MGE Energy (MGEE) 10-Q 8 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document And Entity Information [Line Items]
Entity Registrant Name	MGE Energy Inc
Entity Central Index Key	1,161,728
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Trading Symbol	MGEE
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
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 Common Stock Shares Outstanding		34,668,370
MGE [Member]
Document And Entity Information [Line Items]
Entity Registrant Name	Madison Gas and Electric Company
Entity Central Index Key	61,339
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding		17,347,894

MGE Energy Inc Consolidated Sta

MGE Energy Inc Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Revenues:
Electric revenues	$ 94,867	$ 98,397
Gas revenues	62,765	58,426
Total Operating Revenues	157,632	156,823
Operating Expenses:
Fuel for electric generation	11,900	12,199
Purchased power	17,033	15,354
Cost of gas sold	39,626	35,784
Other operations and maintenance	44,393	43,764
Depreciation and amortization	13,623	12,959
Other general taxes	4,869	4,927
Total Operating Expenses	131,444	124,987
Operating Income	26,188	31,836
Other income, net	4,919	3,525	[1]
Interest expense, net	(4,739)	(4,894)
Income before income taxes	26,368	30,467
Income tax provision	(6,367)	(11,167)
Net Income	$ 20,001	$ 19,300
Earnings Per Share of Common Stock (basic and diluted)	$ 0.58	$ 0.56
Dividends per share of common stock	$ 0.323	$ 0.308
Weighted Average Shares Outstanding (basic and diluted)	34,668	34,668
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information.

Madison Gas and Electric Compan

Madison Gas and Electric Company Consolidated Statements of Income (Unaudited) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Operating Revenues:
Electric revenues		$ 94,867	$ 98,397
Gas revenues		62,765	58,426
Total Operating Revenues		157,632	156,823
Operating Expenses:
Fuel for electric generation		11,900	12,199
Purchased power		17,033	15,354
Cost of gas sold		39,626	35,784
Other operations and maintenance		44,393	43,764
Depreciation and amortization		13,623	12,959
Other general taxes		4,869	4,927
Total Operating Expenses		131,444	124,987
Operating Income		26,188	31,836
Other Income and Deductions:
Equity earnings in MGE Transco		2,451	2,608
Total Other Income and Deductions		4,919	3,525	[1]
Interest Expense:
Net Interest Expense		4,739	4,894
Net Income		20,001	19,300
MGE [Member]
Operating Revenues:
Electric revenues		94,867	98,401
Gas revenues		62,765	58,435
Total Operating Revenues		157,632	156,836
Operating Expenses:
Fuel for electric generation		11,900	12,201
Purchased power		17,033	15,356
Cost of gas sold		39,626	35,793
Other operations and maintenance		44,187	43,395
Depreciation and amortization		13,623	12,959
Other general taxes		4,869	4,927
Income tax provision		5,524	10,265
Total Operating Expenses		136,762	134,896
Operating Income	[2]	20,870	21,940
Other Income and Deductions:
AFUDC - equity funds		595	271
Income tax provision		(57)	(44)
Other income, net		1,902	998
Total Other Income and Deductions	[2]	2,440	1,225	[1]
Income before interest expense		23,310	23,165
Interest Expense:
Interest on long-term debt		5,206	5,043
Other interest, net		49	31
AFUDC - borrowed funds		(201)	(92)
Net Interest Expense		5,054	4,982
Net Income Including Noncontrolling Interest		18,256	18,183
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,806)	(5,389)
Net Income		$ 12,450	$ 12,794
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information.
[2]	Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.

MGE Energy Inc Consolidated St4

MGE Energy Inc Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Comprehensive Income [Abstract]
Net Income	$ 20,001	$ 19,300
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	0	97
Comprehensive Income	$ 20,001	$ 19,397

Madison Gas and Electric Compa5

Madison Gas and Electric Company Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	$ 0	$ 97
Comprehensive Income	20,001	19,397
MGE [Member]
Net Income	18,256	18,183
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	0	(6)
Total comprehensive income including noncontrolling interest	18,256	18,177
Less: Comprehensive income attributable to Noncontrolling Interest, net of tax	(5,806)	(5,389)
Comprehensive Income	$ 12,450	$ 12,788

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) (Parantheticals) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Unrealized gain (loss) on available-for-sale securities, tax expense (benefit)	$ 0	$ 65
MGE [Member]
Unrealized gain (loss) on available-for-sale securities, tax expense (benefit)	$ 0	$ (4)

MGE Energy Inc Consolidated St7

MGE Energy Inc Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities:
Net Income	$ 20,001	$ 19,300
Items not affecting cash:
Depreciation and amortization	13,623	12,959
Deferred income taxes	(1,793)	(3,732)
Provision for doubtful receivables	264	254
Employee benefit plan (credit) cost	(561)	202
Equity earnings in ATC	(2,451)	(2,608)
Other items	(152)	641
Changes in working capital items:
Decrease in current assets	25,208	27,124
Decrease in current liabilities	(7,771)	(9,318)
Dividends from ATC	2,348	2,072
Cash contributions to pension and other postretirement plans	(1,319)	(7,168)
Other noncurrent items, net	(419)	1,526
Cash Provided by Operating Activities	46,978	41,252
Investing Activities:
Capital expenditures	(37,631)	(16,117)
Capital contributions to investments	(1,877)	(2,939)
Other	(35)	928
Cash Used for Investing Activities	(39,543)	(18,128)
Financing Activities:
Cash dividends paid on common stock	(11,181)	(10,660)
Repayment of long-term debt	(1,103)	(31,080)
Issuance of long-term debt	0	40,000
Repayments of short-term debt	(1,000)	0
Other	0	(289)
Cash Used for Financing Activities	(13,284)	(2,029)
Change in cash, cash equivalents, and restricted cash	(5,849)	21,095
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633
Cash, cash equivalents, and restricted cash at end of period	106,245	122,728
Significant noncash investing activities:
Accrued capital expenditures	$ 4,706	$ 6,804

Madison Gas and Electric Compa8

Madison Gas and Electric Company Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Items not affecting cash:
Depreciation and amortization	$ 13,623	$ 12,959
Deferred income taxes	(1,793)	(3,732)
Provision for doubtful receivables	264	254
Employee benefit plan (credit) cost	(561)	202
Equity earnings in MGE Transco	(2,451)	(2,608)
Other items	(152)	641
Changes in working capital items:
Decrease in current assets	25,208	27,124
Decrease in current liabilities	(7,771)	(9,318)
Cash contributions to pension and other postretirement plans	(1,319)	(7,168)
Other noncurrent items, net	(419)	1,526
Cash Provided by Operating Activities	46,978	41,252
Investing Activities:
Capital expenditures	(37,631)	(16,117)
Capital contributions to investments	(1,877)	(2,939)
Other	(35)	928
Cash Used for Investing Activities	(39,543)	(18,128)
Financing Activities:
Repayment of long-term debt	(1,103)	(31,080)
Issuance of long-term debt	0	40,000
Repayments of short-term debt	(1,000)	0
Other	0	(289)
Cash Used for Financing Activities	(13,284)	(2,029)
Change in cash, cash equivalents, and restricted cash	(5,849)	21,095
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633
Cash, cash equivalents, and restricted cash at end of period	106,245	122,728
Significant noncash investing activities:
Accrued capital expenditures	4,706	6,804
MGE [Member]
Operating Activities:
Net Income	18,256	18,183
Items not affecting cash:
Depreciation and amortization	13,623	12,959
Deferred income taxes	(2,229)	(4,242)
Provision for doubtful receivables	264	254
Employee benefit plan (credit) cost	(561)	202
Other items	(17)	690
Changes in working capital items:
Decrease in current assets	24,779	26,166
Decrease in current liabilities	(5,749)	(9,022)
Cash contributions to pension and other postretirement plans	(1,319)	(7,168)
Other noncurrent items, net	(468)	1,488
Cash Provided by Operating Activities	46,579	39,510
Investing Activities:
Capital expenditures	(37,631)	(16,117)
Other	(198)	158
Cash Used for Investing Activities	(37,829)	(15,959)
Financing Activities:
Cash dividends paid to parent by MGE	0	(15,000)
Distributions to parent from noncontrolling interest	(7,500)	(5,500)
Repayment of long-term debt	(1,103)	(31,080)
Issuance of long-term debt	0	40,000
Repayments of short-term debt	(1,000)	0
Other	0	(289)
Cash Used for Financing Activities	(9,603)	(11,869)
Change in cash, cash equivalents, and restricted cash	(853)	11,682
Cash, cash equivalents, and restricted cash at beginning of period	10,093	16,442
Cash, cash equivalents, and restricted cash at end of period	9,240	28,124
Significant noncash investing activities:
Accrued capital expenditures	$ 4,706	$ 6,804

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 101,157	$ 107,952
Accounts receivable, less reserves	43,307	42,299
Other accounts receivables, less reserves	5,851	9,440
Unbilled revenues	25,471	31,400
Materials and supplies, at average cost	23,554	22,614
Fuel for electric generation, at average cost	9,478	8,256
Stored natural gas, at average cost	3,686	12,923
Prepaid taxes	14,956	26,535
Regulatory assets - current	8,721	7,888
Assets held for sale	1,383	8,817
Other current assets	11,176	12,507
Total Current Assets	248,740	290,631
Other long-term receivables	4,449	4,788
Regulatory assets	140,218	142,567
Pension and other postretirement benefit asset	9,631	7,336
Other deferred assets and other	2,150	731
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,290,148	1,283,313
Construction work in progress	76,066	58,044
Total Property, Plant, and Equipment	1,366,214	1,341,357
Investments	72,176	67,772
Total Assets	1,843,578	1,855,182
Current Liabilities:
Long-term debt due within one year	24,477	24,452
Short-term debt	3,000	4,000
Accounts payable	35,026	47,645
Accrued interest and taxes	4,497	5,602
Accrued payroll related items	8,390	12,244
Regulatory liabilities - current	12,325	5,633
Derivative liabilities	8,950	8,180
Other current liabilities	9,565	18,758
Total Current Liabilities	106,230	126,514
Other Credits:
Deferred income taxes	224,309	225,130
Investment tax credit - deferred	893	918
Regulatory liabilities	157,890	154,153
Accrued pension and other postretirement benefits	69,030	69,088
Derivative liabilities	32,340	33,990
Other deferred liabilities and other	68,746	69,041
Total Other Credits	553,208	552,320
Capitalization:
Common shareholders equity	787,007	778,187
Long-term debt	397,133	398,161
Total Capitalization	1,184,140	1,176,348
Commitments and contingencies (see Footnote 9)
Total Liabilities and Capitalization	1,843,578	1,855,182
MGE [Member]
Current Assets:
Cash and cash equivalents	4,152	5,951
Accounts receivable, less reserves	43,307	42,299
Affiliate receivables	690	668
Other accounts receivables, less reserves	5,740	6,984
Unbilled revenues	25,471	31,400
Materials and supplies, at average cost	23,554	22,614
Fuel for electric generation, at average cost	9,478	8,256
Stored natural gas, at average cost	3,686	12,923
Prepaid taxes	13,893	25,073
Regulatory assets - current	8,721	7,888
Assets held for sale	1,383	8,817
Other current assets	11,162	12,484
Total Current Assets	151,237	185,357
Affiliate receivable long-term	3,574	3,707
Regulatory assets	140,218	142,567
Pension and other postretirement benefit asset	9,631	7,336
Other deferred assets and other	4,512	3,280
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,290,176	1,283,341
Construction work in progress	76,066	58,044
Total Property, Plant, and Equipment	1,366,242	1,341,385
Investments	409	409
Total Assets	1,675,823	1,684,041
Current Liabilities:
Long-term debt due within one year	24,477	24,452
Short-term debt	3,000	4,000
Accounts payable	35,026	47,614
Accrued interest and taxes	4,443	5,558
Accrued payroll related items	8,390	12,244
Regulatory liabilities - current	12,325	5,633
Derivative liabilities	8,950	8,180
Other current liabilities	9,557	16,749
Total Current Liabilities	106,168	124,430
Other Credits:
Deferred income taxes	200,093	201,486
Investment tax credit - deferred	893	918
Regulatory liabilities	157,890	154,153
Accrued pension and other postretirement benefits	69,030	69,088
Derivative liabilities	32,340	33,990
Other deferred liabilities and other	68,746	69,041
Total Other Credits	528,992	528,676
Capitalization:
Common shareholders equity	504,322	491,872
Noncontrolling interest	139,208	140,902
Total Equity	643,530	632,774
Long-term debt	397,133	398,161
Total Capitalization	1,040,663	1,030,935
Commitments and contingencies (see Footnote 9)
Total Liabilities and Capitalization	$ 1,675,823	$ 1,684,041

Consolidated Balance Sheets (10

Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Receivables, Net
Reserve for uncollectible accounts receivable	$ 2,804	$ 2,840
Reserve for uncollectible other accounts receivable	317	335
MGE [Member]
Receivables, Net
Reserve for uncollectible accounts receivable	2,804	2,840
Reserve for uncollectible other accounts receivable	$ 317	$ 335

MGE Energy Inc Consolidated S11

MGE Energy Inc Consolidated Statements of Common Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]
Beginning balance, shares at Dec. 31, 2016		34,668
Beginning balance, value at Dec. 31, 2016	$ 724,088	$ 34,668	$ 316,268	$ 372,950	$ 202
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	19,300			19,300
Other comprehensive income (loss)	97				97
Common stock dividends declared	(10,660)			(10,660)
Ending balance, shares at Mar. 31, 2017		34,668
Ending balance, value at Mar. 31, 2017	732,825	$ 34,668	316,268	381,590	299
Beginning balance, shares at Dec. 31, 2017		34,668
Beginning balance, value at Dec. 31, 2017	778,187	$ 34,668	316,268	426,874	377
Cumulative effect of new accounting principle at Dec. 31, 2017	0			377	(377)
Beginning balance, value - Adjusted at Dec. 31, 2017	778,187			427,251	0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	20,001			20,001
Common stock dividends declared	(11,181)			(11,181)
Ending balance, shares at Mar. 31, 2018		34,668
Ending balance, value at Mar. 31, 2018	$ 787,007	$ 34,668	$ 316,268	$ 436,071	$ 0

Madison Gas and Electric Comp12

Madison Gas and Electric Company Consolidated Statements of Common Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	MGE [Member]	Common Stock [Member]	Common Stock [Member]MGE [Member]	Additional Paid-In Capital [Member]MGE [Member]	Retained Earnings [Member]	Retained Earnings [Member]MGE [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]MGE [Member]	Noncontrolling Interest [Member]MGE [Member]
Beginning balance, shares at Dec. 31, 2016			34,668	17,348
Beginning balance, value at Dec. 31, 2016		$ 602,749		$ 17,348	$ 192,417		$ 277,300		$ 19	$ 115,665
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		18,183					12,794			5,389
Other comprehensive income (loss)	$ 97	(6)						$ 97	(6)
Cash dividends paid to parent by MGE		(15,000)					(15,000)
Distributions to parent from noncontrolling interest		(5,500)								(5,500)
Ending balance, shares at Mar. 31, 2017			34,668	17,348
Ending balance, value at Mar. 31, 2017		600,426		$ 17,348	192,417		275,094		13	115,554
Beginning balance, shares at Dec. 31, 2017			34,668	17,348
Beginning balance, value at Dec. 31, 2017		632,774		$ 17,348	192,417		282,135		(28)	140,902
Cumulative effect of new accounting principle at Dec. 31, 2017	0	0				$ 377	(28)	(377)	28
Beginning balance, value - Adjusted at Dec. 31, 2017	$ 778,187	632,774				$ 427,251	282,107	$ 0	0
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income		18,256					12,450			5,806
Distributions to parent from noncontrolling interest		(7,500)								(7,500)
Ending balance, shares at Mar. 31, 2018			34,668	17,348
Ending balance, value at Mar. 31, 2018		$ 643,530		$ 17,348	$ 192,417		$ 294,557		$ 0	$ 139,208

Consolidated Statements of Comm

Consolidated Statements of Common Equity (Unaudited) (Parentheticals) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Consolidated Statements of Common Equity
Dividends per share of common stock	$ 0.323	$ 0.308

Summary of Significant Accounti

Summary of Significant Accounting Principles	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Summary of Significant Accounting Policies. a. Basis of Presentation - MGE Energy and MGE. This report is a combined report of MGE Energy and MGE. References in this report to "MGE Energy " are to MGE Energy, Inc. and its subsidiaries. References in this report to "MGE" are to Madison Gas and Electric Company. MGE Power Elm Road and MGE Power West Campus own electric generating assets and lease those assets to MGE. Both entities are variable interest entities under applicable authoritative accounting guidance. MGE is considered the primary beneficiary of these entities as a result of contractual agreement s. As a result, MGE has consolidated MGE Power Elm Road and MGE Power West Campus . See Footnote 2 of Notes to Consolidated Financial Statements under Item 8, Financial Statements and Supplementary Data, of MGE Energy ' s and MGE ' s 2017 Annual Report on Fo rm 10-K (the 2017 Annual Report on Form 10-K). The accompanying consolidated financial statements as of March 31, 2018 , and for the three months ended , are unaudited, but include all adjustments that MGE Energy and MGE management consider necessary for a fair statement of their respective financial statements. All adjustments are of a normal, recurring nature except as otherwise disclosed. The year-end consolidated balance sheet information was derived from the audited balance sheet appearing in the 2017 Annual Report on Form 10-K, but does not include all disclosures required by accounting principles generally accepted in the United States of America . These notes should be read in conjunction with the financial statements and the notes on pages 54 through 1 03 of the 2017 Annual Report on Form 10-K . b. 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. MGE Energy MGE March 31, December 31, March 31, December 31, (In thousands) 2018 2017 2018 2017 Cash and cash equivalents $ 101,157 $ 107,952 $ 4,152 $ 5,951 Restricted cash 2,763 1,635 2,763 1,635 Receivable - margin account 2,325 2,507 2,325 2,507 Cash, cash equivalents, and restricted cash $ 106,245 $ 112,094 $ 9,240 $ 10,093 Cash Equivalents MGE Energy and MGE consider all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash MGE has certain cash accounts that are restricted to uses other than current operations and designated for a specific purpose. MGE's restricted cash accounts include cash held by trustees for certain employee benefits and cash deposits held by third parties. These are included in "Other current assets" on the consolidated balance s heets. Receivable – Margin Account Cash amounts held by counterparties as margin collateral for certain financial transactions are recorded as receivable – margin account in "Other current assets" on the consolidated balance sheets. The costs being hedged are fuel for electric generation, purchased power, and cost of gas sold. The following table presents the retrospective adjustments to cash flow amounts on MGE Energy ' s and MGE ' s consolidated statements of cash flows in accordance with the adoption of AS U 2016-18, Restricted Cash. Three Months Ended (In thousands) March 31, 2017 Cash provided by operating activities $ (1,035) Cash used for investing activities 387 Change in cash, cash equivalents, and restricted cash (648) Cash, cash equivalents, and restricted cash at beginning of period 5,674 Cash, cash equivalents, and restricted cash at end of period $ 5,026

Adoption of Accounting Principl

Adoption of Accounting Principles and Recently Issued Accounting Pronouncements	3 Months Ended
	Mar. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements	New Accounting Standards - MGE Energy and MGE. a. Recently Adopted R evenue from Contracts with Customers. T he FASB issued authoritative guidance within the c odification's Revenue Recognition topic that provides guidance on the recognition, measurement, and disclosure of revenue from contracts with customers. The new standard establishes a five step model for recognizing and measuring revenue from contracts with customers and replaces existing guidance on revenue recognition. The underlying p rinciple is that an entity will recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. This authoritative guidance became effective January 1, 2018, and MGE Energy and MGE adopt ed the standard upon the effective date. Adoption of this standard is permitted under one of two methods: the full retrospective method or the modified retrospec tive method. MGE Energy and MGE implement ed the standard using the modified retrospective method. The cumulative impact of this guidance on our financial statements is not material, except for additional footnote disclosures . See Footnote 3 for further information. Financial Instruments. In January 2016, the F ASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018, and required equity in vestments to be measured at fair value with changes in fair value recognized in net income rather than in other comprehensive income. As a result of this guidance, MGE Energy and MGE will no longer have other comprehensive income related to equity investme nts. This standard was applied using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the fiscal year of adoption. As of January 1, 2018, MGE Energy recorded a $0.4 million increase in retained earnings and a corresponding decrease in other comprehensive income, and MGE recorded less than a $0.1 million decrease in retained earnings and a corresponding increase in other comprehensive income, related to equity investments with in the scope of this standard. Restricted Cash. In November 2016, the FASB issued authoritative guidance within the codification's Statement of Cash Flows topic that provides guidance on the classification and presentation of changes in restricted cash within the statement of cash flows. Under the new guidance, reporting entities are required to explain the changes in the total of restricted and unrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, investing, or financing activities within the statement of cash flows, as appropriate based on the nature of the restriction. Al so under the new standard, reporting entities are required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restrictions of cash. This authoritative guidance became effective January 1, 2018. Upon the effective date, MGE Energy and MGE changed the presentation of restricted cash on the consolidated statements of cash flows to reflect the new accounting guidance retrospectively to all periods presented. See Footnote 1.b. for further information. Pension and Other Postretirement Benefits. In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net benefit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other com ponents of net benefit cost are required to be presented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense " increased and "Other income, net" increased $1.1 million for the three months ended March 31, 2017 . The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronounceme nt (whereas under previous GAAP, all components of net benefit cost were eligible for capitalization). See Footnote 6 for further information. b . Recently Issued Leases. In February 2016, the FASB issued authoritative guidance within the c odification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liab ility. Prior to the authoritative guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance , as applied by lessors , is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optional practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE plan to adopt this practical expedient. Man agement has begun utilizing a bottoms-up approach to analyze the impact of the standard on our lease portfolio. MGE Energy and MGE have been reviewing current accounting policies and procedures to identify potential differences in accounting treatment that would result from applying the requirements of the new standard to our existing lease portfolio. In addition, we are identifying appropriate changes to our business processes, systems, and controls to support recognition and disclosure requirements under the new standard. This authoritative guidance will become effective January 1, 2019, with early adoption permitted. MGE Energy and MGE anticipate adopting the standard upon the effective date. The new leasing standard requires entities to recognize and mea sure leases at the beginning of the earliest comparative period presented using a modified retrospective approach. MGE Energy and MGE are currently assessing the impact this pronouncement will have on our financial statements .

Revenue

Revenue	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer	Revenue - MGE Energy and MGE. Revenues disaggregated by revenue source were as follows: Three Months Ended (In thousands) March 31, Electric revenues 2018 2017 Residential $ 33,259 $ 33,353 Commercial (a) 47,452 50,164 Industrial 2,895 4,215 Other-retail/municipal 8,287 9,021 Total retail 91,893 96,753 Sales to the market 2,034 972 Other revenues 470 429 Adjustments to revenues (6) 170 Total electric revenues 94,391 98,324 Gas revenues Residential 36,551 33,903 Commercial/Industrial (a) 24,952 23,048 Total retail 61,503 56,951 Gas transportation 1,135 1,350 Other revenues 127 125 Total gas revenues 62,765 58,426 Non-regulated energy revenues 476 73 Total Operating Revenue (a) $ 157,632 $ 156,823 (a) In 2017, MGE had less than $0.1 million of revenues related to CNG vehicle fuel servicing. No revenue was recognized for fuel servicing by MGE Energy in 2017. Performance Obligations A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account. A contract's transaction price is allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The majority of MGE Ene rgy's and MGE's contracts have a single performance obligation. Retail Revenue (Residential, Commercial, Industrial, and Other Retail/Municipal) Retail revenue of electric and gas utility service represent MGE's core business activities. Tariffs are appro ved 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 co nsumes the commodities provided by MGE. MGE recognizes revenues as the commodity is delivered to customers. Meters are read on a systematic basis throughout the month based on established meter-reading schedules and the customer is subsequently billed for their services. At the end of the month, MGE accrues an estimate for the unbilled amount of commodities delivered to customers. The unbilled revenue estimate is based on daily system demand volumes, weather factors, estimated line losses, estimated custome r 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 out side a symmetrical cost tolerance band. Any over/under recovery of the actual costs in a given year is determined in the following year and is then reflected in future billings to electric retail customers. Over-collection of fuel-related costs that are ou tside the approved range will be recognized as a reduction of revenue. Prior to adoption of the new revenue recognition guidance, effective January 1, 2018, over-collected fuel-related costs were reflected in "Purchased Power" expense. Under-collection of these costs will continue to be recognized in "Purchased Power" expense in the consolidated statements of income of MGE Energy and MGE. The cumulative effects of these deferred amounts will be recorded in "Regulatory assets" or "Regulatory liabilities" on the consolidated balance sheets of MGE Energy and MGE until they are reflected in future billings to customers. See Footnote 10.b. for further information. MGE received a PSCW order to defer the over-collection of income tax expense collected in customer rates as a result of the Tax Cuts and Jobs Act (the Tax Act) reduction in the income tax rate to 21 percent. See Footnote 5 for further information. MGE has other cost recovery mechanisms, any over-collection of the difference between actual costs incurr ed 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 s ales 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 availability is provided to 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 written contracts under which MGE provides gas transportation services to customers whom have elected to purchase gas from a third party and have gas delivered via pipelines within MGE's service territory. Revenue is recognized as service is rendered or gas is de livered to customers. Tariffs are approved by the PSCW through a rate order and provide gas transportation customers with the standard terms and conditions, including pricing terms.

Investment in ATC and ATC Holdc

Investment in ATC and ATC Holdco	3 Months Ended
	Mar. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Investment in ATC and ATC Holdco	Investment in ATC and ATC Holdco - MGE Energy and MGE. 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 own ed by MGE Energy. ATC Holdco was formed by several members of ATC, including MGE Energy, to pursue electric tr ansmission development and investments outside of Wisconsin. The ownership interest in ATC Holdco is held by MGEE Transco, a wholly-owned subsidiary of MGE Energy . At March 31, 2018 , and December 31, 2017 , MGE Transco held a 3.6 % ownership interest in ATC. At March 31, 2018 , and December 31, 2017 , 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, res pectively, under the equity method of accounting. Equity earnings from investments are recorded as " Other income " on MGE Energy's consolidated statements of income. For the three months ended March 31, 2018 and 2017 , MGE Transco recorded the following : Three Months Ended March 31, (In thousands) 2018 2017 Equity earnings from investment in ATC $ 2,451 $ 2,608 Dividends from ATC (a) - - Capital contributions to ATC 710 1,420 (a ) MGE Transco recorded a $2.3 million and $2.1 million dividend receivable from ATC as of December 31, 2017 and 2016, respectively. A cash dividend was received in January of each of the proceeding years . ATC Holdco was formed in December 2016. In the near term, it is expected that ATC Holdco will be pursuing transmission development opportunities that typically have long development and investment lead times before becoming operational. For the three months ended March 31, 2018 and 2017 , MGEE Transco recorded capital contributions of $ 0.1 million and $0.2 million, respectively, to ATC Holdco . In April 2018, MGE Transco made a $ 1.1 million capital contribution to ATC and MGEE Tra nsco made a $ 0.1 million contribution to ATC Holdco. ATC ' s summarized financial data for the three months ended March 31, 2018 and 2017 , is as follows: Three Months Ended March 31, (In thousands) 2018 2017 Operating revenues $ 165,429 $ 174,669 Operating expenses (84,893) (82,697) Other income, net 111 682 Interest expense, net (27,762) (26,783) Earnings before members' income taxes $ 52,885 $ 65,871 MGE receives transmission and other related services from ATC. During the three months ended March 31, 2018 , MGE recorded $ 7.2 million for transmission services received compared to $ 9.2 million for the comparable period in 2017 . MGE also provides a variety of operational, maintenance, and project management services for ATC, which is reimbursed by ATC. As of March 31, 2018 , and December 31, 2017 , MGE had a receivable due from ATC of $ 0.2 million.

Taxes

Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Taxes	Taxes - MGE Energy and MGE . Effective Tax Rate. On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the Tax Act). The Tax Act makes broad and complex changes to the U.S. tax code, including the reduction in the U.S. federal corporate tax rate from 35 percent to 21 percent, effective January 1, 2018. MGE Energy and MGE recorded a provisional decrease in deferred tax assets and deferred tax liabilities as of December 31, 201 7. In accordance with Staff Accounting Bulletin 118, any subsequent adjustment to these amounts will be recorded in the quarter of 2018 when the analysis is complete. No adjustments have been recorded in the first quarter of 2018. Beginning January 1, 2018 , MGE began amortization of the regulated utility excess deferred taxes recognized using a normalization method of accounting. For the three months ended March 31, 2018, MGE recognized $0.6 million of excess deferred taxes as a reduction of revenue and a c orresponding incr ease in 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 determined by the PSCW. Customer rates approved for 2018 r eflect an income tax rate of 35 percent. MGE received a PSCW order to defer the over-collection of income tax expense as a result of the decrease in tax rate to 21 percent. As of March 31, 2018, MGE has deferred $ 3.3 million as a re gulatory liability and recorded a corresponding reduction in operating revenues. The PSCW reached a preliminary decision in April 2018 for the return of the over-collection of income tax expense. The preliminary decision includes a one-time bill credit in July of 2018 for the first six months of 2018 over-collection and a monthly bill credit beginning in August 2018 of the estimated remaining annual amount to be returned to customers. Any over/under recovery of the actual costs will be subject to the PSCW ' s annual review in the following year and is then reflected in future billings to retail customers. A final order is expected in May 2018 . 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 Three Months Ended March 31, 2018 2017 2018 2017 Statutory federal income tax rate 21.0 % 35.0 % 21.0 % 35.0 % State income taxes, net of federal benefit 6.4 % 5.3 % 6.0 % 5.1 % Amortized investment tax credits (0.1) % (0.1) % (0.1) % (0.1) % Credit for electricity from wind energy (0.5) % (1.8) % (0.5) % (2.0) % Domestic manufacturing deduction - % (1.3) % - % (1.4) % AFUDC equity, net (0.4) % (0.2) % (0.4) % (0.2) % Amortization of utility excess deferred tax - tax reform (a) (1.8) % - % (2.0) % - % Other, net, individually insignificant (0.4) % (0.2) % (0.6) % (0.2) % Effective income tax rate 24.2 % 36.7 % 23.4 % 36.2 % (a) Included are impacts of the Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting.

Pension and Other Postretiremen

Pension and Other Postretirement Plans	3 Months Ended
	Mar. 31, 2018
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Plans	Pension and Other Postretirement Plans - MGE Energy and MGE. MGE maintains qualified and nonqualified pension plans, health care, and life insurance benefits. Additionally, MGE has def ined co ntribution 401(k) benefit plans. 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 consolidat ed statements of income. Prior to January 1, 2018, a portion of all net periodic benefit cost components were capitalized within the consolidated balance sheets. The FASB issued authoritative guidance within the codification ' s Compensation-Retirement Benef its topic that, beginning January 1, 2018, only allows the service cost component of net periodic benefit cost to be eligible for capitalization within the consolidated balance sheets. MGE has regulatory treatment and recognizes regulatory assets or liabil ities for timing differences between when net periodic benefit costs are recovered and when costs are recognized. The following table presents the components of net periodic benefit costs recognized for the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, (In thousands) 2018 2017 Pension Benefits Components of net periodic benefit cost: Service cost $ 1,457 $ 1,332 Interest cost 3,208 3,119 Expected return on assets (6,568) (5,742) Amortization of: Prior service credit (11) (4) Actuarial loss 1,298 1,464 Net periodic benefit (credit) cost $ (616) $ 169 Postretirement Benefits Components of net periodic benefit cost: Service cost $ 332 $ 206 Interest cost 658 444 Expected return on assets (802) (472) Amortization of: Transition obligation 1 - Prior service credit (667) (436) Actuarial loss 128 129 Net periodic benefit (credit) cost $ (350) $ (129)

Equity and Financing Arrangemen

Equity and Financing Arrangements	3 Months Ended
	Mar. 31, 2018
Equity and Financing Arrangements Disclosure [Abstract]
Equity and Financing Arrangements	Equity and Financing Arrangements - MGE Energy. a. Common Stock. MGE Energy sells shares of its common stock through its Stock Plan. Those shares may be newly issued shares or shares that MGE Energy has purchased in the open market for resale to participants in the Stock Plan. All sales under the Stock Plan are covered by a shelf registration statement that MGE Energy filed with the SEC. For both the three months ended March 31, 2018 and 2017 , MGE Energy did not issue any new shares of common s tock under the Stock Plan. b. Dilutive Shares Calculation. MGE Energy does not have any stock option or stock award programs or any dilutive securities.

Share-Based Compensation

Share-Based Compensation	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation - MGE Energy and MGE. Under MGE Energy ' s Director Incentive Plan and Performance Unit Plan, non-employee directors and eligible employees may receive performance units that entitle the holder to receive a cash payment equal to the value of a designated number of shares of MGE Energy's common stock, plus dividend equivalent payments thereon, at the end of the set performance period. In 2018 , 5,810 units were granted under the Director Incentive Plan and are subject to a three-year graded vesting schedule and 17,830 units were granted under the Performance Unit Plan and are subject to a five-year graded vesting schedule. On the grant d ate, the cost of the director or employee services received in exchange for a performance unit award is measured based on the current market value of MGE Energy common stock. The fair value of the awards is re-measured quarterly, including at March 31, 2018 , as required by applicable accounting standards. Changes in fair value as well as the original grant are recognized as compensation cost. Since this amount is re-measured throughout the vesting period, the compensation cost is subject to variability. For nonretirement eligible employees under the Performance Unit Plan, stock based compensation costs are acc rued 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. During the three months ended March 31, 2018 , MGE recorded $ 0.2 million in compensation expense as a result of awards under the plans compared to $ 0.5 million for the comparable period in 2017 . In January 2018 , cash payments of $ 1.6 million were distributed relating to awards that were granted under the plans. No forfeitures of units occurred during the three months ended March 31, 2018 and 2017 . At March 31, 2018 , $ 4.8 million of outstanding awards are vested, and of this amount, no cash settlements have occurred.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies . a. Environmental - MGE Energy and MGE . MGE Energy and MGE are subject to frequently changing local, state, and federal regulations concerning air quality, water quality, land use, threatened and endangered species, hazardous materials handling, and solid waste disposal. These regulations affect the manner in which they conduct their operations, the costs of those operations, as well as capital and operating expenditures. Several of these environmental rules are subje ct to legal challenges, reconsideration and/or other uncertainties. Regulatory initiatives, proposed rules, and court challenges to adopted rules, have the potential to have a material effect on our capital expenditures and operating costs. Management beli eves compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects. These initiatives, proposed rules, and court challenges include : • The EPA's published water effluent limitations guidelines and stan dards for steam electric power plants, which focus on the reduction of metals and other pollutants in wastewater from new and existing power plants, such as the coal-burning plants at Columbia and the Elm Road Units. • The EPA's cooling water intake rules, which require cooling water intake structures at electric power plants, such as our WCCF, Blount, and Columbia plants, meet best available technology standards so that mortality from entrainment (drawing aquatic life into a plant's cooling system) a nd impingement (trapping aquatic life on screens) are reduced. • Greenhouse Gas (GHG) reduction guidelines and approval criteria established under the Clean Air Act for states to use in developing plans to control GHG emissions from existing fossil fuel-f ired electric generating units (EGUs) and systems (the Clean Power Plan, or CPP). Implementation of the CPP is expected to have a direct impact on existing coal and natural gas fired generating units, including possible changes in dispatch and additional o perating costs. In May 2017, the EPA requested the U.S. Court of Appeals for the D.C. Circuit to put on hold, indefinitely, any ongoing challenges to the CPP while the EPA reviews the rule and undertakes any potential rulemaking. In October 2017, the EPA p ublished a proposed rule announcing the EPA's intention to repeal the CPP and has sought public comment on whether to replace the rule, and if so how. In December 201 7, the EPA published an Advance Notice of Public Rulemaking (ANPR) to solicit information from the public as it considers a future rule to limit GHG emissions from electric generating units. Given the pending legal proceedings, and the ANPR, the nature and timing of any final requirements to control GHG emissions is subject to uncertainty. If the CPP remains substantially in its present form, it is expected to have a material impact on MGE. MGE will continue to monitor developments with this proposed rule. • The EPA's rule to regulate ambient levels of a pollutant through the Ozone National A mbient Air Quality Standards (NAAQS). The EPA issued final designations on May 1, 2018, which designated the northeast portion of Milwaukee County as nonattainment. The Elm Road Units are located outside the designated nonattainment area. MGE expects that Ozone NAAQS will not have a material effect on its existing plants based on final designations . The State of Wisconsin has joined a lawsuit filed by several states challenging the EPA's new ozone standard, alleging that the new standard is not attainabl e and the EPA is not properly considering background levels in setting its ozone attainment levels. The lawsuit has been stayed at the request of the EPA; however the significance of the challenge , as it might relate to MGE, is now diminished with the final ozone designations . • R ules regulating nitrogen oxide ( NO x ) and sulfur dioxide ( SO 2 ) emissions, including the Cross State Air Pollution Rule (CSAPR) and Clean Air Visibility Rule (CAVR). At this time, regulatory obligations, compliance strategies, and costs remain uncertain due to uncertainties surrounding the ongoing implementation of Phase II of CSAPR and the continued legal challenges surrounding CSAPR and CAVR. • The EPA's Coal Combustion Residuals Rule (CCR) , which regulates coal ash as a solid waste, and defines what ash u se activities would be considered generally exempt beneficial reuse of coal ash. The rule also regulates landfills, ash ponds, and other surface impoundments for coal combustion residuals by regulating their design, location, monitoring, and operation. Rev iew of our Elm Road Units has indicated that the costs to comply with this rule are not expected to be significant. Columbia's operator has completed a review of their system and has determined that an onsite ash pond will need to be closed by 2023 and rep lace it with a dry ash handling system. The dry ash handling system installation is planned for 2020-2021. 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. Management believes compliance costs will be recovered in future rates based on pre vious treatment of en vironmental compliance projects . 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 . c. Purchase Contracts - MGE Energy and MGE. The following table shows MGE Energy and MGE 's future commitments related to purchase contracts as of March 31, 2018 : (In thousands) 2018 2019 2020 2021 2022 Thereafter Saratoga wind $ 13,578 $ 858 $ 2,266 $ 1,775 $ 1,784 $ 4,429 In December 2017, the PSCW authorized construction of a 66MW wind farm, consisting of 33 turbines, located near Saratoga, Iowa. MGE received specific approval to recover 100% AFUDC on the project. As of March 31, 2018, MGE has incurred $23.3 million of capital expenditures. Construction of the project is expected to be completed by the end of 2018, with an estimated capital cost of $108 million.

Rate Matters

Rate Matters	3 Months Ended
	Mar. 31, 2018
Regulated Operations [Abstract]
Rate Matters	Rate Matters - MGE Energy and MGE. a. Rate P roceedings. In December 2016, the PSCW authorized MGE, effective January 1, 2017, to decrease 2017 rates for retail electric customers by 0.8 % or $ 3.3 million on an annual basis and to increase rates for retail gas customers by 1.9 % or $ 3.1 million on an annual basis. The decrease in retail electric rates was attributable to declining fuel and purchased power co sts. The increase in retail gas rates covers costs associated with MGE's natural gas system infrastructure improvements. The authorized return on common stock equity for 2017 was 9.8 % based on a capital structure consisting of 57.2 % common equity . The PSCW also approved MGE's request to extend the current accounting treatment for transmission related costs through 2018. This accounting treatment allows MGE to reflect any differential between transmi ssion costs reflected in rates and actual costs incurred in its next rate case filing. b. Fuel R ules. Fuel rules require the PSCW and Wisconsin utilities to defer electric fuel-related costs that fall outside a symmetrical cost tolerance band around the amount approved for a utility in its annual fuel proceedings. Any over/under recovery of the actual costs is determined in the following year and is then reflected in future billings to electric retail customers. The fuel rules bandwidth is currently set at plus or minus 2 %. Under fuel rules, MGE would defer costs, les s any excess revenues, if its actual electric fuel costs exceeded 102 % of the electric fuel costs allowed in its latest rate order. Excess revenues are defined as revenues in the year in question that provide MGE with a greater ret urn on common equity than authorized by the PSCW in MGE's latest rate order. Conversely, MGE is required to defer the benefit of lower costs if actual electric fuel costs were less than 98 % of the electric fuel costs allowed in th at order. In July 2017, the PSCW issued a final order in the fuel rules proceedings requiring MGE to refund additional fuel savings realized during 2015 and 2016 to its retail electric customers over a one-month period. In October 2017, MGE returned $ 6.2 million to customers through bill credits. In December 2017, the PSCW approved a surcharge for 2018 electric fuel-related costs. The surcharge will increase electric retail revenue in 2018 by $ 0.5 million or 0.1 %. As of March 31, 2018 , MGE has deferred $ 1.5 million of 2018 fuel saving s. The 2018 fuel savings will be subject to the PSCW ' s annual review of 2018 fuel costs, expected to be completed in 2019. As of March 31, 2017 , MGE had deferred $ 1.1 million of 2017 fuel savings .

Derivative and Hedging Instrume

Derivative and Hedging Instruments	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and Hedging Instruments	Derivative and Hedging Instruments - MGE Energy and MGE. a. Purpose. As part of its regular operations, MGE enters into contracts, including options, swaps, futures, forwards, and other contractual commitments, to manage its exposure to commodity prices. To the extent that these contracts are derivatives, MGE assesses whether or no t 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 conducte d 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 ca n be hedged is four years. If the derivative qualifies for regulatory deferral, the derivatives are marked to fair value and are offset with a corresponding regulatory asset or liability depending on whether the derivative is in a net loss or net gain posi tion, respectively. The deferred gain or loss is recognized in earnings in the delivery month applicable to the instrument. Gains and losses related to hedges qualifying for regulatory treatment are recoverable in gas rates through the PGA or in electric r ates as a component of the fuel rules mechanism . b. Notional Amounts. The gross notional volume of open derivatives is as follows: March 31, 2018 December 31, 2017 Commodity derivative contracts 538,050 MWh 552,310 MWh Commodity derivative contracts 3,270,000 Dth 5,460,000 Dth FTRs 886 MW 2,226 MW PPA 2,500 MW 2,650 MW c . Financial Statement Presentation . MGE purchases and sells exchange-traded and over-the-counter options, swaps, and future contracts. These arrangements are primarily entered into to help stabilize the price risk associated with gas or power purchases. These transactions are employed by both MGE ' s gas and electric segments. Additionally, as a result of the firm transmission agreements that MGE holds on electricity transmission paths in the MISO market, MGE holds financial transmission rights (FTRs). An FTR is a financial instrument that entitles the holder to a stream of revenues or charges based on the differences in hourly day-ahead energy prices between two p oints on the transmission grid. The fair values of these instruments are offset with a corresp onding regulatory asset/liability depending on whether they are in a net loss/gain position. Depending on the nature of the instrument, the gain or loss associated with these transactions will be reflected as cost of gas sold, fuel for electric generation, or purchased power expense in the delivery month applicable to the instrument. At March 31, 2018 , and December 31 , 2017 , the fair value of exchange traded derivatives and FTRs exceeded their cost basis by $ 0.1 million and $ 0.2 million, respectively. MGE is a party to a purchased power agreement that provides MGE with firm capacity and energy during a base term from June 1, 2012, through May 31, 2022. The agreement also allows MGE an option to extend th e 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 sheet s . However, the derivative qualifies for regulatory deferral and is recognized with a corresponding regulatory asset or liability depending on whether the fair value is in a loss or gain position. The fair value of the contract at March 31, 2018 , and Dec ember 31, 2017 , reflects a loss position of $ 41.3 million and $ 42.2 million, respectively. The actual cost will be recognized in purchased power e xpense in the month of purchase. The following table summarizes the fair v alue of the derivative instruments on the consolidated balance sheet s . All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreemen t as well as the netting of collatera l. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as well as the netting of collatera l . As of March 31, 2018 , and December 31, 2017 , the receiv able margin account balance of $ 2.3 million and $ 2.5 million, respectively, is shown net of any collateral posted against derivative positions. Derivative Derivative (In thousands) Assets Liabilities Balance Sheet Location March 31, 2018 Commodity derivative contracts (a) $ 403 $ 294 Derivative liability (current) (b) Commodity derivative contracts (a) 9 189 Derivative liability (long-term) FTRs 120 - Other current assets PPA N/A 8,950 Derivative liability (current) PPA N/A 32,340 Derivative liability (long-term) December 31, 2017 Commodity derivative contracts (a) $ 566 $ 603 Derivative liability (current) (b) Commodity derivative contracts (a) 110 190 Derivative liability (long-term) FTRs 329 - Other current assets PPA N/A 8,180 Derivative liability (current) PPA N/A 33,990 Derivative liability (long-term) (a ) As of March 31, 2018 , and December 31, 2017 , collateral of $0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. (b) As of March 31, 2018 , and December 31, 2017 , $0.1 million was presented as other current assets on the consolidated balance sheets. The foll owing tables show the ef fect of netting arrangements for recognized derivative assets and liabilities that are subject to a master netting arr angement or simil ar 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 March 31, 2018 Commodity derivative contracts $ 412 $ (390) $ - $ 22 FTRs 120 - - 120 December 31, 2017 Commodity derivative contracts $ 676 $ (654) $ - $ 22 FTRs 329 - - 329 Offsetting of Derivative Liabilities (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets March 31, 2018 Commodity derivative contracts $ 483 $ (390) $ (93) $ - PPA 41,290 - - 41,290 December 31, 2017 Commodity derivative contracts $ 793 $ (654) $ (139) $ - PPA 42,170 - - 42,170 The following table s summarize the unrealized and realized gains (losses) related to the derivative instruments on the consolidated balance sheet s at March 31, 2018 and 2017 , and the consolidated income statement s for the three months ended March 31, 2018 and 2017 . 2018 2017 (In thousands) Current and Long-Term Regulatory Asset Other Current Assets Current and Long-Term Regulatory Asset Other Current Assets Three Months Ended March 31: Balance at January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized loss (gain) 128 - (689) - Realized (loss) gain reclassified to a deferred account (158) 158 (78) 78 Realized loss reclassified to income statement (687) (645) (441) (166) Balance at March 31, $ 41,241 $ 319 $ 48,073 $ 142 Realized losses (gains) 2018 2017 (In thousands) Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Three Months Ended March 31: Commodity derivative contracts $ 374 $ 615 $ 385 $ 146 FTRs (175) - (685) - PPA 518 - 761 - MGE's commodity derivativ e contracts, FTRs, and PPA are subject to regulatory deferral. These derivatives are marked to fair value and are offset with a corresponding regulatory asset or liability. Realized gains and losses are deferred on the consolidated balance sheet s and are recognized in earnings in the delivery month applicable to the instrument. As a result of the above described treatment, there are no unrealized gains or losses that flow through earnings. The PPA has a provision that may require MGE to post collateral if MGE's debt rating falls below investment grade (i.e., below BBB-). The amount of collateral that it may be required to post varies from $ 20.0 million to $ 40.0 million, depending on MGE's nominated capacity amount. As of March 31, 2018 , no collateral is required to be, or has been, posted. Certain counterparties extend MGE a credit limit. If MGE exceeds these limits, the counterparties may require collateral to be pos ted. As of March 31, 2018 , and December 31, 2017 , certain counterparties were in a net liability of $0.1 million. 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 March 31, 2018 , no counterparties have defaulted.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments - MGE Energy and MGE. Fair value is defined as the price that would be received to sell an asset or would be paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. The accounting standard clarifies that fair value should be based on the assumptions market participants would use when pricing the asset or liability including ass umptions about risk. The standard also establishes a three level fair value hierarchy based upon the observability of the assumptions used and requires the use of observable market data when available. The levels are: Level 1 - Pricing inputs are quoted p rices within active markets for identical assets or liabilities. Level 2 - Pricing inputs are quoted prices within active markets for similar assets or liabilities; quoted prices for identical or similar instruments in markets that are not active; and mod el-derived valuations that are correlated with or otherwise verifiable by observable market data. Level 3 - Pricing inputs are unobservable and reflect management ' s best estimate of what market participants would use in pricing the asset or liability. a. Fair Value of Financial Assets and Liabilities Recorded at the Carrying Amount. At March 31, 2018 , and December 31, 2017 , 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 at March 31, 2018 , and December 31, 2017 . 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: March 31, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 101,157 $ 101,157 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper 3,000 3,000 4,000 4,000 Long-term debt (a) 425,780 462,151 426,883 475,282 MGE Assets: Cash and cash equivalents $ 4,152 $ 4,152 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper 3,000 3,000 4,000 4,000 Long-term debt (a) 425,780 462,151 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.2 million and $4.3 million at March 31, 2018, and December 31, 2017, respectively. b. Recurring Fair Value Measurements. The following table presents the balances of assets and liabilities measured at fair value on a recurr ing basis . Fair Value as of March 31, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 531 $ 284 $ - $ 247 Exchange-traded investments 855 855 - - Total Assets $ 1,386 $ 1,139 $ - $ 247 Liabilities: Derivatives, net (b) $ 41,772 $ 62 $ - $ 41,710 Deferred compensation 3,110 - 3,110 - Total Liabilities $ 44,882 $ 62 $ 3,110 $ 41,710 MGE Assets: Derivatives, net $ 531 $ 284 $ - $ 247 Exchange-traded investments 65 65 - - Total Assets $ 596 $ 349 $ - $ 247 Liabilities: Derivatives, net (b) $ 41,772 $ 62 $ - $ 41,710 Deferred compensation 3,110 - 3,110 - Total Liabilities $ 44,882 $ 62 $ 3,110 $ 41,710 Fair Value as of December 31, 2017 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 792 792 - - Total Assets $ 1,797 $ 1,070 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 MGE Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 64 64 - - Total Assets $ 1,069 $ 342 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 (b) These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of March 31, 2018, and December 31, 2017. No transfers were made in or out of Level 1 or Level 2 for the three months ended March 31, 2018 . I nvestments include exchange-traded investment securities valued using quoted prices on active exchanges and are therefore classified as Level 1. Derivatives include exchange-traded derivative c ontracts, over-the-counter transactions, a purchased power agreement, and financial transmission rights ( FTRs ) . Most exchange-traded derivative contracts are valued based on unadjusted quoted prices in active markets and are therefore class ified 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-cou nter 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 sim ilar instruments in a closed market with limited data available and are therefore classified as Level 3. The purchased power agreement (see Footnote 11 ) was valued using an internally-developed pricing model and therefore is classified as Level 3. The mod el 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 histor ical 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 lowe red, 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 li quidity, 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 March 31, 2018 December 31, 2017 Basis adjustment: On peak 91.7 % 92.3 % Off peak 93.1 % 94.1 % Counterparty fuel mix: Internal generation 50% - 75% 55% - 75% Purchased power 50% - 25% 45% - 25% The deferred compensation plan allows participants to defer certain cash compensation into a notional investment account. These amounts are included within other deferred liabilities in the consolidated balance sheets of MGE Energy and MGE . The notional investments earn interest based upon the semiannual rate of U.S. Treasury Bills having a 26 w eek maturity increased by 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 . The following table summarizes the changes in Level 3 commodity derivative assets and liabilities measured at fair value on a recurring b asis . Three Months Ended March 31, (In thousands) 2018 2017 Beginning balance $ (42,026) $ (50,306) Realized and unrealized gains (losses): Included in regulatory assets 563 1,953 Included in other comprehensive income - - Included in earnings (542) (586) Included in current assets (173) 125 Purchases 5,834 5,996 Sales - - Issuances - - Settlements (5,119) (5,536) Transfers in and/or out of Level 3 - - Balance as of March 31, $ (41,463) $ (48,354) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held at March 31, (c) $ - $ - The following table presents total realized and unrealized losses included in income for Level 3 assets and liabilities measured at fair value on a recurring basis (c ) . Three Months Ended March 31, (In thousands) 2018 2017 Purchased power expense $ (723) $ (431) Cost of gas sold expense 181 (155) Total $ (542) $ (586) (c ) 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.

Joint Plant Ownership

Joint Plant Ownership	3 Months Ended
	Mar. 31, 2018
Regulated Operations [Abstract]
Joint Plant Ownership	Joint Plant Ownership - MGE Energy and MGE. Columbia . In 2016, MGE and WPL negotiated an amendment to the existing Columbia joint operating agreement, that has been approved by the PSCW, under which MGE will have the option to reduce its obligation to pay certain capital expenditures (other than SCR-related expenditures) at Columbia in exchange for a proportional reduction in MGE's ownership in Columbia. On January 1 of each year, beginning in 2017 and ending June 1, 2020, the ownership percentage w ill be adjusted, through a partial sale, based on the amount of capital expenditures foregone. In June 2017 , the FERC approved the ownership transfer in Columbia, effective January 1, 2017 . During 2017 , MGE accrued $ 8.8 million of 201 7 capital expenditures that MGE has forgone as part of the ownership transfer agreement with WPL. As of December 31, 2017 , MGE classified $ 8.8 million of Columbia assets as held-for-sale on the consolidated balance sheets. In Januar y 201 8 , MGE reduced its ownership interest in Columbia from 20.4 % to 19.4 % through the partial sale of plant assets to WPL. During three months ended March 31, 2018 , MGE accrued $ 1.4 million of 201 8 capital expenditures that MGE has forgone subject to t he ownership transfer agreement . As of March 31, 2018 , MGE classified $ 1.4 million of Columbia assets as held-for-sale on the consolidated balance sheets. The assets recognized as held-for-sale are subject to a partial sale of plant assets to WPL, expected to occur in January 2019.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information - MGE Energy and MGE. MGE Energy operates in the following business segments: electric utility, gas utility, nonregulated energy, transmission investment, and all other. See the 2017 Annual Report on Form 10-K for additional discussion of each of these segments. The following table s show segment information for MGE Energy ' s operations for the indicated periods : (In thousands) MGE Energy Electric Gas Non-regulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Consolidated Total Three Months Ended March 31, 2018 Operating revenues $ 94,391 $ 62,765 $ 476 $ - $ - $ - $ 157,632 Interdepartmental revenues 31 4,347 9,820 - - (14,198) - Total operating revenues 94,422 67,112 10,296 - - (14,198) 157,632 Depreciation and amortization (9,378) (2,395) (1,850) - - - (13,623) Other operating expenses (76,575) (55,195) (43) (3) (203) 14,198 (117,821) Operating income (loss) 8,469 9,522 8,403 (3) (203) - 26,188 Other income, net 1,730 766 - 2,372 51 - 4,919 Interest (expense) income, net (2,867) (839) (1,348) - 315 - (4,739) Income before taxes 7,332 9,449 7,055 2,369 163 - 26,368 Income tax provision (1,200) (2,458) (1,922) (648) (139) - (6,367) Net income $ 6,132 $ 6,991 $ 5,133 $ 1,721 $ 24 $ - $ 20,001 Three Months Ended March 31, 2017 Operating revenues $ 98,324 $ 58,426 $ 73 $ - $ - $ - $ 156,823 Interdepartmental revenues (105) 4,394 11,070 - - (15,359) - Total operating revenues 98,219 62,820 11,143 - - (15,359) 156,823 Depreciation and amortization (8,900) (2,213) (1,846) - - - (12,959) Other operating expenses (a) (76,006) (50,971) (41) - (369) 15,359 (112,028) Operating income (loss) 13,313 9,636 9,256 - (369) - 31,836 Other income (deductions), net (a) 870 399 - 2,478 (222) - 3,525 Interest (expense) income, net (2,776) (799) (1,407) - 88 - (4,894) Income (loss) before taxes 11,407 9,236 7,849 2,478 (503) - 30,467 Income tax (provision) benefit (3,454) (3,704) (3,151) (997) 139 - (11,167) Net income (loss) $ 7,953 $ 5,532 $ 4,698 $ 1,481 $ (364) $ - $ 19,300 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information. The following table s show segment information for MGE ' s operations for the indicated periods : (In thousands) MGE Electric Gas Non-regulated Energy Consolidation/ Elimination Entries Consolidated Total Three Months Ended March 31, 2018 Operating revenues $ 94,391 $ 62,765 $ 476 $ - $ 157,632 Interdepartmental revenues 31 4,347 9,820 (14,198) - Total operating revenues 94,422 67,112 10,296 (14,198) 157,632 Depreciation and amortization (9,378) (2,395) (1,850) - (13,623) Other operating expenses (b) (77,731) (57,641) (1,965) 14,198 (123,139) Operating income (b) 7,313 7,076 6,481 - 20,870 Other income, net (b) 1,686 754 - - 2,440 Interest expense, net (2,867) (839) (1,348) - (5,054) Net income 6,132 6,991 5,133 - 18,256 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,806) (5,806) Net income attributable to MGE $ 6,132 $ 6,991 $ 5,133 $ (5,806) $ 12,450 Three Months Ended March 31, 2017 Operating revenues $ 98,328 $ 58,435 $ 73 $ - $ 156,836 Interdepartmental revenues (109) 4,385 11,070 (15,346) - Total operating revenues 98,219 62,820 11,143 (15,346) 156,836 Depreciation and amortization (8,900) (2,213) (1,846) - (12,959) Other operating expenses (a), (b) (79,426) (54,665) (3,192) 15,346 (121,937) Operating income (b) 9,893 5,942 6,105 - 21,940 Other income, net (a), (b) 836 389 - - 1,225 Interest expense, net (2,776) (799) (1,407) - (4,982) Net income 7,953 5,532 4,698 - 18,183 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,389) (5,389) Net income attributable to MGE $ 7,953 $ 5,532 $ 4,698 $ (5,389) $ 12,794 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information. (b) Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.

Significant Accounting Policies

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Variable Interest Entities	MGE Power Elm Road and MGE Power West Campus own electric generating assets and lease those assets to MGE. Both entities are variable interest entities under applicable authoritative accounting guidance. MGE is considered the primary beneficiary of these entities as a result of contractual agreement s. As a result, MGE has consolidated MGE Power Elm Road and MGE Power West Campus .
Cash and Cash Equivalents	Cash Equivalents MGE Energy and MGE consider all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents.
Restricted Cash	Restricted Cash MGE has certain cash accounts that are restricted to uses other than current operations and designated for a specific purpose. MGE's restricted cash accounts include cash held by trustees for certain employee benefits and cash deposits held by third parties. These are included in "Other current assets" on the consolidated balance s heets.
Receivable Margin Account	Receivable – Margin Account Cash amounts held by counterparties as margin collateral for certain financial transactions are recorded as receivable – margin account in "Other current assets" on the consolidated balance sheets. The costs being hedged are fuel for electric generation, purchased power, and cost of gas sold.
New Accounting Pronouncements Disclosure	New Accounting Standards - MGE Energy and MGE. a. Recently Adopted R evenue from Contracts with Customers. T he FASB issued authoritative guidance within the c odification's Revenue Recognition topic that provides guidance on the recognition, measurement, and disclosure of revenue from contracts with customers. The new standard establishes a five step model for recognizing and measuring revenue from contracts with customers and replaces existing guidance on revenue recognition. The underlying p rinciple is that an entity will recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. This authoritative guidance became effective January 1, 2018, and MGE Energy and MGE adopt ed the standard upon the effective date. Adoption of this standard is permitted under one of two methods: the full retrospective method or the modified retrospec tive method. MGE Energy and MGE implement ed the standard using the modified retrospective method. The cumulative impact of this guidance on our financial statements is not material, except for additional footnote disclosures . See Footnote 3 for further information. Financial Instruments. In January 2016, the F ASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018, and required equity in vestments to be measured at fair value with changes in fair value recognized in net income rather than in other comprehensive income. As a result of this guidance, MGE Energy and MGE will no longer have other comprehensive income related to equity investme nts. This standard was applied using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the fiscal year of adoption. As of January 1, 2018, MGE Energy recorded a $0.4 million increase in retained earnings and a corresponding decrease in other comprehensive income, and MGE recorded less than a $0.1 million decrease in retained earnings and a corresponding increase in other comprehensive income, related to equity investments with in the scope of this standard. Restricted Cash. In November 2016, the FASB issued authoritative guidance within the codification's Statement of Cash Flows topic that provides guidance on the classification and presentation of changes in restricted cash within the statement of cash flows. Under the new guidance, reporting entities are required to explain the changes in the total of restricted and unrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, investing, or financing activities within the statement of cash flows, as appropriate based on the nature of the restriction. Al so under the new standard, reporting entities are required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restrictions of cash. This authoritative guidance became effective January 1, 2018. Upon the effective date, MGE Energy and MGE changed the presentation of restricted cash on the consolidated statements of cash flows to reflect the new accounting guidance retrospectively to all periods presented. See Footnote 1.b. for further information. Pension and Other Postretirement Benefits. In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net benefit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other com ponents of net benefit cost are required to be presented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense " increased and "Other income, net" increased $1.1 million for the three months ended March 31, 2017 . The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronounceme nt (whereas under previous GAAP, all components of net benefit cost were eligible for capitalization). See Footnote 6 for further information. b . Recently Issued Leases. In February 2016, the FASB issued authoritative guidance within the c odification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liab ility. Prior to the authoritative guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance , as applied by lessors , is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optional practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE plan to adopt this practical expedient. Man agement has begun utilizing a bottoms-up approach to analyze the impact of the standard on our lease portfolio. MGE Energy and MGE have been reviewing current accounting policies and procedures to identify potential differences in accounting treatment that would result from applying the requirements of the new standard to our existing lease portfolio. In addition, we are identifying appropriate changes to our business processes, systems, and controls to support recognition and disclosure requirements under the new standard. This authoritative guidance will become effective January 1, 2019, with early adoption permitted. MGE Energy and MGE anticipate adopting the standard upon the effective date. The new leasing standard requires entities to recognize and mea sure leases at the beginning of the earliest comparative period presented using a modified retrospective approach. MGE Energy and MGE are currently assessing the impact this pronouncement will have on our financial statements .
Investments - ATC and ATC Holdco	MGE Transco and MGEE Transco have accounted for their investment in ATC and ATC Holdco, res pectively, under the equity method of accounting.
Pension and Other Postretirement Benefit Plan Assets	MGE maintains qualified and nonqualified pension plans, health care, and life insurance benefits. Additionally, MGE has def ined co ntribution 401(k) benefit plans. 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 consolidat ed statements of income.
Common Stock	MGE Energy sells shares of its common stock through its Stock Plan. Those shares may be newly issued shares or shares that MGE Energy has purchased in the open market for resale to participants in the Stock Plan. All sales under the Stock Plan are covered by a shelf registration statement that MGE Energy filed with the SEC.
Share-based Compensation	Under MGE Energy ' s Director Incentive Plan and Performance Unit Plan, non-employee directors and eligible employees may receive performance units that entitle the holder to receive a cash payment equal to the value of a designated number of shares of MGE Energy's common stock, plus dividend equivalent payments thereon, at the end of the set performance period. In 2018 , 5,810 units were granted under the Director Incentive Plan and are subject to a three-year graded vesting schedule and 17,830 units were granted under the Performance Unit Plan and are subject to a five-year graded vesting schedule. On the grant d ate, the cost of the director or employee services received in exchange for a performance unit award is measured based on the current market value of MGE Energy common stock. The fair value of the awards is re-measured quarterly, including at March 31, 2018 , as required by applicable accounting standards. Changes in fair value as well as the original grant are recognized as compensation cost. Since this amount is re-measured throughout the vesting period, the compensation cost is subject to variability. For nonretirement eligible employees under the Performance Unit Plan, stock based compensation costs are acc rued 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.
Wisconsin Fuel Rules	Fuel rules require the PSCW and Wisconsin utilities to defer electric fuel-related costs that fall outside a symmetrical cost tolerance band around the amount approved for a utility in its annual fuel proceedings. Any over/under recovery of the actual costs is determined in the following year and is then reflected in future billings to electric retail customers. The fuel rules bandwidth is currently set at plus or minus 2 %. Under fuel rules, MGE would defer costs, les s any excess revenues, if its actual electric fuel costs exceeded 102 % of the electric fuel costs allowed in its latest rate order. Excess revenues are defined as revenues in the year in question that provide MGE with a greater ret urn on common equity than authorized by the PSCW in MGE's latest rate order. Conversely, MGE is required to defer the benefit of lower costs if actual electric fuel costs were less than 98 % of the electric fuel costs allowed in th at order.
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 no t 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 conducte d 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 ca n be hedged is four years. If the derivative qualifies for regulatory deferral, the derivatives are marked to fair value and are offset with a corresponding regulatory asset or liability depending on whether the derivative is in a net loss or net gain posi tion, respectively. The deferred gain or loss is recognized in earnings in the delivery month applicable to the instrument. Gains and losses related to hedges qualifying for regulatory treatment are recoverable in gas rates through the PGA or in electric r ates as a component of the fuel rules mechanism .
Derivative Netting	All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreemen t as well as the netting of collatera l. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as well as the netting of collatera l
Recurring Fair Value Measurements	Fair value is defined as the price that would be received to sell an asset or would be paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. The accounting standard clarifies that fair value should be based on the assumptions market participants would use when pricing the asset or liability including ass umptions about risk. The standard also establishes a three level fair value hierarchy based upon the observability of the assumptions used and requires the use of observable market data when available. The levels are: Level 1 - Pricing inputs are quoted p rices within active markets for identical assets or liabilities. Level 2 - Pricing inputs are quoted prices within active markets for similar assets or liabilities; quoted prices for identical or similar instruments in markets that are not active; and mod el-derived valuations that are correlated with or otherwise verifiable by observable market data. Level 3 - Pricing inputs are unobservable and reflect management ' s best estimate of what market participants would use in pricing the asset or liability. At March 31, 2018 , and December 31, 2017 , 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 at March 31, 2018 , and December 31, 2017 . Since long-term debt is not traded in an active market, it is classified as Level 2. I nvestments include exchange-traded investment securities valued using quoted prices on active exchanges and are therefore classified as Level 1. Derivatives include exchange-traded derivative c ontracts, over-the-counter transactions, a purchased power agreement, and financial transmission rights ( FTRs ) . Most exchange-traded derivative contracts are valued based on unadjusted quoted prices in active markets and are therefore class ified 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-cou nter 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 sim ilar instruments in a closed market with limited data available and are therefore classified as Level 3. The purchased power agreement (see Footnote 11 ) was valued using an internally-developed pricing model and therefore is classified as Level 3. The mod el 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 histor ical 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 lowe red, 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 li quidity, 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 March 31, 2018 December 31, 2017 Basis adjustment: On peak 91.7 % 92.3 % Off peak 93.1 % 94.1 % Counterparty fuel mix: Internal generation 50% - 75% 55% - 75% Purchased power 50% - 25% 45% - 25% The deferred compensation plan allows participants to defer certain cash compensation into a notional investment account. These amounts are included within other deferred liabilities in the consolidated balance sheets of MGE Energy and MGE . The notional investments earn interest based upon the semiannual rate of U.S. Treasury Bills having a 26 w eek maturity increased by 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 .

Summary of Significant Accoun29

Summary of Significant Accounting Principles (Tables)	3 Months Ended
	Mar. 31, 2018
Cash, Cash Equivalents, And Restricted Cash [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. MGE Energy MGE March 31, December 31, March 31, December 31, (In thousands) 2018 2017 2018 2017 Cash and cash equivalents $ 101,157 $ 107,952 $ 4,152 $ 5,951 Restricted cash 2,763 1,635 2,763 1,635 Receivable - margin account 2,325 2,507 2,325 2,507 Cash, cash equivalents, and restricted cash $ 106,245 $ 112,094 $ 9,240 $ 10,093
Retrospective Adjustments to Cash Flows	The following table presents the retrospective adjustments to cash flow amounts on MGE Energy ' s and MGE ' s consolidated statements of cash flows in accordance with the adoption of AS U 2016-18, Restricted Cash. Three Months Ended (In thousands) March 31, 2017 Cash provided by operating activities $ (1,035) Cash used for investing activities 387 Change in cash, cash equivalents, and restricted cash (648) Cash, cash equivalents, and restricted cash at beginning of period 5,674 Cash, cash equivalents, and restricted cash at end of period $ 5,026

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Revenues disaggregated by revenue source were as follows: Three Months Ended (In thousands) March 31, Electric revenues 2018 2017 Residential $ 33,259 $ 33,353 Commercial (a) 47,452 50,164 Industrial 2,895 4,215 Other-retail/municipal 8,287 9,021 Total retail 91,893 96,753 Sales to the market 2,034 972 Other revenues 470 429 Adjustments to revenues (6) 170 Total electric revenues 94,391 98,324 Gas revenues Residential 36,551 33,903 Commercial/Industrial (a) 24,952 23,048 Total retail 61,503 56,951 Gas transportation 1,135 1,350 Other revenues 127 125 Total gas revenues 62,765 58,426 Non-regulated energy revenues 476 73 Total Operating Revenue (a) $ 157,632 $ 156,823 (a) In 2017, MGE had less than $0.1 million of revenues related to CNG vehicle fuel servicing. No revenue was recognized for fuel servicing by MGE Energy in 2017.

Investment in ATC and ATC Hol31

Investment in ATC and ATC Holdco (Tables)	3 Months Ended
	Mar. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments Financial Data	MGE Transco and MGEE Transco have accounted for their investment in ATC and ATC Holdco, res pectively, under the equity method of accounting. Equity earnings from investments are recorded as " Other income " on MGE Energy's consolidated statements of income. For the three months ended March 31, 2018 and 2017 , MGE Transco recorded the following : Three Months Ended March 31, (In thousands) 2018 2017 Equity earnings from investment in ATC $ 2,451 $ 2,608 Dividends from ATC (a) - - Capital contributions to ATC 710 1,420 (a ) MGE Transco recorded a $2.3 million and $2.1 million dividend receivable from ATC as of December 31, 2017 and 2016, respectively. A cash dividend was received in January of each of the proceeding years . ATC ' s summarized financial data for the three months ended March 31, 2018 and 2017 , is as follows: Three Months Ended March 31, (In thousands) 2018 2017 Operating revenues $ 165,429 $ 174,669 Operating expenses (84,893) (82,697) Other income, net 111 682 Interest expense, net (27,762) (26,783) Earnings before members' income taxes $ 52,885 $ 65,871

Taxes (Tables)

Taxes (Tables)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
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 Three Months Ended March 31, 2018 2017 2018 2017 Statutory federal income tax rate 21.0 % 35.0 % 21.0 % 35.0 % State income taxes, net of federal benefit 6.4 % 5.3 % 6.0 % 5.1 % Amortized investment tax credits (0.1) % (0.1) % (0.1) % (0.1) % Credit for electricity from wind energy (0.5) % (1.8) % (0.5) % (2.0) % Domestic manufacturing deduction - % (1.3) % - % (1.4) % AFUDC equity, net (0.4) % (0.2) % (0.4) % (0.2) % Amortization of utility excess deferred tax - tax reform (a) (1.8) % - % (2.0) % - % Other, net, individually insignificant (0.4) % (0.2) % (0.6) % (0.2) % Effective income tax rate 24.2 % 36.7 % 23.4 % 36.2 % (a) Included are impacts of the Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting.

Pension and Other Postretirem33

Pension and Other Postretirement Plans (Tables)	3 Months Ended
	Mar. 31, 2018
Compensation and Retirement Disclosure [Abstract]
Schedule of Net Periodic Benefit Costs	The following table presents the components of net periodic benefit costs recognized for the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, (In thousands) 2018 2017 Pension Benefits Components of net periodic benefit cost: Service cost $ 1,457 $ 1,332 Interest cost 3,208 3,119 Expected return on assets (6,568) (5,742) Amortization of: Prior service credit (11) (4) Actuarial loss 1,298 1,464 Net periodic benefit (credit) cost $ (616) $ 169 Postretirement Benefits Components of net periodic benefit cost: Service cost $ 332 $ 206 Interest cost 658 444 Expected return on assets (802) (472) Amortization of: Transition obligation 1 - Prior service credit (667) (436) Actuarial loss 128 129 Net periodic benefit (credit) cost $ (350) $ (129)

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Purchase Contracts, Fiscal Year Maturity Schedule	The following table shows MGE Energy and MGE 's future commitments related to purchase contracts as of March 31, 2018 : (In thousands) 2018 2019 2020 2021 2022 Thereafter Saratoga wind $ 13,578 $ 858 $ 2,266 $ 1,775 $ 1,784 $ 4,429

Derivative and Hedging Instru35

Derivative and Hedging Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross Notional Volume of Open Derivatives	The gross notional volume of open derivatives is as follows: March 31, 2018 December 31, 2017 Commodity derivative contracts 538,050 MWh 552,310 MWh Commodity derivative contracts 3,270,000 Dth 5,460,000 Dth FTRs 886 MW 2,226 MW PPA 2,500 MW 2,650 MW
Fair Value of Derivative Instruments on the Balance Sheet	The following table summarizes the fair v alue of the derivative instruments on the consolidated balance sheet s . All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreemen t as well as the netting of collatera l. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as well as the netting of collatera l . As of March 31, 2018 , and December 31, 2017 , the receiv able margin account balance of $ 2.3 million and $ 2.5 million, respectively, is shown net of any collateral posted against derivative positions. Derivative Derivative (In thousands) Assets Liabilities Balance Sheet Location March 31, 2018 Commodity derivative contracts (a) $ 403 $ 294 Derivative liability (current) (b) Commodity derivative contracts (a) 9 189 Derivative liability (long-term) FTRs 120 - Other current assets PPA N/A 8,950 Derivative liability (current) PPA N/A 32,340 Derivative liability (long-term) December 31, 2017 Commodity derivative contracts (a) $ 566 $ 603 Derivative liability (current) (b) Commodity derivative contracts (a) 110 190 Derivative liability (long-term) FTRs 329 - Other current assets PPA N/A 8,180 Derivative liability (current) PPA N/A 33,990 Derivative liability (long-term) (a ) As of March 31, 2018 , and December 31, 2017 , collateral of $0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. (b) As of March 31, 2018 , and December 31, 2017 , $0.1 million was presented as other current assets on the consolidated balance sheets.
Offsetting Assets	The foll owing tables show the ef fect of netting arrangements for recognized derivative assets and liabilities that are subject to a master netting arr angement or simil ar 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 March 31, 2018 Commodity derivative contracts $ 412 $ (390) $ - $ 22 FTRs 120 - - 120 December 31, 2017 Commodity derivative contracts $ 676 $ (654) $ - $ 22 FTRs 329 - - 329
Offsetting Liabilities	Offsetting of Derivative Liabilities (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets March 31, 2018 Commodity derivative contracts $ 483 $ (390) $ (93) $ - PPA 41,290 - - 41,290 December 31, 2017 Commodity derivative contracts $ 793 $ (654) $ (139) $ - PPA 42,170 - - 42,170
Derivative Gains and Losses in Balance Sheet	The following table s summarize the unrealized and realized gains (losses) related to the derivative instruments on the consolidated balance sheet s at March 31, 2018 and 2017 , and the consolidated income statement s for the three months ended March 31, 2018 and 2017 . 2018 2017 (In thousands) Current and Long-Term Regulatory Asset Other Current Assets Current and Long-Term Regulatory Asset Other Current Assets Three Months Ended March 31: Balance at January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized loss (gain) 128 - (689) - Realized (loss) gain reclassified to a deferred account (158) 158 (78) 78 Realized loss reclassified to income statement (687) (645) (441) (166) Balance at March 31, $ 41,241 $ 319 $ 48,073 $ 142
Derivative Gains and Losses in Income Statement	Realized losses (gains) 2018 2017 (In thousands) Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Fuel for Electric Generation/ Purchased Power Cost of Gas Sold Three Months Ended March 31: Commodity derivative contracts $ 374 $ 615 $ 385 $ 146 FTRs (175) - (685) - PPA 518 - 761 -

Fair Value of Financial Instr36

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Estimated Fair Market Value of Financial Instruments	The estimated fair market value of financial instruments are as follows: March 31, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 101,157 $ 101,157 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper 3,000 3,000 4,000 4,000 Long-term debt (a) 425,780 462,151 426,883 475,282 MGE Assets: Cash and cash equivalents $ 4,152 $ 4,152 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper 3,000 3,000 4,000 4,000 Long-term debt (a) 425,780 462,151 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.2 million and $4.3 million at March 31, 2018, and December 31, 2017, respectively.
Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table presents the balances of assets and liabilities measured at fair value on a recurr ing basis . Fair Value as of March 31, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 531 $ 284 $ - $ 247 Exchange-traded investments 855 855 - - Total Assets $ 1,386 $ 1,139 $ - $ 247 Liabilities: Derivatives, net (b) $ 41,772 $ 62 $ - $ 41,710 Deferred compensation 3,110 - 3,110 - Total Liabilities $ 44,882 $ 62 $ 3,110 $ 41,710 MGE Assets: Derivatives, net $ 531 $ 284 $ - $ 247 Exchange-traded investments 65 65 - - Total Assets $ 596 $ 349 $ - $ 247 Liabilities: Derivatives, net (b) $ 41,772 $ 62 $ - $ 41,710 Deferred compensation 3,110 - 3,110 - Total Liabilities $ 44,882 $ 62 $ 3,110 $ 41,710 Fair Value as of December 31, 2017 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 792 792 - - Total Assets $ 1,797 $ 1,070 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 MGE Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 64 64 - - Total Assets $ 1,069 $ 342 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 (b) These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of March 31, 2018, and December 31, 2017.
Significant Unobservable Inputs	The following table presents the significant unobservable inputs used in the pricing model. Model Input Significant Unobservable Inputs March 31, 2018 December 31, 2017 Basis adjustment: On peak 91.7 % 92.3 % Off peak 93.1 % 94.1 % Counterparty fuel mix: Internal generation 50% - 75% 55% - 75% Purchased power 50% - 25% 45% - 25%
Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table summarizes the changes in Level 3 commodity derivative assets and liabilities measured at fair value on a recurring b asis . Three Months Ended March 31, (In thousands) 2018 2017 Beginning balance $ (42,026) $ (50,306) Realized and unrealized gains (losses): Included in regulatory assets 563 1,953 Included in other comprehensive income - - Included in earnings (542) (586) Included in current assets (173) 125 Purchases 5,834 5,996 Sales - - Issuances - - Settlements (5,119) (5,536) Transfers in and/or out of Level 3 - - Balance as of March 31, $ (41,463) $ (48,354) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held at March 31, (c) $ - $ - (c ) 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 losses included in income for Level 3 assets and liabilities measured at fair value on a recurring basis (c ) . Three Months Ended March 31, (In thousands) 2018 2017 Purchased power expense $ (723) $ (431) Cost of gas sold expense 181 (155) Total $ (542) $ (586) (c ) 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.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Information	The following table s show segment information for MGE Energy ' s operations for the indicated periods : (In thousands) MGE Energy Electric Gas Non-regulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Consolidated Total Three Months Ended March 31, 2018 Operating revenues $ 94,391 $ 62,765 $ 476 $ - $ - $ - $ 157,632 Interdepartmental revenues 31 4,347 9,820 - - (14,198) - Total operating revenues 94,422 67,112 10,296 - - (14,198) 157,632 Depreciation and amortization (9,378) (2,395) (1,850) - - - (13,623) Other operating expenses (76,575) (55,195) (43) (3) (203) 14,198 (117,821) Operating income (loss) 8,469 9,522 8,403 (3) (203) - 26,188 Other income, net 1,730 766 - 2,372 51 - 4,919 Interest (expense) income, net (2,867) (839) (1,348) - 315 - (4,739) Income before taxes 7,332 9,449 7,055 2,369 163 - 26,368 Income tax provision (1,200) (2,458) (1,922) (648) (139) - (6,367) Net income $ 6,132 $ 6,991 $ 5,133 $ 1,721 $ 24 $ - $ 20,001 Three Months Ended March 31, 2017 Operating revenues $ 98,324 $ 58,426 $ 73 $ - $ - $ - $ 156,823 Interdepartmental revenues (105) 4,394 11,070 - - (15,359) - Total operating revenues 98,219 62,820 11,143 - - (15,359) 156,823 Depreciation and amortization (8,900) (2,213) (1,846) - - - (12,959) Other operating expenses (a) (76,006) (50,971) (41) - (369) 15,359 (112,028) Operating income (loss) 13,313 9,636 9,256 - (369) - 31,836 Other income (deductions), net (a) 870 399 - 2,478 (222) - 3,525 Interest (expense) income, net (2,776) (799) (1,407) - 88 - (4,894) Income (loss) before taxes 11,407 9,236 7,849 2,478 (503) - 30,467 Income tax (provision) benefit (3,454) (3,704) (3,151) (997) 139 - (11,167) Net income (loss) $ 7,953 $ 5,532 $ 4,698 $ 1,481 $ (364) $ - $ 19,300 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information. The following table s show segment information for MGE ' s operations for the indicated periods : (In thousands) MGE Electric Gas Non-regulated Energy Consolidation/ Elimination Entries Consolidated Total Three Months Ended March 31, 2018 Operating revenues $ 94,391 $ 62,765 $ 476 $ - $ 157,632 Interdepartmental revenues 31 4,347 9,820 (14,198) - Total operating revenues 94,422 67,112 10,296 (14,198) 157,632 Depreciation and amortization (9,378) (2,395) (1,850) - (13,623) Other operating expenses (b) (77,731) (57,641) (1,965) 14,198 (123,139) Operating income (b) 7,313 7,076 6,481 - 20,870 Other income, net (b) 1,686 754 - - 2,440 Interest expense, net (2,867) (839) (1,348) - (5,054) Net income 6,132 6,991 5,133 - 18,256 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,806) (5,806) Net income attributable to MGE $ 6,132 $ 6,991 $ 5,133 $ (5,806) $ 12,450 Three Months Ended March 31, 2017 Operating revenues $ 98,328 $ 58,435 $ 73 $ - $ 156,836 Interdepartmental revenues (109) 4,385 11,070 (15,346) - Total operating revenues 98,219 62,820 11,143 (15,346) 156,836 Depreciation and amortization (8,900) (2,213) (1,846) - (12,959) Other operating expenses (a), (b) (79,426) (54,665) (3,192) 15,346 (121,937) Operating income (b) 9,893 5,942 6,105 - 21,940 Other income, net (a), (b) 836 389 - - 1,225 Interest expense, net (2,776) (799) (1,407) - (4,982) Net income 7,953 5,532 4,698 - 18,183 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,389) (5,389) Net income attributable to MGE $ 7,953 $ 5,532 $ 4,698 $ (5,389) $ 12,794 (a) Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information. (b) Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.

Summary of Significant Accoun38

Summary of Significant Accounting Principles (Details-1) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 101,157	$ 107,952
Restricted cash	2,763	1,635
Receivable - margin account	2,325	2,507
Cash, cash equivalents, and restricted cash	106,245	112,094	$ 122,728	$ 101,633
MGE [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	4,152	5,951
Restricted cash	2,763	1,635
Receivable - margin account	2,325	2,507
Cash, cash equivalents, and restricted cash	$ 9,240	$ 10,093	$ 28,124	$ 16,442

Summary of Significant Accoun39

Summary of Significant Accounting Principles (Details-2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities	$ 46,978	$ 41,252
Cash used for investing activities	(39,543)	(18,128)
Change in cash, cash equivalents, and restricted cash	(5,849)	21,095
Cash, cash equivalents, and restricted cash at end of period	$ 106,245	122,728
Accounting Standards Update 2016-18 - Restricted Cash [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities		(1,035)
Cash used for investing activities		387
Change in cash, cash equivalents, and restricted cash		(648)
Cash, cash equivalents, and restricted cash at end of period		$ 5,026

New Accounting Standards (Detai

New Accounting Standards (Details-1) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 0
MGE [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 0
Accounting Standards Update 2016-01 - Financial Instruments - Overall [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Accumulated other comprehensive income (loss)	$ (377,000)
Cumulative Effect of New Accounting Principle in Period of Adoption	377,000
Accounting Standards Update 2016-01 - Financial Instruments - Overall [Member] | MGE [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Accumulated other comprehensive income (loss)	28,000
Cumulative Effect of New Accounting Principle in Period of Adoption	(28,000)
Accounting Standards Update 2017-07 - Compensation - Retirement Benefits [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	1,100,000
Accounting Standards Update 2017-07 - Compensation - Retirement Benefits [Member] | MGE [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 1,100,000

Revenue (Details-1)

Revenue (Details-1) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017		Dec. 31, 2017
Total Operating Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 157,632	$ 156,823	[1]
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	94,391	98,324
Electric [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	33,259	33,353
Electric [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	47,452	50,164	[1]
Electric [Member] | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	2,895	4,215
Electric [Member] | Other-retail/municipal
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	8,287	9,021
Electric [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	91,893	96,753
Electric [Member] | Sales To The Market [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	2,034	972
Electric [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	470	429
Electric [Member] | Adjustments To Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	(6)	170
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	62,765	58,426
Gas [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	36,551	33,903
Gas [Member] | Commercial/Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	24,952	23,048	[1]
Gas [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	61,503	56,951
Gas [Member] | Gas Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	1,135	1,350
Gas [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	127	125
Non Regulated Energy [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 476	$ 73
MGE [Member]
Disaggregation of Revenue [Line Items]
CNG Vehicle Fuel Servicing Revenue				$ 100
[1]	In 2017, MGE had less than $0.1 million of revenues related to CNG vehicle fuel servicing. No revenue was recognized for fuel servicing by MGE Energy in 2017.

Investment in ATC and ATC Hol42

Investment in ATC and ATC Holdco (Details-1) - USD ($) $ in Thousands		Apr. 30, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC			$ 2,451	$ 2,608
Dividends from ATC			2,348	2,072
Capital contributions to investments			1,877	2,939
MGE Transco [Member] | ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC			2,451	2,608
Dividends from ATC	[1]		0	0
Capital contributions to investments			$ 710	1,420
Ownership interest in equity-method investee			3.60%		3.60%
Dividend receivable from ATC			$ 2,300		$ 2,100
MGE Transco [Member] | ATC [Member] | Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments		$ 1,100
MGEE Transco [Member] | ATC Holdco [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments			$ 100	$ 200
Ownership interest in equity-method investee			4.40%		4.40%
MGEE Transco [Member] | ATC Holdco [Member] | Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments		$ 100
[1]	MGE Transco recorded a $2.3 million and $2.1 million dividend receivable from ATC as of December 31, 2017 and 2016, respectively. A cash dividend was received in January of each of the proceeding years .

Investment in ATC and ATC Hol43

Investment in ATC and ATC Holdco (Details-2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Operating revenues	$ 165,429	$ 174,669
Operating expenses	(84,893)	(82,697)
Other income, net	111	682
Interest expense, net	(27,762)	(26,783)
Earnings before members' income taxes	52,885	65,871
ATC [Member]
Related Party Transaction [Line Items]
Related party expenses	7,200	$ 9,200
Due from related parties	$ 200		$ 200

Taxes (Details)

Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate	21.00%		35.00%
State income taxes, net of federal benefit	6.40%		5.30%
Amortized investment tax credits	(0.10%)		(0.10%)
Credit for electricity from wind energy	(0.50%)		(1.80%)
Domestic manufacturing deduction	0.00%		(1.30%)
AFUDC equity, net	(0.40%)		(0.20%)
Amortization of utility excess deferred tax - tax reform	(1.80%)	[1]	0.00%
Other, net, individually significant	(0.40%)		(0.20%)
Effective income tax rate	24.20%		36.70%
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	$ 12,325			$ 5,633
Regulatory liabilities	157,890			154,153
Revenue Subject to Refund | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	3,300
Revenue Subject to Refund | Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities	$ 600
MGE [Member]
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate	21.00%		35.00%
State income taxes, net of federal benefit	6.00%		5.10%
Amortized investment tax credits	(0.10%)		(0.10%)
Credit for electricity from wind energy	(0.50%)		(2.00%)
Domestic manufacturing deduction	0.00%		(1.40%)
AFUDC equity, net	(0.40%)		(0.20%)
Amortization of utility excess deferred tax - tax reform	(2.00%)	[1]	0.00%
Other, net, individually significant	(0.60%)		(0.20%)
Effective income tax rate	23.40%		36.20%
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	$ 12,325			5,633
Regulatory liabilities	$ 157,890			$ 154,153
[1]	Included are impacts of the Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting.

Pension and Other Postretirem45

Pension and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 1,457	$ 1,332
Interest cost	3,208	3,119
Expected return on assets	(6,568)	(5,742)
Amortization of:
Prior service credit	(11)	(4)
Actuarial loss	1,298	1,464
Net periodic benefit (credit) cost	(616)	169
Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	332	206
Interest cost	658	444
Expected return on assets	(802)	(472)
Amortization of:
Transition obligation	1	0
Prior service credit	(667)	(436)
Actuarial loss	128	129
Net periodic benefit (credit) cost	$ (350)	$ (129)

Equity and Financing Arrangem46

Equity and Financing Arrangements (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Common Stock [Abstract]
Common stock issued during period	0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities	$ 0

Share Based Compensation (Detai

Share Based Compensation (Details) - Performance Units [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense		$ 0.2	$ 0.5
Cash payments distributed related to awards previously granted and now payable	$ 1.6
Awards forfeited during period, value		$ 0	$ 0
Awards forfeited during period, units		0	0
Outstanding awards vested during period		$ 4.8
Director Incentive Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted during period (in units)		5,810
Award vesting period		3 years
Performance Unit Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted during period (in units)		17,830
Award vesting period		5 years

Commitments and Contingencies48

Commitments and Contingencies (Details-1) - Saratoga Wind [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)TurbinesMW
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	$ 13,578
Purchase obligation, 2019	858
Purchase obligation, 2020	2,266
Purchase obligation, 2021	1,775
Purchase obligation, 2022	1,784
Purchase obligation, Thereafter	$ 4,429
Saratoga Wind
Saratoga Capacity (MW) | MW	66
Saratoga Turbines | Turbines	33
Projected Saratoga Wind Project Costs	$ 108,000
Saratoga Wind Project Costs Year to Date	$ 23,300
Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC Rate	100.00%

Rate Matters (Details)

Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Rate Proceedings [Abstract]
Authorized return on equity, percentage			9.80%
Approved equity capital structure, percentage			57.20%
Fuel Rules [Abstract]
Fuel rules, bandwidth	2.00%
Fuel rules, electric fuel deferred costs upper threshold	102.00%
Fuel rules, electric fuel deferred costs lower threshold	98.00%
Deferred fuel rules monitored costs	$ 1.5			$ 1.1
Fuel Rules Refund, 2015/2016 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total			$ 6.2
Approved Future Rate Matters [Member]
Fuel Rules [Abstract]
Public Utilities Fuel Surcharge Amount		$ 0.5
Public Utilities Fuel Surcharge Percentage		0.13%
Electric Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage			(0.80%)
Authorized rate increase (decrease), amount			$ (3.3)
Gas Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage			1.90%
Authorized rate increase (decrease), amount			$ 3.1

Derivative and Hedging Instru50

Derivative and Hedging Instruments (Details-1) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2018USD ($)DthMWhMW	Dec. 31, 2017USD ($)DthMWhMW	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Derivative fair values [Abstract]
Receivable, margin account balance, net of collateral posted against derivative positions		$ 2,325	$ 2,507
Other Current Assets [Member]
Derivative fair values [Abstract]
Derivative fair value, net		319	806	$ 142	$ 230
Commodity Contracts And Financial Transimission Rights [Member]
Derivative fair values [Abstract]
Derivative fair value, net		$ 100	$ 200
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		538,050	552,310
Notional amount, decatherm measure (in Dth) | Dth		3,270,000	5,460,000
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 412	$ 676
Liability Derivatives, fair value, gross basis		483	793
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		100	100
Derivative, right to reclaim collateral (receivable)		0	0
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1],[2]	403	566
Liability Derivatives, fair value, gross basis	[1],[2]	294	603
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	9	110
Liability Derivatives, fair value, gross basis	[1]	$ 189	$ 190
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Maximum term of derivative hedging contract		4 years
Financial Transmission Rights [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		886	2,226
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 120	$ 329
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		120	329
Liability Derivatives, fair value, gross basis		$ 0	$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		2,500	2,650
Derivative fair values [Abstract]
Derivative fair value, net		$ (41,300)	$ (42,200)
Liability Derivatives, fair value, gross basis		41,290	42,170
PPA [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		8,950	8,180
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		$ 32,340	$ 33,990
[1]	As of March 31, 2018 , and December 31, 2017 , collateral of $0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets.
[2]	As of March 31, 2018 , and December 31, 2017 , $0.1 million was presented as other current assets on the consolidated balance sheets.

Derivative and Hedging Instru51

Derivative and Hedging Instruments (Details-2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Commodity Derivative Contracts [Member]
Offsetting Assets [Line Items]
Gross amounts	$ 412	$ 676
Gross amounts offset in balance sheet	(390)	(654)
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	22	22
Financial Transmission Rights [Member]
Offsetting Assets [Line Items]
Gross amounts	120	329
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 120	$ 329

Derivative and Hedging Instru52

Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Collateral posted against derivative positions	$ (100)	$ (100)
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	483	793
Gross amounts offset in balance sheet	(390)	(654)
Collateral posted against derivative positions	(93)	(139)
Net amount presented in balance sheet	0	0
Purchased Power Agreement [Member]
Offsetting Liabilities [Line Items]
Gross amounts	41,290	42,170
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 41,290	$ 42,170

Derivative and Hedging Instru53

Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 41,958	$ 49,281
Unrealized loss (gain)	128	(689)
Realized (loss) gain reclassified to a deferred account	(158)	(78)
Realized (loss) gain reclassified to income statement	(687)	(441)
Ending balance,	41,241	48,073
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	806	230
Unrealized loss (gain)	0	0
Realized (loss) gain reclassified to a deferred account	158	78
Realized (loss) gain reclassified to income statement	(645)	(166)
Ending balance,	$ 319	$ 142

Derivative and Hedging Instru54

Derivative and Hedging Instruments (Details-5) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)counterparty	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Counterparties in net liability position or default [Abstract]
Derivative, net liability position of counterparties	$ 100		$ 100
Number of counterparties in default | counterparty	0
Commodity Derivative Contracts [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	$ 374	$ 385
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	615	146
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	(175)	(685)
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
Purchased Power Agreement [Member]
Derivative collateral required to be posted for PPA [Abstract]
Minimum collateral that may be required to be posted	20,000
Maximum collateral that may be required to be posted	40,000
Collateral posted	0
Purchased Power Agreement [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	518	761
Purchased Power Agreement [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 Instr55

Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,200	$ 4,300
Carrying Amount [Member]
Assets:
Cash and cash equivalents		101,157	107,952
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	425,780	426,883
Fair Value [Member]
Assets:
Cash and cash equivalents		101,157	107,952
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	462,151	475,282
MGE [Member] | Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		4,200	4,300
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		4,152	5,951
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	425,780	426,883
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		4,152	5,951
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	$ 462,151	$ 475,282
[1]	Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.2 million and $4.3 million at March 31, 2018 and December 31, 2017, respectively.

Fair Value of Financial Instr56

Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Liabilities:
Derivative liability, collateral offset		$ 100	$ 100
Recurring [Member]
Assets:
Derivatives		531	1,005
Total Assets		1,386	1,797
Liabilities:
Derivatives	[1]	41,772	42,963
Deferred compensation		3,110	3,065
Total liabilities		44,882	46,028
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		855	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivatives		284	278
Total Assets		1,139	1,070
Liabilities:
Derivatives	[1]	62	210
Deferred compensation		0	0
Total liabilities		62	210
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		855	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivatives		0	0
Total Assets		0	0
Liabilities:
Derivatives	[1]	0	0
Deferred compensation		3,110	3,065
Total liabilities		3,110	3,065
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivatives		247	727
Total Assets		247	727
Liabilities:
Derivatives	[1]	41,710	42,753
Deferred compensation		0	0
Total liabilities		41,710	42,753
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
MGE [Member]
Liabilities:
Derivative liability, collateral offset		100	100
MGE [Member] | Recurring [Member]
Assets:
Derivatives		531	1,005
Total Assets		596	1,069
Liabilities:
Derivatives	[1]	41,772	42,963
Deferred compensation		3,110	3,065
Total liabilities		44,882	46,028
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		65	64
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivatives		284	278
Total Assets		349	342
Liabilities:
Derivatives	[1]	62	210
Deferred compensation		0	0
Total liabilities		62	210
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		65	64
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivatives		0	0
Total Assets		0	0
Liabilities:
Derivatives	[1]	0	0
Deferred compensation		3,110	3,065
Total liabilities		3,110	3,065
MGE [Member] | Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
MGE [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Derivatives		247	727
Total Assets		247	727
Liabilities:
Derivatives	[1]	41,710	42,753
Deferred compensation		0	0
Total liabilities		41,710	42,753
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		$ 0	$ 0
[1]	These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of March 31, 2018 and December 31, 2017.

Fair Value of Financial Instr57

Fair Value of Financial Instruments (Details-3)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Basis adjustment:
Basis adjustment - on peak	91.70%	92.30%
Basis adjustment - off peak	93.10%	94.10%
US Treasury Bill Securities [Member]
Deferred compensation plan [Abstract]
Investment interest calculation, investment maturity period (26 weeks)	182 days
Investment interest calculation, monthly compounding rate	1.00%
Investment interest calculation, minimum annual rate compounded monthly	7.00%
Minimum [Member]
Counterparty fuel mix:
Internal generation	50.00%	55.00%
Purchased power	25.00%	25.00%
Maximum [Member]
Counterparty fuel mix:
Internal generation	75.00%	75.00%
Purchased power	50.00%	45.00%

Fair Value of Financial Instr58

Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance,		$ (42,026)	$ (50,306)
Realized and unrealized gains (losses):
Included in regulatory assets		563	1,953
Included in other comprehensive income		0	0
Included in earnings	[1]	(542)	(586)
Included in current assets		(173)	125
Purchases		5,834	5,996
Sales		0	0
Issuances		0	0
Settlements		(5,119)	(5,536)
Transfers in and/or out of level 3		0	0
Ending balance,		(41,463)	(48,354)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	0	0
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	(723)	(431)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ 181	$ (155)
[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.

Joint Plant Ownership (Details)

Joint Plant Ownership (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 01, 2018
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	$ 1,383		$ 8,817
Accrued capital expenditures	4,706	$ 6,804
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	1,383		$ 8,817
Accrued capital expenditures	4,706	$ 6,804
Columbia Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share			20.40%	19.40%
Assets held for sale	1,400		$ 8,800
Accrued capital expenditures	$ 1,400		$ 8,800

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues		$ 157,632	$ 156,823
Depreciation and amortization		(13,623)	(12,959)
Other operating expenses		(117,821)	(112,028)	[1]
Operating income (loss)		26,188	31,836
Other income (deductions), net		4,919	3,525	[1]
Interest (expense) income, net		(4,739)	(4,894)
Income before income taxes		26,368	30,467
Income tax (provision) benefit		(6,367)	(11,167)
Net Income (Loss)		20,001	19,300
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		94,391	98,324
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		62,765	58,426
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		476	73
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		157,632	156,823
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		94,422	98,219
Depreciation and amortization		(9,378)	(8,900)
Other operating expenses		(76,575)	(76,006)	[1]
Operating income (loss)		8,469	13,313
Other income (deductions), net		1,730	870	[1]
Interest (expense) income, net		(2,867)	(2,776)
Income before income taxes		7,332	11,407
Income tax (provision) benefit		(1,200)	(3,454)
Net Income (Loss)		6,132	7,953
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		67,112	62,820
Depreciation and amortization		(2,395)	(2,213)
Other operating expenses		(55,195)	(50,971)	[1]
Operating income (loss)		9,522	9,636
Other income (deductions), net		766	399	[1]
Interest (expense) income, net		(839)	(799)
Income before income taxes		9,449	9,236
Income tax (provision) benefit		(2,458)	(3,704)
Net Income (Loss)		6,991	5,532
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,296	11,143
Depreciation and amortization		(1,850)	(1,846)
Other operating expenses		(43)	(41)	[1]
Operating income (loss)		8,403	9,256
Other income (deductions), net		0	0	[1]
Interest (expense) income, net		(1,348)	(1,407)
Income before income taxes		7,055	7,849
Income tax (provision) benefit		(1,922)	(3,151)
Net Income (Loss)		5,133	4,698
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Depreciation and amortization		0	0
Other operating expenses		(3)	0	[1]
Operating income (loss)		(3)	0
Other income (deductions), net		2,372	2,478	[1]
Interest (expense) income, net		0	0
Income before income taxes		2,369	2,478
Income tax (provision) benefit		(648)	(997)
Net Income (Loss)		1,721	1,481
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Depreciation and amortization		0	0
Other operating expenses		(203)	(369)	[1]
Operating income (loss)		(203)	(369)
Other income (deductions), net		51	(222)	[1]
Interest (expense) income, net		315	88
Income before income taxes		163	(503)
Income tax (provision) benefit		(139)	139
Net Income (Loss)		24	(364)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(14,198)	(15,359)
Depreciation and amortization		0	0
Other operating expenses		14,198	15,359	[1]
Operating income (loss)		0	0
Other income (deductions), net		0	0	[1]
Interest (expense) income, net		0	0
Income before income taxes		0	0
Income tax (provision) benefit		0	0
Net Income (Loss)		0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		31	(105)
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		4,347	4,394
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		9,820	11,070
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues		157,632	156,836
Depreciation and amortization		(13,623)	(12,959)
Other operating expenses	[2]	(123,139)	(121,937)	[1]
Operating income (loss)	[2]	20,870	21,940
Other income (deductions), net	[2]	2,440	1,225	[1]
Interest (expense) income, net		(5,054)	(4,982)
Net Income Including Noncontrolling Interest		18,256	18,183
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,806)	(5,389)
Net Income (Loss)		12,450	12,794
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		94,391	98,328
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		62,765	58,435
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		476	73
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		157,632	156,836
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		94,422	98,219
Depreciation and amortization		(9,378)	(8,900)
Other operating expenses	[2]	(77,731)	(79,426)	[1]
Operating income (loss)	[2]	7,313	9,893
Other income (deductions), net	[2]	1,686	836	[1]
Interest (expense) income, net		(2,867)	(2,776)
Net Income Including Noncontrolling Interest		6,132	7,953
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		6,132	7,953
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		67,112	62,820
Depreciation and amortization		(2,395)	(2,213)
Other operating expenses	[2]	(57,641)	(54,665)	[1]
Operating income (loss)	[2]	7,076	5,942
Other income (deductions), net	[2]	754	389	[1]
Interest (expense) income, net		(839)	(799)
Net Income Including Noncontrolling Interest		6,991	5,532
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		6,991	5,532
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,296	11,143
Depreciation and amortization		(1,850)	(1,846)
Other operating expenses	[2]	(1,965)	(3,192)	[1]
Operating income (loss)	[2]	6,481	6,105
Other income (deductions), net	[2]	0	0	[1]
Interest (expense) income, net		(1,348)	(1,407)
Net Income Including Noncontrolling Interest		5,133	4,698
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0
Net Income (Loss)		5,133	4,698
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(14,198)	(15,346)
Depreciation and amortization		0	0
Other operating expenses	[2]	14,198	15,346	[1]
Operating income (loss)	[2]	0	0
Other income (deductions), net	[2]	0	0	[1]
Interest (expense) income, net		0	0
Net Income Including Noncontrolling Interest		0	0
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,806)	(5,389)
Net Income (Loss)		(5,806)	(5,389)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		31	(109)
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		4,347	4,385
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 9,820	$ 11,070
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information.
[2]	Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.

Uncategorized Items - mgee-2018

Label	Element	Value
Accounting Standards Update 2016-18 - Restricted Cash [Member]
Cash, cash equivalents, and restricted cash	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations	$ 5,674,000