Member]
Credit facilities [Line Items]
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_5

Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 2)	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
MGE Energy [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 27,714,000	$ 28,246,000	$ 26,735,000
First Mortgage Bonds [Member] | 7.70%, 2028 Series [Member]
Dividend Restrictions
Debt covenant, allowable amount available for payment of dividends	529,900,000
MGE [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 0	0
Dividend Restrictions
Common equity ratio	0.602
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	$ 15,500,000	15,500,000	15,500,000
MGE Power West Campus [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	6,000,000	8,000,000	6,500,000
MGE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	5,864,000	4,653,000	4,625,000
MGEE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	350,000	93,000	60,000
NGV Fueling Services [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 0	$ 0	$ 50,000

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory Assets		$ 157,252,000		$ 145,746,000
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of period		3,258,269		3,153,662	$ 3,174,945
Charged to costs and expenses		5,164,943	[1]	1,614,943	1,065,970
Charged to other accounts		26,400		20,160	320,400
Net accounts written off	[2]	(1,373,047)		(1,530,496)	(1,407,653)
Balance at end of period		7,076,565		$ 3,258,269	$ 3,153,662
Deferred COVID Allowance For Credit Loss [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 3,800,000
[1]	As of December 31, 2020, MGE had deferred $ 3.8 million of incremental COVID-19-related costs as a regulatory asset. See Footnote 8 of the Notes to Consolidated Financial Statements in this Report for further information.
[2]	Net of recovery of amounts previously written off