Madison Gas & Electric 10-Q 6 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 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	Sep. 30, 2018
Amendment Flag	false
Trading Symbol	MGEE
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding		34,668,370
Entity Emerging Growth Company	false
Entity Small Business	false
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			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Operating Revenues:
Electric revenues	$ 119,388	$ 120,761		$ 313,537	$ 321,540
Gas revenue	18,407	18,778		106,152	101,285
Total Operating Revenues	137,795	139,539		419,689	422,825
Operating Expenses:
Fuel for electric generation	16,793	15,829		43,944	39,938
Purchased power	13,024	15,984		43,036	48,058
Cost of gas sold	4,921	5,094		54,109	50,109
Other operations and maintenance	44,130	42,533		131,976	131,177
Depreciation and amortization	14,259	13,372		41,754	39,606
Other general taxes	4,870	4,730		14,653	14,509
Total Operating Expenses	97,997	97,542		329,472	323,397
Operating Income	39,798	41,997		90,217	99,428
Other income, net	4,330	4,943	[1]	13,980	12,038	[1]
Interest expense, net	(5,025)	(4,727)		(14,547)	(14,507)
Income before income taxes	39,103	42,213		89,650	96,959
Income tax provision	(9,597)	(15,584)		(21,792)	(35,487)
Net Income	$ 29,506	$ 26,629		$ 67,858	$ 61,472
Earnings Per Share of Common Stock (basic and diluted)	$ 0.85	$ 0.77		$ 1.96	$ 1.77
Dividends per share of common stock	$ 0.338	$ 0.323		$ 0.983	$ 0.938
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			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Operating Revenues:
Electric revenues	$ 119,388	$ 120,761		$ 313,537	$ 321,540
Gas revenue	18,407	18,778		106,152	101,285
Total Operating Revenues	137,795	139,539		419,689	422,825
Operating Expenses:
Fuel for electric generation	16,793	15,829		43,944	39,938
Purchased power	13,024	15,984		43,036	48,058
Cost of gas sold	4,921	5,094		54,109	50,109
Other operations and maintenance	44,130	42,533		131,976	131,177
Depreciation and amortization	14,259	13,372		41,754	39,606
Other general taxes	4,870	4,730		14,653	14,509
Total Operating Expenses	97,997	97,542		329,472	323,397
Operating Income	39,798	41,997		90,217	99,428
Other Income and Deductions:
Equity earnings in MGE Transco	1,672	2,338		6,113	7,432
Total Other Income and Deductions	4,330	4,943	[1]	13,980	12,038	[1]
Interest Expense:
Net Interest Expense	5,025	4,727		14,547	14,507
Net Income	29,506	26,629		67,858	61,472
MGE [Member]
Operating Revenues:
Electric revenues	119,388	120,760		313,537	321,543
Gas revenue	18,407	18,779		106,152	101,294
Total Operating Revenues	137,795	139,539		419,689	422,837
Operating Expenses:
Fuel for electric generation	16,793	15,828		43,944	39,939
Purchased power	13,024	15,985		43,036	48,061
Cost of gas sold	4,921	5,094		54,109	50,117
Other operations and maintenance	43,987	42,331		131,175	130,389
Depreciation and amortization	14,259	13,372		41,754	39,606
Other general taxes	4,870	4,730		14,653	14,509
Income tax provision	9,048	14,059		19,701	32,080
Total Operating Expenses	106,902	111,399		348,372	354,701
Operating Income	30,893	28,140	[2]	71,317	68,136	[2]
Other Income and Deductions:
AFUDC - equity funds	764	310		2,023	875
Income tax provision	(69)	(663)		(218)	(754)
Other income, net	1,828	2,492		5,380	4,335
Total Other Income and Deductions	2,523	2,139	[1],[2]	7,185	4,456	[1],[2]
Income before interest expense	33,416	30,279		78,502	72,592
Interest Expense:
Interest on long-term debt	5,696	4,995		16,093	15,051
Other interest, net	62	54		317	150
AFUDC - borrowed funds	(258)	(123)		(683)	(295)
Net Interest Expense	5,500	4,926		15,727	14,906
Net Income Including Noncontrolling Interest	27,916	25,353		62,775	57,686
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,629)	(5,439)		(16,940)	(16,224)
Net Income	$ 22,287	$ 19,914		$ 45,835	$ 41,462
[1]	Reflects retrospective application of new accounting pronouncement related to pension and other postretirement benefits, see Footnote 2 for further information.
[2]	Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.

MGE Energy Inc Consolidated S_2

MGE Energy Inc Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income [Abstract]
Net Income	$ 29,506	$ 26,629	$ 67,858	$ 61,472
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	0	60	0	189
Comprehensive Income	$ 29,506	$ 26,689	$ 67,858	$ 61,661

Madison Gas and Electric Comp_2

Madison Gas and Electric Company Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	$ 0	$ 60	$ 0	$ 189
Comprehensive Income	29,506	26,689	67,858	61,661
MGE [Member]
Net Income	27,916	25,353	62,775	57,686
Other comprehensive income, net of tax:
Unrealized gain (loss) on available-for-sale securities, net of tax	0	(7)	0	(38)
Total comprehensive income including noncontrolling interest	27,916	25,346	62,775	57,648
Less: Comprehensive income attributable to Noncontrolling Interest, net of tax	(5,629)	(5,439)	(16,940)	(16,224)
Comprehensive Income	$ 22,287	$ 19,907	$ 45,835	$ 41,424

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) (Parantheticals) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Unrealized gain (loss) on available-for-sale securities, tax expense (benefit)	$ 0	$ 40	$ 0	$ 127
MGE [Member]
Unrealized gain (loss) on available-for-sale securities, tax expense (benefit)	$ 0	$ (5)	$ 0	$ (26)

MGE Energy Inc Consolidated S_3

MGE Energy Inc Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating Activities:
Net Income	$ 67,858	$ 61,472
Items not affecting cash:
Depreciation and amortization	41,754	39,606
Deferred income taxes	2,352	4,810
Provision for doubtful receivables	642	650
Employee benefit plan (credit) cost	(1,544)	778
Equity earnings in ATC	(6,113)	(7,432)
Gain on sale of property	0	(1,581)
Other items	31	1,103
Changes in working capital items:
Decrease in current assets	25,530	15,259
Increase (decrease) in current liabilities	6,026	(17,615)
Dividends from ATC	5,336	6,142
Cash contributions to pension and other postretirement plans	(3,967)	(9,717)
Other noncurrent items, net	527	2,671
Cash Provided by Operating Activities	138,432	96,146
Investing Activities:
Capital expenditures	(149,001)	(66,286)
Capital contributions to investments	(4,801)	(6,863)
Proceeds from sale of property	0	2,399
Other	368	161
Cash Used for Investing Activities	(153,434)	(70,589)
Financing Activities:
Cash dividends paid on common stock	(34,062)	(32,502)
Repayment of long-term debt	(23,330)	(33,260)
Issuance of long-term debt	100,000	40,000
(Repayments of) proceeds from short-term debt	(4,000)	7,000
Other	(659)	(366)
Cash Provided by (Used for) Financing Activities	37,949	(19,128)
Change in cash, cash equivalents, and restricted cash	22,947	6,429
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633
Cash, cash equivalents, and restricted cash at end of period	135,041	108,062
Significant noncash investing activities:
Accrued capital expenditures	$ 10,991	$ 12,469

Madison Gas and Electric Comp_3

Madison Gas and Electric Company Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Items not affecting cash:
Depreciation and amortization	$ 41,754	$ 39,606
Deferred income taxes	2,352	4,810
Provision for doubtful receivables	642	650
Employee benefit plan (credit) cost	(1,544)	778
Equity earnings in MGE Transco	(6,113)	(7,432)
Gain on sale of property	0	(1,581)
Other items	31	1,103
Changes in working capital items:
Decrease in current assets	25,530	15,259
Increase (decrease) in current liabilities	6,026	(17,615)
Cash contributions to pension and other postretirement plans	(3,967)	(9,717)
Other noncurrent items, net	527	2,671
Cash Provided by Operating Activities	138,432	96,146
Investing Activities:
Capital expenditures	(149,001)	(66,286)
Capital contributions to investments	(4,801)	(6,863)
Proceeds from sale of property	0	2,399
Other	368	161
Cash Used for Investing Activities	(153,434)	(70,589)
Financing Activities:
Repayment of long-term debt	(23,330)	(33,260)
Issuance of long-term debt	100,000	40,000
(Repayments of) proceeds from short-term debt	(4,000)	7,000
Other	(659)	(366)
Cash Provided by (Used for) Financing Activities	37,949	(19,128)
Change in cash, cash equivalents, and restricted cash	22,947	6,429
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633
Cash, cash equivalents, and restricted cash at end of period	135,041	108,062
Significant noncash investing activities:
Accrued capital expenditures	10,991	12,469
MGE [Member]
Operating Activities:
Net Income	62,775	57,686
Items not affecting cash:
Depreciation and amortization	41,754	39,606
Deferred income taxes	(580)	2,255
Provision for doubtful receivables	642	650
Employee benefit plan (credit) cost	(1,544)	778
Gain on sale of property	0	(1,581)
Other items	768	1,376
Changes in working capital items:
Decrease in current assets	24,864	14,634
Increase (decrease) in current liabilities	9,941	(16,670)
Cash contributions to pension and other postretirement plans	(3,967)	(9,717)
Other noncurrent items, net	374	2,479
Cash Provided by Operating Activities	135,027	91,496
Investing Activities:
Capital expenditures	(149,001)	(66,286)
Proceeds from sale of property	0	1,751
Other	(680)	(45)
Cash Used for Investing Activities	(149,681)	(64,580)
Financing Activities:
Cash dividends paid to parent by MGE	0	(35,000)
Distributions to parent from noncontrolling interest	(19,000)	(16,500)
Repayment of long-term debt	(23,330)	(33,260)
Issuance of long-term debt	100,000	40,000
(Repayments of) proceeds from short-term debt	(4,000)	7,000
Other	(659)	(315)
Cash Provided by (Used for) Financing Activities	53,011	(38,075)
Change in cash, cash equivalents, and restricted cash	38,357	(11,159)
Cash, cash equivalents, and restricted cash at beginning of period	10,093	16,442
Cash, cash equivalents, and restricted cash at end of period	48,450	5,283
Significant noncash investing activities:
Accrued capital expenditures	$ 10,991	$ 12,469

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 133,855	$ 107,952
Accounts receivable, less reserves	41,693	42,299
Other accounts receivables, less reserves	7,565	9,440
Unbilled revenues	20,979	31,400
Materials and supplies, at average cost	24,869	22,614
Fuel for electric generation, at average cost	6,945	8,256
Stored natural gas, at average cost	13,614	12,923
Prepaid taxes	12,239	26,535
Regulatory assets - current	8,739	7,888
Assets held for sale	1,755	8,817
Other current assets	8,459	12,507
Total Current Assets	280,712	290,631
Other long-term receivables	3,747	4,788
Regulatory assets	133,936	142,567
Pension and other postretirement benefit asset	14,266	7,336
Other deferred assets and other	8,729	731
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,350,253	1,283,313
Construction work in progress	109,209	58,044
Total Property, Plant, and Equipment	1,459,462	1,341,357
Investments	73,445	67,772
Total Assets	1,974,297	1,855,182
Current Liabilities:
Long-term debt due within one year	4,527	24,452
Short-term debt	0	4,000
Accounts payable	50,340	47,645
Accrued interest and taxes	5,554	5,602
Accrued payroll related items	10,879	12,244
Regulatory liabilities - current	7,330	5,633
Derivative liabilities	9,350	8,180
Other current liabilities	10,509	18,758
Total Current Liabilities	98,489	126,514
Other Credits:
Deferred income taxes	229,197	225,130
Investment tax credit - deferred	843	918
Regulatory liabilities	171,057	154,153
Accrued pension and other postretirement benefits	69,346	69,088
Derivative liabilities	26,920	33,990
Other deferred liabilities and other	72,064	69,041
Total Other Credits	569,427	552,320
Capitalization:
Common shareholders equity	811,983	778,187
Long-term debt	494,398	398,161
Total Capitalization	1,306,381	1,176,348
Commitments and contingencies (see Footnote 9)
Total Liabilities and Capitalization	1,974,297	1,855,182
MGE [Member]
Current Assets:
Cash and cash equivalents	47,264	5,951
Accounts receivable, less reserves	41,693	42,299
Affiliate receivables	686	668
Other accounts receivables, less reserves	5,856	6,984
Unbilled revenues	20,979	31,400
Materials and supplies, at average cost	24,869	22,614
Fuel for electric generation, at average cost	6,945	8,256
Stored natural gas, at average cost	13,614	12,923
Prepaid taxes	11,486	25,073
Regulatory assets - current	8,739	7,888
Assets held for sale	1,755	8,817
Other current assets	8,424	12,484
Total Current Assets	192,310	185,357
Affiliate receivable long-term	3,310	3,707
Regulatory assets	133,936	142,567
Pension and other postretirement benefit asset	14,266	7,336
Other deferred assets and other	10,517	3,280
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,350,281	1,283,341
Construction work in progress	109,209	58,044
Total Property, Plant, and Equipment	1,459,490	1,341,385
Investments	415	409
Total Assets	1,814,244	1,684,041
Current Liabilities:
Long-term debt due within one year	4,527	24,452
Short-term debt	0	4,000
Accounts payable	50,315	47,614
Accrued interest and taxes	7,409	5,558
Accrued payroll related items	10,879	12,244
Regulatory liabilities - current	7,330	5,633
Derivative liabilities	9,350	8,180
Other current liabilities	10,509	16,749
Total Current Liabilities	100,319	124,430
Other Credits:
Deferred income taxes	202,748	201,486
Investment tax credit - deferred	843	918
Regulatory liabilities	171,057	154,153
Accrued pension and other postretirement benefits	69,346	69,088
Derivative liabilities	26,920	33,990
Other deferred liabilities and other	72,064	69,041
Total Other Credits	542,978	528,676
Capitalization:
Common shareholders equity	537,707	491,872
Noncontrolling interest	138,842	140,902
Total Equity	676,549	632,774
Long-term debt	494,398	398,161
Total Capitalization	1,170,947	1,030,935
Commitments and contingencies (see Footnote 9)
Total Liabilities and Capitalization	$ 1,814,244	$ 1,684,041

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Receivables, Net
Reserve for uncollectible accounts receivable	$ 2,416	$ 2,840
Reserve for uncollectible other accounts receivable	571	335
MGE [Member]
Receivables, Net
Reserve for uncollectible accounts receivable	2,416	2,840
Reserve for uncollectible other accounts receivable	$ 571	$ 335

MGE Energy Inc Consolidated S_4

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	61,472			61,472
Other comprehensive income (loss)	189				189
Common stock dividends declared	(32,502)			(32,502)
Ending balance, shares at Sep. 30, 2017		34,668
Ending balance, value at Sep. 30, 2017	753,247	$ 34,668	316,268	401,920	391
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	67,858			67,858
Common stock dividends declared	(34,062)			(34,062)
Ending balance, shares at Sep. 30, 2018		34,668
Ending balance, value at Sep. 30, 2018	$ 811,983	$ 34,668	$ 316,268	$ 461,047	$ 0

Madison Gas and Electric Comp_4

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		57,686					41,462			16,224
Other comprehensive income (loss)	$ 189	(38)						$ 189	(38)
Cash dividends paid to parent by MGE		(35,000)					(35,000)
Distributions to parent from noncontrolling interest		(16,500)								(16,500)
Ending balance, shares at Sep. 30, 2017			34,668	17,348
Ending balance, value at Sep. 30, 2017		608,897		$ 17,348	192,417		283,762		(19)	115,389
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		62,775					45,835			16,940
Distributions to parent from noncontrolling interest		(19,000)								(19,000)
Ending balance, shares at Sep. 30, 2018			34,668	17,348
Ending balance, value at Sep. 30, 2018		$ 676,549		$ 17,348	$ 192,417		$ 327,942		$ 0	$ 138,842

Consolidated Statements of Comm

Consolidated Statements of Common Equity (Unaudited) (Parentheticals) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Consolidated Statements of Common Equity
Dividends per share of common stock	$ 0.338	$ 0.323	$ 0.983	$ 0.938

Summary of Significant Accounti

Summary of Significant Accounting Principles	9 Months Ended
	Sep. 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 September 30, 2018 , and for the three and nine 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 September 30, December 31, September 30, December 31, (In thousands) 2018 2017 2018 2017 Cash and cash equivalents $ 133,855 $ 107,952 $ 47,264 $ 5,951 Restricted cash 406 1,635 406 1,635 Receivable - margin account 780 2,507 780 2,507 Cash, cash equivalents, and restricted cash $ 135,041 $ 112,094 $ 48,450 $ 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 R eceivable – 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. Nine Months Ended (In thousands) September 30, 2017 Cash provided by operating activities $ (2,870) Cash used for investing activities 525 Change in cash, cash equivalents, and restricted cash (2,345) Cash, cash equivalents, and restricted cash at beginning of period 5,674 Cash, cash equivalents, and restricted cash at end of period $ 3,329 c. Capitalized Software Assets – Hosting Arrangements – MGE Energy and MGE. The FASB issued authoritative guidance of accounting for software in a hosted arrangement. MGE Energy and MGE adopted the authoritative guidance as of September 30, 2018. See Footnote 2.a. for further information. As of September 30, 2018, and December 31, 2017, the net book value of capitalized costs of internal use software incurred in a hosting arrangement was $6.2 million and $0.5 million, respectively. As of September 30, 2018, accumulated amortization expense is less than $0.1 million. As of December 31, 2017, there was no accumulated amortization expense. Capitalized software assets for hosted arrangements and the related accumulated amortization expense are recorded in " Other deferred assets and other " on the consolidated balance sheets of MGE Energy and MGE. For the three and nine months ended September 30, 2018, MGE recorded less than $0.1 million of amortization expense related to software assets for hosted arrangeme nts. For the three and nine months ended September 30, 2017, no amortization expense was recorded. These costs are recognized in " Other operations and maintenance " expense in the consolidated statements of income of MGE Energy and MGE and are amortized on a straight-line basis over the estimated useful lives of the assets. Software assets for hosted arrangements have useful lives ranging from five to fifteen years.

Adoption of Accounting Principl

Adoption of Accounting Principles and Recently Issued Accounting Pronouncements	9 Months Ended
	Sep. 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 present the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. This authoritative guidance became effective Januar y 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 FASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018, and required equity i nvestments 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 investm ents. 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 related to equity investments within the scope of this standard. As of January 1, 2018, MGE recorded less than a $0.1 million decrease in retained earning s 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 guidance, reporting entities are required to explain the changes in the total of restricted and u nrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, investing, or finan cing activities within the statement of cash flows based on the nature of the restriction. Reporting entities are now also required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restriction s 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 retrospecti vely for all periods presented. See Footnote 1.b. for further information. Pension and Other Postretirement Benefits. In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net ben efit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense " increased and "Other income, net" increased $1.0 million and $3.0 million for the three and nine months ended September 30, 2017 , respectively . The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronouncement (whereas under previous GAAP all com ponents of net benefit cost were eligible for capitalization). See Footnote 6 for further information. Internal-Use Software – Hosting Arrangements . In August 2018, the FASB issued amended authoritative guidance within the codification's Intangibles – Goodwill and Other – Internal-Use Software topic. The amended authoritative guidance aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement (hosting arrangement) that is a service contract with the requireme nts for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangement that include an internal-use software license). Costs for implementation activities in the development stage are capitalized depending on the nature of the costs and presented in the same line item on the balance sheet as amounts prepaid for the hosted service. Costs incurred during the preliminary and postimplementation stages are expensed as the activities are performed. The costs capital ized as part of implementation stage should be expensed over the term of the hosting contract, which includes any renewable option periods, and presented in the same line on the income statement as the fees for the associated hosted service. This amende d authoritative guidance will become effective January 1, 2020. Early adoption of the amendment is permitted, including adoption in any interim period. Entities can choose to adopt the new guidance either prospectively, for eligible costs incurred on or af ter the date this guidance is first applied, or retrospectively. MGE Energy and MGE early adopted these amendments retrospectively as of September 30, 2018 . The cumulative impact of this guidance on our financial statement was not material, except for addit ional footnote disclosures. See F ootnote 1.c. for further information. b . Recently Issued Leases. In February 2016, the FASB issued authoritative guidance within the c odification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liab ility. Prior to the authoritative guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance , as applied by lessors , is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optional practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE plan to adopt this practical expedient. Management 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 t hat 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 und er 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 measure leases at the beginning of the earliest comparative period presented using a modified retrospective approach. MGE Energy and MGE expect to recognize additional lease assets and liabilities for their operating leases under the standard. MGE Energy a nd MGE are continuing to evaluate the impact of this pronouncement; however, we do not expect that it will have a material impact on our consolidated net income or cash flows.

Revenue

Revenue	9 Months Ended
	Sep. 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 Nine Months Ended (In thousands) September 30, September 30, Electric revenues 2018 2017 2018 2017 Residential $ 42,371 $ 39,905 $ 107,847 $ 104,892 Commercial (a) 61,638 64,036 159,264 168,921 Industrial 3,668 4,555 11,193 13,286 Other-retail/municipal 9,431 10,459 26,245 29,141 Total retail 117,108 118,955 304,549 316,240 Sales to the market 1,505 1,068 6,334 3,090 Other revenues 482 445 1,406 1,436 Adjustments to revenues 80 181 344 513 Total electric revenues 119,175 120,649 312,633 321,279 Gas revenues Residential 11,916 12,121 64,087 61,164 Commercial/Industrial (a) 5,570 5,622 38,728 36,512 Total retail 17,486 17,743 102,815 97,676 Gas transportation 829 944 3,018 3,285 Other revenues 92 91 319 324 Total gas revenues 18,407 18,778 106,152 101,285 Non-regulated energy revenues 213 112 904 261 Total Operating Revenue (a) $ 137,795 $ 139,539 419,689 $ 422,825 (a) In 2017, MGE had less than $0.1 million of revenues related to CNG vehicle fuel servicing. No revenue was recognized for fuel servicing by MGE Energy in 2017. Performance Obligations A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account. A contract's transaction price is allocated to each distinct performance obligation and recognized as revenue when, or as, the performance obligation is satisfied. The majority of MGE Ene rgy's and MGE's contracts have a single performance obligation. Retail Revenue (Residential, Commercial, Industrial, and Other Retail/Municipal) Retail revenue of electric and gas utility service represent MGE's core business activities. Tariffs are appro ved by the PSCW through a rate order and provide MGE's customers with the standard terms and conditions, including pricing terms. The performance obligation to deliver electricity or gas is satisfied over time as the customer simultaneously receives and co nsumes the commodities provided by MGE. MGE recognizes revenues as the commodity is delivered to customers. Meters are read on a systematic basis throughout the month based on established meter-reading schedules and the customer is subsequently billed for their services. At the end of the month, MGE accrues an estimate for the unbilled amount of commodities delivered to customers. The unbilled revenue estimate is based on daily system demand volumes, weather factors, estimated line losses, estimated custome r usage by class, and applicable customer rates. Utility Cost Recovery Mechanisms MGE's tariff rates include a provision for fuel cost recovery. The PSCW allows Wisconsin utilities to defer electric fuel-related costs, less excess revenues, that fall out side a symmetrical cost tolerance band. Any over/under recovery of the actual costs in a given year is determined in the following year and is then reflected in future billings to electric retail customers. Over-collection of fuel-related costs that are ou tside the approved range will be recognized as a reduction of revenue. Prior to adoption of the new revenue recognition guidance, effective January 1, 2018, over-collected fuel-related costs were reflected in "Purchased power" expense. Under-collection of these costs will continue to be recognized in "Purchased power" expense in the consolidated statements of income of MGE Energy and MGE. The cumulative effects of these deferred amounts will be recorded in "Regulatory assets" or "Regulatory liabilities" on the consolidated balance sheets of MGE Energy and MGE until they are reflected in future billings to customers. See Footnote 10.b. for further information. MGE received a PSCW order 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. For example, any over-collection of the differenc e between actual costs incurred and the amount of costs collected from customers is recorded as a reduction of revenue in the period incurred. Sales to the Market Sales to the market include energy charges, capacity or demand charges, and ancillary charg es represented by wholesale sales of electricity made to third parties who are not ultimate users of the electricity. Most of these sales are spot market transactions on the markets operated by MISO. Each transaction is considered a performance obligation and revenue is recognized in the period in which energy charges, capacity or demand charges, and ancillary services are sold into MISO. MGE reports, on a net basis, transactions on the MISO markets in which it buys and sells power within the same hour to m eet electric energy delivery requirements. Transportation of Gas MGE has contracts under which MGE provides gas transportation services to customers who have elected to purchase gas from a third party and have the gas delivered via pipelines within MGE's service territory. 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 term s.

Investment in ATC and ATC Holdc

Investment in ATC and ATC Holdco	9 Months Ended
	Sep. 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 owned 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 . As of September 30, 2018 , and December 31, 2017 , MGE Transco held a 3.6 % ownership interest in ATC. As of September 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 s in ATC and ATC Holdco, respectively, under the equity method of accounting. Equity earnings from investments are recorded as " Other income " on the consolidated statements of income of MGE Energy. For the three and nine months ended September 30, 2018 and 2017 , MGE Transco recorde d the following : Three Months Ended Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Equity earnings from investment in ATC $ 1,672 $ 2,338 $ 6,113 $ 7,432 Dividends from ATC (a) 1,581 2,070 4,540 4,070 Capital contributions to ATC 533 710 2,308 3,018 (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 $ 1.6 million dividend receivable from ATC as of September 30, 2018 . A cash dividend was received in October 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 typically have long development and investment lead times before becoming operational. During the three and nine months ended September 30, 2018 , MGEE Transco recorded capital contributions of $ 0.1 million and $ 0.3 million, respectively, to ATC Holdco . During the nine months ended September 30, 2017 , MGEE Transco recorded capital contributions of $ 0.7 million to ATC Holdco . During the three months ended September 30, 2017 , MGEE Transco recorded no capital contributions to ATC Holdco. In October 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 nine months ended September 30, 2018 and 2017 , is as follows: Three Months Ended Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Operating revenues $ 170,341 $ 171,123 $ 501,276 $ 522,402 Operating expenses (87,959) (85,372) (264,326) (251,042) Other income, net 439 1,272 2,070 3,043 Interest expense, net (27,754) (28,440) (82,411) (81,690) Earnings before members' income taxes $ 55,067 $ 58,583 $ 156,609 $ 192,713 MGE receives transmission and other related services from ATC. During the three and nine months ended September 30, 2018 , MGE recorded $ 7.2 million and $ 21.7 million, respectively, for transmission services received compared to $ 7.3 million and $ 21.9 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 September 30, 2018 , and December 31, 2017 , MGE had a receivable due from ATC of $ 0.1 million and $ 0.2 million, respectively.

Taxes

Taxes	9 Months Ended
	Sep. 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 fourth quarter of 2018 when the analysis is complete. No adjustments have been recorded during 2018. Beginning January 1, 2018, MGE began amortizing the regulated utility excess deferred taxes recognized using a normalization method of accounting. For the three and nine months ended September 30, 2018 , MGE recognized $ 0.7 million and $ 1.9 million, 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 customers, 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-time bill credit on customer bills to reflect the estimate of the over - co llection for January through June 2018, along with a monthly volumetric bill credit which bega n in July 2018 and continue s through the remainder of 2018 for the estimated remaining annual amount. As of September 30, 2018 , MGE returned $ 5.9 million to customers through bill credits. Any over/under recovery of the actual costs will be subject to the PSCW ' s review in a future rate case. As of September 30, 2018 , MGE has deferred $ 2.6 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 September 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) % (1.1) % (0.2) % (1.1) % Domestic manufacturing deduction - % (1.5) % - % (1.4) % AFUDC equity, net (0.6) % (0.1) % (0.6) % (0.1) % Amortization of utility excess deferred tax - tax reform (a) (1.8) % - % (1.8) % - % Other, net, individually insignificant - % (0.3) % 0.1 % (0.4) % Effective income tax rate 24.5 % 36.9 % 24.6 % 36.7 % MGE Energy MGE Nine Months Ended September 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) % (1.3) % (0.3) % (1.4) % Domestic manufacturing deduction - % (1.6) % - % (1.7) % AFUDC equity, net (0.8) % (0.2) % (0.8) % (0.2) % Amortization of utility excess deferred tax - tax reform (a) (1.8) % - % (2.0) % - % Other, net, individually insignificant - % (0.2) % 0.1 % (0.1) % Effective income tax rate 24.3 % 36.6 % 24.1 % 36.3 % (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	9 Months Ended
	Sep. 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 nine months ended September 30, 2018 and 2017 . Three Months Ended Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Pension Benefits Components of net periodic benefit cost: Service cost $ 1,431 $ 1,351 $ 4,292 $ 4,043 Interest cost 3,215 3,168 9,645 9,481 Expected return on assets (6,560) (5,762) (19,680) (17,244) Amortization of: Prior service credit (11) (4) (33) (12) Actuarial loss 1,319 1,594 3,958 4,769 Net periodic benefit (credit) cost $ (606) $ 347 $ (1,818) $ 1,037 Postretirement Benefits Components of net periodic benefit cost: Service cost $ 320 $ 315 $ 962 $ 944 Interest cost 653 678 1,959 2,034 Expected return on assets (808) (722) (2,424) (2,165) Amortization of: Transition obligation 1 1 2 2 Prior service credit (667) (667) (2,001) (2,001) Actuarial loss 122 190 366 570 Net periodic benefit (credit) cost $ (379) $ (205) $ (1,136) $ (616)

Equity and Financing Arrangemen

Equity and Financing Arrangements	9 Months Ended
	Sep. 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 nine months ended September 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 . In September 2018, MGE issued $60 million of new long-term unsecured debt carrying an interest rate of 4.19% per annum over its 30-year term . MGE used the net proceeds from these debt financings to assist with financi ng capital expenditures, such as the Saratoga Wind Farm , and to refinance $20 million of long-term debt which matured in September 2018. The covenants of the new long-term unsecured debt are substantially consistent with MGE's existing unsecured long-term debt .

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 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 u nits 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 vest ing 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 remeasured quarterly, including as of September 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. Comp ensation cost for retirement eligible employees or employees that will become retirement eligible during the vesting schedule are recognized on an abridged horizon as retirement eligibility accelerates vesting. During the three and nine months ended September 30, 2018 , MGE recorded $ 0.3 million and $ 1.3 million, respectively, in compensation expense as a result of awards under the plans compared to $ 0.3 millio n and $ 1.0 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 nine months ended September 30, 2018 and 2017 . As of September 30, 2018 , $ 5.5 million of outstanding awards are vested. Of this amount, no cash settlements have occurred as ca sh payments are only made at the end of the period covered by the awards.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 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 belie ves 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 stand ards 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, to meet best available technology standards so that mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens) are reduced. • 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-fired electric generating units (EGUs). In 2015, the EPA finalized the Clean Power Plan (CPP) which directed states to submit plans to reduce GHG emissions from the electric generation sector. In February 2016, the U.S. Supreme Court stayed implementation of the CPP and the stay remains in effect. In October 2017, the EPA issued a proposed rule to repeal the CPP. In August 2018, the EPA proposed the Affordable Clean Energy (ACE) rule which would replace the CPP, if successfully implemented. The ACE proposal directs states to submit plans to the EPA for approval that implem ent standards of performance (called Best System of Emissions Reductions, or BSER) for individual EGUs over 25 MW. ACE defines BSER as on-site, heat-rate efficiency improvements, whereas the CPP defines BSERs using carbon dioxide emission performance rates . Simple cycle units such as our smaller combustion units, and combined cycle units such as our WCCF are exempt from the proposed rule. If a state fails to prepare a plan, or their plan is not approved by the EPA a federal implementation plan (FIP) will be issued for that state . The proposed ACE as it is currently written has the potential to impact our Blount Generating Station, Columbia, and Elm Road Units. MGE cannot yet determine with any certainty the impact of the proposed ACE rule on our opera tions. MGE previously determined that i f the CPP were to be implemented in its present form, it would have a material impact on MGE. MGE will continue to monitor developments with the proposed ACE rule and the CPP rule and litigation. • The EPA's rule to regulate ambient levels of ozone through the 2015 Ozone National Ambient Air Quality Standards (NAAQS). On May 1, 2018, EPA issued a final rule which designated the northeast portion of Milwaukee County as being in nonattainment with this NAAQS. The Elm Ro ad Units are located in Milwaukee County, yet outside the designated nonattainment area. In August 2018, several environmental groups, the City of Chicago and the State of Illinois filed federal lawsuits challenging the EPA's attainment designation decisio ns, including the partial Milwaukee County designation as being too narrow and not sufficiently protective. MGE is monitoring the outcome of this lawsuit and how it may affect our Elm Road Units in Milwaukee County. At this time MGE expects that the 2015 O zone 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 2015 Ozone NAAQS, alleging that the new standard is not attainable 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 attainment designations. • Rules regulating nitrogen oxide (NO x ) and sulfur dioxide (SO 2 ) emissions, including the Cross State Air Pollution Rule (CSAPR), CSAPR Update Rule and Clean Air Visibility Rule (CAVR). At this time, regulatory obligations, compliance strategies, and costs remain unclear due to uncertainties surrounding the ongoing implementation of Phase II of CSAPR and the continued legal challenges surrounding CSAPR, the CSAPR Update Rule and CAVR. • The EPA's Coal Combustion Residuals Rule (CCR), which regulates coal a sh from burning coal for the purpose of generating electricity as a solid waste, and defines what ash use activities would be considered generally exempt beneficial reuse of coal ash. The CCR rule also regulates landfills, ash ponds, and other surface impo undments used 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 comp leted a review of their system and has determined that an onsite ash pond will need to be closed and replaced with a dry ash handling system. The dry ash handling system installation is planned for 2020-2021. In July 2018, the EPA published a final rule th at included amendments to the CCR (which include the allowance of alternative performance standards for landfills and surface impoundments, revised risk-based groundwater protection standards, and an extension of the deadline by which certain facilities mu st cease the placement of waste in CCR units). In August 2018, the Court of Appeals for the D.C. Circuit vacated parts of the CCR for not being sufficiently protective of the environment. It is unclear how the EPA will respond to that decision. MGE will co ntinue to monitor potential rule modifications to assess potential impacts on our operations. In 2015, MGE recorded an asset retirement obligation for its share of the legal liability associated with the effect of the CCR. Actual costs of compliance may b e 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 September 30, 2018 : (In thousands) 2018 2019 2020 2021 2022 Thereafter Coal (a) $ 6,716 $ 21,188 $ 8,434 $ 828 $ - $ - Natural gas supply (b) 12,245 13,287 - - - - Saratoga wind (c) 1,006 858 2,266 1,775 1,784 4,459 Other 1,772 502 502 502 502 502 $ 21,739 $ 35,835 $ 11,202 $ 3,105 $ 2,286 $ 4,961 (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 September 30, 2018 , MGE has incurred $ 66.5 million of capital expenditures. After tax, MGE has recognized $0.6 million and $1.3 million, respectively, in AFUDC equity related to this project for the three and nine months ended September 30, 2018 . Construction of the pro ject is expected to be completed by early 2019 , with an estimated capital cost of $108 million. d . Other Commitments - MGE Energy. In September 2018, MGE Energy entered into two subscription agreement s to invest in nonpublic venture capital funds. From time to time, these funds make capital calls to their investors. MGE Energy has committed to contribute $ 2.3 million in capital for such capital calls. The timing of these capital calls is dependent on the needs of the funds and is therefore uncertain at this time .

Rate Matters

Rate Matters	9 Months Ended
	Sep. 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 adjust electric and gas rates for 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 electric rates will be adjusted accordingly. The decrease reflect s the ongoing tax impacts of the Tax Act and the addition of lower-cost renewable generation capac ity. The settlement agreement increase s gas rates by 1.06% in 2019 and 1.46% in 2020. The requested gas increase covers infrastructure costs. It also reflects the impacts of the Tax Act. The 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 infrastructure improvements. The authoriz ed return on common stock equity for 2017 was 9.8 % based on a capital structure consisting of 57.2 % common equity . 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 August 2018, the PSCW issued a final decision in the fuel rules proceedings for MGE to refund $ 4.2 million of additional fuel savings re alized during 2017 to its retail electric customers over a one-month period in October 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 September 30, 2018 , MGE has deferred $ 7.2 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 December 31, 2017 , MGE had deferred $ 4.2 million of 2017 fuel savings .

Derivative and Hedging Instrume

Derivative and Hedging Instruments	9 Months Ended
	Sep. 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: September 30, 2018 December 31, 2017 Commodity derivative contracts 482,450 MWh 552,310 MWh Commodity derivative contracts 8,557,000 Dth 5,460,000 Dth FTRs 3,681 MW 2,226 MW PPA 2,200 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. As of September 30, 2018 , and December 31 , 2017 , the fair value of exchange traded derivatives and FTRs exceeded their cost basis by $ 1.6 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 as of September 30, 2018 , and Dec ember 31, 2017 , reflects a loss position of $ 36.3 million and $ 42.2 million, respectively. The actual cost will be recognized in purchased power e xpense in the month of purchase. The following table summarizes the fair v alue of the derivative instruments on the consolidated balance sheet s . All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreemen t as well as the netting of collatera l. For financial statement purposes, instruments are netted with the same counterparty under a master netting agreement as well as the netting of collatera l . As of September 30, 2018 , and December 31, 2017 , the receiv able margin account balance of $ 0.8 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 September 30, 2018 Commodity derivative contracts (a) $ 1,363 $ 232 Other current assets Commodity derivative contracts (a) 86 55 Other deferred charges FTRs 478 - Other current assets PPA N/A 9,350 Derivative liability (current) PPA N/A 26,920 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 September 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 September 30, 2018 Commodity derivative contracts $ 1,449 $ (287) $ - $ 1,162 FTRs 478 - - 478 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 September 30, 2018 Commodity derivative contracts $ 287 $ (287) $ - $ - PPA 36,270 - - 36,270 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 as of September 30, 2018 and 2017 , and the consolidated statements of income for the three and nine months ended September 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 September 30: Balance at July 1, $ 36,924 $ 640 $ 45,316 $ 618 Unrealized gain (2,007) - (1,277) - Realized (loss) gain reclassified to a deferred account (316) 316 (313) 313 Realized gain (loss) reclassified to income statement 29 (62) (1,450) (57) Balance at September 30, $ 34,630 $ 894 $ 42,276 $ 874 Nine Months Ended September 30: Balance at January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized gain (5,906) - (3,698) - Realized (loss) gain reclassified to a deferred account (837) 837 (935) 935 Realized loss reclassified to income statement (585) (749) (2,372) (291) Balance at September 30, $ 34,630 $ 894 $ 42,276 $ 874 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 September 30: Commodity derivative contracts $ (145) $ - $ 362 $ 18 FTRs (150) - (224) - PPA 328 - 1,351 - Nine Months Ended September 30: Commodity derivative contracts $ 39 $ 637 $ 764 $ 227 FTRs (625) - (1,349) - PPA 1,283 - 3,021 - 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 September 30, 2018 , no collateral is required to be, or has been, posted. Certain counterparties extend MGE a credit limit. If MGE exceeds these limits, the counterparties may require collateral to be pos ted. As of September 30, 2018 , no counterparties were in a net liability position. As of December 31, 2017 , certain counterparties were in a net liability position 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 ongo ing basis to mitigate nonperformance risk in its portfolio. As of September 30, 2018 , no counterparties have defaulted.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 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 st andard 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: September 30, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 133,855 $ 133,855 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper - - 4,000 4,000 Long-term debt (a) 503,553 523,075 426,883 475,282 MGE Assets: Cash and cash equivalents $ 47,264 $ 47,264 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper - - 4,000 4,000 Long-term debt (a) 503,553 523,075 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.6 million and $4.3 million as of September 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 September 30, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,927 $ 824 $ - $ 1,103 Exchange-traded investments 1,005 1,005 - - Total Assets $ 2,932 $ 1,829 $ - $ 1,103 Liabilities: Derivatives, net $ 36,557 $ 140 $ - $ 36,417 Deferred compensation 2,985 - 2,985 - Total Liabilities $ 39,542 $ 140 $ 2,985 $ 36,417 MGE Assets: Derivatives, net $ 1,927 $ 824 $ - $ 1,103 Exchange-traded investments 70 70 - - Total Assets $ 1,997 $ 894 $ - $ 1,103 Liabilities: Derivatives, net $ 36,557 $ 140 $ - $ 36,417 Deferred compensation 2,985 - 2,985 - Total Liabilities $ 39,542 $ 140 $ 2,985 $ 36,417 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 nine months ended September 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 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 model projects future market energy prices and compares those prices to the projected power costs to be incurred under the contract. Inputs to the model require significant management judgmen t 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 counterpa rty delivery point. The historical relationship between the delivery points is reviewed and a discount (below 100%) or premium (above 100%) is derived. This comparison is done for both peak times when demand is high and off- peak times when demand is low. I f the basis adjustment is lowered, the fair value measurement will decrease, and if the basis adjustment is increased, the fair value measurement will increase. The projected power costs anticipated to be incurred under the purchased power agreement are d etermined 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 assumption s about market risk such as liquidity, volatility , and contract duration. The fair value model uses a discount rate that incorporates discounting, credit, and model risks. The following table presents the significant unobservable inputs used in the pricin g model. Model Input Significant Unobservable Inputs September 30, 2018 December 31, 2017 Basis adjustment: On peak 91.9 % 92.3 % Off peak 93.2 % 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 Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Beginning balance $ (37,332) $ (45,605) $ (42,026) $ (50,305) Realized and unrealized gains (losses): Included in regulatory assets 2,018 2,846 6,711 7,547 Included in other comprehensive income - - - - Included in earnings 26 (1,478) (434) (2,614) Included in current assets (25) (14) (496) (111) Purchases 5,736 6,299 17,602 18,481 Sales - - - - Issuances - - - - Settlements (5,737) (4,807) (16,671) (15,757) Transfers in and/or out of Level 3 - - - - Balance as of September 30, $ (35,314) $ (42,759) $ (35,314) $ (42,759) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held at September 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 Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Purchased Power Expense $ 26 $ (1,460) $ (637) $ (2,377) Cost of Gas Sold Expense - (18) 203 (237) Total $ 26 $ (1,478) $ (434) $ (2,614) (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	9 Months Ended
	Sep. 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 tha t has been approved by the PSCW. Under the terms of the amendments, MGE has reduce d its obligation to pay certain capital expenditures (other than SCR-related expenditures) at Columbia in exchange for a proportional reduction in MGE's ownership in Columbia. On January 1 of each year from 2017 through 20 19 and then on June 1, 2020, the ownership percentage is adjusted through a partial sale based on the amount of capital expenditures foregone. In June 2017, the FERC approved the ownership transfer in Columbia , effective January 1, 2017. During 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 nine months ended September 30, 2018 , MGE accrued $ 0.4 million and $ 1.8 million, respectively, of 201 8 foregone capital expenditures as part of t he ownership transfer agreement . As of September 30, 2018 , MGE classified $ 1.8 million of Columbia assets as held-for-sale on the consolidated balance sheets. The assets recognized as held-for-sale are covered by the ownership transfer agreement relating to the sale of plant assets to WPL, and are expected to be sold and transferred in Ja nuary 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. The purchase of Forward Wind replaced an existing purchase power agreement, under which MGE purchased 12.8% of the facility's energy output. MGE Energy a nd 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 September 30, 2018 , MGE recorded an obligation of $ 1.6 million for the fair value of its legal liability for AROs associated with Forward Wind . MGE has regulatory treatment and recogn izes regulatory assets or liabilities for the timing differences between when we recover legal AROs in rates and when those costs would actually be recognized.

Segment Information

Segment Information	9 Months Ended
	Sep. 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 September 30, 2018 Operating revenues $ 119,175 $ 18,407 $ 213 $ - $ - $ - $ 137,795 Interdepartmental revenues (20) 4,219 9,912 - - (14,111) - Total operating revenues 119,155 22,626 10,125 - - (14,111) 137,795 Depreciation and amortization (9,864) (2,534) (1,861) - - - (14,259) Other operating expenses (77,847) (19,824) (36) (4) (138) 14,111 (83,738) Operating income (loss) 31,444 268 8,228 (4) (138) - 39,798 Other income, net 1,763 829 - 1,620 118 - 4,330 Interest (expense) income, net (3,217) (963) (1,320) - 475 - (5,025) Income before taxes 29,990 134 6,908 1,616 455 - 39,103 Income tax (provision) benefit (7,306) 42 (1,852) (441) (40) - (9,597) Net income $ 22,684 $ 176 $ 5,056 $ 1,175 $ 415 $ - $ 29,506 Three Months Ended September 30, 2017 Operating revenues $ 120,649 $ 18,778 $ 112 $ - $ - $ - $ 139,539 Interdepartmental revenues (110) 3,892 11,130 - - (14,912) - Total operating revenues 120,539 22,670 11,242 - - (14,912) 139,539 Depreciation and amortization (9,256) (2,258) (1,858) - - - (13,372) Other operating expenses (a) (79,506) (19,324) (50) (9) (193) 14,912 (84,170) Operating income (loss) 31,777 1,088 9,334 (9) (193) - 41,997 Other income (deductions), net (a) 2,060 742 - 2,258 (117) - 4,943 Interest (expense) income, net (2,760) (795) (1,371) - 199 - (4,727) Income (loss) before taxes 31,077 1,035 7,963 2,249 (111) - 42,213 Income tax (provision) benefit (11,175) (351) (3,196) (906) 44 - (15,584) Net income (loss) $ 19,902 $ 684 $ 4,767 $ 1,343 $ (67) $ - $ 26,629 Nine Months Ended September 30, 2018 Operating revenues $ 312,633 $ 106,152 $ 904 $ - $ - $ - $ 419,689 Interdepartmental revenues (234) 12,059 29,579 - - (41,404) - Total operating revenues 312,399 118,211 30,483 - - (41,404) 419,689 Depreciation and amortization (28,817) (7,374) (5,563) - - - (41,754) Other operating expenses (228,957) (99,251) (113) (12) (789) 41,404 (287,718) Operating income (loss) 54,625 11,586 24,807 (12) (789) - 90,217 Other income, net 5,055 2,347 - 5,908 670 - 13,980 Interest (expense) income, net (9,036) (2,689) (4,002) - 1,180 - (14,547) Income before taxes 50,644 11,244 20,805 5,896 1,061 - 89,650 Income tax provision (11,492) (2,788) (5,638) (1,611) (263) - (21,792) Net income $ 39,152 $ 8,456 $ 15,167 $ 4,285 $ 798 $ - $ 67,858 Nine Months Ended September 30, 2017 Operating revenues $ 321,279 $ 101,285 $ 261 $ - $ - $ - $ 422,825 Interdepartmental revenues (334) 11,708 33,307 - - (44,681) - Total operating revenues 320,945 112,993 33,568 - - (44,681) 422,825 Depreciation and amortization (27,341) (6,703) (5,562) - - - (39,606) Other operating expenses (a) (233,714) (93,817) (153) (9) (779) 44,681 (283,791) Operating income (loss) 59,890 12,473 27,853 (9) (779) - 99,428 Other income (deductions), net (a) 3,708 1,502 - 7,242 (414) - 12,038 Interest (expense) income, net (8,337) (2,399) (4,170) - 399 - (14,507) Income (loss) before taxes 55,261 11,576 23,683 7,233 (794) - 96,959 Income tax (provision) benefit (18,753) (4,576) (9,505) (2,909) 256 - (35,487) Net income (loss) $ 36,508 $ 7,000 $ 14,178 $ 4,324 $ (538) $ - $ 61,472 (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 September 30, 2018 Operating revenues $ 119,175 $ 18,407 $ 213 $ - $ 137,795 Interdepartmental revenues (20) 4,219 9,912 (14,111) - Total operating revenues 119,155 22,626 10,125 (14,111) 137,795 Depreciation and amortization (9,864) (2,534) (1,861) - (14,259) Other operating expenses (b) (85,127) (19,739) (1,888) 14,111 (92,643) Operating income (b) 24,164 353 6,376 - 30,893 Other income, net (b) 1,737 786 - - 2,523 Interest expense, net (3,217) (963) (1,320) - (5,500) Net income 22,684 176 5,056 - 27,916 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,629) (5,629) Net income attributable to MGE $ 22,684 $ 176 $ 5,056 $ (5,629) $ 22,287 Three Months Ended September 30, 2017 Operating revenues $ 120,648 $ 18,779 $ 112 $ - $ 139,539 Interdepartmental revenues (109) 3,891 11,130 (14,912) - Total operating revenues 120,539 22,670 11,242 (14,912) 139,539 Depreciation and amortization (9,256) (2,258) (1,858) - (13,372) Other operating expenses (a), (b) (90,164) (19,529) (3,246) 14,912 (98,027) Operating income (b) 21,119 883 6,138 - 28,140 Other income, net (a), (b) 1,543 596 - - 2,139 Interest expense, net (2,760) (795) (1,371) - (4,926) Net income 19,902 684 4,767 - 25,353 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,439) (5,439) Net income attributable to MGE $ 19,902 $ 684 $ 4,767 $ (5,439) $ 19,914 Nine Months Ended September 30, 2018 Operating revenues $ 312,633 $ 106,152 $ 904 $ - $ 419,689 Interdepartmental revenues (234) 12,059 29,579 (41,404) - Total operating revenues 312,399 118,211 30,483 (41,404) 419,689 Depreciation and amortization (28,817) (7,374) (5,563) - (41,754) Other operating expenses (b) (240,333) (101,938) (5,751) 41,404 (306,618) Operating income (b) 43,249 8,899 19,169 - 71,317 Other income, net (b) 4,939 2,246 - - 7,185 Interest expense, net (9,036) (2,689) (4,002) - (15,727) Net income 39,152 8,456 15,167 - 62,775 Less: Net income attributable to noncontrolling interest, net of tax - - - (16,940) (16,940) Net income attributable to MGE $ 39,152 $ 8,456 $ 15,167 $ (16,940) $ 45,835 Nine Months Ended September 30, 2017 Operating revenues $ 321,282 $ 101,294 $ 261 $ - $ 422,837 Interdepartmental revenues (337) 11,699 33,307 (44,669) - Total operating revenues 320,945 112,993 33,568 (44,669) 422,837 Depreciation and amortization (27,341) (6,703) (5,562) - (39,606) Other operating expenses (a), (b) (251,879) (98,227) (9,658) 44,669 (315,095) Operating income (b) 41,725 8,063 18,348 - 68,136 Other income, net (a), (b) 3,120 1,336 - - 4,456 Interest expense, net (8,337) (2,399) (4,170) - (14,906) Net income 36,508 7,000 14,178 - 57,686 Less: Net income attributable to noncontrolling interest, net of tax - - - (16,224) (16,224) Net income attributable to MGE $ 36,508 $ 7,000 $ 14,178 $ (16,224) $ 41,462 (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 Non-regulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Total Assets: September 30, 2018 $ 1,141,370 $ 345,349 $ 64,016 $ 264,735 $ 64,722 $ 472,740 $ (378,635) $ 1,974,297 December 31, 2017 1,043,181 344,337 26,345 270,384 61,783 485,548 (376,396) 1,855,182 Capital Expenditures: Nine Months Ended Sept. 30, 2018 $ 122,108 $ 22,406 $ - $ 4,487 $ - $ - $ - $ 149,001 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - - - 108,131 Utility Consolidated (In thousands) MGE Electric Gas Assets not Allocated Non-regulated Energy Elimination Entries Total Assets: September 30, 2018 $ 1,141,370 $ 345,349 $ 64,016 $ 264,685 $ (1,176) $ 1,814,244 December 31, 2017 1,043,181 344,337 26,345 270,334 (156) 1,684,041 Capital Expenditures: Nine Months Ended Sept. 30, 2018 $ 122,108 $ 22,406 $ - $ 4,487 $ - $ 149,001 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - 108,131

Significant Accounting Policies

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 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.
Capitalized Software Assets Hosting Arrangements	Capitalized Software Assets – Hosting Arrangements – MGE Energy and MGE. Capitalized software assets for hosted arrangements and the related accumulated amortization expense are recorded in " Other deferred assets and other " on the consolidated balance sheets of MGE Energy and MGE. These costs are recognized in " Other operations and maintenance " expense in the consolidated statements of income of MGE Energy and MGE and are amortized on a straight-line basis over the estimated useful lives of the assets. Software assets for hosted arrangements have useful lives ranging from five to fifteen years.
Receivable Margin Account	Receivable – Margin Account Cash amounts held by counterparties as margin collateral for certain financial transactions are recorded as R eceivable – 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 present the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. This authoritative guidance became effective Januar y 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 FASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018, and required equity i nvestments 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 investm ents. 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 related to equity investments within the scope of this standard. As of January 1, 2018, MGE recorded less than a $0.1 million decrease in retained earning s 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 guidance, reporting entities are required to explain the changes in the total of restricted and u nrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, investing, or finan cing activities within the statement of cash flows based on the nature of the restriction. Reporting entities are now also required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restriction s 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 retrospecti vely for all periods presented. See Footnote 1.b. for further information. Pension and Other Postretirement Benefits. In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net ben efit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense " increased and "Other income, net" increased $1.0 million and $3.0 million for the three and nine months ended September 30, 2017 , respectively . The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronouncement (whereas under previous GAAP all com ponents of net benefit cost were eligible for capitalization). See Footnote 6 for further information. Internal-Use Software – Hosting Arrangements . In August 2018, the FASB issued amended authoritative guidance within the codification's Intangibles – Goodwill and Other – Internal-Use Software topic. The amended authoritative guidance aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement (hosting arrangement) that is a service contract with the requireme nts for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangement that include an internal-use software license). Costs for implementation activities in the development stage are capitalized depending on the nature of the costs and presented in the same line item on the balance sheet as amounts prepaid for the hosted service. Costs incurred during the preliminary and postimplementation stages are expensed as the activities are performed. The costs capital ized as part of implementation stage should be expensed over the term of the hosting contract, which includes any renewable option periods, and presented in the same line on the income statement as the fees for the associated hosted service. This amende d authoritative guidance will become effective January 1, 2020. Early adoption of the amendment is permitted, including adoption in any interim period. Entities can choose to adopt the new guidance either prospectively, for eligible costs incurred on or af ter the date this guidance is first applied, or retrospectively. MGE Energy and MGE early adopted these amendments retrospectively as of September 30, 2018 . The cumulative impact of this guidance on our financial statement was not material, except for addit ional footnote disclosures. See F ootnote 1.c. for further information. b . Recently Issued Leases. In February 2016, the FASB issued authoritative guidance within the c odification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liab ility. Prior to the authoritative guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance , as applied by lessors , is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optional practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE plan to adopt this practical expedient. Management 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 t hat 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 und er 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 measure leases at the beginning of the earliest comparative period presented using a modified retrospective approach. MGE Energy and MGE expect to recognize additional lease assets and liabilities for their operating leases under the standard. MGE Energy a nd MGE are continuing to evaluate the impact of this pronouncement; however, we do not expect that it will have a material impact on our consolidated net income or cash flows.
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 power" expense. Under-collection of these costs will continue to be recognized in "Purchased power" expense in the consolidated statements of income of MGE Energy and MGE. The cumulative effects of these deferred amounts will be recorded in "Regulatory assets" or "Regulatory liabilities" on the consolidated balance sheets of MGE Energy and MGE until they are reflected in future billings to customers. See Footnote 10.b. for further information. MGE received a PSCW order 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. For example, any over-collection of the differenc e between actual costs incurred and the amount of costs collected from customers is recorded as a reduction of revenue in the period incurred. Sales to the Market Sales to the market include energy charges, capacity or demand charges, and ancillary charg es represented by wholesale sales of electricity made to third parties who are not ultimate users of the electricity. Most of these sales are spot market transactions on the markets operated by MISO. Each transaction is considered a performance obligation and revenue is recognized in the period in which energy charges, capacity or demand charges, and ancillary services are sold into MISO. MGE reports, on a net basis, transactions on the MISO markets in which it buys and sells power within the same hour to m eet electric energy delivery requirements. Transportation of Gas MGE has contracts under which MGE provides gas transportation services to customers who have elected to purchase gas from a third party and have the gas delivered via pipelines within MGE's service territory. 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 term s.
Investments - ATC and ATC Holdco	MGE Transco and MGEE Transco have accounted for their investment s in ATC and ATC Holdco, respectively, 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 u nits 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 vest ing 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 remeasured quarterly, including as of September 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. Comp ensation cost for retirement eligible employees or employees that will become retirement eligible during the vesting schedule are recognized on an abridged horizon as retirement eligibility accelerates vesting.
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 st andard 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 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 model projects future market energy prices and compares those prices to the projected power costs to be incurred under the contract. Inputs to the model require significant management judgmen t 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 counterpa rty delivery point. The historical relationship between the delivery points is reviewed and a discount (below 100%) or premium (above 100%) is derived. This comparison is done for both peak times when demand is high and off- peak times when demand is low. I f the basis adjustment is lowered, the fair value measurement will decrease, and if the basis adjustment is increased, the fair value measurement will increase. The projected power costs anticipated to be incurred under the purchased power agreement are d etermined 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 assumption s about market risk such as liquidity, volatility , and contract duration. The fair value model uses a discount rate that incorporates discounting, credit, and model risks. The following table presents the significant unobservable inputs used in the pricin g model. Model Input Significant Unobservable Inputs September 30, 2018 December 31, 2017 Basis adjustment: On peak 91.9 % 92.3 % Off peak 93.2 % 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 Accoun_2

Summary of Significant Accounting Principles (Tables)	9 Months Ended
	Sep. 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 September 30, December 31, September 30, December 31, (In thousands) 2018 2017 2018 2017 Cash and cash equivalents $ 133,855 $ 107,952 $ 47,264 $ 5,951 Restricted cash 406 1,635 406 1,635 Receivable - margin account 780 2,507 780 2,507 Cash, cash equivalents, and restricted cash $ 135,041 $ 112,094 $ 48,450 $ 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. Nine Months Ended (In thousands) September 30, 2017 Cash provided by operating activities $ (2,870) Cash used for investing activities 525 Change in cash, cash equivalents, and restricted cash (2,345) Cash, cash equivalents, and restricted cash at beginning of period 5,674 Cash, cash equivalents, and restricted cash at end of period $ 3,329

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Revenues disaggregated by revenue source were as follows: Three Months Ended Nine Months Ended (In thousands) September 30, September 30, Electric revenues 2018 2017 2018 2017 Residential $ 42,371 $ 39,905 $ 107,847 $ 104,892 Commercial (a) 61,638 64,036 159,264 168,921 Industrial 3,668 4,555 11,193 13,286 Other-retail/municipal 9,431 10,459 26,245 29,141 Total retail 117,108 118,955 304,549 316,240 Sales to the market 1,505 1,068 6,334 3,090 Other revenues 482 445 1,406 1,436 Adjustments to revenues 80 181 344 513 Total electric revenues 119,175 120,649 312,633 321,279 Gas revenues Residential 11,916 12,121 64,087 61,164 Commercial/Industrial (a) 5,570 5,622 38,728 36,512 Total retail 17,486 17,743 102,815 97,676 Gas transportation 829 944 3,018 3,285 Other revenues 92 91 319 324 Total gas revenues 18,407 18,778 106,152 101,285 Non-regulated energy revenues 213 112 904 261 Total Operating Revenue (a) $ 137,795 $ 139,539 419,689 $ 422,825 (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 Hol_2

Investment in ATC and ATC Holdco (Tables)	9 Months Ended
	Sep. 30, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments Financial Data	MGE Transco and MGEE Transco have accounted for their investment s in ATC and ATC Holdco, respectively, under the equity method of accounting. Equity earnings from investments are recorded as " Other income " on the consolidated statements of income of MGE Energy. For the three and nine months ended September 30, 2018 and 2017 , MGE Transco recorde d the following : Three Months Ended Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Equity earnings from investment in ATC $ 1,672 $ 2,338 $ 6,113 $ 7,432 Dividends from ATC (a) 1,581 2,070 4,540 4,070 Capital contributions to ATC 533 710 2,308 3,018 (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 $ 1.6 million dividend receivable from ATC as of September 30, 2018 . A cash dividend was received in October 2018 . ATC ' s summarized financial data for the three and nine months ended September 30, 2018 and 2017 , is as follows: Three Months Ended Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Operating revenues $ 170,341 $ 171,123 $ 501,276 $ 522,402 Operating expenses (87,959) (85,372) (264,326) (251,042) Other income, net 439 1,272 2,070 3,043 Interest expense, net (27,754) (28,440) (82,411) (81,690) Earnings before members' income taxes $ 55,067 $ 58,583 $ 156,609 $ 192,713

Taxes (Tables)

Taxes (Tables)	9 Months Ended
	Sep. 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 September 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) % (1.1) % (0.2) % (1.1) % Domestic manufacturing deduction - % (1.5) % - % (1.4) % AFUDC equity, net (0.6) % (0.1) % (0.6) % (0.1) % Amortization of utility excess deferred tax - tax reform (a) (1.8) % - % (1.8) % - % Other, net, individually insignificant - % (0.3) % 0.1 % (0.4) % Effective income tax rate 24.5 % 36.9 % 24.6 % 36.7 % MGE Energy MGE Nine Months Ended September 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) % (1.3) % (0.3) % (1.4) % Domestic manufacturing deduction - % (1.6) % - % (1.7) % AFUDC equity, net (0.8) % (0.2) % (0.8) % (0.2) % Amortization of utility excess deferred tax - tax reform (a) (1.8) % - % (2.0) % - % Other, net, individually insignificant - % (0.2) % 0.1 % (0.1) % Effective income tax rate 24.3 % 36.6 % 24.1 % 36.3 % (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 Postretirem_2

Pension and Other Postretirement Plans (Tables)	9 Months Ended
	Sep. 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 nine months ended September 30, 2018 and 2017 . Three Months Ended Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Pension Benefits Components of net periodic benefit cost: Service cost $ 1,431 $ 1,351 $ 4,292 $ 4,043 Interest cost 3,215 3,168 9,645 9,481 Expected return on assets (6,560) (5,762) (19,680) (17,244) Amortization of: Prior service credit (11) (4) (33) (12) Actuarial loss 1,319 1,594 3,958 4,769 Net periodic benefit (credit) cost $ (606) $ 347 $ (1,818) $ 1,037 Postretirement Benefits Components of net periodic benefit cost: Service cost $ 320 $ 315 $ 962 $ 944 Interest cost 653 678 1,959 2,034 Expected return on assets (808) (722) (2,424) (2,165) Amortization of: Transition obligation 1 1 2 2 Prior service credit (667) (667) (2,001) (2,001) Actuarial loss 122 190 366 570 Net periodic benefit (credit) cost $ (379) $ (205) $ (1,136) $ (616)

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 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 September 30, 2018 : (In thousands) 2018 2019 2020 2021 2022 Thereafter Coal (a) $ 6,716 $ 21,188 $ 8,434 $ 828 $ - $ - Natural gas supply (b) 12,245 13,287 - - - - Saratoga wind (c) 1,006 858 2,266 1,775 1,784 4,459 Other 1,772 502 502 502 502 502 $ 21,739 $ 35,835 $ 11,202 $ 3,105 $ 2,286 $ 4,961 (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 September 30, 2018 , MGE has incurred $ 66.5 million of capital expenditures. After tax, MGE has recognized $0.6 million and $1.3 million, respectively, in AFUDC equity related to this project for the three and nine months ended September 30, 2018 . Construction of the pro ject is expected to be completed by early 2019 , with an estimated capital cost of $108 million.

Derivative and Hedging Instru_2

Derivative and Hedging Instruments (Tables)	9 Months Ended
	Sep. 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: September 30, 2018 December 31, 2017 Commodity derivative contracts 482,450 MWh 552,310 MWh Commodity derivative contracts 8,557,000 Dth 5,460,000 Dth FTRs 3,681 MW 2,226 MW PPA 2,200 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 September 30, 2018 , and December 31, 2017 , the receiv able margin account balance of $ 0.8 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 September 30, 2018 Commodity derivative contracts (a) $ 1,363 $ 232 Other current assets Commodity derivative contracts (a) 86 55 Other deferred charges FTRs 478 - Other current assets PPA N/A 9,350 Derivative liability (current) PPA N/A 26,920 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 September 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 September 30, 2018 Commodity derivative contracts $ 1,449 $ (287) $ - $ 1,162 FTRs 478 - - 478 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 September 30, 2018 Commodity derivative contracts $ 287 $ (287) $ - $ - PPA 36,270 - - 36,270 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 as of September 30, 2018 and 2017 , and the consolidated statements of income for the three and nine months ended September 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 September 30: Balance at July 1, $ 36,924 $ 640 $ 45,316 $ 618 Unrealized gain (2,007) - (1,277) - Realized (loss) gain reclassified to a deferred account (316) 316 (313) 313 Realized gain (loss) reclassified to income statement 29 (62) (1,450) (57) Balance at September 30, $ 34,630 $ 894 $ 42,276 $ 874 Nine Months Ended September 30: Balance at January 1, $ 41,958 $ 806 $ 49,281 $ 230 Unrealized gain (5,906) - (3,698) - Realized (loss) gain reclassified to a deferred account (837) 837 (935) 935 Realized loss reclassified to income statement (585) (749) (2,372) (291) Balance at September 30, $ 34,630 $ 894 $ 42,276 $ 874
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 September 30: Commodity derivative contracts $ (145) $ - $ 362 $ 18 FTRs (150) - (224) - PPA 328 - 1,351 - Nine Months Ended September 30: Commodity derivative contracts $ 39 $ 637 $ 764 $ 227 FTRs (625) - (1,349) - PPA 1,283 - 3,021 -

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Estimated Fair Market Value of Financial Instruments	The estimated fair market value of financial instruments are as follows: September 30, 2018 December 31, 2017 (In thousands) Carrying Amount Fair Value Carrying Amount Fair Value MGE Energy Assets: Cash and cash equivalents $ 133,855 $ 133,855 $ 107,952 $ 107,952 Liabilities: Short-term debt - commercial paper - - 4,000 4,000 Long-term debt (a) 503,553 523,075 426,883 475,282 MGE Assets: Cash and cash equivalents $ 47,264 $ 47,264 $ 5,951 $ 5,951 Liabilities: Short-term debt - commercial paper - - 4,000 4,000 Long-term debt (a) 503,553 523,075 426,883 475,282 (a) Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.6 million and $4.3 million as of September 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 September 30, 2018 (In thousands) Total Level 1 Level 2 Level 3 MGE Energy Assets: Derivatives, net $ 1,927 $ 824 $ - $ 1,103 Exchange-traded investments 1,005 1,005 - - Total Assets $ 2,932 $ 1,829 $ - $ 1,103 Liabilities: Derivatives, net $ 36,557 $ 140 $ - $ 36,417 Deferred compensation 2,985 - 2,985 - Total Liabilities $ 39,542 $ 140 $ 2,985 $ 36,417 MGE Assets: Derivatives, net $ 1,927 $ 824 $ - $ 1,103 Exchange-traded investments 70 70 - - Total Assets $ 1,997 $ 894 $ - $ 1,103 Liabilities: Derivatives, net $ 36,557 $ 140 $ - $ 36,417 Deferred compensation 2,985 - 2,985 - Total Liabilities $ 39,542 $ 140 $ 2,985 $ 36,417 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 pricin g model. Model Input Significant Unobservable Inputs September 30, 2018 December 31, 2017 Basis adjustment: On peak 91.9 % 92.3 % Off peak 93.2 % 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 Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Beginning balance $ (37,332) $ (45,605) $ (42,026) $ (50,305) Realized and unrealized gains (losses): Included in regulatory assets 2,018 2,846 6,711 7,547 Included in other comprehensive income - - - - Included in earnings 26 (1,478) (434) (2,614) Included in current assets (25) (14) (496) (111) Purchases 5,736 6,299 17,602 18,481 Sales - - - - Issuances - - - - Settlements (5,737) (4,807) (16,671) (15,757) Transfers in and/or out of Level 3 - - - - Balance as of September 30, $ (35,314) $ (42,759) $ (35,314) $ (42,759) Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities held at September 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 Nine Months Ended September 30, September 30, (In thousands) 2018 2017 2018 2017 Purchased Power Expense $ 26 $ (1,460) $ (637) $ (2,377) Cost of Gas Sold Expense - (18) 203 (237) Total $ 26 $ (1,478) $ (434) $ (2,614) (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)	9 Months Ended
	Sep. 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 September 30, 2018 Operating revenues $ 119,175 $ 18,407 $ 213 $ - $ - $ - $ 137,795 Interdepartmental revenues (20) 4,219 9,912 - - (14,111) - Total operating revenues 119,155 22,626 10,125 - - (14,111) 137,795 Depreciation and amortization (9,864) (2,534) (1,861) - - - (14,259) Other operating expenses (77,847) (19,824) (36) (4) (138) 14,111 (83,738) Operating income (loss) 31,444 268 8,228 (4) (138) - 39,798 Other income, net 1,763 829 - 1,620 118 - 4,330 Interest (expense) income, net (3,217) (963) (1,320) - 475 - (5,025) Income before taxes 29,990 134 6,908 1,616 455 - 39,103 Income tax (provision) benefit (7,306) 42 (1,852) (441) (40) - (9,597) Net income $ 22,684 $ 176 $ 5,056 $ 1,175 $ 415 $ - $ 29,506 Three Months Ended September 30, 2017 Operating revenues $ 120,649 $ 18,778 $ 112 $ - $ - $ - $ 139,539 Interdepartmental revenues (110) 3,892 11,130 - - (14,912) - Total operating revenues 120,539 22,670 11,242 - - (14,912) 139,539 Depreciation and amortization (9,256) (2,258) (1,858) - - - (13,372) Other operating expenses (a) (79,506) (19,324) (50) (9) (193) 14,912 (84,170) Operating income (loss) 31,777 1,088 9,334 (9) (193) - 41,997 Other income (deductions), net (a) 2,060 742 - 2,258 (117) - 4,943 Interest (expense) income, net (2,760) (795) (1,371) - 199 - (4,727) Income (loss) before taxes 31,077 1,035 7,963 2,249 (111) - 42,213 Income tax (provision) benefit (11,175) (351) (3,196) (906) 44 - (15,584) Net income (loss) $ 19,902 $ 684 $ 4,767 $ 1,343 $ (67) $ - $ 26,629 Nine Months Ended September 30, 2018 Operating revenues $ 312,633 $ 106,152 $ 904 $ - $ - $ - $ 419,689 Interdepartmental revenues (234) 12,059 29,579 - - (41,404) - Total operating revenues 312,399 118,211 30,483 - - (41,404) 419,689 Depreciation and amortization (28,817) (7,374) (5,563) - - - (41,754) Other operating expenses (228,957) (99,251) (113) (12) (789) 41,404 (287,718) Operating income (loss) 54,625 11,586 24,807 (12) (789) - 90,217 Other income, net 5,055 2,347 - 5,908 670 - 13,980 Interest (expense) income, net (9,036) (2,689) (4,002) - 1,180 - (14,547) Income before taxes 50,644 11,244 20,805 5,896 1,061 - 89,650 Income tax provision (11,492) (2,788) (5,638) (1,611) (263) - (21,792) Net income $ 39,152 $ 8,456 $ 15,167 $ 4,285 $ 798 $ - $ 67,858 Nine Months Ended September 30, 2017 Operating revenues $ 321,279 $ 101,285 $ 261 $ - $ - $ - $ 422,825 Interdepartmental revenues (334) 11,708 33,307 - - (44,681) - Total operating revenues 320,945 112,993 33,568 - - (44,681) 422,825 Depreciation and amortization (27,341) (6,703) (5,562) - - - (39,606) Other operating expenses (a) (233,714) (93,817) (153) (9) (779) 44,681 (283,791) Operating income (loss) 59,890 12,473 27,853 (9) (779) - 99,428 Other income (deductions), net (a) 3,708 1,502 - 7,242 (414) - 12,038 Interest (expense) income, net (8,337) (2,399) (4,170) - 399 - (14,507) Income (loss) before taxes 55,261 11,576 23,683 7,233 (794) - 96,959 Income tax (provision) benefit (18,753) (4,576) (9,505) (2,909) 256 - (35,487) Net income (loss) $ 36,508 $ 7,000 $ 14,178 $ 4,324 $ (538) $ - $ 61,472 (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 September 30, 2018 Operating revenues $ 119,175 $ 18,407 $ 213 $ - $ 137,795 Interdepartmental revenues (20) 4,219 9,912 (14,111) - Total operating revenues 119,155 22,626 10,125 (14,111) 137,795 Depreciation and amortization (9,864) (2,534) (1,861) - (14,259) Other operating expenses (b) (85,127) (19,739) (1,888) 14,111 (92,643) Operating income (b) 24,164 353 6,376 - 30,893 Other income, net (b) 1,737 786 - - 2,523 Interest expense, net (3,217) (963) (1,320) - (5,500) Net income 22,684 176 5,056 - 27,916 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,629) (5,629) Net income attributable to MGE $ 22,684 $ 176 $ 5,056 $ (5,629) $ 22,287 Three Months Ended September 30, 2017 Operating revenues $ 120,648 $ 18,779 $ 112 $ - $ 139,539 Interdepartmental revenues (109) 3,891 11,130 (14,912) - Total operating revenues 120,539 22,670 11,242 (14,912) 139,539 Depreciation and amortization (9,256) (2,258) (1,858) - (13,372) Other operating expenses (a), (b) (90,164) (19,529) (3,246) 14,912 (98,027) Operating income (b) 21,119 883 6,138 - 28,140 Other income, net (a), (b) 1,543 596 - - 2,139 Interest expense, net (2,760) (795) (1,371) - (4,926) Net income 19,902 684 4,767 - 25,353 Less: Net income attributable to noncontrolling interest, net of tax - - - (5,439) (5,439) Net income attributable to MGE $ 19,902 $ 684 $ 4,767 $ (5,439) $ 19,914 Nine Months Ended September 30, 2018 Operating revenues $ 312,633 $ 106,152 $ 904 $ - $ 419,689 Interdepartmental revenues (234) 12,059 29,579 (41,404) - Total operating revenues 312,399 118,211 30,483 (41,404) 419,689 Depreciation and amortization (28,817) (7,374) (5,563) - (41,754) Other operating expenses (b) (240,333) (101,938) (5,751) 41,404 (306,618) Operating income (b) 43,249 8,899 19,169 - 71,317 Other income, net (b) 4,939 2,246 - - 7,185 Interest expense, net (9,036) (2,689) (4,002) - (15,727) Net income 39,152 8,456 15,167 - 62,775 Less: Net income attributable to noncontrolling interest, net of tax - - - (16,940) (16,940) Net income attributable to MGE $ 39,152 $ 8,456 $ 15,167 $ (16,940) $ 45,835 Nine Months Ended September 30, 2017 Operating revenues $ 321,282 $ 101,294 $ 261 $ - $ 422,837 Interdepartmental revenues (337) 11,699 33,307 (44,669) - Total operating revenues 320,945 112,993 33,568 (44,669) 422,837 Depreciation and amortization (27,341) (6,703) (5,562) - (39,606) Other operating expenses (a), (b) (251,879) (98,227) (9,658) 44,669 (315,095) Operating income (b) 41,725 8,063 18,348 - 68,136 Other income, net (a), (b) 3,120 1,336 - - 4,456 Interest expense, net (8,337) (2,399) (4,170) - (14,906) Net income 36,508 7,000 14,178 - 57,686 Less: Net income attributable to noncontrolling interest, net of tax - - - (16,224) (16,224) Net income attributable to MGE $ 36,508 $ 7,000 $ 14,178 $ (16,224) $ 41,462 (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 Non-regulated Energy Transmission Investment All Others Consolidation/ Elimination Entries Total Assets: September 30, 2018 $ 1,141,370 $ 345,349 $ 64,016 $ 264,735 $ 64,722 $ 472,740 $ (378,635) $ 1,974,297 December 31, 2017 1,043,181 344,337 26,345 270,384 61,783 485,548 (376,396) 1,855,182 Capital Expenditures: Nine Months Ended Sept. 30, 2018 $ 122,108 $ 22,406 $ - $ 4,487 $ - $ - $ - $ 149,001 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - - - 108,131 Utility Consolidated (In thousands) MGE Electric Gas Assets not Allocated Non-regulated Energy Elimination Entries Total Assets: September 30, 2018 $ 1,141,370 $ 345,349 $ 64,016 $ 264,685 $ (1,176) $ 1,814,244 December 31, 2017 1,043,181 344,337 26,345 270,334 (156) 1,684,041 Capital Expenditures: Nine Months Ended Sept. 30, 2018 $ 122,108 $ 22,406 $ - $ 4,487 $ - $ 149,001 Year ended Dec. 31, 2017 77,353 26,847 - 3,931 - 108,131

Summary of Significant Accoun_3

Summary of Significant Accounting Principles (Details-1) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 133,855	$ 107,952
Restricted cash	406	1,635
Receivable - margin account	780	2,507
Cash, cash equivalents, and restricted cash	135,041	112,094	$ 108,062	$ 101,633
MGE [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	47,264	5,951
Restricted cash	406	1,635
Receivable - margin account	780	2,507
Cash, cash equivalents, and restricted cash	$ 48,450	$ 10,093	$ 5,283	$ 16,442

Summary of Significant Accoun_4

Summary of Significant Accounting Principles (Details-2) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities			$ 138,432,000	$ 96,146,000
Cash used for investing activities			(153,434,000)	(70,589,000)
Change in cash, cash equivalents, and restricted cash			22,947,000	6,429,000
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	$ 135,041,000	$ 108,062,000	135,041,000	108,062,000
Capitalized Software Hosting Agreement Costs
Capitalized software hosting agreement	6,200,000		6,200,000		$ 500,000
Capitalized software hosting agreement amortization expense	100,000	0	100,000	0
Capitalized software hosting agreement accumulated amortization	$ 100,000		$ 100,000		$ 0
Accounting Standards Update 2016-18 - Restricted Cash [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash provided by operating activities				(2,870,000)
Cash used for investing activities				525,000
Change in cash, cash equivalents, and restricted cash				(2,345,000)
Cash, cash equivalents, and restricted cash at beginning of period				5,674,000
Cash, cash equivalents, and restricted cash at end of period		$ 3,329,000		$ 3,329,000

New Accounting Standards (Detai

New Accounting Standards (Details-1) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 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	1,000	3,000
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	$ 1,000	$ 3,000

Revenue (Details-1)

Revenue (Details-1) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017		Dec. 31, 2017
Total Operating Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 137,795	$ 139,539	[1]	$ 419,689	$ 422,825	[1]
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	119,175	120,649		312,633	321,279
Electric [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	42,371	39,905		107,847	104,892
Electric [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	61,638	64,036	[1]	159,264	168,921	[1]
Electric [Member] | Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	3,668	4,555		11,193	13,286
Electric [Member] | Other-retail/municipal
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	9,431	10,459		26,245	29,141
Electric [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	117,108	118,955		304,549	316,240
Electric [Member] | Sales To The Market [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	1,505	1,068		6,334	3,090
Electric [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	482	445		1,406	1,436
Electric [Member] | Adjustments To Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	80	181		344	513
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	18,407	18,778		106,152	101,285
Gas [Member] | Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	11,916	12,121		64,087	61,164
Gas [Member] | Commercial/Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	5,570	5,622	[1]	38,728	36,512	[1]
Gas [Member] | Total Retail [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	17,486	17,743		102,815	97,676
Gas [Member] | Gas Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	829	944		3,018	3,285
Gas [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	92	91		319	324
Non Regulated Energy [Member]
Disaggregation of Revenue [Line Items]
Revenues recognized from contracts with customers	$ 213	$ 112		$ 904	$ 261
MGE [Member]
Disaggregation of Revenue [Line Items]
CNG Vehicle Fuel Servicing Revenue							$ 100
[1]	(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 Hol_3

Investment in ATC and ATC Holdco (Details-1) - USD ($) $ in Thousands		Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC			$ 1,672	$ 2,338	$ 6,113	$ 7,432
Dividends from ATC			1,581	2,070	5,336	6,142
Capital contributions to investments			533	710	4,801	6,863
MGE Transco [Member] | ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC			1,672	2,338	6,113	7,432
Dividends from ATC	[1]		1,581	2,070	4,540	4,070
Capital contributions to investments			$ 533	710	$ 2,308	3,018
Ownership interest in equity-method investee			3.60%		3.60%		3.60%
Dividend receivable from ATC			$ 1,600		$ 1,600		$ 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	$ 0	$ 300	$ 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 $ 1.6 million dividend receivable from ATC as of September 30, 2018 . A cash dividend was received in October 2018 .

Investment in ATC and ATC Hol_4

Investment in ATC and ATC Holdco (Details-2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Operating revenues	$ 170,341	$ 171,123	$ 501,276	$ 522,402
Operating expenses	(87,959)	(85,372)	(264,326)	(251,042)
Other income, net	439	1,272	2,070	3,043
Interest expense, net	(27,754)	(28,440)	(82,411)	(81,690)
Earnings before members' income taxes	55,067	58,583	156,609	192,713
ATC [Member]
Related Party Transaction [Line Items]
Related party expenses	7,200	$ 7,300	21,700	$ 21,900
Due from related parties	$ 100		$ 100		$ 200

Taxes (Details)

Taxes (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 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	(0.30%)		(1.10%)	(0.30%)		(1.30%)
Domestic manufacturing deduction	0.00%		(1.50%)	0.00%		(1.60%)
AFUDC equity, net	(0.60%)		(0.10%)	(0.80%)		(0.20%)
Amortization of utility excess deferred tax - tax reform	(1.80%)	[1]	0.00%	(1.80%)	[1]	0.00%
Other, net, individually significant	0.00%		(0.30%)	0.00%		(0.20%)
Effective income tax rate	24.50%		36.90%	24.30%		36.60%
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	$ 7,330			$ 7,330			$ 5,633
Revenue Subject to Refund | Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	2,600			2,600
Return of tax credit	5,900			5,900
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	$ 700			$ 1,900
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	(0.20%)		(1.10%)	(0.30%)		(1.40%)
Domestic manufacturing deduction	0.00%		(1.40%)	0.00%		(1.70%)
AFUDC equity, net	(0.60%)		(0.10%)	(0.80%)		(0.20%)
Amortization of utility excess deferred tax - tax reform	(1.80%)	[1]	0.00%	(2.00%)	[1]	0.00%
Other, net, individually significant	0.10%		(0.40%)	0.10%		(0.10%)
Effective income tax rate	24.60%		36.70%	24.10%		36.30%
Effects Of The Tax Cuts And Jobs Act [Abstract]
Regulatory liabilities - current	$ 7,330			$ 7,330			$ 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 Postretirem_3

Pension and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 1,431	$ 1,351	$ 4,292	$ 4,043
Interest cost	3,215	3,168	9,645	9,481
Expected return on assets	(6,560)	(5,762)	(19,680)	(17,244)
Amortization of:
Prior service credit	(11)	(4)	(33)	(12)
Actuarial loss	1,319	1,594	3,958	4,769
Net periodic benefit (credit) cost	(606)	347	(1,818)	1,037
Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	320	315	962	944
Interest cost	653	678	1,959	2,034
Expected return on assets	(808)	(722)	(2,424)	(2,165)
Amortization of:
Transition obligation	1	1	2	2
Prior service credit	(667)	(667)	(2,001)	(2,001)
Actuarial loss	122	190	366	570
Net periodic benefit (credit) cost	$ (379)	$ (205)	$ (1,136)	$ (616)

Equity and Financing Arrangem_2

Equity and Financing Arrangements (Details) - USD ($)	Sep. 07, 2018	Jul. 16, 2018	Sep. 30, 2018	Sep. 30, 2017
Common Stock [Abstract]
Common stock issued during period			0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities			$ 0
Senior Notes, 4.24% due 2053
Debt Instrument [Line Items]
Face amount		$ 20,000,000
Interest rate		4.24%
Term		35 years
Senior Notes, 4.34% due 2058
Debt Instrument [Line Items]
Face amount		$ 20,000,000
Interest rate		4.34%
Term		40 years
Senior Notes, 4.19% due 2048
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		9 Months Ended
	Jan. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense		$ 0.3	$ 0.3	$ 1.3	$ 1
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				$ 5.5
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 Contingencies_2

Commitments and Contingencies (Details-1) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)TurbinesMW		Sep. 30, 2018USD ($)TurbinesMW
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	$ 21,739		$ 21,739
Purchase obligation, 2019	35,835		35,835
Purchase obligation, 2020	11,202		11,202
Purchase obligation, 2021	3,105		3,105
Purchase obligation, 2022	2,286		2,286
Purchase obligation, Thereafter	4,961		4,961
Coal [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	6,716	[1]	6,716	[1]
Purchase obligation, 2019	21,188	[1]	21,188	[1]
Purchase obligation, 2020	8,434	[1]	8,434	[1]
Purchase obligation, 2021	828	[1]	828	[1]
Purchase obligation, 2022	0	[1]	0	[1]
Purchase obligation, Thereafter	0	[1]	0	[1]
Natual Gas, Supply [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	12,245	[2]	12,245	[2]
Purchase obligation, 2019	13,287	[2]	13,287	[2]
Purchase obligation, 2020	0	[2]	0	[2]
Purchase obligation, 2021	0	[2]	0	[2]
Purchase obligation, 2022	0	[2]	0	[2]
Purchase obligation, Thereafter	0	[2]	0	[2]
Saratoga Wind [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	1,006	[3]	1,006	[3]
Purchase obligation, 2019	858	[3]	858	[3]
Purchase obligation, 2020	2,266	[3]	2,266	[3]
Purchase obligation, 2021	1,775	[3]	1,775	[3]
Purchase obligation, 2022	1,784	[3]	1,784	[3]
Purchase obligation, Thereafter	$ 4,459	[3]	$ 4,459	[3]
Saratoga Wind
Saratoga Capacity (MW) | MW	66		66
Saratoga Turbines | Turbines	33		33
Projected Saratoga Wind Project Costs	$ 108,000		$ 108,000
Saratoga Wind Project Costs Year to Date	66,500		66,500
Allowance for Funds Used During Construction
AFUDC - equity funds	$ 600		$ 1,300
Saratoga Wind [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC Rate	100.00%		100.00%
Other [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2018	$ 1,772		$ 1,772
Purchase obligation, 2019	502		502
Purchase obligation, 2020	502		502
Purchase obligation, 2021	502		502
Purchase obligation, 2022	502		502
Purchase obligation, Thereafter	502		502
MGE Energy [Member] | Venture Capital Funds [Member]
Other Commitments [Line Items]
Other commitment, initial agreed upon commitment total	$ 2,300		$ 2,300
[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 September 30, 2018 , MGE has incurred $ 66.5 million of capital expenditures. After tax, MGE has recognized $0.6 million and $1.3 million, respectively, in AFUDC equity related to this project for the three and nine months ended September 30, 2018 . Construction of the pro ject is expected to be completed by early 2019 , with an estimated capital cost of $108 million.

Rate Matters (Details)

Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($) $ in Millions	Aug. 31, 2018	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Rate Proceedings [Abstract]
Authorized return on equity, percentage						9.80%
Approved equity capital structure, percentage						57.20%
Fuel Rules [Abstract]
Fuel rules, bandwidth		2.00%
Fuel rules, electric fuel deferred costs upper threshold		102.00%
Fuel rules, electric fuel deferred costs lower threshold		98.00%
Deferred fuel rules monitored costs		$ 7.2				$ 4.2
Public Utilities Fuel Surcharge Amount					$ 0.5
Public Utilities Fuel Surcharge Percentage					0.10%
Fuel Rules Refund, 2015/2016 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total						$ 6.2
Fuel Rules Refund, 2017 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total	$ 4.2
Proposed Future Rate Matters [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]
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]
Rate Proceedings [Abstract]
Proposed rate increase (decrease), percentage			1.46%	1.06%

Derivative and Hedging Instru_3

Derivative and Hedging Instruments (Details-1) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2018USD ($)DthMWhMW		Dec. 31, 2017USD ($)DthMWhMW	Jun. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2016USD ($)
Derivative fair values [Abstract]
Receivable, margin account balance, net of collateral posted against derivative positions		$ 780		$ 2,507
Other Current Assets [Member]
Derivative fair values [Abstract]
Derivative fair value, net		894		806	$ 640	$ 874	$ 618	$ 230
Commodity Contracts And Financial Transimission Rights [Member]
Derivative fair values [Abstract]
Derivative fair value, net		$ 1,600		$ 200
Commodity Derivative Contracts [Member]
Gross Notional Volume of Open Derivatives
Notional amount, energy measure (in MWh) | MWh		482,450		552,310
Notional amount, decatherm measure (in Dth) | Dth		8,557,000		5,460,000
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 1,449		$ 676
Liability Derivatives, fair value, gross basis		287		793
Commodity Derivative Contracts [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis	[1]	1,363
Liability Derivatives, fair value, gross basis		232	[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]	86
Liability Derivatives, fair value, gross basis	[1]	$ 55
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		3,681		2,226
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		$ 478		$ 329
Financial Transmission Rights [Member] | Other Current Assets [Member]
Derivative fair values [Abstract]
Asset Derivatives, fair value, gross basis		478		329
Liability Derivatives, fair value, gross basis		$ 0		$ 0
PPA [Member]
Gross Notional Volume of Open Derivatives
Notional amount, power measure (in MW) | MW		2,200		2,650
Derivative fair values [Abstract]
Derivative fair value, net		$ (36,300)		$ (42,200)
Liability Derivatives, fair value, gross basis		36,270		42,170
PPA [Member] | Derivative Liability (Current) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		9,350		8,180
PPA [Member] | Derivative Liability (Long-term) [Member]
Derivative fair values [Abstract]
Liability Derivatives, fair value, gross basis		$ 26,920		$ 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 September 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 Instru_4

Derivative and Hedging Instruments (Details-2) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Commodity Derivative Contracts [Member]
Offsetting Assets [Line Items]
Gross amounts	$ 1,449	$ 676
Gross amounts offset in balance sheet	(287)	(654)
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	1,162	22
Financial Transmission Rights [Member]
Offsetting Assets [Line Items]
Gross amounts	478	329
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 478	$ 329

Derivative and Hedging Instru_5

Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Sep. 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	287	793
Gross amounts offset in balance sheet	(287)	(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	36,270	42,170
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 36,270	$ 42,170

Derivative and Hedging Instru_6

Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 36,924	$ 45,316	$ 41,958	$ 49,281
Unrealized loss (gain)	(2,007)	(1,277)	(5,906)	(3,698)
Realized (loss) gain reclassified to a deferred account	(316)	(313)	(837)	(935)
Realized gain (loss) reclassified to income statement	29	(1,450)	(585)	(2,372)
Ending balance,	34,630	42,276	34,630	42,276
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	640	618	806	230
Unrealized loss (gain)	0	0	0	0
Realized (loss) gain reclassified to a deferred account	316	313	837	935
Realized gain (loss) reclassified to income statement	(62)	(57)	(749)	(291)
Ending balance,	$ 894	$ 874	$ 894	$ 874

Derivative and Hedging Instru_7

Derivative and Hedging Instruments (Details-5) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)counterparty	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)counterparty	Sep. 30, 2017USD ($)	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	$ (145)	$ 362	$ 39	$ 764
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	0	18	637	227
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	(150)	(224)	(625)	(1,349)
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	328	1,351	1,283	3,021
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 Instr_3

Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,600	$ 4,300
Carrying Amount [Member]
Assets:
Cash and cash equivalents		133,855	107,952
Liabilities:
Short-term debt - commercial paper		0	4,000
Long-term debt	[1]	503,553	426,883
Fair Value [Member]
Assets:
Cash and cash equivalents		133,855	107,952
Liabilities:
Short-term debt - commercial paper		0	4,000
Long-term debt	[1]	523,075	475,282
MGE [Member] | Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		4,600	4,300
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		47,264	5,951
Liabilities:
Short-term debt - commercial paper		0	4,000
Long-term debt	[1]	503,553	426,883
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		47,264	5,951
Liabilities:
Short-term debt - commercial paper		0	4,000
Long-term debt	[1]	$ 523,075	$ 475,282
[1]	Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.6 million and $4.3 million at September 30, 2018 and December 31, 2017, respectively.

Fair Value of Financial Instr_4

Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Liabilities:
Derivative liability, collateral offset	$ 0	$ 100
Recurring [Member]
Assets:
Derivatives	1,927	1,005
Total Assets	2,932	1,797
Liabilities:
Derivatives	36,557	42,963	[1]
Deferred compensation	2,985	3,065
Total liabilities	39,542	46,028
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	1,005	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	824	278
Total Assets	1,829	1,070
Liabilities:
Derivatives	140	210	[1]
Deferred compensation	0	0
Total liabilities	140	210
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	1,005	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	0
Total Assets	0	0
Liabilities:
Derivatives	0	0	[1]
Deferred compensation	2,985	3,065
Total liabilities	2,985	3,065
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivatives	1,103	727
Total Assets	1,103	727
Liabilities:
Derivatives	36,417	42,753	[1]
Deferred compensation	0	0
Total liabilities	36,417	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	1,927	1,005
Total Assets	1,997	1,069
Liabilities:
Derivatives	36,557	42,963	[1]
Deferred compensation	2,985	3,065
Total liabilities	39,542	46,028
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	70	64
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	824	278
Total Assets	894	342
Liabilities:
Derivatives	140	210	[1]
Deferred compensation	0	0
Total liabilities	140	210
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	70	64
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	0
Total Assets	0	0
Liabilities:
Derivatives	0	0	[1]
Deferred compensation	2,985	3,065
Total liabilities	2,985	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	1,103	727
Total Assets	1,103	727
Liabilities:
Derivatives	36,417	42,753	[1]
Deferred compensation	0	0
Total liabilities	36,417	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 Instr_5

Fair Value of Financial Instruments (Details-3)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Basis adjustment:
Basis adjustment - on peak	91.90%	92.30%
Basis adjustment - off peak	93.20%	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 Instr_6

Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance,		$ (37,332)	$ (45,605)	$ (42,026)	$ (50,305)
Realized and unrealized gains (losses):
Included in regulatory assets		2,018	2,846	6,711	7,547
Included in other comprehensive income		0	0	0	0
Included in earnings	[1]	26	(1,478)	(434)	(2,614)
Included in current assets		(25)	(14)	(496)	(111)
Purchases		5,736	6,299	17,602	18,481
Sales		0	0	0	0
Issuances		0	0	0	0
Settlements		(5,737)	(4,807)	(16,671)	(15,757)
Transfers in and/or out of level 3		0	0	0	0
Ending balance,		(35,314)	(42,759)	(35,314)	(42,759)
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]	26	(1,460)	(637)	(2,377)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ 0	$ (18)	$ 203	$ (237)
[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	9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)TurbinesMW	Sep. 30, 2018USD ($)TurbinesMW	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2018	Jan. 01, 2018
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	$ 1,755	$ 1,755		$ 8,817
Accrued capital expenditures		10,991	$ 12,469
Forward Wind Purchase Power Energy Output				12.80%	12.80%
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	1,755	1,755		$ 8,817
Accrued capital expenditures		10,991	$ 12,469
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	1,800	1,800		$ 8,800
Accrued capital expenditures	$ 400	$ 1,800		$ 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			9 Months Ended			12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Operating revenues	$ 137,795	$ 139,539		$ 419,689	$ 422,825
Depreciation and amortization	(14,259)	(13,372)		(41,754)	(39,606)
Other operating expenses	(83,738)	(84,170)	[1]	(287,718)	(283,791)	[1]
Operating income (loss)	39,798	41,997		90,217	99,428
Other income (deductions), net	4,330	4,943	[1]	13,980	12,038	[1]
Interest (expense) income, net	(5,025)	(4,727)		(14,547)	(14,507)
Income before income taxes	39,103	42,213		89,650	96,959
Income tax (provision) benefit	(9,597)	(15,584)		(21,792)	(35,487)
Net Income (Loss)	29,506	26,629		67,858	61,472
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,974,297			1,974,297			$ 1,855,182
Capital expenditures				149,001	66,286		108,131
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	119,175	120,649		312,633	321,279
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	18,407	18,778		106,152	101,285
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	213	112		904	261
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	137,795	139,539		419,689	422,825
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	119,155	120,539		312,399	320,945
Depreciation and amortization	(9,864)	(9,256)		(28,817)	(27,341)
Other operating expenses	(77,847)	(79,506)	[1]	(228,957)	(233,714)	[1]
Operating income (loss)	31,444	31,777		54,625	59,890
Other income (deductions), net	1,763	2,060	[1]	5,055	3,708	[1]
Interest (expense) income, net	(3,217)	(2,760)		(9,036)	(8,337)
Income before income taxes	29,990	31,077		50,644	55,261
Income tax (provision) benefit	(7,306)	(11,175)		(11,492)	(18,753)
Net Income (Loss)	22,684	19,902		39,152	36,508
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,141,370			1,141,370			1,043,181
Capital expenditures				122,108			77,353
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	22,626	22,670		118,211	112,993
Depreciation and amortization	(2,534)	(2,258)		(7,374)	(6,703)
Other operating expenses	(19,824)	(19,324)	[1]	(99,251)	(93,817)	[1]
Operating income (loss)	268	1,088		11,586	12,473
Other income (deductions), net	829	742	[1]	2,347	1,502	[1]
Interest (expense) income, net	(963)	(795)		(2,689)	(2,399)
Income before income taxes	134	1,035		11,244	11,576
Income tax (provision) benefit	42	(351)		(2,788)	(4,576)
Net Income (Loss)	176	684		8,456	7,000
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	345,349			345,349			344,337
Capital expenditures				22,406			26,847
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,125	11,242		30,483	33,568
Depreciation and amortization	(1,861)	(1,858)		(5,563)	(5,562)
Other operating expenses	(36)	(50)	[1]	(113)	(153)	[1]
Operating income (loss)	8,228	9,334		24,807	27,853
Other income (deductions), net	0	0	[1]	0	0	[1]
Interest (expense) income, net	(1,320)	(1,371)		(4,002)	(4,170)
Income before income taxes	6,908	7,963		20,805	23,683
Income tax (provision) benefit	(1,852)	(3,196)		(5,638)	(9,505)
Net Income (Loss)	5,056	4,767		15,167	14,178
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	264,735			264,735			270,384
Capital expenditures				4,487			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	(4)	(9)	[1]	(12)	(9)	[1]
Operating income (loss)	(4)	(9)		(12)	(9)
Other income (deductions), net	1,620	2,258	[1]	5,908	7,242	[1]
Interest (expense) income, net	0	0		0	0
Income before income taxes	1,616	2,249		5,896	7,233
Income tax (provision) benefit	(441)	(906)		(1,611)	(2,909)
Net Income (Loss)	1,175	1,343		4,285	4,324
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	64,722			64,722			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	(138)	(193)	[1]	(789)	(779)	[1]
Operating income (loss)	(138)	(193)		(789)	(779)
Other income (deductions), net	118	(117)	[1]	670	(414)	[1]
Interest (expense) income, net	475	199		1,180	399
Income before income taxes	455	(111)		1,061	(794)
Income tax (provision) benefit	(40)	44		(263)	256
Net Income (Loss)	415	(67)		798	(538)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	472,740			472,740			485,548
Capital expenditures				0			0
Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	64,016			64,016			26,345
Capital expenditures				0			0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(14,111)	(14,912)		(41,404)	(44,681)
Depreciation and amortization	0	0		0	0
Other operating expenses	14,111	14,912	[1]	41,404	44,681	[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	(378,635)			(378,635)			(376,396)
Capital expenditures				0			0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	(20)	(110)		(234)	(334)
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,219	3,892		12,059	11,708
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,912	11,130		29,579	33,307
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	137,795	139,539		419,689	422,837
Depreciation and amortization	(14,259)	(13,372)		(41,754)	(39,606)
Other operating expenses	(92,643)	(98,027)	[1],[2]	(306,618)	(315,095)	[1],[2]
Operating income (loss)	30,893	28,140	[2]	71,317	68,136	[2]
Other income (deductions), net	2,523	2,139	[1],[2]	7,185	4,456	[1],[2]
Interest (expense) income, net	(5,500)	(4,926)		(15,727)	(14,906)
Net Income Including Noncontrolling Interest	27,916	25,353		62,775	57,686
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,629)	(5,439)		(16,940)	(16,224)
Net Income (Loss)	22,287	19,914		45,835	41,462
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,814,244			1,814,244			1,684,041
Capital expenditures				149,001	66,286		108,131
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	119,175	120,648		312,633	321,282
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	18,407	18,779		106,152	101,294
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	213	112		904	261
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	137,795	139,539		419,689	422,837
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	119,155	120,539		312,399	320,945
Depreciation and amortization	(9,864)	(9,256)		(28,817)	(27,341)
Other operating expenses	(85,127)	(90,164)	[1],[2]	(240,333)	(251,879)	[1],[2]
Operating income (loss)	24,164	21,119	[2]	43,249	41,725	[2]
Other income (deductions), net	1,737	1,543	[1],[2]	4,939	3,120	[1],[2]
Interest (expense) income, net	(3,217)	(2,760)		(9,036)	(8,337)
Net Income Including Noncontrolling Interest	22,684	19,902		39,152	36,508
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0		0	0
Net Income (Loss)	22,684	19,902		39,152	36,508
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,141,370			1,141,370			1,043,181
Capital expenditures				122,108			77,353
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	22,626	22,670		118,211	112,993
Depreciation and amortization	(2,534)	(2,258)		(7,374)	(6,703)
Other operating expenses	(19,739)	(19,529)	[1],[2]	(101,938)	(98,227)	[1],[2]
Operating income (loss)	353	883	[2]	8,899	8,063	[2]
Other income (deductions), net	786	596	[1],[2]	2,246	1,336	[1],[2]
Interest (expense) income, net	(963)	(795)		(2,689)	(2,399)
Net Income Including Noncontrolling Interest	176	684		8,456	7,000
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0		0	0
Net Income (Loss)	176	684		8,456	7,000
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	345,349			345,349			344,337
Capital expenditures				22,406			26,847
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,125	11,242		30,483	33,568
Depreciation and amortization	(1,861)	(1,858)		(5,563)	(5,562)
Other operating expenses	(1,888)	(3,246)	[1],[2]	(5,751)	(9,658)	[1],[2]
Operating income (loss)	6,376	6,138	[2]	19,169	18,348	[2]
Other income (deductions), net	0	0	[1],[2]	0	0	[1],[2]
Interest (expense) income, net	(1,320)	(1,371)		(4,002)	(4,170)
Net Income Including Noncontrolling Interest	5,056	4,767		15,167	14,178
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0		0	0
Net Income (Loss)	5,056	4,767		15,167	14,178
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	264,685			264,685			270,334
Capital expenditures				4,487			3,931
MGE [Member] | Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	64,016			64,016			26,345
Capital expenditures				0			0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(14,111)	(14,912)		(41,404)	(44,669)
Depreciation and amortization	0	0		0	0
Other operating expenses	14,111	14,912	[1],[2]	41,404	44,669	[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	(5,629)	(5,439)		(16,940)	(16,224)
Net Income (Loss)	(5,629)	(5,439)		(16,940)	(16,224)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(1,176)			(1,176)			(156)
Capital expenditures				0			$ 0
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	(20)	(109)		(234)	(337)
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,219	3,891		12,059	11,699
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 9,912	$ 11,130		$ 29,579	$ 33,307
[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.