MGE Energy (MGEE) 10-Q 7 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 31, 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	Jun. 30, 2018
Amendment Flag	false
Trading Symbol	MGEE
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
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			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Operating Revenues:
Electric revenues	$ 99,282	$ 102,382		$ 194,149	$ 200,779
Gas revenues	24,980	24,081		87,745	82,507
Total Operating Revenues	124,262	126,463		281,894	283,286
Operating Expenses:
Fuel for electric generation	15,251	11,910		27,151	24,109
Purchased power	12,979	16,720		30,012	32,074
Cost of gas sold	9,562	9,231		49,188	45,015
Other operations and maintenance	43,453	44,880		87,846	88,644
Depreciation and amortization	13,872	13,275		27,495	26,234
Other general taxes	4,914	4,852		9,783	9,779
Total Operating Expenses	100,031	100,868		231,475	225,855
Operating Income	24,231	25,595		50,419	57,431
Other income, net	4,731	3,570	[1]	9,650	7,095	[1]
Interest expense, net	(4,783)	(4,886)		(9,522)	(9,780)
Income before income taxes	24,179	24,279		50,547	54,746
Income tax provision	(5,828)	(8,736)		(12,195)	(19,903)
Net Income	$ 18,351	$ 15,543		$ 38,352	$ 34,843
Earnings Per Share of Common Stock (basic and diluted)	$ 0.53	$ 0.45		$ 1.11	$ 1.01
Dividends per share of common stock	$ 0.323	$ 0.308		$ 0.645	$ 0.615
Weighted Average Shares Outstanding (basic and diluted)	34,668	34,668		34,668	34,668
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information.

Madison Gas and Electric Compan

Madison Gas and Electric Company Consolidated Statements of Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Operating Revenues:
Electric revenues	$ 99,282	$ 102,382		$ 194,149	$ 200,779
Gas revenues	24,980	24,081		87,745	82,507
Total Operating Revenues	124,262	126,463		281,894	283,286
Operating Expenses:
Fuel for electric generation	15,251	11,910		27,151	24,109
Purchased power	12,979	16,720		30,012	32,074
Cost of gas sold	9,562	9,231		49,188	45,015
Other operations and maintenance	43,453	44,880		87,846	88,644
Depreciation and amortization	13,872	13,275		27,495	26,234
Other general taxes	4,914	4,852		9,783	9,779
Total Operating Expenses	100,031	100,868		231,475	225,855
Operating Income	24,231	25,595		50,419	57,431
Other Income and Deductions:
Equity earnings in MGE Transco	1,990	2,486		4,441	5,094
Total Other Income and Deductions	4,731	3,570	[1]	9,650	7,095	[1]
Interest Expense:
Net Interest Expense	4,783	4,886		9,522	9,780
Net Income	18,351	15,543		38,352	34,843
MGE [Member]
Operating Revenues:
Electric revenues	99,282	102,382		194,149	200,783
Gas revenues	24,980	24,080		87,745	82,515
Total Operating Revenues	124,262	126,462		281,894	283,298
Operating Expenses:
Fuel for electric generation	15,251	11,910		27,151	24,111
Purchased power	12,979	16,720		30,012	32,076
Cost of gas sold	9,562	9,230		49,188	45,023
Other operations and maintenance	43,001	44,663		87,188	88,058
Depreciation and amortization	13,872	13,275		27,495	26,234
Other general taxes	4,914	4,852		9,783	9,779
Income tax provision	5,129	7,756		10,653	18,021
Total Operating Expenses	104,708	108,406		241,470	243,302
Operating Income	19,554	18,056	[2]	40,424	39,996	[2]
Other Income and Deductions:
AFUDC - equity funds	664	294		1,259	565
Income tax provision	(92)	(47)		(149)	(91)
Other income, net	1,650	845		3,552	1,843
Total Other Income and Deductions	2,222	1,092	[1],[2]	4,662	2,317	[1],[2]
Income before interest expense	21,776	19,148		45,086	42,313
Interest Expense:
Interest on long-term debt	5,191	5,013		10,397	10,056
Other interest, net	206	65		255	96
AFUDC - borrowed funds	(224)	(80)		(425)	(172)
Net Interest Expense	5,173	4,998		10,227	9,980
Net Income Including Noncontrolling Interest	16,603	14,150		34,859	32,333
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,505)	(5,396)		(11,311)	(10,785)
Net Income	$ 11,098	$ 8,754		$ 23,548	$ 21,548
[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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Comprehensive Income [Abstract]
Net Income	$ 18,351	$ 15,543	$ 38,352	$ 34,843
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	0	32	0	129
Comprehensive Income	$ 18,351	$ 15,575	$ 38,352	$ 34,972

Madison Gas and Electric Compa5

Madison Gas and Electric Company Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	$ 0	$ 32	$ 0	$ 129
Comprehensive Income	18,351	15,575	38,352	34,972
MGE [Member]
Net Income	16,603	14,150	34,859	32,333
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	0	(25)	0	(31)
Total comprehensive income including noncontrolling interest	16,603	14,125	34,859	32,302
Less: Comprehensive income attributable to Noncontrolling Interest, net of tax	(5,505)	(5,396)	(11,311)	(10,785)
Comprehensive Income	$ 11,098	$ 8,729	$ 23,548	$ 21,517

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) (Parantheticals) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Unrealized gain (loss) on available-for-sale securities, tax expense (benefit)	$ 0	$ 21	$ 0	$ 86
MGE [Member]
Unrealized gain (loss) on available-for-sale securities, tax expense (benefit)	$ 0	$ (17)	$ 0	$ (21)

MGE Energy Inc Consolidated St7

MGE Energy Inc Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating Activities:
Net Income	$ 38,352	$ 34,843
Items not affecting cash:
Depreciation and amortization	27,495	26,234
Deferred income taxes	(664)	1,037
Provision for doubtful receivables	354	367
Employee benefit plan (credit) cost	(1,076)	727
Equity earnings in ATC	(4,441)	(5,094)
Other items	160	778
Changes in working capital items:
Decrease in current assets	29,120	20,595
Decrease in current liabilities	(1,333)	(11,516)
Dividends from ATC	3,905	4,072
Cash contributions to pension and other postretirement plans	(2,640)	(8,284)
Other noncurrent items, net	2,386	3,257
Cash Provided by Operating Activities	91,618	67,016
Investing Activities:
Capital expenditures	(100,389)	(42,169)
Capital contributions to investments	(3,280)	(5,557)
Other	598	852
Cash Used for Investing Activities	(103,071)	(46,874)
Financing Activities:
Cash dividends paid on common stock	(22,361)	(21,321)
Repayment of long-term debt	(2,213)	(32,167)
Issuance of long-term debt	0	40,000
Proceeds from short-term debt	24,200	0
Other	0	(317)
Cash Provided by (Used for) Financing Activities	(374)	(13,805)
Change in cash, cash equivalents, and restricted cash	(11,827)	6,337
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633
Cash, cash equivalents, and restricted cash at end of period	100,267	107,970
Significant noncash investing activities:
Accrued capital expenditures	$ 6,467	$ 8,450

Madison Gas and Electric Compa8

Madison Gas and Electric Company Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Items not affecting cash:
Depreciation and amortization	$ 27,495	$ 26,234
Deferred income taxes	(664)	1,037
Provision for doubtful receivables	354	367
Employee benefit plan (credit) cost	(1,076)	727
Equity earnings in MGE Transco	(4,441)	(5,094)
Other items	160	778
Changes in working capital items:
Decrease in current assets	29,120	20,595
Increase (decrease) in current liabilities	(1,333)	(11,516)
Cash contributions to pension and other postretirement plans	(2,640)	(8,284)
Other noncurrent items, net	2,386	3,257
Cash Provided by Operating Activities	91,618	67,016
Investing Activities:
Capital expenditures	(100,389)	(42,169)
Capital contributions to investments	(3,280)	(5,557)
Other	598	852
Cash Used for Investing Activities	(103,071)	(46,874)
Financing Activities:
Repayment of long-term debt	(2,213)	(32,167)
Issuance of long-term debt	0	40,000
Proceeds from short-term debt	24,200	0
Other	0	(317)
Cash Provided by (Used for) Financing Activities	(374)	(13,805)
Change in cash, cash equivalents, and restricted cash	(11,827)	6,337
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633
Cash, cash equivalents, and restricted cash at end of period	100,267	107,970
Significant noncash investing activities:
Accrued capital expenditures	6,467	8,450
MGE [Member]
Operating Activities:
Net Income	34,859	32,333
Items not affecting cash:
Depreciation and amortization	27,495	26,234
Deferred income taxes	(2,574)	(149)
Provision for doubtful receivables	354	367
Employee benefit plan (credit) cost	(1,076)	727
Other items	707	969
Changes in working capital items:
Decrease in current assets	28,686	19,702
Increase (decrease) in current liabilities	1,943	(11,021)
Cash contributions to pension and other postretirement plans	(2,640)	(8,284)
Other noncurrent items, net	2,293	3,141
Cash Provided by Operating Activities	90,047	64,019
Investing Activities:
Capital expenditures	(100,389)	(42,169)
Other	(422)	65
Cash Used for Investing Activities	(100,811)	(42,104)
Financing Activities:
Cash dividends paid to parent by MGE	0	(25,000)
Distributions to parent from noncontrolling interest	(13,500)	(10,000)
Repayment of long-term debt	(2,213)	(32,167)
Issuance of long-term debt	0	40,000
Proceeds from short-term debt	24,200	0
Other	0	(305)
Cash Provided by (Used for) Financing Activities	8,487	(27,472)
Change in cash, cash equivalents, and restricted cash	(2,277)	(5,557)
Cash, cash equivalents, and restricted cash at beginning of period	10,093	16,442
Cash, cash equivalents, and restricted cash at end of period	7,816	10,885
Significant noncash investing activities:
Accrued capital expenditures	$ 6,467	$ 8,450

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 95,579	$ 107,952
Accounts receivable, less reserves	35,473	42,299
Other accounts receivables, less reserves	7,808	9,440
Unbilled revenues	24,031	31,400
Materials and supplies, at average cost	24,595	22,614
Fuel for electric generation, at average cost	9,451	8,256
Stored natural gas, at average cost	7,763	12,923
Prepaid taxes	16,042	26,535
Regulatory assets - current	7,462	7,888
Assets held for sale	1,392	8,817
Other current assets	12,714	12,507
Total Current Assets	242,310	290,631
Other long-term receivables	4,188	4,788
Regulatory assets	137,267	142,567
Pension and other postretirement benefit asset	11,956	7,336
Other deferred assets and other	5,379	731
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,345,255	1,283,313
Construction work in progress	75,007	58,044
Total Property, Plant, and Equipment	1,420,262	1,341,357
Investments	72,083	67,772
Total Assets	1,893,445	1,855,182
Current Liabilities:
Long-term debt due within one year	4,502	24,452
Short-term debt	28,200	4,000
Accounts payable	37,498	47,645
Accrued interest and taxes	5,350	5,602
Accrued payroll related items	10,449	12,244
Regulatory liabilities - current	9,110	5,633
Derivative liabilities	8,860	8,180
Other current liabilities	14,457	18,758
Total Current Liabilities	118,426	126,514
Other Credits:
Deferred income taxes	226,300	225,130
Investment tax credit - deferred	868	918
Regulatory liabilities	166,316	154,153
Accrued pension and other postretirement benefits	69,249	69,088
Derivative liabilities	29,890	33,990
Other deferred liabilities and other	72,120	69,041
Total Other Credits	564,743	552,320
Capitalization:
Common shareholders equity	794,178	778,187
Long-term debt	416,098	398,161
Total Capitalization	1,210,276	1,176,348
Commitments and contingencies (see Footnote 9)
Total Liabilities and Capitalization	1,893,445	1,855,182
MGE [Member]
Current Assets:
Cash and cash equivalents	3,128	5,951
Accounts receivable, less reserves	35,473	42,299
Affiliate receivables	592	668
Other accounts receivables, less reserves	6,297	6,984
Unbilled revenues	24,031	31,400
Materials and supplies, at average cost	24,595	22,614
Fuel for electric generation, at average cost	9,451	8,256
Stored natural gas, at average cost	7,763	12,923
Prepaid taxes	15,073	25,073
Regulatory assets - current	7,462	7,888
Assets held for sale	1,392	8,817
Other current assets	12,709	12,484
Total Current Assets	147,966	185,357
Affiliate receivable long-term	3,442	3,707
Regulatory assets	137,267	142,567
Pension and other postretirement benefit asset	11,956	7,336
Other deferred assets and other	7,558	3,280
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,345,283	1,283,341
Construction work in progress	75,007	58,044
Total Property, Plant, and Equipment	1,420,290	1,341,385
Investments	422	409
Total Assets	1,728,901	1,684,041
Current Liabilities:
Long-term debt due within one year	4,502	24,452
Short-term debt	28,200	4,000
Accounts payable	37,498	47,614
Accrued interest and taxes	6,551	5,558
Accrued payroll related items	10,449	12,244
Regulatory liabilities - current	9,110	5,633
Derivative liabilities	8,860	8,180
Other current liabilities	14,448	16,749
Total Current Liabilities	119,618	124,430
Other Credits:
Deferred income taxes	200,609	201,486
Investment tax credit - deferred	868	918
Regulatory liabilities	166,316	154,153
Accrued pension and other postretirement benefits	69,249	69,088
Derivative liabilities	29,890	33,990
Other deferred liabilities and other	72,120	69,041
Total Other Credits	539,052	528,676
Capitalization:
Common shareholders equity	515,420	491,872
Noncontrolling interest	138,713	140,902
Total Equity	654,133	632,774
Long-term debt	416,098	398,161
Total Capitalization	1,070,231	1,030,935
Commitments and contingencies (see Footnote 9)
Total Liabilities and Capitalization	$ 1,728,901	$ 1,684,041

Consolidated Balance Sheets (10

Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Receivables, Net
Reserve for uncollectible accounts receivable	$ 2,434	$ 2,840
Reserve for uncollectible other accounts receivable	588	335
MGE [Member]
Receivables, Net
Reserve for uncollectible accounts receivable	2,434	2,840
Reserve for uncollectible other accounts receivable	$ 588	$ 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	34,843			34,843
Other comprehensive income (loss)	129				129
Common stock dividends declared	(21,321)			(21,321)
Ending balance, shares at Jun. 30, 2017		34,668
Ending balance, value at Jun. 30, 2017	737,739	$ 34,668	316,268	386,472	331
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	38,352			38,352
Common stock dividends declared	(22,361)			(22,361)
Ending balance, shares at Jun. 30, 2018		34,668
Ending balance, value at Jun. 30, 2018	$ 794,178	$ 34,668	$ 316,268	$ 443,242	$ 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		32,333					21,548			10,785
Other comprehensive income (loss)	$ 129	(31)						$ 129	(31)
Cash dividends paid to parent by MGE		(25,000)					(25,000)
Distributions to parent from noncontrolling interest		(10,000)								(10,000)
Ending balance, shares at Jun. 30, 2017			34,668	17,348
Ending balance, value at Jun. 30, 2017		600,051		$ 17,348	192,417		273,848		(12)	116,450
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		34,859					23,548			11,311
Distributions to parent from noncontrolling interest		(13,500)								(13,500)
Ending balance, shares at Jun. 30, 2018			34,668	17,348
Ending balance, value at Jun. 30, 2018		$ 654,133		$ 17,348	$ 192,417		$ 305,655		$ 0	$ 138,713

Consolidated Statements of Comm

Consolidated Statements of Common Equity (Unaudited) (Parentheticals) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Consolidated Statements of Common Equity
Dividends per share of common stock	$ 0.323	$ 0.308	$ 0.645	$ 0.615

Summary of Significant Accounti

Summary of Significant Accounting Principles	6 Months Ended
	Jun. 30, 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 June 30, 2018 , and for the three and six 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 June 30, December 31, June 30, December 31, (In thousands) 2018 2017 2018 2017 Cash and cash equivalents $ 95,579 $ 107,952 $ 3,128 $ 5,951 Restricted cash 3,516 1,635 3,516 1,635 Receivable - margin account 1,172 2,507 1,172 2,507 Cash, cash equivalents, and restricted cash $ 100,267 $ 112,094 $ 7,816 $ 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. Six Months Ended (In thousands) June 30, 2017 Cash provided by operating activities $ (694) Cash used for investing activities 74 Change in cash, cash equivalents, and restricted cash (620) Cash, cash equivalents, and restricted cash at beginning of period 5,674 Cash, cash equivalents, and restricted cash at end of period $ 5,054

Adoption of Accounting Principl

Adoption of Accounting Principles and Recently Issued Accounting Pronouncements	6 Months Ended
	Jun. 30, 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 accumulated other comprehensive income, and MGE recorded less than a $0.1 million decrease in retained earnings and a corresponding increase in accumulated other comprehensive income, related to equity investments within the scope of this standard. Restricted Cash. In November 2016, the FASB issued authoritative guidance within the 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 g uidance, 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, ch anges 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. Also under the new standard, reporting entities are r equired 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 ben efit 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 ren dered by the pertinent employees during the period. The other components 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 $0.9 million and $2.0 million for the three and six months ended June 30, 2017 , respectively . The standard also only allows the service cost comp onent to be eligible for capitalization prospectively from the effective date of the pronouncement (whereas under previous GAAP, all components of net benefit cost were eligible for capitalization). See Footnote 6 for further information. b . Recently Iss ued 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	6 Months Ended
	Jun. 30, 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 Six Months Ended (In thousands) June 30, June 30, Electric revenues 2018 2017 2018 2017 Residential $ 32,217 $ 31,634 $ 65,476 $ 64,987 Commercial (a) 50,174 54,721 97,626 104,885 Industrial 4,630 4,516 7,525 8,731 Other-retail/municipal 8,527 9,661 16,814 18,682 Total retail 95,548 100,532 187,441 197,285 Sales to the market 2,795 1,050 4,829 2,022 Other revenues 454 562 924 991 Adjustments to revenues 270 162 264 332 Total electric revenues 99,067 102,306 193,458 200,630 Gas revenues Residential 15,620 15,140 52,171 49,043 Commercial/Industrial (a) 8,206 7,842 33,158 30,890 Total retail 23,826 22,982 85,329 79,933 Gas transportation 1,053 991 2,189 2,341 Other revenues 101 108 227 233 Total gas revenues 24,980 24,081 87,745 82,507 Non-regulated energy revenues 215 76 691 149 Total Operating Revenue (a) $ 124,262 $ 126,463 281,894 $ 283,286 (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 p ower" expense. Under-collection of these costs will continue to be recognized in "Purchased p ower" 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 in January 2018 to defer the over-collection of income tax expense collec ted 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 act ual costs incurred and the amount of costs collected from customers is recorded as a reduction of revenue in the period incurred. Sales to the Market Sales to the market include energy charges, capacity or demand charges, and ancillary charges represente d by wholesale sales of electricity made to third parties who are not ultimate users of the electricity. Most of these sales are spot market transactions on the markets operated by MISO. Each transaction is considered a performance obligation and revenue i s recognized in the period in which energy charges, capacity or demand charges, and ancillary services are sold into MISO. MGE reports on a net basis, transactions on the MISO markets in which it buys and sells power within the same hour to meet electric energy delivery requirements. Transportation of Gas MGE has contracts under which MGE provides gas transportation services to customers whom have elected to purchase gas from a third party and have the gas delivered via pipelines within MGE's service ter ritory. Revenue is recognized as service is rendered or gas is delivered to customers. Tariffs are approved by the PSCW through a rate order and provide gas transportation customers with the standard terms and conditions, including pricing terms.

Investment in ATC and ATC Holdc

Investment in ATC and ATC Holdco	6 Months Ended
	Jun. 30, 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 June 30, 2018 , and December 31, 2017 , MGE Transco held a 3.6 % ownership interest in ATC. At June 30, 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 and six months ended June 30, 2018 and 2017 , MGE Transco recorded the following : Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Equity earnings from investment in ATC $ 1,990 $ 2,486 $ 4,441 $ 5,094 Dividends from ATC (a) 2,959 2,000 2,959 2,000 Capital contributions to ATC 1,065 888 1,775 2,308 (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 . MGE Transco recorded a $ 1.4 million dividend receivable from ATC as of June 30, 2018 . A cash dividend was received in July 2018 . ATC Holdco was formed in December 2016. In the near term, it is expected that ATC Holdco will be pursuing transmission development opportunities that typ ically have long development and investment lead times before becoming operational. During the three and six months ended June 30, 2018 , MGEE Transco recorded capital contributions of $ 0.1 million and $ 0.2 million, respectively, to ATC Holdco compared to $ 0.5 million and $ 0.7 million for the comparable periods in 2017 . In July 2018, MGE Transco made a $ 0.5 million capital contribution to ATC and MGEE Transco made a $ 0.1 million contribution to ATC Holdco. ATC ' s summarized financial data for the three and six months ended June 30, 2018 and 2017 , is as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Operating revenues $ 165,506 $ 176,610 $ 330,935 $ 351,279 Operating expenses (91,474) (82,974) (176,367) (165,670) Other income, net 1,520 1,088 1,631 1,771 Interest expense, net (26,895) (26,466) (54,657) (53,250) Earnings before members' income taxes $ 48,657 $ 68,258 $ 101,542 $ 134,130 MGE receives transmission and other related services from ATC. During the three and six months ended June 30, 2018 , MGE recorded $ 7.2 million and $ 14.4 million, respectively, for transmission services received compared to $ 7.3 million and $ 14.6 million for the comparable periods in 2017 . MGE also provides a variety of operational, maintenance, and project management services for ATC, which is reimbursed by ATC. As of June 30, 2018 , and December 31, 2017 , MGE had a receivable due from ATC of $ 0.1 million and $ 0.2 million, respectively.

Taxes

Taxes	6 Months Ended
	Jun. 30, 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 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, 2017. In acco rdance 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 half of 2018. Beginning January 1, 2018, MGE began a mortization of the regulated utility excess deferred taxes recognized using a normalization method of accounting. For the three and six months ended June 30, 2018 , MGE recognized $ 0.6 million and $ 1.2 mill ion, respectively, of excess deferred taxes as a reduction of revenue and a corresponding increase 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 custome rs, which will be determined by the PSCW. Customer rates approved for 2018 reflect an income tax rate of 35 percent. In January 2018 , the PSCW issued an order directing Wisconsin investor-owned utilities to defer the over-collection of income tax expense as a result of the decrease in tax rate to 21 percent. The PSCW issued an order in May 2018 to return to customers the estimated 2018 over-collection of income tax expense. The decision includes a one-tim e bill credit on customer bills to reflect the estimate of the over - collection for January through June 2018. A monthly volumetric bill credit will begin in July 2018 and continue through the remainder of 2018 for the estimated remaining annual amount. In June 2018, customers received a $ 4.1 million bill credit. Any over/under recovery of the actual costs will be subject to the PSCW ' s review in a future rate case. As of June 30, 2018 , MGE has deferred $ 1.7 million as a regulatory liability and recorded a corresponding r eduction in operating revenues for over-collection of income tax expense (net of customer bill credits). 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 June 30, 2018 2017 2018 2017 Statutory federal income tax rate 21.0 % 35.0 % 21.0 % 35.0 % State income taxes, net of federal benefit 6.3 % 5.2 % 6.2 % 5.1 % Amortized investment tax credits (0.1) % (0.3) % (0.1) % (0.4) % Credit for electricity from wind energy (0.4) % (1.5) % (0.4) % (1.6) % Domestic manufacturing deduction - % (1.9) % - % (2.0) % AFUDC equity, net (1.1) % (0.3) % (1.1) % (0.3) % Amortization of utility excess deferred tax - tax reform (a) (1.9) % - % (1.9) % (0.1) % Other, net, individually insignificant 0.3 % (0.2) % 0.2 % (0.2) % Effective income tax rate 24.1 % 36.0 % 23.9 % 35.5 % MGE Energy MGE Six Months Ended June 30, 2018 2017 2018 2017 Statutory federal income tax rate 21.0 % 35.0 % 21.0 % 35.0 % State income taxes, net of federal benefit 6.3 % 5.2 % 6.2 % 5.1 % Amortized investment tax credits (0.1) % (0.3) % (0.1) % (0.4) % Credit for electricity from wind energy (0.3) % (1.4) % (0.3) % (1.6) % Domestic manufacturing deduction - % (1.7) % - % (1.8) % AFUDC equity, net (0.9) % (0.3) % (1.0) % (0.3) % Amortization of utility excess deferred tax - tax reform (a) (1.9) % - % (2.1) % - % Other, net, individually insignificant - % (0.1) % - % (0.1) % Effective income tax rate 24.1 % 36.4 % 23.7 % 35.9 % (a) Included are impacts of the Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting.

Pension and Other Postretiremen

Pension and Other Postretirement Plans	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2018 and 2017 . Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Pension Benefits Components of net periodic benefit cost: Service cost $ 1,404 $ 1,360 $ 2,861 $ 2,692 Interest cost 3,222 3,194 6,430 6,313 Expected return on assets (6,552) (5,740) (13,120) (11,482) Amortization of: Prior service credit (11) (4) (22) (8) Actuarial loss 1,341 1,711 2,639 3,175 Net periodic benefit (credit) cost $ (596) $ 521 $ (1,212) $ 690 Postretirement Benefits Components of net periodic benefit cost: Service cost $ 310 $ 423 $ 642 $ 629 Interest cost 648 912 1,306 1,356 Expected return on assets (814) (971) (1,616) (1,443) Amortization of: Transition obligation - 1 1 1 Prior service credit (667) (898) (1,334) (1,334) Actuarial loss 116 251 244 380 Net periodic benefit (credit) cost $ (407) $ (282) $ (757) $ (411)

Equity and Financing Arrangemen

Equity and Financing Arrangements	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 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. c. Long-term Debt - MGE Energy and MGE. In July 2018, MGE issued $20 million of new long-term unsecured debt carrying an interest rate of 4.24% per annum over its 35-year term and $20 million of new long-term unsecured debt carrying an interest rate of 4.34% per annum over its 40-year term. MGE has also committed to issue $60 million of new long-term unsecured debt that will carry an interest rate of 4.19% per annum over its 3 0 -year life with funding expected to occur in September 2018 . The proceeds of these debt financings will be used to assist with capital expenditures, such as the Saratoga Wind Farm, and to refinance $20 million of long-term debt at its maturity in September 2018. The covenants of this debt are substantially consisten t with MGE's existing unsecured long-term debt . In accordance with applicable accounting guidance, MGE has classified the $20 million of maturing unsecured debt as long-t erm debt on the consolidated balance sheets for the quarter ended June 30, 2018.

Share-Based Compensation

Share-Based Compensation	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation - MGE Energy and MGE. Under MGE Energy ' s Director Incentive Plan and its Performance Unit Plan, non-employee directors and eligible employees, respectively, may receive performance units that entitle the holder to receive a cash payment equal to the value of a designated number of shares of MGE Energy's common stock, plus dividend equivalent payments thereon, at the end of the performance period set in the award . 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 date, the cost of the director or employee services received in exchange for a performance unit award is measured based on the current market value of MGE Energy common stock. The fair value of the awards is re-measured quarterly, including at June 30, 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 accrued and recognized using the graded vesting method. Compensation cost for retirement eligible employees or employees that will become retirement eligible during the vesting schedule are recognized on an abridged horizon as retirement eligibility accelerated vesting . During the three and six months ended June 30, 2018 , MGE recorded $ 0.8 million and $ 1.0 million, respectively, in compensation expense as a result of awards under the plans compared to $ 0.2 million and $ 0.7 million for the comparable periods 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 and six months ended June 30, 2018 and 2017 . At June 30, 2018 , $ 5.4 million of outstanding awards are vested, and of this amount, no cash settlements have occurred as cash payments are only made at the end of the period covered by the awards .

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 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 is ongoing ; however the significance of the challenge , as it might relate to MGE, is now diminished with the final ozone designations . • Rule s 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 use 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. Review 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 replac e 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 co mpliance 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 . 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. MGE Energy and MGE have entered into various commodity supply, transportation, and storage contracts to meet their obligations to deliver electricity and natural gas to customers. Management expects to recover these costs in future customer rates. The foll owing table shows future commitments related to purchase contracts as of June 30, 2018 : (In thousands) 2018 2019 2020 2021 2022 Thereafter Coal (a) $ 13,301 $ 17,831 $ 5,297 $ - $ - $ - Natural gas supply (b) 11,624 12,587 - - - - Saratoga wind (c) 1,038 858 2,266 1,775 1,784 4,429 Other 1,772 502 502 502 502 502 $ 27,735 $ 31,778 $ 8,065 $ 2,277 $ 2,286 $ 4,931 (a ) Total coal commitments for the Columbia and Elm Road Units, including transportation. Fuel procurement for MGE's jointly owned Columbia and Elm Road Units is handled by WPL and WEPCO, respectively, who are the operators of those facilities. (b) These commitments include market-based pricing. (c) 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 June 30, 2018, MGE has incurred $ 42.6 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	6 Months Ended
	Jun. 30, 2018
Regulated Operations [Abstract]
Rate Matters	Rate Matters - MGE Energy and MGE. a. Rate P roceedings. In July 2018, MGE filed an application with the PSCW to decrease electric rates and increase gas rates in 2019 and 2020. MGE filed its application through a settlement agreement between MGE and intervening parties in the rate case, subject to PSCW approval. The settlement proposal would decrease electric rates by 1.94% in 2019. This amount is subject to change based on the final outcome of MGE's 2019 Fuel Cost Plan. MGE will maintain this rate l evel for 2020, with the exception that MGE will file a 2020 Fuel Cost Plan in 2019 and MGE's rates will decrease or increase accordingly. The decrease reflect s the ongoing tax impacts of the Tax Act and the addition of lower-cost rene wable generation capacity. The settlement proposal would increase gas rates by 1.06% in 2019 and 1.46% in 2020. The requested increase covers infrastructure costs. It also reflects the impacts of the Tax Act. The proposed return on common stock equity for 2019 and 2020 will be 9.8 % based on a capital structure consisting of 56.6 % common equity in 2019 and 56.1 % common equity in 20 20 . 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 costs. The increase in retail gas rates covers costs associated with MGE's natural gas system infrastructur e 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 transmission 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 %. In July 2018, the PSCW issued a preliminary decision in the fuel rules proceedings for MGE to refund $ 4.2 million of additional fuel saving s realized during 2017 to its retail electric customers over a one-month period in the second half of 2018. There was no change to the refund in the fuel rules proceedings from the amount MGE deferred as of December 31, 2017. As of June 30, 2018 , MGE has deferred $ 5.2 million of 2018 fuel savings. 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 June 30, 2017 , MGE had deferred $ 1.8 million of 2017 fuel savings .

Derivative and Hedging Instrume

Derivative and Hedging Instruments	6 Months Ended
	Jun. 30, 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: June 30, 2018 December 31, 2017 Commodity derivative contracts 525,570 MWh 552,310 MWh Commodity derivative contracts 6,002,500 Dth 5,460,000 Dth FTRs 5,326 MW 2,226 MW PPA 2,350 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 June 30, 2018 , and December 31 , 2017 , the fair value of exchange traded derivatives and FTRs exceeded their cost basis by $ 1.8 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 June 30, 2018 , and Dec ember 31, 2017 , reflects a loss position of $ 38.8 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 June 30, 2018 , and December 31, 2017 , the receiv able margin account balance of $ 1.2 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 June 30, 2018 Commodity derivative contracts (a) $ 1,109 $ 209 Other current assets Commodity derivative contracts (a) 71 86 Other deferred charges FTRs 941 - Other current assets PPA N/A 8,860 Derivative liability (current) PPA N/A 29,890 Derivative liability (long-term) December 31, 2017 Commodity derivative contracts (a) $ 566 $ 603 Derivative liability (current) (b) Commodity derivative contracts (a) 110 190 Derivative liability (long-term) FTRs 329 - Other current assets PPA N/A 8,180 Derivative liability (current) PPA N/A 33,990 Derivative liability (long-term) (a ) As of December 31, 2017 , collateral of $0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions a s of June 30, 2018 . (b) As of December 31, 2017 , MGE presented $0.1 million 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 similar arrangement on the consolidated balance sheets. Offsetting of Derivative Assets (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets June 30, 2018 Commodity derivative contracts $ 1,180 $ (295) $ - $ 885 FTRs 941 - - 941 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 June 30, 2018 Commodity derivative contracts $ 295 $ (295) $ - $ - PPA 38,750 - - 38,750 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 June 30, 2018 and 2017 , and the consolidated income statement s for the three and six months ended June 30, 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 June 30: Balance at April 1, $ 41,241 $ 319 $ 48,073 $ 142 Unrealized gain (4,027) - (1,731) - Realized (loss) gain reclassified to a deferred account (363) 363 (544) 544 Realized gain (loss) reclassified to income statement 73 (42) (482) (68) Balance at June 30, $ 36,924 $ 640 $ 45,316 $ 618 Six Months Ended June 30: Balance at January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized gain (3,899) - (2,420) - Realized (loss) gain reclassified to a deferred account (521) 521 (622) 622 Realized loss reclassified to income statement (614) (687) (923) (234) Balance at June 30, $ 36,924 $ 640 $ 45,316 $ 618 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 June 30: Commodity derivative contracts $ (190) $ 22 $ 17 $ 63 FTRs (300) - (439) - PPA 437 - 909 - Six Months Ended June 30: Commodity derivative contracts $ 184 $ 637 $ 402 $ 209 FTRs (475) - (1,124) - PPA 955 - 1,670 - 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 June 30, 2018 , no collateral is required to be, or has been, posted. Certain count erparties extend MGE a credit limit. If MGE exceeds these limits, the counterparties may require collateral to be pos ted. As of June 30, 2018 , no counterparties were in a net liability position. As of 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 June 30, 2018 , no counterparties have defaulted.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments - MGE Energy and MGE. Fair value is defined as the price that would be received to sell an asset or would be paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. The accounting standard clarifies that fair value should be based on the assumptions market participants would use when pricing the asset or liability including ass umptions about risk. The standard also establishes a three level fair value hierarchy based upon the observability of the assumptions used and requires the use of observable market data when available. The levels are: Level 1 - Pricing inputs are quoted p rices within active markets for identical assets or liabilities. Level 2 - Pricing inputs are quoted prices within active markets for similar assets or liabilities; quoted prices for identical or similar instruments in markets that are not active; and mod el-derived valuations that are correlated with or otherwise verifiable by observable market data. Level 3 - Pricing inputs are unobservable and reflect management ' s best estimate of what market participants would use in pricing the asset or liability. a. Fair Value of Financial Assets and Liabilities Recorded at the Carrying Amount. T he carrying amount of cash , cash equivalents, and outstanding commercial paper approximates fair market value due to the short maturity of those investments and obligations. The estimated fair market value of long-term debt is based on quoted market prices for similar financial instruments . 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: June 30, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 95,579 $ 95,579 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper 28,200 28,200 4,000 4,000 Long-term debt (a) 424,670 464,428 426,883 475,282 MGE Assets: Cash and cash equivalents $ 3,128 $ 3,128 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper 28,200 28,200 4,000 4,000 Long-term debt (a) 424,670 464,428 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.1 million and $4.3 million at June 30, 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 June 30, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 2,121 $ 502 $ - $ 1,619 Exchange-traded investments 902 902 - - Total Assets $ 3,023 $ 1,404 $ - $ 1,619 Liabilities: Derivatives, net $ 39,045 $ 94 $ - $ 38,951 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 42,110 $ 94 $ 3,065 $ 38,951 MGE Assets: Derivatives, net $ 2,121 $ 502 $ - $ 1,619 Exchange-traded investments 77 77 - - Total Assets $ 2,198 $ 579 $ - $ 1,619 Liabilities: Derivatives, net $ 39,045 $ 94 $ - $ 38,951 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 42,110 $ 94 $ 3,065 $ 38,951 Fair Value as of December 31, 2017 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 792 792 - - Total Assets $ 1,797 $ 1,070 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 MGE Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 64 64 - - Total Assets $ 1,069 $ 342 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 (b) These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of December 31, 2017. No transfers were made in or out of Level 1 or Level 2 for the six months ended June 30, 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 June 30, 2018 December 31, 2017 Basis adjustment: On peak 91.1 % 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 Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Beginning balance $ (41,463) $ (48,354) $ (42,026) $ (50,305) Realized and unrealized gains (losses): Included in regulatory assets 4,130 2,748 4,693 4,701 Included in other comprehensive income - - - - Included in earnings 82 (550) (460) (1,136) Included in current assets (297) (222) (470) (97) Purchases 6,032 6,186 11,866 12,182 Sales - - - - Issuances - - - - Settlements (5,816) (5,413) (10,935) (10,950) Transfers in and/or out of Level 3 - - - - Balance as of June 30, $ (37,332) $ (45,605) $ (37,332) $ (45,605) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held at June 30, (c) $ - $ - $ - $ - The following table presents total realized and unrealized gains ( losses ) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis (c ) . Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Purchased Power Expense $ 60 $ (487) $ (663) $ (918) Cost of Gas Sold Expense 22 (63) 203 (218) Total $ 82 $ (550) $ (460) $ (1,136) (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	6 Months Ended
	Jun. 30, 2018
Regulated Operations [Abstract]
Joint Plant Ownership	Joint Plant Ownership - MGE Energy and MGE. a. 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, that began in 2017 and will end June 1, 2020, the ownership pe rcentage is adjusted, through a partial sale, based on the amount of capital expenditures foregone. In June 2017, the FERC approved the ownership transfer in Columbia , effective January 1, 2017. During 201 7 , MGE accrued $ 8.8 million of 201 7 foregone capital expenditures 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 January 201 8 , MGE reduced its ownership interest in Columbia from 20.4 % to 19.4 % as a result of the partial sale of plant assets to WPL. During the three and six months ended June 30, 2018 , MGE accr ued less than $0.1 million and $ 1.4 million, respectively, of 201 8 foregone capital expenditures as part of t he ownership transfer agreement . As of June 30, 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 the ownership transfer agreement covering the sale of plant assets to WPL, expected to occur in January 2019. b. Forward Wind. In April 2018, MGE, along with two other utilities, purchased the Forward Wind Energy Center (Forward Wind) , which consists of 86 wind turbines located in Wisconsin with a total capacity of 129 MWs. The aggregate purchase price was approximately $174 million of which MGE's proportionate share is 12.8%, or approximately $23 million. T he purchase of Forward Wind replaced an existing purchase power agreement, under which MGE purchased 12.8% of the facility's energy output. MGE Energy and MGE are required to record a liability for the fair value of an asset retirement obligation ( ARO ) to be recognized in the period in which it is incurred if it can be reasonably estimated. The offsetting associated asset retirement costs are capitalized as a long-lived asset and depreciated over the asset's useful life. As of June 30, 2018 , MGE recorded an obligation of $ 1.6 mill ion for the fair value of its legal liability for AROs associated with Forward Wind . MGE has regulatory treatment and recognizes regulatory assets or liabilities for the timing differences between when we recover legal AROs in rates and when those costs wo uld actually be recognized.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 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 Nonregulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Consolidated Total Three Months Ended June 30, 2018 Operating revenues $ 99,067 $ 24,980 $ 215 $ - $ - $ - $ 124,262 Interdepartmental revenues (245) 3,493 9,847 - - (13,095) - Total operating revenues 98,822 28,473 10,062 - - (13,095) 124,262 Depreciation and amortization (9,575) (2,445) (1,852) - - - (13,872) Other operating expenses (74,535) (24,232) (34) (5) (448) 13,095 (86,159) Operating income (loss) 14,712 1,796 8,176 (5) (448) - 24,231 Other income, net 1,562 752 - 1,916 501 - 4,731 Interest (expense) income, net (2,952) (887) (1,334) - 390 - (4,783) Income before taxes 13,322 1,661 6,842 1,911 443 - 24,179 Income tax provision (2,986) (372) (1,864) (522) (84) - (5,828) Net income $ 10,336 $ 1,289 $ 4,978 $ 1,389 $ 359 $ - $ 18,351 Three Months Ended June 30, 2017 Operating revenues $ 102,306 $ 24,081 $ 76 $ - $ - $ - $ 126,463 Interdepartmental revenues (119) 3,422 11,107 - - (14,410) - Total operating revenues 102,187 27,503 11,183 - - (14,410) 126,463 Depreciation and amortization (9,185) (2,232) (1,858) - - - (13,275) Other operating expenses (a) (78,202) (23,522) (62) - (217) 14,410 (87,593) Operating income (loss) 14,800 1,749 9,263 - (217) - 25,595 Other income (deductions), net (a) 778 361 - 2,506 (75) - 3,570 Interest (expense) income, net (2,801) (805) (1,392) - 112 - (4,886) Income (loss) before taxes 12,777 1,305 7,871 2,506 (180) - 24,279 Income tax (provision) benefit (4,124) (521) (3,158) (1,006) 73 - (8,736) Net income (loss) $ 8,653 $ 784 $ 4,713 $ 1,500 $ (107) $ - $ 15,543 Six Months Ended June 30, 2018 Operating revenues $ 193,458 $ 87,745 $ 691 $ - $ - $ - $ 281,894 Interdepartmental revenues (214) 7,840 19,667 - - (27,293) - Total operating revenues 193,244 95,585 20,358 - - (27,293) 281,894 Depreciation and amortization (18,953) (4,840) (3,702) - - - (27,495) Other operating expenses (151,110) (79,427) (77) (8) (651) 27,293 (203,980) Operating income (loss) 23,181 11,318 16,579 (8) (651) - 50,419 Other income, net 3,292 1,518 - 4,288 552 - 9,650 Interest (expense) income, net (5,819) (1,726) (2,682) - 705 - (9,522) Income before taxes 20,654 11,110 13,897 4,280 606 - 50,547 Income tax provision (4,186) (2,830) (3,786) (1,170) (223) - (12,195) Net income $ 16,468 $ 8,280 $ 10,111 $ 3,110 $ 383 $ - $ 38,352 Six Months Ended June 30, 2017 Operating revenues $ 200,630 $ 82,507 $ 149 $ - $ - $ - $ 283,286 Interdepartmental revenues (224) 7,816 22,177 - - (29,769) - Total operating revenues 200,406 90,323 22,326 - - (29,769) 283,286 Depreciation and amortization (18,085) (4,445) (3,704) - - - (26,234) Other operating expenses (a) (154,208) (74,493) (103) - (586) 29,769 (199,621) Operating income (loss) 28,113 11,385 18,519 - (586) - 57,431 Other income (deductions), net (a) 1,648 760 - 4,984 (297) - 7,095 Interest (expense) income, net (5,577) (1,604) (2,799) - 200 - (9,780) Income (loss) before taxes 24,184 10,541 15,720 4,984 (683) - 54,746 Income tax (provision) benefit (7,578) (4,225) (6,309) (2,003) 212 - (19,903) Net income (loss) $ 16,606 $ 6,316 $ 9,411 $ 2,981 $ (471) $ - $ 34,843 (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 Nonregulated Energy Consolidation/ Elimination Entries Consolidated Total Three Months Ended June 30, 2018 Operating revenues $ 99,067 $ 24,980 $ 215 $ - $ 124,262 Interdepartmental revenues (245) 3,493 9,847 (13,095) - Total operating revenues 98,822 28,473 10,062 (13,095) 124,262 Depreciation and amortization (9,575) (2,445) (1,852) - (13,872) Other operating expenses (b) (77,475) (24,558) (1,898) 13,095 (90,836) Operating income (b) 11,772 1,470 6,312 - 19,554 Other income, net (b) 1,516 706 - - 2,222 Interest expense, net (2,952) (887) (1,334) - (5,173) Net income 10,336 1,289 4,978 - 16,603 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,505) (5,505) Net income attributable to MGE $ 10,336 $ 1,289 $ 4,978 $ (5,505) $ 11,098 Three Months Ended June 30, 2017 Operating revenues $ 102,306 $ 24,080 $ 76 $ - $ 126,462 Interdepartmental revenues (119) 3,423 11,107 (14,411) - Total operating revenues 102,187 27,503 11,183 (14,411) 126,462 Depreciation and amortization (9,185) (2,232) (1,858) - (13,275) Other operating expenses (a), (b) (82,289) (24,033) (3,220) 14,411 (95,131) Operating income (b) 10,713 1,238 6,105 - 18,056 Other income, net (a), (b) 741 351 - - 1,092 Interest expense, net (2,801) (805) (1,392) - (4,998) Net income 8,653 784 4,713 - 14,150 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,396) (5,396) Net income attributable to MGE $ 8,653 $ 784 $ 4,713 $ (5,396) $ 8,754 Six Months Ended June 30, 2018 Operating revenues $ 193,458 $ 87,745 $ 691 $ - $ 281,894 Interdepartmental revenues (214) 7,840 19,667 (27,293) - Total operating revenues 193,244 95,585 20,358 (27,293) 281,894 Depreciation and amortization (18,953) (4,840) (3,702) - (27,495) Other operating expenses (b) (155,206) (82,199) (3,863) 27,293 (213,975) Operating income (b) 19,085 8,546 12,793 - 40,424 Other income, net (b) 3,202 1,460 - - 4,662 Interest expense, net (5,819) (1,726) (2,682) - (10,227) Net income 16,468 8,280 10,111 - 34,859 Less: Net income attributable to noncontrolling interest, net of tax - - - (11,311) (11,311) Net income attributable to MGE $ 16,468 $ 8,280 $ 10,111 $ (11,311) $ 23,548 Six Months Ended June 30, 2017 Operating revenues $ 200,634 $ 82,515 $ 149 $ - $ 283,298 Interdepartmental revenues (228) 7,808 22,177 (29,757) - Total operating revenues 200,406 90,323 22,326 (29,757) 283,298 Depreciation and amortization (18,085) (4,445) (3,704) - (26,234) Other operating expenses (a), (b) (161,715) (78,698) (6,412) 29,757 (217,068) Operating income (b) 20,606 7,180 12,210 - 39,996 Other income, net (a), (b) 1,577 740 - - 2,317 Interest expense, net (5,577) (1,604) (2,799) - (9,980) Net income 16,606 6,316 9,411 - 32,333 Less: Net income attributable to noncontrolling interest, net of tax - - - (10,785) (10,785) Net income attributable to MGE $ 16,606 $ 6,316 $ 9,411 $ (10,785) $ 21,548 (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. The following table shows segment information for assets and capital expenditures: Utility Consolidated (In thousands) MGE Energy Electric Gas Assets not Allocated Nonregulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Total Assets: June 30, 2018 $ 1,112,411 $ 333,621 $ 17,648 $ 266,154 $ 64,135 $ 477,257 $ (377,781) $ 1,893,445 December 31, 2017 1,043,181 344,337 26,345 270,384 61,783 485,548 (376,396) 1,855,182 Capital Expenditures: Six Months Ended June 30, 2018 $ 82,148 $ 14,774 $ - $ 3,467 $ - $ - $ - $ 100,389 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - - - 108,131 Utility Consolidated (In thousands) MGE Electric Gas Assets not Allocated Nonregulated Energy Elimination Entries Total Assets: June 30, 2018 $ 1,112,411 $ 333,621 $ 17,648 $ 266,104 $ (883) $ 1,728,901 December 31, 2017 1,043,181 344,337 26,345 270,334 (156) 1,684,041 Capital Expenditures: Six Months Ended June 30, 2018 $ 82,148 $ 14,774 $ - $ 3,467 $ - $ 100,389 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - 108,131

Significant Accounting Policies

Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 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 accumulated other comprehensive income, and MGE recorded less than a $0.1 million decrease in retained earnings and a corresponding increase in accumulated other comprehensive income, related to equity investments within the scope of this standard. Restricted Cash. In November 2016, the FASB issued authoritative guidance within the 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 g uidance, 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, ch anges 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. Also under the new standard, reporting entities are r equired 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 ben efit 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 ren dered by the pertinent employees during the period. The other components 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 $0.9 million and $2.0 million for the three and six months ended June 30, 2017 , respectively . The standard also only allows the service cost comp onent to be eligible for capitalization prospectively from the effective date of the pronouncement (whereas under previous GAAP, all components of net benefit cost were eligible for capitalization). See Footnote 6 for further information. b . Recently Iss ued 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 Recognition	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 p ower" expense. Under-collection of these costs will continue to be recognized in "Purchased p ower" 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 in January 2018 to defer the over-collection of income tax expense collec ted 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 act ual costs incurred and the amount of costs collected from customers is recorded as a reduction of revenue in the period incurred. Sales to the Market Sales to the market include energy charges, capacity or demand charges, and ancillary charges represente d by wholesale sales of electricity made to third parties who are not ultimate users of the electricity. Most of these sales are spot market transactions on the markets operated by MISO. Each transaction is considered a performance obligation and revenue i s recognized in the period in which energy charges, capacity or demand charges, and ancillary services are sold into MISO. MGE reports on a net basis, transactions on the MISO markets in which it buys and sells power within the same hour to meet electric energy delivery requirements. Transportation of Gas MGE has contracts under which MGE provides gas transportation services to customers whom have elected to purchase gas from a third party and have the gas delivered via pipelines within MGE's service ter ritory. Revenue is recognized as service is rendered or gas is delivered to customers. Tariffs are approved by the PSCW through a rate order and provide gas transportation customers with the standard terms and conditions, including pricing terms.
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 its Performance Unit Plan, non-employee directors and eligible employees, respectively, may receive performance units that entitle the holder to receive a cash payment equal to the value of a designated number of shares of MGE Energy's common stock, plus dividend equivalent payments thereon, at the end of the performance period set in the award . 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 date, the cost of the director or employee services received in exchange for a performance unit award is measured based on the current market value of MGE Energy common stock. The fair value of the awards is re-measured quarterly, including at June 30, 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 accrued and recognized using the graded vesting method. Compensation cost for retirement eligible employees or employees that will become retirement eligible during the vesting schedule are recognized on an abridged horizon as retirement eligibility accelerated vesting .
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. T he carrying amount of cash , cash equivalents, and outstanding commercial paper approximates fair market value due to the short maturity of those investments and obligations. The estimated fair market value of long-term debt is based on quoted market prices for similar financial instruments . 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 June 30, 2018 December 31, 2017 Basis adjustment: On peak 91.1 % 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)	6 Months Ended
	Jun. 30, 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 June 30, December 31, June 30, December 31, (In thousands) 2018 2017 2018 2017 Cash and cash equivalents $ 95,579 $ 107,952 $ 3,128 $ 5,951 Restricted cash 3,516 1,635 3,516 1,635 Receivable - margin account 1,172 2,507 1,172 2,507 Cash, cash equivalents, and restricted cash $ 100,267 $ 112,094 $ 7,816 $ 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. Six Months Ended (In thousands) June 30, 2017 Cash provided by operating activities $ (694) Cash used for investing activities 74 Change in cash, cash equivalents, and restricted cash (620) Cash, cash equivalents, and restricted cash at beginning of period 5,674 Cash, cash equivalents, and restricted cash at end of period $ 5,054

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Revenues disaggregated by revenue source were as follows: Three Months Ended Six Months Ended (In thousands) June 30, June 30, Electric revenues 2018 2017 2018 2017 Residential $ 32,217 $ 31,634 $ 65,476 $ 64,987 Commercial (a) 50,174 54,721 97,626 104,885 Industrial 4,630 4,516 7,525 8,731 Other-retail/municipal 8,527 9,661 16,814 18,682 Total retail 95,548 100,532 187,441 197,285 Sales to the market 2,795 1,050 4,829 2,022 Other revenues 454 562 924 991 Adjustments to revenues 270 162 264 332 Total electric revenues 99,067 102,306 193,458 200,630 Gas revenues Residential 15,620 15,140 52,171 49,043 Commercial/Industrial (a) 8,206 7,842 33,158 30,890 Total retail 23,826 22,982 85,329 79,933 Gas transportation 1,053 991 2,189 2,341 Other revenues 101 108 227 233 Total gas revenues 24,980 24,081 87,745 82,507 Non-regulated energy revenues 215 76 691 149 Total Operating Revenue (a) $ 124,262 $ 126,463 281,894 $ 283,286 (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)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2018 and 2017 , MGE Transco recorded the following : Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Equity earnings from investment in ATC $ 1,990 $ 2,486 $ 4,441 $ 5,094 Dividends from ATC (a) 2,959 2,000 2,959 2,000 Capital contributions to ATC 1,065 888 1,775 2,308 (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 . MGE Transco recorded a $ 1.4 million dividend receivable from ATC as of June 30, 2018 . A cash dividend was received in July 2018 . ATC ' s summarized financial data for the three and six months ended June 30, 2018 and 2017 , is as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Operating revenues $ 165,506 $ 176,610 $ 330,935 $ 351,279 Operating expenses (91,474) (82,974) (176,367) (165,670) Other income, net 1,520 1,088 1,631 1,771 Interest expense, net (26,895) (26,466) (54,657) (53,250) Earnings before members' income taxes $ 48,657 $ 68,258 $ 101,542 $ 134,130

Taxes (Tables)

Taxes (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2018 2017 2018 2017 Statutory federal income tax rate 21.0 % 35.0 % 21.0 % 35.0 % State income taxes, net of federal benefit 6.3 % 5.2 % 6.2 % 5.1 % Amortized investment tax credits (0.1) % (0.3) % (0.1) % (0.4) % Credit for electricity from wind energy (0.4) % (1.5) % (0.4) % (1.6) % Domestic manufacturing deduction - % (1.9) % - % (2.0) % AFUDC equity, net (1.1) % (0.3) % (1.1) % (0.3) % Amortization of utility excess deferred tax - tax reform (a) (1.9) % - % (1.9) % (0.1) % Other, net, individually insignificant 0.3 % (0.2) % 0.2 % (0.2) % Effective income tax rate 24.1 % 36.0 % 23.9 % 35.5 % MGE Energy MGE Six Months Ended June 30, 2018 2017 2018 2017 Statutory federal income tax rate 21.0 % 35.0 % 21.0 % 35.0 % State income taxes, net of federal benefit 6.3 % 5.2 % 6.2 % 5.1 % Amortized investment tax credits (0.1) % (0.3) % (0.1) % (0.4) % Credit for electricity from wind energy (0.3) % (1.4) % (0.3) % (1.6) % Domestic manufacturing deduction - % (1.7) % - % (1.8) % AFUDC equity, net (0.9) % (0.3) % (1.0) % (0.3) % Amortization of utility excess deferred tax - tax reform (a) (1.9) % - % (2.1) % - % Other, net, individually insignificant - % (0.1) % - % (0.1) % Effective income tax rate 24.1 % 36.4 % 23.7 % 35.9 % (a) Included are impacts of the Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting.

Pension and Other Postretirem33

Pension and Other Postretirement Plans (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2018 and 2017 . Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Pension Benefits Components of net periodic benefit cost: Service cost $ 1,404 $ 1,360 $ 2,861 $ 2,692 Interest cost 3,222 3,194 6,430 6,313 Expected return on assets (6,552) (5,740) (13,120) (11,482) Amortization of: Prior service credit (11) (4) (22) (8) Actuarial loss 1,341 1,711 2,639 3,175 Net periodic benefit (credit) cost $ (596) $ 521 $ (1,212) $ 690 Postretirement Benefits Components of net periodic benefit cost: Service cost $ 310 $ 423 $ 642 $ 629 Interest cost 648 912 1,306 1,356 Expected return on assets (814) (971) (1,616) (1,443) Amortization of: Transition obligation - 1 1 1 Prior service credit (667) (898) (1,334) (1,334) Actuarial loss 116 251 244 380 Net periodic benefit (credit) cost $ (407) $ (282) $ (757) $ (411)

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Purchase Contracts, Fiscal Year Maturity Schedule	MGE Energy and MGE have entered into various commodity supply, transportation, and storage contracts to meet their obligations to deliver electricity and natural gas to customers. Management expects to recover these costs in future customer rates. The foll owing table shows future commitments related to purchase contracts as of June 30, 2018 : (In thousands) 2018 2019 2020 2021 2022 Thereafter Coal (a) $ 13,301 $ 17,831 $ 5,297 $ - $ - $ - Natural gas supply (b) 11,624 12,587 - - - - Saratoga wind (c) 1,038 858 2,266 1,775 1,784 4,429 Other 1,772 502 502 502 502 502 $ 27,735 $ 31,778 $ 8,065 $ 2,277 $ 2,286 $ 4,931 (a ) Total coal commitments for the Columbia and Elm Road Units, including transportation. Fuel procurement for MGE's jointly owned Columbia and Elm Road Units is handled by WPL and WEPCO, respectively, who are the operators of those facilities. (b) These commitments include market-based pricing. (c) 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 June 30, 2018, MGE has incurred $ 42.6 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.

Derivative and Hedging Instru35

Derivative and Hedging Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross Notional Volume of Open Derivatives	The gross notional volume of open derivatives is as follows: June 30, 2018 December 31, 2017 Commodity derivative contracts 525,570 MWh 552,310 MWh Commodity derivative contracts 6,002,500 Dth 5,460,000 Dth FTRs 5,326 MW 2,226 MW PPA 2,350 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 June 30, 2018 , and December 31, 2017 , the receiv able margin account balance of $ 1.2 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 June 30, 2018 Commodity derivative contracts (a) $ 1,109 $ 209 Other current assets Commodity derivative contracts (a) 71 86 Other deferred charges FTRs 941 - Other current assets PPA N/A 8,860 Derivative liability (current) PPA N/A 29,890 Derivative liability (long-term) December 31, 2017 Commodity derivative contracts (a) $ 566 $ 603 Derivative liability (current) (b) Commodity derivative contracts (a) 110 190 Derivative liability (long-term) FTRs 329 - Other current assets PPA N/A 8,180 Derivative liability (current) PPA N/A 33,990 Derivative liability (long-term) (a ) As of December 31, 2017 , collateral of $0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions a s of June 30, 2018 . (b) As of December 31, 2017 , MGE presented $0.1 million 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 similar arrangement on the consolidated balance sheets. Offsetting of Derivative Assets (In thousands) Gross Amounts Gross Amounts Offset in Balance Sheets Collateral Posted Against Derivative Positions Net Amount Presented in Balance Sheets June 30, 2018 Commodity derivative contracts $ 1,180 $ (295) $ - $ 885 FTRs 941 - - 941 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 June 30, 2018 Commodity derivative contracts $ 295 $ (295) $ - $ - PPA 38,750 - - 38,750 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 June 30, 2018 and 2017 , and the consolidated income statement s for the three and six months ended June 30, 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 June 30: Balance at April 1, $ 41,241 $ 319 $ 48,073 $ 142 Unrealized gain (4,027) - (1,731) - Realized (loss) gain reclassified to a deferred account (363) 363 (544) 544 Realized gain (loss) reclassified to income statement 73 (42) (482) (68) Balance at June 30, $ 36,924 $ 640 $ 45,316 $ 618 Six Months Ended June 30: Balance at January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized gain (3,899) - (2,420) - Realized (loss) gain reclassified to a deferred account (521) 521 (622) 622 Realized loss reclassified to income statement (614) (687) (923) (234) Balance at June 30, $ 36,924 $ 640 $ 45,316 $ 618
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 June 30: Commodity derivative contracts $ (190) $ 22 $ 17 $ 63 FTRs (300) - (439) - PPA 437 - 909 - Six Months Ended June 30: Commodity derivative contracts $ 184 $ 637 $ 402 $ 209 FTRs (475) - (1,124) - PPA 955 - 1,670 -

Fair Value of Financial Instr36

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Estimated Fair Market Value of Financial Instruments	The estimated fair market value of financial instruments are as follows: June 30, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 95,579 $ 95,579 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper 28,200 28,200 4,000 4,000 Long-term debt (a) 424,670 464,428 426,883 475,282 MGE Assets: Cash and cash equivalents $ 3,128 $ 3,128 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper 28,200 28,200 4,000 4,000 Long-term debt (a) 424,670 464,428 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.1 million and $4.3 million at June 30, 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 June 30, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 2,121 $ 502 $ - $ 1,619 Exchange-traded investments 902 902 - - Total Assets $ 3,023 $ 1,404 $ - $ 1,619 Liabilities: Derivatives, net $ 39,045 $ 94 $ - $ 38,951 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 42,110 $ 94 $ 3,065 $ 38,951 MGE Assets: Derivatives, net $ 2,121 $ 502 $ - $ 1,619 Exchange-traded investments 77 77 - - Total Assets $ 2,198 $ 579 $ - $ 1,619 Liabilities: Derivatives, net $ 39,045 $ 94 $ - $ 38,951 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 42,110 $ 94 $ 3,065 $ 38,951 Fair Value as of December 31, 2017 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 792 792 - - Total Assets $ 1,797 $ 1,070 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 MGE Assets: Derivatives, net $ 1,005 $ 278 $ - $ 727 Exchange-traded investments 64 64 - - Total Assets $ 1,069 $ 342 $ - $ 727 Liabilities: Derivatives, net (b) $ 42,963 $ 210 $ - $ 42,753 Deferred compensation 3,065 - 3,065 - Total Liabilities $ 46,028 $ 210 $ 3,065 $ 42,753 (b) These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of December 31, 2017.
Significant Unobservable Inputs	The following table presents the significant unobservable inputs used in the pricing model. Model Input Significant Unobservable Inputs June 30, 2018 December 31, 2017 Basis adjustment: On peak 91.1 % 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 Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Beginning balance $ (41,463) $ (48,354) $ (42,026) $ (50,305) Realized and unrealized gains (losses): Included in regulatory assets 4,130 2,748 4,693 4,701 Included in other comprehensive income - - - - Included in earnings 82 (550) (460) (1,136) Included in current assets (297) (222) (470) (97) Purchases 6,032 6,186 11,866 12,182 Sales - - - - Issuances - - - - Settlements (5,816) (5,413) (10,935) (10,950) Transfers in and/or out of Level 3 - - - - Balance as of June 30, $ (37,332) $ (45,605) $ (37,332) $ (45,605) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held at June 30, (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 gains ( losses ) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis (c ) . Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2018 2017 2018 2017 Purchased Power Expense $ 60 $ (487) $ (663) $ (918) Cost of Gas Sold Expense 22 (63) 203 (218) Total $ 82 $ (550) $ (460) $ (1,136) (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)	6 Months Ended
	Jun. 30, 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 Nonregulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Consolidated Total Three Months Ended June 30, 2018 Operating revenues $ 99,067 $ 24,980 $ 215 $ - $ - $ - $ 124,262 Interdepartmental revenues (245) 3,493 9,847 - - (13,095) - Total operating revenues 98,822 28,473 10,062 - - (13,095) 124,262 Depreciation and amortization (9,575) (2,445) (1,852) - - - (13,872) Other operating expenses (74,535) (24,232) (34) (5) (448) 13,095 (86,159) Operating income (loss) 14,712 1,796 8,176 (5) (448) - 24,231 Other income, net 1,562 752 - 1,916 501 - 4,731 Interest (expense) income, net (2,952) (887) (1,334) - 390 - (4,783) Income before taxes 13,322 1,661 6,842 1,911 443 - 24,179 Income tax provision (2,986) (372) (1,864) (522) (84) - (5,828) Net income $ 10,336 $ 1,289 $ 4,978 $ 1,389 $ 359 $ - $ 18,351 Three Months Ended June 30, 2017 Operating revenues $ 102,306 $ 24,081 $ 76 $ - $ - $ - $ 126,463 Interdepartmental revenues (119) 3,422 11,107 - - (14,410) - Total operating revenues 102,187 27,503 11,183 - - (14,410) 126,463 Depreciation and amortization (9,185) (2,232) (1,858) - - - (13,275) Other operating expenses (a) (78,202) (23,522) (62) - (217) 14,410 (87,593) Operating income (loss) 14,800 1,749 9,263 - (217) - 25,595 Other income (deductions), net (a) 778 361 - 2,506 (75) - 3,570 Interest (expense) income, net (2,801) (805) (1,392) - 112 - (4,886) Income (loss) before taxes 12,777 1,305 7,871 2,506 (180) - 24,279 Income tax (provision) benefit (4,124) (521) (3,158) (1,006) 73 - (8,736) Net income (loss) $ 8,653 $ 784 $ 4,713 $ 1,500 $ (107) $ - $ 15,543 Six Months Ended June 30, 2018 Operating revenues $ 193,458 $ 87,745 $ 691 $ - $ - $ - $ 281,894 Interdepartmental revenues (214) 7,840 19,667 - - (27,293) - Total operating revenues 193,244 95,585 20,358 - - (27,293) 281,894 Depreciation and amortization (18,953) (4,840) (3,702) - - - (27,495) Other operating expenses (151,110) (79,427) (77) (8) (651) 27,293 (203,980) Operating income (loss) 23,181 11,318 16,579 (8) (651) - 50,419 Other income, net 3,292 1,518 - 4,288 552 - 9,650 Interest (expense) income, net (5,819) (1,726) (2,682) - 705 - (9,522) Income before taxes 20,654 11,110 13,897 4,280 606 - 50,547 Income tax provision (4,186) (2,830) (3,786) (1,170) (223) - (12,195) Net income $ 16,468 $ 8,280 $ 10,111 $ 3,110 $ 383 $ - $ 38,352 Six Months Ended June 30, 2017 Operating revenues $ 200,630 $ 82,507 $ 149 $ - $ - $ - $ 283,286 Interdepartmental revenues (224) 7,816 22,177 - - (29,769) - Total operating revenues 200,406 90,323 22,326 - - (29,769) 283,286 Depreciation and amortization (18,085) (4,445) (3,704) - - - (26,234) Other operating expenses (a) (154,208) (74,493) (103) - (586) 29,769 (199,621) Operating income (loss) 28,113 11,385 18,519 - (586) - 57,431 Other income (deductions), net (a) 1,648 760 - 4,984 (297) - 7,095 Interest (expense) income, net (5,577) (1,604) (2,799) - 200 - (9,780) Income (loss) before taxes 24,184 10,541 15,720 4,984 (683) - 54,746 Income tax (provision) benefit (7,578) (4,225) (6,309) (2,003) 212 - (19,903) Net income (loss) $ 16,606 $ 6,316 $ 9,411 $ 2,981 $ (471) $ - $ 34,843 (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 Nonregulated Energy Consolidation/ Elimination Entries Consolidated Total Three Months Ended June 30, 2018 Operating revenues $ 99,067 $ 24,980 $ 215 $ - $ 124,262 Interdepartmental revenues (245) 3,493 9,847 (13,095) - Total operating revenues 98,822 28,473 10,062 (13,095) 124,262 Depreciation and amortization (9,575) (2,445) (1,852) - (13,872) Other operating expenses (b) (77,475) (24,558) (1,898) 13,095 (90,836) Operating income (b) 11,772 1,470 6,312 - 19,554 Other income, net (b) 1,516 706 - - 2,222 Interest expense, net (2,952) (887) (1,334) - (5,173) Net income 10,336 1,289 4,978 - 16,603 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,505) (5,505) Net income attributable to MGE $ 10,336 $ 1,289 $ 4,978 $ (5,505) $ 11,098 Three Months Ended June 30, 2017 Operating revenues $ 102,306 $ 24,080 $ 76 $ - $ 126,462 Interdepartmental revenues (119) 3,423 11,107 (14,411) - Total operating revenues 102,187 27,503 11,183 (14,411) 126,462 Depreciation and amortization (9,185) (2,232) (1,858) - (13,275) Other operating expenses (a), (b) (82,289) (24,033) (3,220) 14,411 (95,131) Operating income (b) 10,713 1,238 6,105 - 18,056 Other income, net (a), (b) 741 351 - - 1,092 Interest expense, net (2,801) (805) (1,392) - (4,998) Net income 8,653 784 4,713 - 14,150 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,396) (5,396) Net income attributable to MGE $ 8,653 $ 784 $ 4,713 $ (5,396) $ 8,754 Six Months Ended June 30, 2018 Operating revenues $ 193,458 $ 87,745 $ 691 $ - $ 281,894 Interdepartmental revenues (214) 7,840 19,667 (27,293) - Total operating revenues 193,244 95,585 20,358 (27,293) 281,894 Depreciation and amortization (18,953) (4,840) (3,702) - (27,495) Other operating expenses (b) (155,206) (82,199) (3,863) 27,293 (213,975) Operating income (b) 19,085 8,546 12,793 - 40,424 Other income, net (b) 3,202 1,460 - - 4,662 Interest expense, net (5,819) (1,726) (2,682) - (10,227) Net income 16,468 8,280 10,111 - 34,859 Less: Net income attributable to noncontrolling interest, net of tax - - - (11,311) (11,311) Net income attributable to MGE $ 16,468 $ 8,280 $ 10,111 $ (11,311) $ 23,548 Six Months Ended June 30, 2017 Operating revenues $ 200,634 $ 82,515 $ 149 $ - $ 283,298 Interdepartmental revenues (228) 7,808 22,177 (29,757) - Total operating revenues 200,406 90,323 22,326 (29,757) 283,298 Depreciation and amortization (18,085) (4,445) (3,704) - (26,234) Other operating expenses (a), (b) (161,715) (78,698) (6,412) 29,757 (217,068) Operating income (b) 20,606 7,180 12,210 - 39,996 Other income, net (a), (b) 1,577 740 - - 2,317 Interest expense, net (5,577) (1,604) (2,799) - (9,980) Net income 16,606 6,316 9,411 - 32,333 Less: Net income attributable to noncontrolling interest, net of tax - - - (10,785) (10,785) Net income attributable to MGE $ 16,606 $ 6,316 $ 9,411 $ (10,785) $ 21,548 (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. The following table shows segment information for assets and capital expenditures: Utility Consolidated (In thousands) MGE Energy Electric Gas Assets not Allocated Nonregulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Total Assets: June 30, 2018 $ 1,112,411 $ 333,621 $ 17,648 $ 266,154 $ 64,135 $ 477,257 $ (377,781) $ 1,893,445 December 31, 2017 1,043,181 344,337 26,345 270,384 61,783 485,548 (376,396) 1,855,182 Capital Expenditures: Six Months Ended June 30, 2018 $ 82,148 $ 14,774 $ - $ 3,467 $ - $ - $ - $ 100,389 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - - - 108,131 Utility Consolidated (In thousands) MGE Electric Gas Assets not Allocated Nonregulated Energy Elimination Entries Total Assets: June 30, 2018 $ 1,112,411 $ 333,621 $ 17,648 $ 266,104 $ (883) $ 1,728,901 December 31, 2017 1,043,181 344,337 26,345 270,334 (156) 1,684,041 Capital Expenditures: Six Months Ended June 30, 2018 $ 82,148 $ 14,774 $ - $ 3,467 $ - $ 100,389 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - 108,131

Summary of Significant Accoun38

Summary of Significant Accounting Principles (Details-1) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 95,579	$ 107,952
Restricted cash	3,516	1,635
Receivable - margin account	1,172	2,507
Cash, cash equivalents, and restricted cash	100,267	112,094	$ 107,970	$ 101,633
MGE [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	3,128	5,951
Restricted cash	3,516	1,635
Receivable - margin account	1,172	2,507
Cash, cash equivalents, and restricted cash	$ 7,816	$ 10,093	$ 10,885	$ 16,442

Summary of Significant Accoun39

Summary of Significant Accounting Principles (Details-2) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities	$ 91,618,000	$ 67,016,000
Cash used for investing activities	(103,071,000)	(46,874,000)
Change in cash, cash equivalents, and restricted cash	(11,827,000)	6,337,000
Cash, cash equivalents, and restricted cash at beginning of period	112,094,000	101,633,000
Cash, cash equivalents, and restricted cash at end of period	$ 100,267,000	107,970,000
Accounting Standards Update 2016-18 - Restricted Cash [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities		(694,000)
Cash used for investing activities		74,000
Change in cash, cash equivalents, and restricted cash		(620,000)
Cash, cash equivalents, and restricted cash at beginning of period		5,674,000
Cash, cash equivalents, and restricted cash at end of period		$ 5,054,000

New Accounting Standards (Detai

New Accounting Standards (Details-1) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 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)	$ (377)
Cumulative Effect of New Accounting Principle in Period of Adoption	377	377
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	28
Cumulative Effect of New Accounting Principle in Period of Adoption	(28)	(28)
Accounting Standards Update 2017-07 - Compensation - Retirement Benefits [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Effect of New Accounting Principle on Prior Period Presentation	900	2,000
Accounting Standards Update 2017-07 - Compensation - Retirement Benefits [Member] | MGE [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Effect of New Accounting Principle on Prior Period Presentation	$ 900	$ 2,000

Revenue (Details-1)

Revenue (Details-1) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended			12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017		Dec. 31, 2017
Total Operating Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 124,262	$ 126,463	[1]	$ 281,894	$ 283,286	[1]
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	99,067	102,306		193,458	200,630
Electric [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	32,217	31,634		65,476	64,987
Electric [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	50,174	54,721	[1]	97,626	104,885	[1]
Electric [Member] | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	4,630	4,516		7,525	8,731
Electric [Member] | Other-retail/municipal
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	8,527	9,661		16,814	18,682
Electric [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	95,548	100,532		187,441	197,285
Electric [Member] | Sales To The Market [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	2,795	1,050		4,829	2,022
Electric [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	454	562		924	991
Electric [Member] | Adjustments To Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	270	162		264	332
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	24,980	24,081		87,745	82,507
Gas [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	15,620	15,140		52,171	49,043
Gas [Member] | Commercial/Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	8,206	7,842	[1]	33,158	30,890	[1]
Gas [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	23,826	22,982		85,329	79,933
Gas [Member] | Gas Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	1,053	991		2,189	2,341
Gas [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	101	108		227	233
Non Regulated Energy [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 215	$ 76		$ 691	$ 149
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		Jul. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC			$ 1,990	$ 2,486	$ 4,441	$ 5,094
Dividends from ATC			2,959	2,000	3,905	4,072
Capital contributions to investments			1,065	888	3,280	5,557
MGE Transco [Member] | ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC			1,990	2,486	4,441	5,094
Dividends from ATC	[1]		2,959	2,000	2,959	2,000
Capital contributions to investments			$ 1,065	888	$ 1,775	2,308
Ownership interest in equity-method investee			3.60%		3.60%		3.60%
Dividend receivable from ATC			$ 1,400		$ 1,400		$ 2,300	$ 2,100
MGE Transco [Member] | ATC [Member] | Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments		$ 500
MGEE Transco [Member] | ATC Holdco [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments			$ 100	$ 500	$ 200	$ 700
Ownership interest in equity-method investee			4.40%		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 . MGE Transco recorded a $ 1.4 million dividend receivable from ATC as of June 30, 2018 . A cash dividend was received in July 2018 .

Investment in ATC and ATC Hol43

Investment in ATC and ATC Holdco (Details-2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Operating revenues	$ 165,506	$ 176,610	$ 330,935	$ 351,279
Operating expenses	(91,474)	(82,974)	(176,367)	(165,670)
Other income, net	1,520	1,088	1,631	1,771
Interest expense, net	(26,895)	(26,466)	(54,657)	(53,250)
Earnings before members' income taxes	48,657	68,258	101,542	134,130
ATC [Member]
Related Party Transaction [Line Items]
Related party expenses	7,200	$ 7,300	14,400	$ 14,600
Due from related parties	$ 100		$ 100		$ 200

Taxes (Details)

Taxes (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017	Dec. 31, 2017
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate	21.00%		35.00%	21.00%		35.00%
State income taxes, net of federal benefit	6.30%		5.20%	6.30%		5.20%
Amortized investment tax credits	(0.10%)		(0.30%)	(0.10%)		(0.30%)
Credit for electricity from wind energy	(0.40%)		(1.50%)	(0.30%)		(1.40%)
Domestic manufacturing deduction	0.00%		(1.90%)	0.00%		(1.70%)
AFUDC equity, net	(1.10%)		(0.30%)	(0.90%)		(0.30%)
Amortization of utility excess deferred tax - tax reform	(1.90%)	[1]	0.00%	(1.90%)	[1]	0.00%
Other, net, individually significant	0.30%		(0.20%)	0.00%		(0.10%)
Effective income tax rate	24.10%		36.00%	24.10%		36.40%
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	$ 9,110			$ 9,110			$ 5,633
Revenue Subject to Refund | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	1,700			1,700
Return of tax credit	4,100			4,100
Revenue Subject to Refund | Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Return of tax credit, total	$ 600			$ 1,200
MGE [Member]
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate	21.00%		35.00%	21.00%		35.00%
State income taxes, net of federal benefit	6.20%		5.10%	6.20%		5.10%
Amortized investment tax credits	(0.10%)		(0.40%)	(0.10%)		(0.40%)
Credit for electricity from wind energy	(0.40%)		(1.60%)	(0.30%)		(1.60%)
Domestic manufacturing deduction	0.00%		(2.00%)	0.00%		(1.80%)
AFUDC equity, net	(1.10%)		(0.30%)	(1.00%)		(0.30%)
Amortization of utility excess deferred tax - tax reform	(1.90%)	[1]	(0.10%)	(2.10%)	[1]	0.00%
Other, net, individually significant	0.20%		(0.20%)	0.00%		(0.10%)
Effective income tax rate	23.90%		35.50%	23.70%		35.90%
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	$ 9,110			$ 9,110			$ 5,633
[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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 1,404	$ 1,360	$ 2,861	$ 2,692
Interest cost	3,222	3,194	6,430	6,313
Expected return on assets	(6,552)	(5,740)	(13,120)	(11,482)
Amortization of:
Prior service credit	(11)	(4)	(22)	(8)
Actuarial loss	1,341	1,711	2,639	3,175
Net periodic benefit (credit) cost	(596)	521	(1,212)	690
Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	310	423	642	629
Interest cost	648	912	1,306	1,356
Expected return on assets	(814)	(971)	(1,616)	(1,443)
Amortization of:
Transition obligation	0	1	1	1
Prior service credit	(667)	(898)	(1,334)	(1,334)
Actuarial loss	116	251	244	380
Net periodic benefit (credit) cost	$ (407)	$ (282)	$ (757)	$ (411)

Equity and Financing Arrangem46

Equity and Financing Arrangements (Details) - USD ($)	Jul. 16, 2018	Jun. 30, 2018	Jun. 30, 2017
Common Stock [Abstract]
Common stock issued during period		0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities		$ 0
Future Debt Issuance, 4.24% due 2053 | Subsequent Event [Member]
Debt Instrument [Line Items]
Face amount	$ 20,000,000
Interest rate	4.24%
Term	35 years
Future Debt Issuance, 4.34% due 2058 | Subsequent Event [Member]
Debt Instrument [Line Items]
Face amount	$ 20,000,000
Interest rate	4.34%
Term	40 years
Future Debt Issuance, 4.19% due 2048 | Subsequent Event [Member]
Debt Instrument [Line Items]
Face amount	$ 60,000,000
Interest rate	4.19%
Term	30 years
Senior Notes, 5.59% due 2018
Debt Instrument [Line Items]
Long-term debt, gross		$ 20,000,000

Share Based Compensation (Detai

Share Based Compensation (Details) - Performance Units [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense		$ 0.8	$ 0.2	$ 1	$ 0.7
Cash payments distributed related to awards previously granted and now payable	$ 1.6
Awards forfeited during period, value		$ 0	$ 0	$ 0	$ 0
Awards forfeited during period, units		0	0	0	0
Outstanding awards vested during period				$ 5.4
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) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)TurbinesMW
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	$ 27,735
Purchase obligation, 2019	31,778
Purchase obligation, 2020	8,065
Purchase obligation, 2021	2,277
Purchase obligation, 2022	2,286
Purchase obligation, Thereafter	4,931
Coal [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	13,301	[1]
Purchase obligation, 2019	17,831	[1]
Purchase obligation, 2020	5,297	[1]
Purchase obligation, 2021	0	[1]
Purchase obligation, 2022	0	[1]
Purchase obligation, Thereafter	0	[1]
Natual Gas, Supply [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	11,624	[2]
Purchase obligation, 2019	12,587	[2]
Purchase obligation, 2020	0	[2]
Purchase obligation, 2021	0	[2]
Purchase obligation, 2022	0	[2]
Purchase obligation, Thereafter	0	[2]
Saratoga Wind [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	1,038	[3]
Purchase obligation, 2019	858	[3]
Purchase obligation, 2020	2,266	[3]
Purchase obligation, 2021	1,775	[3]
Purchase obligation, 2022	1,784	[3]
Purchase obligation, Thereafter	$ 4,429	[3]
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	$ 42,600
Saratoga Wind [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC Rate	100.00%
Other [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	$ 1,772
Purchase obligation, 2019	502
Purchase obligation, 2020	502
Purchase obligation, 2021	502
Purchase obligation, 2022	502
Purchase obligation, Thereafter	$ 502
[1]	Total coal commitments for the Columbia and Elm Road Units, including transportation. Fuel procurement for MGE's jointly owned Columbia and Elm Road Units is handled by WPL and WEPCO, respectively, who are the operators of those facilities.
[2]	These commitments include market-based pricing.
[3]	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 June 30, 2018, MGE has incurred $ 42.6 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 (Details)

Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2018	Jun. 30, 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	$ 5.2						$ 1.8
Public Utilities Fuel Surcharge Amount				$ 0.5
Public Utilities Fuel Surcharge Percentage				0.13%
Fuel Rules Refund, 2015/2016 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total					$ 6.2
Fuel Rules Refund, 2017 [Member] | Subsequent Event [Member]
Fuel Rules [Abstract]
Electric fuel credit ($)						$ 4.2
Proposed Future Rate Matters [Member] | Subsequent Event [Member]
Rate Proceedings [Abstract]
Proposed return on equity, percentage		9.80%	9.80%
Proposed equity capital structure, percentage		56.10%	56.60%
Electric Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					(0.80%)
Authorized rate increase (decrease), amount					$ (3.3)
Electric Rate Proceeding [Member] | Proposed Future Rate Matters [Member] | Subsequent Event [Member]
Rate Proceedings [Abstract]
Proposed rate increase (decrease), percentage		0.00%	(1.94%)
Gas Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					1.90%
Authorized rate increase (decrease), amount					$ 3.1
Gas Rate Proceeding [Member] | Proposed Future Rate Matters [Member] | Subsequent Event [Member]
Rate Proceedings [Abstract]
Proposed rate increase (decrease), percentage		1.46%	1.06%

Derivative and Hedging Instru50

Derivative and Hedging Instruments (Details-1) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2018USD ($)DthMWhMW		Dec. 31, 2017USD ($)DthMWhMW	Mar. 31, 2018USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Derivative fair values [Abstract]
Receivable, margin account balance, net of collateral posted against derivative positions		$ 1,172		$ 2,507
Other Current Assets [Member]
Derivative fair values [Abstract]
Derivative fair value, net		640		806	$ 319	$ 618	$ 142	$ 230
Commodity Contracts And Financial Transimission Rights [Member]
Derivative fair values [Abstract]
Derivative fair value, net		$ 1,800		$ 200
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		525,570		552,310
Notional amount, decatherm measure (in Dth) | Dth		6,002,500		5,460,000
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 1,180		$ 676
Liability Derivatives, fair value, gross basis		295		793
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	1,109
Liability Derivatives, fair value, gross basis		209	[1]	100
Derivative, right to reclaim collateral (receivable)		0
Commodity Derivative Contracts [Member] | Other Deferred Charges [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	71
Liability Derivatives, fair value, gross basis	[1]	$ 86
Commodity Derivative Contracts [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1],[2]			566
Liability Derivatives, fair value, gross basis	[1],[2]			603
Derivative, right to reclaim collateral (receivable)				100
Commodity Derivative Contracts [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]			110
Liability Derivatives, fair value, gross basis	[1]			$ 190
Energy Related Commodity Contract [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Maximum term of derivative hedging contract		4 years
Financial Transmission Rights [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		5,326		2,226
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 941		$ 329
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		941		329
Liability Derivatives, fair value, gross basis		$ 0		$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		2,350		2,650
Derivative fair values [Abstract]
Derivative fair value, net		$ (38,800)		$ (42,200)
Liability Derivatives, fair value, gross basis		38,750		42,170
PPA [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		8,860		8,180
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		$ 29,890		$ 33,990
[1]	As of December 31, 2017 , collateral of $0.1 million was posted against and netted with derivative liability positions on the consolidated balance sheets. No collateral was posted against derivative positions a s of June 30, 2018 .
[2]	As of December 31, 2017 , MGE presented $0.1 million as other current assets on the consolidated balance sheets.

Derivative and Hedging Instru51

Derivative and Hedging Instruments (Details-2) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Commodity Derivative Contracts [Member]
Offsetting Assets [Line Items]
Gross amounts	$ 1,180	$ 676
Gross amounts offset in balance sheet	(295)	(654)
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	885	22
Financial Transmission Rights [Member]
Offsetting Assets [Line Items]
Gross amounts	941	329
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 941	$ 329

Derivative and Hedging Instru52

Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Collateral posted against derivative positions	$ 0	$ (100)
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	295	793
Gross amounts offset in balance sheet	(295)	(654)
Collateral posted against derivative positions	0	(139)
Net amount presented in balance sheet	0	0
Purchased Power Agreement [Member]
Offsetting Liabilities [Line Items]
Gross amounts	38,750	42,170
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 38,750	$ 42,170

Derivative and Hedging Instru53

Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 41,241	$ 48,073	$ 41,958	$ 49,281
Unrealized loss (gain)	(4,027)	(1,731)	(3,899)	(2,420)
Realized (loss) gain reclassified to a deferred account	(363)	(544)	(521)	(622)
Realized gain (loss) reclassified to income statement	73	(482)	(614)	(923)
Ending balance,	36,924	45,316	36,924	45,316
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	319	142	806	230
Unrealized loss (gain)	0	0	0	0
Realized (loss) gain reclassified to a deferred account	363	544	521	622
Realized gain (loss) reclassified to income statement	(42)	(68)	(687)	(234)
Ending balance,	$ 640	$ 618	$ 640	$ 618

Derivative and Hedging Instru54

Derivative and Hedging Instruments (Details-5) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018USD ($)counterparty	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)counterparty	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Counterparties in net liability position or default [Abstract]
Derivative, net liability position of counterparties	$ 0		$ 0		$ 100
Number of counterparties in default | counterparty	0		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	$ (190)	$ 17	$ 184	$ 402
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	22	63	637	209
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	(300)	(439)	(475)	(1,124)
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	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		20,000
Maximum collateral that may be required to be posted	40,000		40,000
Collateral posted	0		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	437	909	955	1,670
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	$ 0	$ 0

Fair Value of Financial Instr55

Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,100	$ 4,300
Carrying Amount [Member]
Assets:
Cash and cash equivalents		95,579	107,952
Liabilities:
Short-term debt - commercial paper		28,200	4,000
Long-term debt	[1]	424,670	426,883
Fair Value [Member]
Assets:
Cash and cash equivalents		95,579	107,952
Liabilities:
Short-term debt - commercial paper		28,200	4,000
Long-term debt	[1]	464,428	475,282
MGE [Member] | Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		4,100	4,300
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		3,128	5,951
Liabilities:
Short-term debt - commercial paper		28,200	4,000
Long-term debt	[1]	424,670	426,883
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		3,128	5,951
Liabilities:
Short-term debt - commercial paper		28,200	4,000
Long-term debt	[1]	$ 464,428	$ 475,282
[1]	Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.1 million and $4.3 million at June 30, 2018 and December 31, 2017, respectively.

Fair Value of Financial Instr56

Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Liabilities:
Derivative liability, collateral offset	$ 0	$ 100
Recurring [Member]
Assets:
Derivatives	2,121	1,005
Total Assets	3,023	1,797
Liabilities:
Derivatives	39,045	42,963	[1]
Deferred compensation	3,065	3,065
Total liabilities	42,110	46,028
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	902	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	502	278
Total Assets	1,404	1,070
Liabilities:
Derivatives	94	210	[1]
Deferred compensation	0	0
Total liabilities	94	210
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	902	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	0
Total Assets	0	0
Liabilities:
Derivatives	0	0	[1]
Deferred compensation	3,065	3,065
Total liabilities	3,065	3,065
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivatives	1,619	727
Total Assets	1,619	727
Liabilities:
Derivatives	38,951	42,753	[1]
Deferred compensation	0	0
Total liabilities	38,951	42,753
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
MGE [Member]
Liabilities:
Derivative liability, collateral offset	0	100
MGE [Member] | Recurring [Member]
Assets:
Derivatives	2,121	1,005
Total Assets	2,198	1,069
Liabilities:
Derivatives	39,045	42,963	[1]
Deferred compensation	3,065	3,065
Total liabilities	42,110	46,028
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	77	64
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	502	278
Total Assets	579	342
Liabilities:
Derivatives	94	210	[1]
Deferred compensation	0	0
Total liabilities	94	210
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	77	64
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	0
Total Assets	0	0
Liabilities:
Derivatives	0	0	[1]
Deferred compensation	3,065	3,065
Total liabilities	3,065	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	1,619	727
Total Assets	1,619	727
Liabilities:
Derivatives	38,951	42,753	[1]
Deferred compensation	0	0
Total liabilities	38,951	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 December 31, 2017.

Fair Value of Financial Instr57

Fair Value of Financial Instruments (Details-3)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Basis adjustment:
Basis adjustment - on peak	91.10%	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		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance,		$ (41,463)	$ (48,354)	$ (42,026)	$ (50,305)
Realized and unrealized gains (losses):
Included in regulatory assets		4,130	2,748	4,693	4,701
Included in other comprehensive income		0	0	0	0
Included in earnings	[1]	82	(550)	(460)	(1,136)
Included in current assets		(297)	(222)	(470)	(97)
Purchases		6,032	6,186	11,866	12,182
Sales		0	0	0	0
Issuances		0	0	0	0
Settlements		(5,816)	(5,413)	(10,935)	(10,950)
Transfers in and/or out of level 3		0	0	0	0
Ending balance,		(37,332)	(45,605)	(37,332)	(45,605)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	0	0	0	0
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	60	(487)	(663)	(918)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ 22	$ (63)	$ 203	$ (218)
[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) $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2018USD ($)TurbinesMW	Jun. 30, 2018USD ($)TurbinesMW	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2018	Jan. 01, 2018
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	$ 1,392	$ 1,392		$ 8,817
Accrued capital expenditures		6,467	$ 8,450
Forward Wind Purchase Power Energy Output				12.80%	12.80%
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	1,392	1,392		$ 8,817
Accrued capital expenditures		6,467	$ 8,450
Columbia Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest				20.40%		19.40%
Assets held for sale	1,400	1,400		$ 8,800
Accrued capital expenditures	$ 100	$ 1,400		$ 8,800
Forward Wind Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	12.80%	12.80%
Jointly owned utility plant, plant capacity (in MW) | MW	129	129
Forward Wind Turbines | Turbines	86	86
Forward Wind Proportionate Purchase Price	$ 23,000	$ 23,000
Forward Wind Purchase Power Energy Output				12.80%	12.80%
Forward Wind Asset Retirement Obligation	1,600	1,600
Forward Wind Units [Member] | Joint Owners [Member]
Jointly Owned Utility Plant Interests [Line Items]
Forward Wind Aggregate Purchase Price	$ 174,000	$ 174,000

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended			12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 124,262	$ 126,463		$ 281,894	$ 283,286
Depreciation and amortization	(13,872)	(13,275)		(27,495)	(26,234)
Other operating expenses	(86,159)	(87,593)	[1]	(203,980)	(199,621)	[1]
Operating income (loss)	24,231	25,595		50,419	57,431
Other income (deductions), net	4,731	3,570	[1]	9,650	7,095	[1]
Interest (expense) income, net	(4,783)	(4,886)		(9,522)	(9,780)
Income before income taxes	24,179	24,279		50,547	54,746
Income tax (provision) benefit	(5,828)	(8,736)		(12,195)	(19,903)
Net Income (Loss)	18,351	15,543		38,352	34,843
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,893,445			1,893,445			$ 1,855,182
Capital expenditures				100,389	42,169		108,131
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	99,067	102,306		193,458	200,630
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	24,980	24,081		87,745	82,507
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	215	76		691	149
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0		0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0		0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	124,262	126,463		281,894	283,286
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,822	102,187		193,244	200,406
Depreciation and amortization	(9,575)	(9,185)		(18,953)	(18,085)
Other operating expenses	(74,535)	(78,202)	[1]	(151,110)	(154,208)	[1]
Operating income (loss)	14,712	14,800		23,181	28,113
Other income (deductions), net	1,562	778	[1]	3,292	1,648	[1]
Interest (expense) income, net	(2,952)	(2,801)		(5,819)	(5,577)
Income before income taxes	13,322	12,777		20,654	24,184
Income tax (provision) benefit	(2,986)	(4,124)		(4,186)	(7,578)
Net Income (Loss)	10,336	8,653		16,468	16,606
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,112,411			1,112,411			1,043,181
Capital expenditures				82,148			77,353
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	28,473	27,503		95,585	90,323
Depreciation and amortization	(2,445)	(2,232)		(4,840)	(4,445)
Other operating expenses	(24,232)	(23,522)	[1]	(79,427)	(74,493)	[1]
Operating income (loss)	1,796	1,749		11,318	11,385
Other income (deductions), net	752	361	[1]	1,518	760	[1]
Interest (expense) income, net	(887)	(805)		(1,726)	(1,604)
Income before income taxes	1,661	1,305		11,110	10,541
Income tax (provision) benefit	(372)	(521)		(2,830)	(4,225)
Net Income (Loss)	1,289	784		8,280	6,316
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	333,621			333,621			344,337
Capital expenditures				14,774			26,847
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,062	11,183		20,358	22,326
Depreciation and amortization	(1,852)	(1,858)		(3,702)	(3,704)
Other operating expenses	(34)	(62)	[1]	(77)	(103)	[1]
Operating income (loss)	8,176	9,263		16,579	18,519
Other income (deductions), net	0	0	[1]	0	0	[1]
Interest (expense) income, net	(1,334)	(1,392)		(2,682)	(2,799)
Income before income taxes	6,842	7,871		13,897	15,720
Income tax (provision) benefit	(1,864)	(3,158)		(3,786)	(6,309)
Net Income (Loss)	4,978	4,713		10,111	9,411
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	266,154			266,154			270,384
Capital expenditures				3,467			3,931
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0		0	0
Depreciation and amortization	0	0		0	0
Other operating expenses	(5)	0	[1]	(8)	0	[1]
Operating income (loss)	(5)	0		(8)	0
Other income (deductions), net	1,916	2,506	[1]	4,288	4,984	[1]
Interest (expense) income, net	0	0		0	0
Income before income taxes	1,911	2,506		4,280	4,984
Income tax (provision) benefit	(522)	(1,006)		(1,170)	(2,003)
Net Income (Loss)	1,389	1,500		3,110	2,981
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	64,135			64,135			61,783
Capital expenditures				0			0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0		0	0
Depreciation and amortization	0	0		0	0
Other operating expenses	(448)	(217)	[1]	(651)	(586)	[1]
Operating income (loss)	(448)	(217)		(651)	(586)
Other income (deductions), net	501	(75)	[1]	552	(297)	[1]
Interest (expense) income, net	390	112		705	200
Income before income taxes	443	(180)		606	(683)
Income tax (provision) benefit	(84)	73		(223)	212
Net Income (Loss)	359	(107)		383	(471)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	477,257			477,257			485,548
Capital expenditures				0			0
Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	17,648			17,648			26,345
Capital expenditures				0			0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(13,095)	(14,410)		(27,293)	(29,769)
Depreciation and amortization	0	0		0	0
Other operating expenses	13,095	14,410	[1]	27,293	29,769	[1]
Operating income (loss)	0	0		0	0
Other income (deductions), net	0	0	[1]	0	0	[1]
Interest (expense) income, net	0	0		0	0
Income before income taxes	0	0		0	0
Income tax (provision) benefit	0	0		0	0
Net Income (Loss)	0	0		0	0
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(377,781)			(377,781)			(376,396)
Capital expenditures				0			0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	(245)	(119)		(214)	(224)
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,493	3,422		7,840	7,816
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,847	11,107		19,667	22,177
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0		0	0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0		0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	124,262	126,462		281,894	283,298
Depreciation and amortization	(13,872)	(13,275)		(27,495)	(26,234)
Other operating expenses	(90,836)	(95,131)	[1],[2]	(213,975)	(217,068)	[1],[2]
Operating income (loss)	19,554	18,056	[2]	40,424	39,996	[2]
Other income (deductions), net	2,222	1,092	[1],[2]	4,662	2,317	[1],[2]
Interest (expense) income, net	(5,173)	(4,998)		(10,227)	(9,980)
Net Income Including Noncontrolling Interest	16,603	14,150		34,859	32,333
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,505)	(5,396)		(11,311)	(10,785)
Net Income (Loss)	11,098	8,754		23,548	21,548
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,728,901			1,728,901			1,684,041
Capital expenditures				100,389	42,169		108,131
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	99,067	102,306		193,458	200,634
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	24,980	24,080		87,745	82,515
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	215	76		691	149
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	124,262	126,462		281,894	283,298
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,822	102,187		193,244	200,406
Depreciation and amortization	(9,575)	(9,185)		(18,953)	(18,085)
Other operating expenses	(77,475)	(82,289)	[1],[2]	(155,206)	(161,715)	[1],[2]
Operating income (loss)	11,772	10,713	[2]	19,085	20,606	[2]
Other income (deductions), net	1,516	741	[1],[2]	3,202	1,577	[1],[2]
Interest (expense) income, net	(2,952)	(2,801)		(5,819)	(5,577)
Net Income Including Noncontrolling Interest	10,336	8,653		16,468	16,606
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0		0	0
Net Income (Loss)	10,336	8,653		16,468	16,606
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,112,411			1,112,411			1,043,181
Capital expenditures				82,148			77,353
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	28,473	27,503		95,585	90,323
Depreciation and amortization	(2,445)	(2,232)		(4,840)	(4,445)
Other operating expenses	(24,558)	(24,033)	[1],[2]	(82,199)	(78,698)	[1],[2]
Operating income (loss)	1,470	1,238	[2]	8,546	7,180	[2]
Other income (deductions), net	706	351	[1],[2]	1,460	740	[1],[2]
Interest (expense) income, net	(887)	(805)		(1,726)	(1,604)
Net Income Including Noncontrolling Interest	1,289	784		8,280	6,316
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0		0	0
Net Income (Loss)	1,289	784		8,280	6,316
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	333,621			333,621			344,337
Capital expenditures				14,774			26,847
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,062	11,183		20,358	22,326
Depreciation and amortization	(1,852)	(1,858)		(3,702)	(3,704)
Other operating expenses	(1,898)	(3,220)	[1],[2]	(3,863)	(6,412)	[1],[2]
Operating income (loss)	6,312	6,105	[2]	12,793	12,210	[2]
Other income (deductions), net	0	0	[1],[2]	0	0	[1],[2]
Interest (expense) income, net	(1,334)	(1,392)		(2,682)	(2,799)
Net Income Including Noncontrolling Interest	4,978	4,713		10,111	9,411
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0		0	0
Net Income (Loss)	4,978	4,713		10,111	9,411
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	266,104			266,104			270,334
Capital expenditures				3,467			3,931
MGE [Member] | Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	17,648			17,648			26,345
Capital expenditures				0			0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(13,095)	(14,411)		(27,293)	(29,757)
Depreciation and amortization	0	0		0	0
Other operating expenses	13,095	14,411	[1],[2]	27,293	29,757	[1],[2]
Operating income (loss)	0	0	[2]	0	0	[2]
Other income (deductions), net	0	0	[1],[2]	0	0	[1],[2]
Interest (expense) income, net	0	0		0	0
Net Income Including Noncontrolling Interest	0	0		0	0
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,505)	(5,396)		(11,311)	(10,785)
Net Income (Loss)	(5,505)	(5,396)		(11,311)	(10,785)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(883)			(883)			(156)
Capital expenditures				0			$ 0
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	(245)	(119)		(214)	(228)
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,493	3,423		7,840	7,808
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 9,847	$ 11,107		$ 19,667	$ 22,177
[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.