NorthWestern (NWE) 10-Q 22 Oct 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Oct. 16, 2020
Cover [Abstract]
Document Type		10-Q
Document Quarterly Report		true
Document Period End Date	Sep. 30, 2020
Document Transition Report		false
Entity File Number		1-10499
Entity Registrant Name		NORTHWESTERN CORP
Entity Central Index Key		0000073088
Current Fiscal Year End Date		--12-31
Document Fiscal Year Focus		2020
Document Fiscal Period Focus		Q3
Amendment Flag		false
Entity Incorporation, State or Country Code		DE
Entity Tax Identification Number		46-0172280
Entity Address, Address Line One		3010 W. 69th Street
Entity Address, City or Town		Sioux Falls
Entity Address, State or Province		SD
Entity Address, Postal Zip Code		57108
City Area Code		605
Local Phone Number		978-2900
Title of 12(b) Security		Common stock
Trading Symbol		NWE
Security Exchange Name		NASDAQ
Entity Current Reporting Status		Yes
Entity Interactive Data Current		Yes
Entity Filer Category		Large Accelerated Filer
Entity Small Business		false
Entity Emerging Growth Company		false
Entity Shell Company		false
Entity Common Stock, Shares Outstanding			50,581,973

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Electric	$ 244,155	$ 241,237	$ 706,718	$ 733,933
Gas	36,455	33,599	178,507	195,842
Total Revenues	280,610	274,836	885,225	929,775
Operating Expenses
Cost of revenue	68,038	64,227	220,353	235,706
Operating, general and administrative	73,322	76,998	224,042	238,916
Property and other taxes	45,306	44,089	136,786	133,188
Depreciation and depletion	44,289	43,166	134,336	129,766
Total Operating Expenses	230,955	228,480	715,517	737,576
Operating Income	49,655	46,356	169,708	192,199
Interest Expense, net	(23,677)	(23,722)	(72,298)	(71,023)
Other Income (Expense), net	785	(409)	(973)	864
Income Before Income Taxes	26,763	22,225	96,437	122,040
Income Tax Benefit (Expense)	2,703	(555)	5,227	20,098
Net Income	$ 29,466	$ 21,670	$ 101,664	$ 142,138
Average Common Shares Outstanding	50,576,564	50,443,866	50,551,121	50,422,028
Basic Earnings per Average Common Share	$ 0.58	$ 0.43	$ 2.01	$ 2.82
Diluted Earnings per Average Common Share	0.58	0.42	2.01	2.80
Dividends Declared per Common Share	$ 0.600	$ 0.575	$ 1.80	$ 1.725

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Comprehensive Income (Loss)
Net Income	$ 29,466	$ 21,670	$ 101,664	$ 142,138
Other comprehensive income, net of tax:
Foreign currency translation adjustment	(3)	42	90	18
Reclassification of net losses on derivative instruments	113	114	339	339
Total Other Comprehensive Income	110	156	429	357
Comprehensive Income	$ 29,576	$ 21,826	$ 102,093	$ 142,495

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEET - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 3,512	$ 5,145
Restricted cash	10,497	6,925
Accounts receivable, net	133,115	167,405
Inventories	69,055	53,925
Regulatory assets	47,060	54,432
Other	18,089	13,895
Total current assets	281,328	301,727
Property, plant, and equipment, net	4,860,759	4,700,924
Goodwill	357,586	357,586
Regulatory assets	511,459	484,131
Other noncurrent assets	64,507	66,334
Total Assets	6,075,639	5,910,702
Current Liabilities:
Current maturities of finance leases	2,618	2,476
Short term borrowings	100,000	0
Accounts payable	74,663	96,690
Accrued expenses	269,722	202,021
Regulatory liabilities	46,513	33,080
Total current liabilities	493,516	334,267
Long-term finance leases	15,463	17,439
Long-term debt	2,188,901	2,233,281
Deferred income taxes	456,735	447,986
Noncurrent regulatory liabilities	468,350	451,483
Other noncurrent liabilities	398,124	387,152
Total Liabilities	4,021,089	3,871,608
Commitments and Contingencies (Note 10)
Shareholders' Equity:
Common Stock, Value, Issued	541	541
Treasury stock at cost	(98,242)	(96,015)
Paid-in capital	1,514,820	1,508,970
Retained earnings	646,650	635,246
Accumulated other comprehensive loss	(9,219)	(9,648)
Total Shareholders' Equity	2,054,550	2,039,094
Total Liabilities and Shareholders' Equity	$ 6,075,639	$ 5,910,702
Preferred Stock, Shares Issued	0
Common Stock, Par or Stated Value Per Share	$ 0.01
Common Stock, Shares Authorized	200,000,000
Common Stock, Shares, Issued	54,144,775
Common Stock, Shares, Outstanding	50,581,098
Preferred Stock, Par or Stated Value Per Share	$ 0.01
Preferred Stock, Shares Authorized	50,000,000
Preferred Stock, Shares Outstanding	0

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
OPERATING ACTIVITIES:
Net Income	$ 101,664	$ 142,138
Items not affecting cash:
Depreciation and depletion	134,336	129,766
Amortization of debt issuance costs, discount and deferred hedge gain	3,604	3,482
Stock-based compensation costs	5,347	4,778
Equity portion of allowance for funds used during construction	(4,503)	(4,118)
Gain on disposition of assets	(26)	(176)
Deferred income taxes	(3,759)	(16,350)
Changes in current assets and liabilities:
Accounts receivable	34,290	36,000
Inventories	(15,130)	(4,353)
Other current assets	(4,194)	(3,332)
Accounts payable	(4,181)	(13,942)
Accrued expenses	67,553	24,945
Regulatory assets	7,372	(17,662)
Regulatory liabilities	13,433	(19,265)
Other noncurrent assets	(6,225)	(5,366)
Other noncurrent liabilities	(7,066)	(2,684)
Cash Provided by Operating Activities	322,515	253,861
INVESTING ACTIVITIES:
Property, plant, and equipment additions	(282,987)	(242,874)
Investment in equity securities	(42)	0
Cash Used in Investing Activities	(283,029)	(242,874)
FINANCING ACTIVITIES:
Treasury stock activity	(1,723)	1,220
Dividends on common stock	(90,260)	(86,343)
Issuance of long-term debt	150,000	150,000
Line of credit repayments, net	(193,000)	(76,000)
Issuance of short-term borrowings	100,000	0
Financing costs	(2,564)	(1,074)
Cash Used in Financing Activities	(37,547)	(12,197)
Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	1,939	(1,210)
Cash, Cash Equivalents, and Restricted Cash, beginning of period	12,070	15,311
Cash, Cash Equivalents, and Restricted Cash, end of period	14,009	14,101
Cash paid during the period for:
Income taxes	100	68
Interest	55,220	55,515
Significant non-cash transactions:
Capital expenditures included in accounts payable	$ 15,986	$ 15,508

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance, shares at Dec. 31, 2018		53,889	3,566
Balance, beginning of period at Dec. 31, 2018	$ 1,942,382	$ 539	$ (95,546)	$ 1,499,070	$ 548,253	$ (9,934)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	142,138	0	0	0	142,138	0
Foreign currency translation adjustment	18	0	0	0	0	18
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	339	$ 0	$ 0	0	0	339
Stock based compensation, shares		107	25
Stock based compensation, value	3,098	$ 0	$ (1,646)	4,744	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(41)
Issuance of shares, value	2,892	$ 1	$ 1,100	1,791	0	0
Dividends on common stock	$ (86,343)	0	0	0	(86,343)	0
Dividends per share	$ 1.725
Balance, end of period at Sep. 30, 2019	$ 2,004,524	$ 540	$ (96,092)	1,505,605	604,048	(9,577)
Balance, shares at Sep. 30, 2019		53,996	3,550
Balance, shares at Jun. 30, 2019		53,996	3,553
Balance, beginning of period at Jun. 30, 2019	2,010,078	$ 540	$ (96,178)	1,504,290	611,159	(9,733)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	21,670	0	0	0	21,670	0
Foreign currency translation adjustment	42	0	0	0	0	42
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	114	$ 0	$ 0	0	0	114
Stock based compensation, shares		0	0
Stock based compensation, value	1,169	$ 0	$ 0	1,169	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(3)
Issuance of shares, value	232	$ 0	$ 86	146	0	0
Dividends on common stock	$ (28,781)	0	0	0	(28,781)	0
Dividends per share	$ 0.575
Balance, end of period at Sep. 30, 2019	$ 2,004,524	$ 540	$ (96,092)	1,505,605	604,048	(9,577)
Balance, shares at Sep. 30, 2019		53,996	3,550
Balance, shares at Dec. 31, 2019		53,999	3,547
Balance, beginning of period at Dec. 31, 2019	2,039,094	$ 541	$ (96,015)	1,508,970	635,246	(9,648)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	101,664	0	0	0	101,664	0
Foreign currency translation adjustment	90	0	0	0	0	90
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	339	$ 0	$ 0	0	0	339
Stock based compensation, shares		146	35
Stock based compensation, value	2,570	$ 0	$ (2,740)	5,310	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(18)
Issuance of shares, value	1,053	$ 0	$ 513	540	0	0
Dividends on common stock	$ (90,260)	0	0	0	(90,260)	0
Dividends per share	$ 1.80
Balance, end of period at Sep. 30, 2020	$ 2,054,550	$ 541	$ (98,242)	1,514,820	646,650	(9,219)
Balance, shares at Sep. 30, 2020		54,145	3,564
Balance, shares at Jun. 30, 2020		54,145	3,571
Balance, beginning of period at Jun. 30, 2020	2,053,556	$ 541	$ (98,438)	1,513,510	647,272	(9,329)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	29,466	0	0	0	29,466	0
Foreign currency translation adjustment	(3)	0	0	0	0	(3)
Reclassification of net losses on derivative instruments from OCI to net income, net of tax	113	$ 0	$ 0	0	0	113
Stock based compensation, shares		0	0
Stock based compensation, value	1,140	$ 0	$ 0	1,140	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(7)
Issuance of shares, value	366	$ 0	$ 196	170	0	0
Dividends on common stock	$ (30,088)	0	0	0	(30,088)	0
Dividends per share	$ 0.600
Balance, end of period at Sep. 30, 2020	$ 2,054,550	$ 541	$ (98,242)	$ 1,514,820	$ 646,650	$ (9,219)
Balance, shares at Sep. 30, 2020		54,145	3,564

Nature of Operations and Basis

Nature of Operations and Basis of Consolidation	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure	Nature of Operations and Basis of Consolidation NorthWestern Corporation, doing business as NorthWestern Energy, provides electricity and/or natural gas to approximately 734,800 customers in Montana, South Dakota and Nebraska. The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires management to make estimates and assumptions that may affect the reported amounts of assets, liabilities, revenues and expenses during the reporting period. Actual results could differ from those estimates. The unaudited Condensed Consolidated Financial Statements (Financial Statements) reflect all adjustments (which unless otherwise noted are normal and recurring in nature) that are, in the opinion of management, necessary to fairly present our financial position, results of operations and cash flows. The actual results for the interim periods are not necessarily indicative of the operating results to be expected for a full year or for other interim periods. Events occurring subsequent to September 30, 2020, have been evaluated as to their potential impact to the Financial Statements through the date of issuance. The Financial Statements included herein have been prepared by NorthWestern, without audit, pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations; however, management believes that the condensed disclosures provided are adequate to make the information presented not misleading. Management recommends that these Financial Statements be read in conjunction with the audited financial statements and related footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2019 . Variable Interest Entities A reporting company is required to consolidate a variable interest entity (VIE) as its primary beneficiary, which means it has a controlling financial interest, when it has both the power to direct the activities of the VIE that most significantly impact the VIE's economic performance, and the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. An entity is considered to be a VIE when its total equity investment at risk is not sufficient to permit the entity to finance its activities without additional subordinated financial support, or its equity investors, as a group, lack the characteristics of having a controlling financial interest. The determination of whether a company is required to consolidate an entity is based on, among other things, an entity’s purpose and design and a company’s ability to direct the activities of the entity that most significantly impact the entity’s economic performance. Certain long-term purchase power and tolling contracts may be considered variable interests. We have various long-term purchase power contracts with other utilities and certain qualifying co-generation facilities and qualifying small power production facilities (QF). We identified one QF contract that may constitute a VIE. We entered into a 40-year power purchase contract in 1984 with this 35 megawatt (MW) coal-fired QF to purchase substantially all of the facility’s capacity and electrical output over a substantial portion of its estimated useful life. We absorb a portion of the facility’s variability through annual changes to the price we pay per megawatt hour (MWH). After making exhaustive efforts, we have been unable to obtain the information from the facility necessary to determine whether the facility is a VIE or whether we are the primary beneficiary of the facility. The contract with the facility contains no provision which legally obligates the facility to release this information. We have accounted for this QF contract as an executory contract. Based on the current contract terms with this QF, as of September 30, 2020 our estimated remaining gross contractual payments aggregate approximately $123.9 million through 2024. Supplemental Cash Flow Information The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statements of Cash Flows (in thousands): September 30, December 31, September 30, December 31, 2020 2019 2019 2018 Cash and cash equivalents $ 3,512 $ 5,145 $ 5,046 $ 7,860 Restricted cash 10,497 6,925 9,055 7,451 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 14,009 $ 12,070 $ 14,101 $ 15,311 Goodwill

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2020
Regulated Operations [Abstract]
Public Utilities Disclosure [Text Block]	Regulatory Matters COVID-19 Accounting Order Filings In the second and third quarters of 2020, we experienced lower revenues and an increase in certain operating expenses as a result of the COVID-19 pandemic. In March we voluntarily informed both our retail customers and state regulators that disconnections for non-payment would be temporarily suspended. During August we advised customers that we would resume the disconnection process for customers whose accounts are in arrears. South Dakota - On May 1, 2020, we submitted a joint filing with four other investor owned utilities to the South Dakota Public Utilities Commission (SDPUC) seeking approval for an accounting order to defer certain costs related to the COVID-19 pandemic as a regulatory asset, subject to future review for recovery from customers. We limited our specific request to uncollectible accounts expense in excess of amounts included in the latest electric and natural gas test periods. In August, the SDPUC issued an order granting deferral of our excess uncollectible accounts expense. As of September 30, 2020 we have deferred $0.4 million of uncollectible accounts expense into a regulatory asset in the Condensed Consolidated Balance Sheet. Montana - On May 29, 2020, we filed a petition for an accounting order with the Montana Public Service Commission (MPSC) seeking approval of an accounting order to (i) defer uncollectible accounts expense in excess of amounts included in the latest electric and natural gas test periods; and (ii) requesting approval of a proposed pension contribution up to $40 million in 2020 to be recognized over a five-year period. The MPSC held a work session in October 2020 voting to allow tracking of uncollectible accounts expense and amortization of incremental pension contributions. We expect a final order on our request during the fourth quarter of 2020, and cannot determine the impact, if any, of the MPSC's decision until a final order is issued. Pension costs in Montana are included in expense on a pay as you go (cash funding) basis. We contributed $10.2 million to the Montana pension plan during the nine months ended September 30, 2020. We have not yet determined whether we will contribute incremental amounts during the fourth quarter of 2020. FERC Filing - Montana Transmission Service Rates In May 2019, we submitted a filing with the Federal Energy Regulatory Commission (FERC) for our Montana transmission assets. The revenue requirement associated with our Montana FERC assets is reflected in our Montana MPSC-jurisdictional rates as a credit to retail customers. We will submit a compliance filing with the MPSC upon resolution of our Montana FERC case adjusting the proposed credit in our Montana retail rates. In June 2019, the FERC issued an order accepting our filing, granting interim rates (subject to refund) effective July 1, 2019, establishing settlement procedures and terminating our related Tax Cuts and Jobs Act filing. A settlement judge was appointed and settlement negotiations are ongoing. Cost Recovery Mechanisms - Montana Montana Electric and Natural Gas Supply Cost Trackers - Each year we submit electric and natural gas tracker filings for recovery of supply costs for the 12-month period ended June 30. The MPSC reviews such filings and makes its cost recovery determination based on whether or not our supply procurement activities were prudent. The MPSC approved a new design for our electric tracker effective July 1, 2017. The revised electric tracker, or Power Costs and Credits Adjustment Mechanism (PCCAM), established a baseline of power supply costs and tracks the differences between the actual costs and associated base rate revenues. Rates are adjusted annually for variances between actual costs and associated revenues with the variances allocated 90% to customers and 10% to shareholders. The initial design of the PCCAM also included a “deadband” which required us to absorb the variances within +/- $4.1 million from the base revenues. In 2019, the Montana legislature made two statutory changes which affected the PCCAM by prohibiting a deadband and allowing 100% recovery of QF purchases. The 90%/10% sharing ratio for other costs remains in place . In September 2019, we submitted our annual PCCAM filing for the period July 1, 2018 to June 30, 2019, requesting recovery of approximately $23.8 million in electric supply costs. The Montana Consumer Counsel (MCC) and the Montana Environmental Information Center (MEIC) submitted testimony advocating for a disallowance of approximately $6.0 million of replacement power costs incurred during a 2018 third quarter intermittent outage at our Colstrip generating facility necessary to ensure compliance with air permit limits. In addition, the MCC advocated for an application of the deadband and QF cost sharing from July 2018 to the May 2019 statutory change, which would result in an additional under recovery of costs of approximately $4.0 million. The MPSC held a hearing on this matter in June 2020 and we expect a decision in the fourth quarter of 2020. We began collecting costs for the July 2018 - June 2019 tracker period on October 1, 2019, and as of September 30, 2020, the remaining under collection of approximately $2.1 million was reflected in regulatory assets in the Condensed Consolidated Balance Sheets. Montana QF Power Purchase Cases Under the Public Utility Regulatory Policies Act (PURPA), electric utilities are required, with certain exceptions, to purchase energy and capacity from independent power producers that are QFs. We track the costs of these purchases through our PCCAM. These purchases are also the subject of proceedings before the MPSC, whose orders are subject to judicial review by Montana state courts. In May 2016, we filed our biennial update of standard rates for small QFs (3 MW or less). In November 2017, the MPSC approved new, lower rates, reduced the maximum contract term from 25 to 15 years, and ordered that it would apply the same 15-year contract term to our future owned and contracted electric supply resources (Symmetry Finding). We sought judicial review with the Montana State District Court (District Court) of the Symmetry Finding. Cypress Creek Renewables, LLC, Vote Solar, and MEIC, sought judicial review with the District Court of the rates and contract term. The District Court reversed and modified the MPSC’s decisions on rates, contract term, and the Symmetry Finding. We appealed the District Court’s order regarding rates and contract term to the Montana Supreme Court, which also granted our request to stay the District Court's decision. The MPSC did not appeal the District Court’s Symmetry Finding. On August 24, 2020, the Montana Supreme Court found that the MPSC's order on rates and contract length was arbitrary, left the stay in place, and remanded to the MPSC for consideration when setting rates and contract lengths for small QF's in future regulatory proceedings. The MPSC adopted the Symmetry Finding in another order when setting the rates and contract term for a large QF - MT Sun, LLC (MTSun). We, as well as MTSun, sought judicial review of the MPSC’s order. The District Court reversed and modified the MPSC’s order regarding rates, contract length, and the Symmetry Finding. We appealed the District Court’s order to the Montana Supreme Court on the issues of rates and contract length, and the MPSC did not appeal the District Court’s reversal of the Symmetry Finding. On September 22, 2020, the Montana Supreme Court found the MPSC's order on rates and contract length was arbitrary and that MTSun is entitled to the rates and contract term determined by the District Court. We are authorized through our PCCAM tariff to recover 100% of our QF purchased power costs. Montana Community Renewable Energy Projects (CREPs) We were required to acquire, as of December 31, 2019, approximately 66 MW of CREPs. While we have made progress towards meeting this obligation by acquiring approximately 36 MW of CREPs, we have been unable to acquire the remaining MWs required for various reasons, including the fact that proposed projects fail to qualify as CREPs or do not meet the statutory cost cap. The MPSC granted us waivers for 2012 through 2016. The validity of the MPSC’s action as it related to waivers granted for 2015 and 2016 has been challenged legally and we are waiting on a final decision from the Montana Supreme Court. We expect to file waiver requests for 2017, 2018, and 2019 after resolution of that litigation. If the Montana Supreme Court rules that the 2015 and 2016 waivers were invalid or if the requested waivers for 2017 through 2019 are not

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes We compute income tax expense for each quarter based on the estimated annual effective tax rate for the year, adjusted for certain discrete items. Our effective tax rate typically differs from the federal statutory tax rate due to the regulatory impact of flowing through the federal and state tax benefit of repairs deductions, state tax benefit of accelerated tax depreciation deductions (including bonus depreciation when applicable) and production tax credits. The regulatory accounting treatment of these deductions requires immediate income recognition for temporary tax differences of this type, which is referred to as the flow-through method. When the flow-through method of accounting for temporary differences is reflected in regulated revenues, we record deferred income taxes and establish related regulatory assets and liabilities. The following table summarizes the differences between our effective tax rate and the federal statutory rate (in thousands): Three Months Ended September 30, 2020 2019 Income Before Income Taxes $ 26,763 $ 22,225 Income tax calculated at federal statutory rate 5,621 21.0 % 4,667 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 46 0.2 65 0.3 Flow-through repairs deductions (4,213) (15.7) (2,606) (11.7) Production tax credits (2,205) (8.2) (1,414) (6.3) Amortization of excess deferred income tax (222) (0.8) (374) (1.7) Plant and depreciation of flow-through items 103 0.4 (263) (1.2) Prior year permanent return to accrual adjustments (1,728) (6.5) 559 2.5 Other, net (105) (0.5) (79) (0.4) (8,324) (31.1) (4,112) (18.5) Income tax (benefit) expense $ (2,703) (10.1) % $ 555 2.5 % Nine Months Ended September 30, 2020 2019 Income Before Income Taxes $ 96,437 $ 122,040 Income tax calculated at federal statutory rate 20,252 21.0 % 25,628 21.0 % Permanent or flow through adjustments: State income, net of federal provisions 73 0.1 1,230 1.0 Flow-through repairs deductions (14,859) (15.4) (12,694) (10.4) Production tax credits (7,553) (7.8) (7,252) (5.9) Share-based compensation (609) (0.6) 186 0.2 Amortization of excess deferred income tax (731) (0.8) (1,939) (1.6) Prior year permanent return to accrual adjustments (1,728) (1.8) 559 0.4 Plant and depreciation of flow through items 299 0.3 (2,449) (2.0) Recognition of unrecognized tax benefit — — (22,825) (18.7) Other, net (371) (0.4) (542) (0.5) (25,479) (26.4) (45,726) (37.5) Income tax benefit $ (5,227) (5.4) % $ (20,098) (16.5) % The income tax benefit for 2019 reflects the recognition of approximately $22.8 million of unrecognized tax benefits, including approximately $2.7 million of accrued interest and penalties, net of tax, due to the lapse of statutes of limitation in the second quarter of 2019. Coronavirus Aid, Relief, and Economic Security Act (the CARES Act) In response to the COVID-19 pandemic, on March 27, 2020, President Donald Trump signed into law the CARES Act. We evaluated the provisions of the CARES Act as of September 30, 2020, and determined it had no material effect on our Financial Statements. Certain tax provisions may result in immaterial cash refunds. Uncertain Tax Positions We recognize tax positions that meet the more-likely-than-not threshold as the largest amount of tax benefit that is greater than 50 percent likely of being realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. We have unrecognized tax benefits of approximately $33.9 million as of September 30, 2020, including approximately $28.0 million that, if recognized, would impact our effective tax rate. We do not anticipate that total unrecognized tax benefits will significantly change due to the settlement of audits or the expiration of statutes of limitation within the next twelve months. Our policy is to recognize interest and penalties related to uncertain tax positions in income tax expense. As of September 30, 2020, we do not have any amounts accrued for the payment of interest and penalties. As discussed above, during the nine months ended September 30, 2019, we released $2.7 million of accrued interest in the Condensed Consolidated Statements of Income. Tax years 2016 and forward remain subject to examination by the Internal Revenue Service (IRS) and state taxing authorities. In addition, the available federal net operating loss carryforward may be reduced by the IRS for losses originating in certain tax years from 2002 forward.

Comprehensive Income (Loss)

Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Comprehensive Income (Loss) The following tables display the components of Other Comprehensive Income (Loss), after-tax, and the related tax effects (in thousands): Three Months Ended September 30, 2020 September 30, 2019 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (3) $ — $ (3) $ 42 $ — $ 42 Reclassification of net income (loss) on derivative instruments 153 (40) 113 154 (40) 114 Other comprehensive income (loss) $ 150 $ (40) $ 110 $ 196 $ (40) $ 156 Nine Months Ended September 30, 2020 September 30, 2019 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ 90 $ — $ 90 $ 18 $ — $ 18 Reclassification of net income (loss) on derivative instruments 459 (120) 339 460 (121) 339 Other comprehensive income (loss) $ 549 $ (120) $ 429 $ 478 $ (121) $ 357 Balances by classification included within accumulated other comprehensive loss (AOCL) on the Condensed Consolidated Balance Sheets are as follows, net of tax (in thousands): September 30, 2020 December 31, 2019 Foreign currency translation $ 1,503 $ 1,413 Derivative instruments designated as cash flow hedges (10,842) (11,181) Postretirement medical plans 120 120 Accumulated other comprehensive loss $ (9,219) $ (9,648) The following tables display the changes in AOCL by component, net of tax (in thousands): Three Months Ended September 30, 2020 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (10,955) $ 120 $ 1,506 $ (9,329) Other comprehensive income before reclassifications — — (3) (3) Amounts reclassified from AOCL Interest Expense 113 — — 113 Net current-period other comprehensive income (loss) 113 — (3) 110 Ending balance $ (10,842) $ 120 $ 1,503 $ (9,219) Three Months Ended September 30, 2019 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (11,408) $ 251 $ 1,424 $ (9,733) Other comprehensive income before reclassifications 42 42 Amounts reclassified from AOCL Interest Expense 114 114 Net current-period other comprehensive income 114 — 42 156 Ending balance $ (11,294) $ 251 $ 1,466 $ (9,577) Nine Months Ended September 30, 2020 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (11,181) $ 120 $ 1,413 $ (9,648) Other comprehensive income before reclassifications — — 90 90 Amounts reclassified from AOCL Interest Expense 339 — — 339 Net current-period other comprehensive income 339 — 90 429 Ending balance $ (10,842) $ 120 $ 1,503 $ (9,219) Nine Months Ended September 30, 2019 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (11,633) $ 251 $ 1,448 $ (9,934) Other comprehensive income before reclassifications — — 18 18 Amounts reclassified from AOCL Interest Expense 339 — — 339 Net current-period other comprehensive income 339 — 18 357 Ending balance $ (11,294) $ 251 $ 1,466 $ (9,577)

Financing Activities

Financing Activities	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt Disclosure	Financing Activities In April 2020, we entered into a $100 million Term Loan Agreement (Term Loan) and borrowed the full amount. The Term Loan bears interest at variable rates tied to the Eurodollar rate plus a credit spread of 1.50%. Proceeds were used to repay a portion of our outstanding revolving credit facility borrowings and for general corporate purposes. All principal and unpaid interest under the Term Loan is due and payable on April 2, 2021. The Term Loan provides for prepayment of the principal and interest; however, amounts prepaid may not be reborrowed. The Term Loan requires us to maintain a consolidated indebtedness to total capitalization ratio of 65 percent or less. It also contains covenants which, among other things, limit our ability to engage in any consolidation or merger or otherwise liquidate or dissolve, dispose of property, and enter into transactions with affiliates. A default on the South Dakota or Montana First Mortgage Bonds would trigger a cross default on the Term Loan; however a default on the Term Loan would not trigger a default on the South Dakota or Montana First Mortgage Bonds. In May 2020, we issued $100 million principal amount of Montana First Mortgage Bonds and $50 million principal amount of South Dakota First Mortgage Bonds, each at a fixed interest rate of 3.21% maturing on May 15, 2030. These bonds were issued in a transaction exempt from the registration requirements of the Securities Act of 1933. Proceeds were used to repay a portion of our outstanding borrowings under our revolving credit facilities and for other general corporate purposes. The bonds are secured by our electric and natural gas assets in Montana and South Dakota. On September 2, 2020, we entered into a new $425 million Credit Agreement (Credit Facility) to replace our existing facility. The Credit Facility increases the capacity from that of the prior facility by $25 million to $425 million and extended the maturity date to September 2, 2023 (from December 12, 2021), with uncommitted features that allow us to request up to two one-year extensions to the maturity date and increase the size by an additional $75 million with the consent of the lenders. The facility does not amortize and is unsecured. Borrowings may be made at interest rates equal to the Eurodollar rate, plus a margin of 112.5 to 175.0 basis points, or a base rate, plus a margin of 12.5 to 75.0 basis points. A total of ten banks participate in the facility, with no one bank providing more than 13% of the total availability. The Credit Facility includes covenants that require us to meet certain financial tests, including a maximum debt to capitalization ratio not to exceed 65%. The facility also contains covenants which, among other things, limit our ability to engage in any consolidation or merger or otherwise liquidate or dissolve, dispose of property, and enter into transactions with affiliates. A default on the South Dakota or Montana First Mortgage Bonds would trigger a cross default on the Credit Facility; however a default on the Credit Facility would not trigger a default on the South Dakota or Montana First Mortgage Bonds.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2020
Segment Reporting Information [Line Items]
Segment Reporting Disclosure [Text Block]	Segment Information Our reportable business segments are primarily engaged in the electric and natural gas business. The remainder of our operations are presented as other, which primarily consists of unallocated corporate costs and unregulated activity. We evaluate the performance of these segments based on gross margin. The accounting policies of the operating segments are the same as the parent except that the parent allocates some of its operating expenses to the operating segments according to a methodology designed by management for internal reporting purposes and involves estimates and assumptions. Financial data for the business segments are as follows (in thousands): Three Months Ended September 30, 2020 Electric Gas Other Eliminations Total Operating revenues $ 244,155 $ 36,455 $ — $ — $ 280,610 Cost of sales 61,155 6,883 — — 68,038 Gross margin 183,000 29,572 — — 212,572 Operating, general and administrative 54,367 20,059 (1,104) — 73,322 Property and other taxes 35,532 9,772 2 — 45,306 Depreciation and depletion 36,670 7,619 — — 44,289 Operating income (loss) 56,431 (7,878) 1,102 — 49,655 Interest expense, net (21,286) (1,574) (817) — (23,677) Other income (expense), net 1,559 459 (1,233) — 785 Income tax benefit 1,197 607 899 — 2,703 Net income (loss) $ 37,901 $ (8,386) $ (49) $ — $ 29,466 Total assets $ 4,430,279 $ 1,634,606 $ 10,754 $ — $ 6,075,639 Capital expenditures $ 87,432 $ 19,073 $ — $ — $ 106,505 Three Months Ended September 30, 2019 Electric Gas Other Eliminations Total Operating revenues $ 241,237 $ 33,599 $ — $ — $ 274,836 Cost of sales 58,768 5,459 — — 64,227 Gross margin 182,469 28,140 — — 210,609 Operating, general and administrative 57,433 18,830 735 — 76,998 Property and other taxes 34,731 9,355 3 — 44,089 Depreciation and depletion 35,824 7,342 — — 43,166 Operating income (loss) 54,481 (7,387) (738) — 46,356 Interest expense, net (19,481) (1,588) (2,653) — (23,722) Other (expense) income, net (677) (344) 612 — (409) Income tax (expense) benefit (1,415) (232) 1,092 — (555) Net income (loss) $ 32,908 $ (9,551) $ (1,687) $ — $ 21,670 Total assets $ 4,632,077 $ 1,173,513 $ 4,590 $ — $ 5,810,180 Capital expenditures $ 70,063 $ 25,784 $ — $ — $ 95,847 Nine Months Ended September 30, 2020 Electric Gas Other Eliminations Total Operating revenues $ 706,718 $ 178,507 $ — $ — $ 885,225 Cost of sales 173,294 47,059 — — 220,353 Gross margin 533,424 131,448 — — 664,872 Operating, general and administrative 166,854 61,348 (4,160) — 224,042 Property and other taxes 107,079 29,700 7 — 136,786 Depreciation and depletion 110,692 23,644 — — 134,336 Operating income 148,799 16,756 4,153 — 169,708 Interest expense, net (63,585) (4,824) (3,889) — (72,298) Other income (expense) 3,131 863 (4,967) — (973) Income tax benefit (expense) 2,609 (467) 3,085 — 5,227 Net income (loss) $ 90,954 $ 12,328 $ (1,618) $ — $ 101,664 Total assets $ 4,430,279 $ 1,634,606 $ 10,754 $ — $ 6,075,639 Capital expenditures $ 230,524 $ 52,463 $ — $ — $ 282,987 Nine Months Ended September 30, 2019 Electric Gas Other Eliminations Total Operating revenues $ 733,933 $ 195,842 $ — $ — $ 929,775 Cost of sales 178,423 57,283 — — 235,706 Gross margin 555,510 138,559 — — 694,069 Operating, general and administrative 174,544 60,803 3,569 — 238,916 Property and other taxes 104,612 28,569 7 — 133,188 Depreciation and depletion 107,595 22,171 — — 129,766 Operating income (loss) 168,759 27,016 (3,576) — 192,199 Interest expense, net (58,301) (4,599) (8,123) — (71,023) Other (expense) income (1,458) (874) 3,196 — 864 Income tax (expense) benefit (4,937) 493 24,542 — 20,098 Net income $ 104,063 $ 22,036 $ 16,039 $ — $ 142,138 Total assets $ 4,632,077 $ 1,173,513 $ 4,590 $ — $ 5,810,180 Capital expenditures $ 186,155 $ 56,719 $ — $ — $ 242,874

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue from Contracts with Customers Nature of Goods and Services We provide retail electric and natural gas services to three primary customer classes. Our residential customers include single private dwellings and individual apartments. Our commercial customers consist primarily of main street businesses, and our industrial customers consist primarily of manufacturing and processing businesses that turn raw materials into products. Electric Segment - Our regulated electric utility business primarily provides generation, transmission, and distribution services to customers in our Montana and South Dakota jurisdictions. We recognize revenue when electricity is delivered to the customer. Payments on our tariff based sales are generally due 20-30 days after the billing date. Natural Gas Segment - Our regulated natural gas utility business primarily provides production, storage, transmission, and distribution services to customers in our Montana, South Dakota, and Nebraska jurisdictions. We recognize revenue when natural gas is delivered to the customer. Payments on our tariff based sales are generally due 20-30 days after the billing date. Disaggregation of Revenue The following tables disaggregate our revenue by major source and customer class (in millions): Three Months Ended September 30, 2020 September 30, 2019 Electric Natural Gas Total Electric Natural Gas Total Montana $ 78.5 $ 9.9 $ 88.4 $ 68.4 $ 8.9 $ 77.3 South Dakota 18.9 1.7 20.6 16.0 1.7 17.7 Nebraska — 1.7 1.7 — 1.8 1.8 Residential 97.4 13.3 110.7 84.4 12.4 96.8 Montana 89.1 5.6 94.7 87.7 5.5 93.2 South Dakota 27.4 1.0 28.4 26.3 1.3 27.6 Nebraska — 0.7 0.7 — 0.9 0.9 Commercial 116.5 7.3 123.8 114.0 7.7 121.7 Industrial 9.2 0.1 9.3 10.6 0.1 10.7 Lighting, Governmental, Irrigation, and Interdepartmental 11.9 0.1 12.0 12.4 0.1 12.5 Total Customer Revenues 235.0 20.8 255.8 221.4 20.3 241.7 Other Tariff and Contract Based Revenues 14.9 8.3 23.2 15.3 7.7 23.0 Total Revenue from Contracts with Customers 249.9 29.1 279.0 236.7 28.0 264.7 Regulatory amortization (5.7) 7.4 1.7 4.5 5.6 10.1 Total Revenues $ 244.2 $ 36.5 $ 280.7 $ 241.2 $ 33.6 $ 274.8 Nine Months Ended September 30, 2020 September 30, 2019 Electric Natural Gas Total Electric Natural Gas Total Montana $ 237.7 $ 65.7 $ 303.4 $ 225.4 $ 73.3 $ 298.7 South Dakota 52.4 16.7 69.1 47.4 20.4 67.8 Nebraska — 12.9 12.9 — 15.7 15.7 Residential 290.1 95.3 385.4 272.8 109.4 382.2 Montana 252.5 33.0 285.5 257.3 38.0 295.3 South Dakota 77.1 11.2 88.3 71.2 14.1 85.3 Nebraska — 6.2 6.2 — 8.3 8.3 Commercial 329.6 50.4 380.0 328.5 60.4 388.9 Industrial 27.2 0.5 27.7 32.4 0.7 33.1 Lighting, Governmental, Irrigation, and Interdepartmental 26.4 0.7 27.1 25.2 0.6 25.8 Total Customer Revenues 673.3 146.9 820.2 658.9 171.1 830.0 Other Tariff and Contract Based Revenues 44.1 26.5 70.6 46.5 26.6 73.1 Total Revenue from Contracts with Customers 717.4 173.4 890.8 705.4 197.7 903.1 Regulatory amortization (10.7) 5.1 (5.6) 28.5 (1.9) 26.6 Total Revenues $ 706.7 $ 178.5 $ 885.2 $ 733.9 $ 195.8 $ 929.7

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Earnings Per Share Basic earnings per share are computed by dividing earnings applicable to common stock by the weighted average number of common shares outstanding for the period. Diluted earnings per share reflect the potential dilution of common stock equivalent shares that could occur if unvested shares were to vest. Common stock equivalent shares are calculated using the treasury stock method, as applicable. The dilutive effect is computed by dividing earnings applicable to common stock by the weighted average number of common shares outstanding plus the effect of the outstanding unvested restricted stock and performance share awards. Average shares used in computing the basic and diluted earnings per share are as follows: Three Months Ended September 30, 2020 September 30, 2019 Basic computation 50,576,564 50,443,866 Dilutive effect of: Performance share awards (1) 97,529 335,371 Diluted computation 50,674,093 50,779,237 Nine Months Ended September 30, 2020 September 30, 2019 Basic computation 50,551,121 50,422,028 Dilutive effect of: Performance share awards (1) 105,395 334,002 Diluted computation 50,656,516 50,756,030 _______________________

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	Employee Benefit Plans We sponsor and/or contribute to pension and postretirement health care and life insurance benefit plans for eligible employees. Net periodic benefit cost (credit) for our pension and other postretirement plans consists of the following (in thousands): Pension Benefits Other Postretirement Benefits Three Months Ended September 30, Three Months Ended September 30, 2020 2019 2020 2019 Components of Net Periodic Benefit Cost (Credit) Service cost $ 2,779 $ 2,409 $ 93 $ 82 Interest cost 5,710 6,622 123 152 Expected return on plan assets (6,541) (6,360) (246) (217) Amortization of prior service cost (credit) — 1,636 (471) (471) Recognized actuarial loss (gain) 1,257 — (15) (24) Plan settlements — 715 — — Net periodic benefit cost (credit) $ 3,205 $ 5,022 $ (516) $ (478) Pension Benefits Other Postretirement Benefits Nine Months Ended Nine Months Ended 2020 2019 2020 2019 Components of Net Periodic Benefit Cost (Credit) Service cost $ 8,337 $ 7,228 $ 278 $ 248 Interest cost 17,130 19,866 369 457 Expected return on plan assets (19,622) (19,082) (738) (652) Amortization of prior service cost (credit) — 4,908 (1,412) (1,412) Recognized actuarial loss (gain) 3,771 — (45) (72) Plan settlements — 715 — — Net periodic benefit cost (credit) $ 9,616 $ 13,635 $ (1,548) $ (1,431) We contributed $11.4 million to our pension plans during the nine months ended September 30, 2020. As discussed in Note 2 Regulatory Matters , we have not yet determined whether we will contribute incremental amounts to the Montana pension plan during the fourth quarter of 2020.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies ENVIRONMENTAL LIABILITIES AND REGULATION Environmental Matters The operation of electric generating, transmission and distribution facilities, and gas gathering, storage, transportation and distribution facilities, along with the development (involving site selection, environmental assessments, and permitting) and construction of these assets, are subject to extensive federal, state, and local environmental and land use laws and regulations. Our activities involve compliance with diverse laws and regulations that address emissions and impacts to the environment, including air and water, protection of natural resources, avian and wildlife. We monitor federal, state, and local environmental initiatives to determine potential impacts on our financial results. As new laws or regulations are implemented, our policy is to assess their applicability and implement the necessary modifications to our facilities or their operation to maintain ongoing compliance. Our environmental exposure includes a number of components, including remediation expenses related to the cleanup of current or former properties, and costs to comply with changing environmental regulations related to our operations. At present, our environmental reserve, which relates primarily to the remediation of former manufactured gas plant sites owned by us, is estimated to range between $27.8 million to $30.5 million. As of September 30, 2020, we had a reserve of approximately $28.8 million, which has not been discounted. Environmental costs are recorded when it is probable we are liable for the remediation and we can reasonably estimate the liability. We use a combination of site investigations and monitoring to formulate an estimate of environmental remediation costs for specific sites. Our monitoring procedures and development of actual remediation plans depend not only on site specific information but also on coordination with the different environmental regulatory agencies in our respective jurisdictions; therefore, while remediation exposure exists, it may be many years before costs are incurred. Over time, as costs become determinable, we may seek authorization to recover such costs in rates or seek insurance reimbursement as available and applicable; therefore, although we cannot guarantee regulatory recovery, we do not expect these costs to have a material effect on our consolidated financial position or results of operations. Manufactured Gas Plants - Approximately $22.6 million of our environmental reserve accrual is related to the following manufactured gas plants. South Dakota - A formerly operated manufactured gas plant located in Aberdeen, South Dakota, has been identified on the Federal Comprehensive Environmental Response, Compensation, and Liability Information System list as contaminated with coal tar residue. We are currently conducting feasibility studies, implementing remedial actions pursuant to work plans approved by the South Dakota Department of Environment and Natural Resources, and conducting ongoing monitoring and operation and maintenance activities. As of September 30, 2020, the reserve for remediation costs at this site is approximately $7.8 million, and we estimate that approximately $2.4 million of this amount will be incurred during the next five years. Nebraska - We own sites in North Platte, Kearney, and Grand Island, Nebraska on which former manufactured gas facilities were located. We are currently working independently to fully characterize the nature and extent of potential impacts associated with these Nebraska sites. Our reserve estimate includes assumptions for site assessment and remedial action work. At present, we cannot determine with a reasonable degree of certainty the nature and timing of any risk-based remedial action at our Nebraska locations. Montana - We own or have responsibility for sites in Butte, Missoula, and Helena, Montana on which former manufactured gas plants were located. The Butte and Helena sites, both listed as high priority sites on Montana’s state superfund list, were placed into the Montana Department of Environmental Quality (MDEQ) voluntary remediation program for cleanup due to soil and groundwater impacts. Soil and coal tar were removed at the sites in accordance with the MDEQ requirements. Groundwater monitoring is conducted semiannually at both sites. At this time, we cannot estimate with a reasonable degree of certainty the nature and timing of additional remedial actions and/or investigations, if any, at the Butte site. In August 2016, the MDEQ sent us a Notice of Potential Liability and Request for Remedial Action regarding the Helena site. In October 2019, we submitted a third revised Remedial Investigation Work Plan (RIWP) for the Helena site addressing MDEQ comments. The MDEQ approved the RIWP in March 2020 and we expect work at the Helena site to continue through 2020 and into 2021. MDEQ has indicated it expects to proceed in listing the Missoula site as a Montana superfund site. After researching historical ownership we have identified another potentially responsible party with whom we have entered into an agreement allocating third-party costs to be incurred in addressing the site. The other party is assuming the lead role at the site and has expressed its intent to pursue a voluntary remediation at the Missoula site. At this time, we cannot estimate with a reasonable degree of certainty the nature and timing of risk-based remedial action, if any, at the Missoula site. Global Climate Change - National and international actions have been initiated to address global climate change and the contribution of greenhouse gas (GHG) including, most significantly, carbon dioxide (CO 2 ). These actions include legislative proposals, Executive and Environmental Protection Agency (EPA) actions at the federal level, actions at the state level, investor activism and private party litigation relating to GHG emissions. Coal-fired plants have come under particular scrutiny due to their level of GHG emissions. We have joint ownership interests in four coal-fired electric generating plants, all of which are operated by other companies. We are responsible for our proportionate share of the capital and operating costs while being entitled to our proportionate share of the power generated. While numerous bills have been introduced that address climate change from different perspectives, Congress has not passed any federal climate change legislation and we cannot predict the timing or form of any potential legislation. In 2019, the EPA finalized the Affordable Clean Energy Rule (ACE), which repealed the 2015 Clean Power Plan (CPP) in regulating GHG emissions from coal-fired plants. Various challenges to ACE are pending in the District of Columbia Circuit (D.C. Circuit). Oral arguments in the cases were heard before the D.C. Circuit on October 8, 2020. No decision has been issued in the cases. Generally, ACE provides more regulatory flexibility to individual states and likely will not reduce CO 2 emissions as much as the CPP. Under the ACE, states must establish unit-specific standards that reflect emissions achievable through heat rate improvements, which the EPA designated as the best system of emissions reduction, and if the state chooses, take into account the remaining useful life of the unit and other source specific factors. States generally have three years to submit the standards to the EPA and coal-fired plants will have two additional years to comply with the standards. We cannot predict whether or how ACE will be applied to our plants, including actions taken by the relevant state authorities. In addition, it is unclear how pending or future litigation relating to GHG matters will impact us. As GHG regulations are implemented, it could result in additional compliance costs impacting our future results of operations and financial position if such costs are not recovered through regulated rates. We will continue working with federal and state regulatory authorities, other utilities, and stakeholders to seek relief from any GHG regulations that, in our view, disproportionately impact customers in our region. Future additional environmental requirements could cause us to incur material costs of compliance, increase our costs of procuring electricity, decrease transmission revenue and impact cost recovery. Technology to efficiently capture, remove and/or sequester such GHG emissions may not be available within a timeframe consistent with the implementation of any such requirements. Physical impacts of climate change also may present potential risks for severe weather, such as droughts, fires, floods, ice storms and tornadoes, in the locations where we operate or have interests. These potential risks may impact costs for electric and natural gas supply and maintenance of generation, distribution, and transmission facilities. Jointly Owned Plants - We have joint ownership in generation plants located in South Dakota, North Dakota, Iowa, and Montana that are or may become subject to the various regulations discussed above that have been issued or proposed. Regarding the ACE, as discussed above, we cannot predict the impact on us until state plans are adopted and any judicial reviews are completed. Clean Air Act Rules and Associated Emission Control Equipment Expenditures - The EPA has proposed or issued a number of rules under different provisions of the Clean Air Act (CAA) that could require the installation of emission control equipment at the generation plants in which we have joint ownership. Air emissions at our thermal generating plants are managed by the use of emissions and combustion controls and monitoring, and sulfur dioxide allowances. These measures are anticipated to be sufficient to permit the facilities to continue to meet current air emissions compliance requirements. Regional Haze Rules - In January 2017, the EPA published amendments to the requirements under the CAA for state plans for protection of visibility - regional haze rules. Among other things, these amendments revised the process and requirements for the state implementation plans and extended the due date for the next periodic comprehensive regional haze state implementation plan revisions from 2018 to 2021. By July 31, 2021, Montana must develop and submit to the EPA for approval a revised plan that demonstrates reasonable progress toward eliminating man-made emissions of visibility impairing pollutants, which could impact Colstrip Unit 4. In March 2017, we filed a Petition for Review of these amendments with the D.C. Circuit, which was consolidated with other petitions challenging the final rule. The D.C. Circuit has granted the EPA’s request to hold the case in abeyance while the EPA considers further administrative action to revisit the rule. The North Dakota Department of Environmental Quality (ND DEQ) is expected to decide on statewide reduction strategy later in 2020 which could impact the Coyote generating facility. Once the ND DEQ establishes a State Implementation Plan (SIP) for regional haze compliance, the SIP will be submitted for approval to the North Dakota Governor’s office and finally to EPA for approval. Following EPA’s approval, which is not expected to occur until the second half of 2021, the joint owners of the Coyote generating facility will assess the requirements, if any, and determine whether to move forward with the installation of additional emissions controls. Additional controls, if any, to meet new emission restrictions would have to be in place by the end of 2028 under the current schedule. Other - We continue to manage equipment containing polychlorinated biphenyl (PCB) oil in accordance with the EPA's Toxic Substance Control Act regulations. We will continue to use certain PCB-contaminated equipment for its remaining useful life and will, thereafter, dispose of the equipment according to pertinent regulations that govern the use and disposal of such equipment. We routinely engage the services of a third-party environmental consulting firm to assist in performing a comprehensive evaluation of our environmental reserve. Based upon information available at this time, we believe that the current environmental reserve properly reflects our remediation exposure for the sites currently and previously owned by us. The portion of our environmental reserve applicable to site remediation may be subject to change as a result of the following uncertainties: • We may not know all sites for which we are alleged or will be found to be responsible for remediation; and • Absent performance of certain testing at sites where we have been identified as responsible for remediation, we cannot estimate with a reasonable degree of certainty the total costs of remediation. LEGAL PROCEEDINGS Pacific Northwest Solar Litigation Pacific Northwest Solar, LLC (PNWS) is a solar QF developer seeking to construct small solar facilities in Montana. We began negotiating with PNWS in early 2016 to purchase the output from 21 of its proposed facilities pursuant to our standard QF-1 Tariff, which is applicable to projects no larger than 3 MWs. On June 16, 2016, however, the MPSC suspended the availability of the QF-1 Tariff standard rates for that category of solar projects, which included the projects proposed by PNWS. The MPSC exempted from the suspension any projects for which a QF had both submitted a signed power purchase agreement and had executed an interconnection agreement with us by June 16, 2016. Although we had signed four power purchase agreements with PNWS as of that date, we had not entered into interconnection agreements with PNWS for any of those projects. As a result, none of the PNWS projects in Montana qualified for the exemption. In November 2016, PNWS sued us in state court seeking unspecified damages for breach of contract and a judicial declaration that some or all of the 21 proposed power purchase agreements it had proposed to us were in effect despite the MPSC's Order. We removed the state lawsuit to the United States District Court for the District of Montana (Court). PNWS also requested the MPSC to exempt its projects from the tariff suspension and allow those projects to receive the QF-1 tariff rate that had been in effect prior to the suspension. We joined in PNWS’s request for relief with respect to four of the projects, but the MPSC did not grant any of the relief requested by PNWS or us. In August 2017, pursuant to a non-monetary, partial settlement with us, PNWS amended its original complaint to limit its claims for enforcement and/or damages to only four of the 21 power purchase agreements. As a result, the amount of damages sought by the plaintiff was reduced to approximately $8 million for the alleged breach of the four power purchase agreements. We participated in an unsuccessful mediation on January 24, 2019 and subsequent settlement efforts also have been unsuccessful. A jury trial was scheduled to begin on June 2, 2020, but the trial was postponed because of the court closure due to the COVID-19 pandemic and has not yet been rescheduled. We dispute the remaining claims in PNWS’ lawsuit and will continue to vigorously defend against them. We cannot currently predict an outcome in this litigation. If the plaintiff prevails and obtains damages for a breach of contract, we may seek to recover those damages in rates from customers. We cannot predict the outcome of any such effort. State of Montana - Riverbed Rents On April 1, 2016, the State of Montana (State) filed a complaint on remand (the State’s Complaint) with the Montana First Judicial District Court (State District Court), naming us, along with Talen Montana, LLC (Talen) as defendants. The State claimed it owns the riverbeds underlying 10 of our, and formerly Talen’s, hydroelectric facilities (dams, along with reservoirs and tailraces) on the Missouri, Madison and Clark Fork Rivers, and seeks rents for Talen’s and our use and occupancy of such lands. The facilities at issue include the Hebgen, Madison, Hauser, Holter, Black Eagle, Rainbow, Cochrane, Ryan, and Morony facilities on the Missouri and Madison Rivers and the Thompson Falls facility on the Clark Fork River. We acquired these facilities from Talen in November 2014. The litigation has a long prior history. In 2012, the United States Supreme Court issued a decision holding that the Montana Supreme Court erred in not considering a segment-by-segment approach to determine navigability and relying on present day recreational use of the rivers. It also held that what it referred to as the Great Falls Reach “at least from the head of the first waterfall to the foot of the last” was not navigable for title purposes, and thus the State did not own the riverbeds in that segment. The United States Supreme Court remanded the case to the Montana Supreme Court for further proceedings not inconsistent with its opinion. Following the 2012 remand, the case laid dormant for four years until the State’s Complaint was filed with the State District Court. On April 20, 2016, we removed the case from State District Court to the United States District Court for the District of Montana (Federal District Court). The State filed a motion to remand. Following briefing and argument, on October 10, 2017, the Federal District Court entered an order denying the State’s motion. Because the State’s Complaint included a claim that the State owned the riverbeds in the Great Falls Reach, on October 16, 2017, we and Talen renewed our earlier-filed motions seeking to dismiss the portion of the State’s Complaint concerning the Great Falls Reach in light of the United States Supreme Court’s decision. On August 1, 2018, the Federal District Court granted the motions to dismiss the State’s Complaint as it pertains to approximately 8.2 miles of riverbed from “the head of the Black Eagle Falls to the foot of the Great Falls.” In particular, the dismissal pertained to the Black Eagle Dam, Rainbow Dam and reservoir, Cochrane Dam and reservoir, and Ryan Dam and reservoir. While the dismissal of these four facilities may be subject to appeal, that appeal would not likely occur until after judgment in the case. On February 12, 2019, the Federal District Court granted our motion to join the United States as a defendant to the litigation. As a result, on October 31, 2019, the State filed and served an Amended Complaint including the United States as a defendant and removing claims of ownership for the hydroelectric facilities on the Great Falls Reach, except for the Morony and the Black Eagle Developments. We and Talen filed answers to the Amended Complaint on December 13, 2019, and the United States answered on February 5, 2020. The Federal District Court held a scheduling conference on June 18, 2020 at which it approved a plan for discovery, and set deadlines in the case, including a trial date of September 27, 2021 on the issue of navigability. Damages were bifurcated by agreement and will be tried separately, should the Federal District Court find any segments navigable. The parties are engaged in discovery and the State has served its expert reports. We, along with the other Defendants, are scheduled to serve our expert reports in December. We dispute the State’s claims and intend to vigorously defend the lawsuit. This matter is still at its early stages, and we cannot predict an outcome. If the Federal District Court determines the riverbeds are navigable under the remaining six facilities that were not dismissed and if it calculates damages as the State District Court did in 2008, we estimate the annual rents could be approximately $3.8 million commencing when we acquired the facilities in November 2014. We anticipate that any obligation to pay the State rent for use and occupancy of the riverbeds would be recoverable in rates from customers, although there can be no assurances that the MPSC would approve any such recovery. Other Legal Proceedings We are also subject to various other legal proceedings, governmental audits and claims that arise in the ordinary course of business. In the opinion of management, the amount of ultimate liability with respect to these other actions will not materially affect our financial position, results of operations, or cash flows.

Organization, Consolidation and

Organization, Consolidation and Presentation of Financial Statements (Tables)	9 Months Ended
	Sep. 30, 2020
Cash, Cash Equivalents, and Restricted Cash [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statements of Cash Flows (in thousands): September 30, December 31, September 30, December 31, 2020 2019 2019 2018 Cash and cash equivalents $ 3,512 $ 5,145 $ 5,046 $ 7,860 Restricted cash 10,497 6,925 9,055 7,451 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 14,009 $ 12,070 $ 14,101 $ 15,311

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following table summarizes the differences between our effective tax rate and the federal statutory rate (in thousands): Three Months Ended September 30, 2020 2019 Income Before Income Taxes $ 26,763 $ 22,225 Income tax calculated at federal statutory rate 5,621 21.0 % 4,667 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 46 0.2 65 0.3 Flow-through repairs deductions (4,213) (15.7) (2,606) (11.7) Production tax credits (2,205) (8.2) (1,414) (6.3) Amortization of excess deferred income tax (222) (0.8) (374) (1.7) Plant and depreciation of flow-through items 103 0.4 (263) (1.2) Prior year permanent return to accrual adjustments (1,728) (6.5) 559 2.5 Other, net (105) (0.5) (79) (0.4) (8,324) (31.1) (4,112) (18.5) Income tax (benefit) expense $ (2,703) (10.1) % $ 555 2.5 % Nine Months Ended September 30, 2020 2019 Income Before Income Taxes $ 96,437 $ 122,040 Income tax calculated at federal statutory rate 20,252 21.0 % 25,628 21.0 % Permanent or flow through adjustments: State income, net of federal provisions 73 0.1 1,230 1.0 Flow-through repairs deductions (14,859) (15.4) (12,694) (10.4) Production tax credits (7,553) (7.8) (7,252) (5.9) Share-based compensation (609) (0.6) 186 0.2 Amortization of excess deferred income tax (731) (0.8) (1,939) (1.6) Prior year permanent return to accrual adjustments (1,728) (1.8) 559 0.4 Plant and depreciation of flow through items 299 0.3 (2,449) (2.0) Recognition of unrecognized tax benefit — — (22,825) (18.7) Other, net (371) (0.4) (542) (0.5) (25,479) (26.4) (45,726) (37.5) Income tax benefit $ (5,227) (5.4) % $ (20,098) (16.5) %

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Income) Loss (Tables)	9 Months Ended
	Sep. 30, 2020
Statement of Financial Position [Abstract]
Comprehensive Income (Loss) [Table Text Block]	The following tables display the components of Other Comprehensive Income (Loss), after-tax, and the related tax effects (in thousands): Three Months Ended September 30, 2020 September 30, 2019 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (3) $ — $ (3) $ 42 $ — $ 42 Reclassification of net income (loss) on derivative instruments 153 (40) 113 154 (40) 114 Other comprehensive income (loss) $ 150 $ (40) $ 110 $ 196 $ (40) $ 156 Nine Months Ended September 30, 2020 September 30, 2019 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ 90 $ — $ 90 $ 18 $ — $ 18 Reclassification of net income (loss) on derivative instruments 459 (120) 339 460 (121) 339 Other comprehensive income (loss) $ 549 $ (120) $ 429 $ 478 $ (121) $ 357
Accumulated Other Comprehensive Income [Table Text Block]	Balances by classification included within accumulated other comprehensive loss (AOCL) on the Condensed Consolidated Balance Sheets are as follows, net of tax (in thousands): September 30, 2020 December 31, 2019 Foreign currency translation $ 1,503 $ 1,413 Derivative instruments designated as cash flow hedges (10,842) (11,181) Postretirement medical plans 120 120 Accumulated other comprehensive loss $ (9,219) $ (9,648)
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following tables display the changes in AOCL by component, net of tax (in thousands): Three Months Ended September 30, 2020 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (10,955) $ 120 $ 1,506 $ (9,329) Other comprehensive income before reclassifications — — (3) (3) Amounts reclassified from AOCL Interest Expense 113 — — 113 Net current-period other comprehensive income (loss) 113 — (3) 110 Ending balance $ (10,842) $ 120 $ 1,503 $ (9,219) Three Months Ended September 30, 2019 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (11,408) $ 251 $ 1,424 $ (9,733) Other comprehensive income before reclassifications 42 42 Amounts reclassified from AOCL Interest Expense 114 114 Net current-period other comprehensive income 114 — 42 156 Ending balance $ (11,294) $ 251 $ 1,466 $ (9,577) Nine Months Ended September 30, 2020 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (11,181) $ 120 $ 1,413 $ (9,648) Other comprehensive income before reclassifications — — 90 90 Amounts reclassified from AOCL Interest Expense 339 — — 339 Net current-period other comprehensive income 339 — 90 429 Ending balance $ (10,842) $ 120 $ 1,503 $ (9,219) Nine Months Ended September 30, 2019 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Pension and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (11,633) $ 251 $ 1,448 $ (9,934) Other comprehensive income before reclassifications — — 18 18 Amounts reclassified from AOCL Interest Expense 339 — — 339 Net current-period other comprehensive income 339 — 18 357 Ending balance $ (11,294) $ 251 $ 1,466 $ (9,577)

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting Information [Line Items]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Financial data for the business segments are as follows (in thousands): Three Months Ended September 30, 2020 Electric Gas Other Eliminations Total Operating revenues $ 244,155 $ 36,455 $ — $ — $ 280,610 Cost of sales 61,155 6,883 — — 68,038 Gross margin 183,000 29,572 — — 212,572 Operating, general and administrative 54,367 20,059 (1,104) — 73,322 Property and other taxes 35,532 9,772 2 — 45,306 Depreciation and depletion 36,670 7,619 — — 44,289 Operating income (loss) 56,431 (7,878) 1,102 — 49,655 Interest expense, net (21,286) (1,574) (817) — (23,677) Other income (expense), net 1,559 459 (1,233) — 785 Income tax benefit 1,197 607 899 — 2,703 Net income (loss) $ 37,901 $ (8,386) $ (49) $ — $ 29,466 Total assets $ 4,430,279 $ 1,634,606 $ 10,754 $ — $ 6,075,639 Capital expenditures $ 87,432 $ 19,073 $ — $ — $ 106,505 Three Months Ended September 30, 2019 Electric Gas Other Eliminations Total Operating revenues $ 241,237 $ 33,599 $ — $ — $ 274,836 Cost of sales 58,768 5,459 — — 64,227 Gross margin 182,469 28,140 — — 210,609 Operating, general and administrative 57,433 18,830 735 — 76,998 Property and other taxes 34,731 9,355 3 — 44,089 Depreciation and depletion 35,824 7,342 — — 43,166 Operating income (loss) 54,481 (7,387) (738) — 46,356 Interest expense, net (19,481) (1,588) (2,653) — (23,722) Other (expense) income, net (677) (344) 612 — (409) Income tax (expense) benefit (1,415) (232) 1,092 — (555) Net income (loss) $ 32,908 $ (9,551) $ (1,687) $ — $ 21,670 Total assets $ 4,632,077 $ 1,173,513 $ 4,590 $ — $ 5,810,180 Capital expenditures $ 70,063 $ 25,784 $ — $ — $ 95,847 Nine Months Ended September 30, 2020 Electric Gas Other Eliminations Total Operating revenues $ 706,718 $ 178,507 $ — $ — $ 885,225 Cost of sales 173,294 47,059 — — 220,353 Gross margin 533,424 131,448 — — 664,872 Operating, general and administrative 166,854 61,348 (4,160) — 224,042 Property and other taxes 107,079 29,700 7 — 136,786 Depreciation and depletion 110,692 23,644 — — 134,336 Operating income 148,799 16,756 4,153 — 169,708 Interest expense, net (63,585) (4,824) (3,889) — (72,298) Other income (expense) 3,131 863 (4,967) — (973) Income tax benefit (expense) 2,609 (467) 3,085 — 5,227 Net income (loss) $ 90,954 $ 12,328 $ (1,618) $ — $ 101,664 Total assets $ 4,430,279 $ 1,634,606 $ 10,754 $ — $ 6,075,639 Capital expenditures $ 230,524 $ 52,463 $ — $ — $ 282,987 Nine Months Ended September 30, 2019 Electric Gas Other Eliminations Total Operating revenues $ 733,933 $ 195,842 $ — $ — $ 929,775 Cost of sales 178,423 57,283 — — 235,706 Gross margin 555,510 138,559 — — 694,069 Operating, general and administrative 174,544 60,803 3,569 — 238,916 Property and other taxes 104,612 28,569 7 — 133,188 Depreciation and depletion 107,595 22,171 — — 129,766 Operating income (loss) 168,759 27,016 (3,576) — 192,199 Interest expense, net (58,301) (4,599) (8,123) — (71,023) Other (expense) income (1,458) (874) 3,196 — 864 Income tax (expense) benefit (4,937) 493 24,542 — 20,098 Net income $ 104,063 $ 22,036 $ 16,039 $ — $ 142,138 Total assets $ 4,632,077 $ 1,173,513 $ 4,590 $ — $ 5,810,180 Capital expenditures $ 186,155 $ 56,719 $ — $ — $ 242,874

Revenue from Contracts with C_2

Revenue from Contracts with Customers Disaggregation of Revenue (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	The following tables disaggregate our revenue by major source and customer class (in millions): Three Months Ended September 30, 2020 September 30, 2019 Electric Natural Gas Total Electric Natural Gas Total Montana $ 78.5 $ 9.9 $ 88.4 $ 68.4 $ 8.9 $ 77.3 South Dakota 18.9 1.7 20.6 16.0 1.7 17.7 Nebraska — 1.7 1.7 — 1.8 1.8 Residential 97.4 13.3 110.7 84.4 12.4 96.8 Montana 89.1 5.6 94.7 87.7 5.5 93.2 South Dakota 27.4 1.0 28.4 26.3 1.3 27.6 Nebraska — 0.7 0.7 — 0.9 0.9 Commercial 116.5 7.3 123.8 114.0 7.7 121.7 Industrial 9.2 0.1 9.3 10.6 0.1 10.7 Lighting, Governmental, Irrigation, and Interdepartmental 11.9 0.1 12.0 12.4 0.1 12.5 Total Customer Revenues 235.0 20.8 255.8 221.4 20.3 241.7 Other Tariff and Contract Based Revenues 14.9 8.3 23.2 15.3 7.7 23.0 Total Revenue from Contracts with Customers 249.9 29.1 279.0 236.7 28.0 264.7 Regulatory amortization (5.7) 7.4 1.7 4.5 5.6 10.1 Total Revenues $ 244.2 $ 36.5 $ 280.7 $ 241.2 $ 33.6 $ 274.8 Nine Months Ended September 30, 2020 September 30, 2019 Electric Natural Gas Total Electric Natural Gas Total Montana $ 237.7 $ 65.7 $ 303.4 $ 225.4 $ 73.3 $ 298.7 South Dakota 52.4 16.7 69.1 47.4 20.4 67.8 Nebraska — 12.9 12.9 — 15.7 15.7 Residential 290.1 95.3 385.4 272.8 109.4 382.2 Montana 252.5 33.0 285.5 257.3 38.0 295.3 South Dakota 77.1 11.2 88.3 71.2 14.1 85.3 Nebraska — 6.2 6.2 — 8.3 8.3 Commercial 329.6 50.4 380.0 328.5 60.4 388.9 Industrial 27.2 0.5 27.7 32.4 0.7 33.1 Lighting, Governmental, Irrigation, and Interdepartmental 26.4 0.7 27.1 25.2 0.6 25.8 Total Customer Revenues 673.3 146.9 820.2 658.9 171.1 830.0 Other Tariff and Contract Based Revenues 44.1 26.5 70.6 46.5 26.6 73.1 Total Revenue from Contracts with Customers 717.4 173.4 890.8 705.4 197.7 903.1 Regulatory amortization (10.7) 5.1 (5.6) 28.5 (1.9) 26.6 Total Revenues $ 706.7 $ 178.5 $ 885.2 $ 733.9 $ 195.8 $ 929.7

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Weighted Average Number of Shares [Table Text Block]	Average shares used in computing the basic and diluted earnings per share are as follows: Three Months Ended September 30, 2020 September 30, 2019 Basic computation 50,576,564 50,443,866 Dilutive effect of: Performance share awards (1) 97,529 335,371 Diluted computation 50,674,093 50,779,237 Nine Months Ended September 30, 2020 September 30, 2019 Basic computation 50,551,121 50,422,028 Dilutive effect of: Performance share awards (1) 105,395 334,002 Diluted computation 50,656,516 50,756,030 _______________________

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Schedule of Defined Benefit Plans Disclosures [Table Text Block]	Net periodic benefit cost (credit) for our pension and other postretirement plans consists of the following (in thousands): Pension Benefits Other Postretirement Benefits Three Months Ended September 30, Three Months Ended September 30, 2020 2019 2020 2019 Components of Net Periodic Benefit Cost (Credit) Service cost $ 2,779 $ 2,409 $ 93 $ 82 Interest cost 5,710 6,622 123 152 Expected return on plan assets (6,541) (6,360) (246) (217) Amortization of prior service cost (credit) — 1,636 (471) (471) Recognized actuarial loss (gain) 1,257 — (15) (24) Plan settlements — 715 — — Net periodic benefit cost (credit) $ 3,205 $ 5,022 $ (516) $ (478) Pension Benefits Other Postretirement Benefits Nine Months Ended Nine Months Ended 2020 2019 2020 2019 Components of Net Periodic Benefit Cost (Credit) Service cost $ 8,337 $ 7,228 $ 278 $ 248 Interest cost 17,130 19,866 369 457 Expected return on plan assets (19,622) (19,082) (738) (652) Amortization of prior service cost (credit) — 4,908 (1,412) (1,412) Recognized actuarial loss (gain) 3,771 — (45) (72) Plan settlements — 715 — — Net periodic benefit cost (credit) $ 9,616 $ 13,635 $ (1,548) $ (1,431)

Nature of Operations and Basi_2

Nature of Operations and Basis of Consolidation (Details) $ in Millions	3 Months Ended
	Sep. 30, 2020USD ($)watts	Dec. 31, 2019customers
Number of customers | customers		734,800
Number of megawatts of qualifying facility | watts	35
Estimated aggregate gross contractual payments for qualifying facilities through 2024	$ 123.9
Goodwill, Impairment Loss	$ 0

Nature of Operations and Basi_3

Nature of Operations and Basis of Consolidation Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash, Cash Equivalents, and Restricted Cash [Abstract]
Cash and cash equivalents	$ 3,512	$ 5,145	$ 5,046	$ 7,860
Restricted cash	10,497	6,925	9,055	7,451
Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows	$ 14,009	$ 12,070	$ 14,101	$ 15,311

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]
Payment for pension benefits				$ 11.4
NorthWestern Energy Pension Plan (MT) [Member]
Public Utilities, General Disclosures [Line Items]
Payment for pension benefits				10.2
Power cost and Credit Adjustment Mechanism (PCCAM) [Member]
Public Utilities, General Disclosures [Line Items]
Deadband around base electric supply costs			$ 4.1
Customer sharing percentage of amounts exceeding deadband			90.00%
Company sharing percentage of amounts exceeding deadband			10.00%
Under collected supply costs		$ 23.8			$ 23.8
Proposed disallowance of replacement power costs		$ 6
Proposed under recovery due to statute change					$ 4
Customer sharing percentage of over/under collection of QF costs			100.00%
Regulatory assets associated with PCCAM	$ 2.1			2.1
Montana Accounting Order [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Request to Recognize Pension Contribution over 5 years	40
South Dakota Accounting Order [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Asset for COVID Uncollectable Accounts	$ 0.4			$ 0.4

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		$ 22.8
Unrecognized Tax Benefit Reduction Resulting from Lapse of Applicable Statute of Limitations Unrecognized Tax Benefits, Income Tax Penalties and Interest Portion		$ 2.7
Unrecognized tax benefit more likely than not percentage threshold	50.00%
Unrecognized tax benefits	$ 33.9
Unrecognized tax benefits that would impact effective tax rate	28
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 0
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2002

Income Taxes Effective Tax Rate

Income Taxes Effective Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Effective tax rate reconciliation
Income Before Income Taxes	$ 26,763	$ 22,225	$ 96,437	$ 122,040
Income tax calculated at federal statutory rate	$ 5,621	$ 4,667	$ 20,252	$ 25,628
Income tax calculated at federal statutory rate	21.00%	21.00%	21.00%	21.00%
State income tax, net of federal provisions	$ 46	$ 65	$ 73	$ 1,230
State income tax, net of federal provisions	0.20%	0.30%	0.10%	1.00%
Flow-through repairs deductions	$ (4,213)	$ (2,606)	$ (14,859)	$ (12,694)
Flow-through repairs deductions	(15.70%)	(11.70%)	(15.40%)	(10.40%)
Production tax credits	$ (2,205)	$ (1,414)	$ (7,553)	$ (7,252)
Production tax credits	(8.20%)	(6.30%)	(7.80%)	(5.90%)
Share-based compensation			$ (609)	$ 186
Share-based compensation			(0.60%)	0.20%
Amortization of excess deferred income tax	$ (222)	$ (374)	$ (731)	$ (1,939)
Amortization of excess deferred income tax	(0.80%)	(1.70%)	(0.80%)	(1.60%)
Plant and depreciation of flow-through items	$ 103	$ (263)	$ 299	$ (2,449)
Plant and depreciation of flow-through items	0.40%	(1.20%)	0.30%	(2.00%)
Prior year permanent return to accrual adjustments	(6.50%)	2.50%	(1.80%)	0.40%
Prior year permanent return to accrual adjustments	$ (1,728)	$ 559	$ (1,728)	$ 559
Effective Income Tax Rate Reconciliation, Reduction Resulting from Lapse of Applicable Statute of Limitations			$ 0	$ (22,825)
Effective IncomeTax Rate Reconciliation Unrecognized Tax Benefits, Percent			0.00%	(18.70%)
Other, net	$ (105)	$ (79)	$ (371)	$ (542)
Other, net	(0.50%)	(0.40%)	(0.40%)	(0.50%)
Total Other Reconciling Items	$ (8,324)	$ (4,112)	$ (25,479)	$ (45,726)
Total Other Reconciling Items	(31.10%)	(18.50%)	(26.40%)	(37.50%)
Income tax benefit	$ (2,703)	$ 555	$ (5,227)	$ (20,098)
Income tax benefit	(10.10%)	2.50%	(5.40%)	(16.50%)

Comprehensive Income (Loss) (De

Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Comprehensive Income (Loss), before Tax [Abstract]
Foreign currency translation adjustment	$ (3)	$ 42	$ 90	$ 18
Reclassification of net income (loss) on derivative instruments	153	154	459	460
Other Comprehensive Income (Loss), before Tax	150	196	549	478
Other Comprehensive Income (Loss), Tax [Abstract]
Foreign currency translation adjustment	0	0	0	0
Reclassification of net income (loss) on derivative instruments	(40)	(40)	(120)	(121)
Other Comprehensive Income (Loss), Tax	40	40	120	121
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	(3)	42	90	18
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax, Total	(113)	(114)	(339)	(339)
Total Other Comprehensive Income	$ 110	$ 156	$ 429	$ 357

Classification within AOCL on t

Classification within AOCL on the Condenced Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Foreign currency translation	$ 1,503	$ 1,413
Derivative instruments designated as cash flow hedges	(10,842)	(11,181)
Postretirement medical plans	120	120
Accumulated other comprehensive loss	$ (9,219)	$ (9,648)

Changes in AOCI by Component (D

Changes in AOCI by Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (9,648)
Total Other Comprehensive Income	$ 110	$ 156	429	$ 357
Ending balance	(9,219)		(9,219)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(10,955)	(11,408)	(11,181)	(11,633)
Other comprehensive income before reclassifications	0		0	0
Amounts reclassified from AOCL	113	114	339	339
Total Other Comprehensive Income	113	114	339	339
Ending balance	(10,842)	(11,294)	(10,842)	(11,294)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	120	251	120	251
Other comprehensive income before reclassifications	0		0	0
Amounts reclassified from AOCL	0		0	0
Total Other Comprehensive Income	0	0	0	0
Ending balance	120	251	120	251
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,506	1,424	1,413	1,448
Other comprehensive income before reclassifications	(3)	42	90	18
Amounts reclassified from AOCL	0		0	0
Total Other Comprehensive Income	(3)	42	90	18
Ending balance	1,503	1,466	1,503	1,466
Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(9,329)	(9,733)	(9,648)	(9,934)
Other comprehensive income before reclassifications	(3)	42	90	18
Amounts reclassified from AOCL	113	114	339	339
Total Other Comprehensive Income	110	156	429	357
Ending balance	$ (9,219)	$ (9,577)	$ (9,219)	$ (9,577)

Financing Activities (Details)

Financing Activities (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)banks	Dec. 31, 2019USD ($)
Short-term Debt [Line Items]
Short term borrowings	$ 100,000	$ 100,000	$ 0
Unsecured Revolving Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 425,000	$ 425,000
Line of Credit Facility, Expiration Date		Sep. 2, 2023
Line of Credit Facility, Number of Institutions Participating in the Facility | banks		10
Line of Credit Facility, Maximum Number Of Institutions Participating In The Facility Pertaining to Maximum Contributory Percentage | banks		1
Line of Credit Facility, Maximum Percentage of Total Availability Provided by a Single Lender	13.00%	13.00%
Credit Facility Covenant on Maximum Ratio of Indebtedness		65.00%
Unsecured Revolving Line of Credit, Additional Amount Available Under Accordion Feature [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 75,000	$ 75,000
Eurodollar [Member] | Minimum [Member] | Unsecured Revolving Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		112.50%
Eurodollar [Member] | Maximum [Member] | Unsecured Revolving Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		175.00%
Base Rate [Member] | Minimum [Member] | Unsecured Revolving Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		12.50%
Base Rate [Member] | Maximum [Member] | Unsecured Revolving Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		75.00%
Secured Debt Montana Due 2030 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 100,000	$ 100,000
Debt Instrument, Interest Rate, Stated Percentage	3.21%	3.21%
Long-term Debt, Maturity Date	May 15, 2030	May 15, 2030
Secured Debt South Dakota Due 2030 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 50,000	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	3.21%	3.21%
Long-term Debt, Maturity Date	May 15, 2030	May 15, 2030
Term Loan Due 2021 [Member]
Short-term Debt [Line Items]
Short term borrowings	$ 100,000	$ 100,000
Maximum Ratio Of Indebtedness To Net Capital Threshold Percentage	65.00%
Term Loan Due 2021 [Member] | Eurodollar [Member]
Short-term Debt [Line Items]
Short Term Debt Basis Spread On Variable Rate	1.50%

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 280,610	$ 274,836	$ 885,225	$ 929,775
Cost of sales	68,038	64,227	220,353	235,706
Gross margin	212,572	210,609	664,872	694,069
Operating, general and administrative	73,322	76,998	224,042	238,916
Property and other taxes	45,306	44,089	136,786	133,188
Depreciation and depletion	44,289	43,166	134,336	129,766
Operating income (loss)	49,655	46,356	169,708	192,199
Interest expense, net	(23,677)	(23,722)	(72,298)	(71,023)
Other income (expense), net	785	(409)	(973)	864
Income Tax Benefit (Expense)	2,703	(555)	5,227	20,098
Net Income	29,466	21,670	101,664	142,138
Total assets	6,075,639	5,810,180	6,075,639	5,810,180	$ 5,910,702
Capital expenditures	106,505	95,847	282,987	242,874
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	244,155	241,237	706,718	733,933
Cost of sales	61,155	58,768	173,294	178,423
Gross margin	183,000	182,469	533,424	555,510
Operating, general and administrative	54,367	57,433	166,854	174,544
Property and other taxes	35,532	34,731	107,079	104,612
Depreciation and depletion	36,670	35,824	110,692	107,595
Operating income (loss)	56,431	54,481	148,799	168,759
Interest expense, net	(21,286)	(19,481)	(63,585)	(58,301)
Other income (expense), net	1,559	(677)	3,131	(1,458)
Income Tax Benefit (Expense)	1,197	(1,415)	2,609	(4,937)
Net Income	37,901	32,908	90,954	104,063
Total assets	4,430,279	4,632,077	4,430,279	4,632,077
Capital expenditures	87,432	70,063	230,524	186,155
Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	36,455	33,599	178,507	195,842
Cost of sales	6,883	5,459	47,059	57,283
Gross margin	29,572	28,140	131,448	138,559
Operating, general and administrative	20,059	18,830	61,348	60,803
Property and other taxes	9,772	9,355	29,700	28,569
Depreciation and depletion	7,619	7,342	23,644	22,171
Operating income (loss)	(7,878)	(7,387)	16,756	27,016
Interest expense, net	(1,574)	(1,588)	(4,824)	(4,599)
Other income (expense), net	459	(344)	863	(874)
Income Tax Benefit (Expense)	607	(232)	(467)	493
Net Income	(8,386)	(9,551)	12,328	22,036
Total assets	1,634,606	1,173,513	1,634,606	1,173,513
Capital expenditures	19,073	25,784	52,463	56,719
All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Cost of sales	0	0	0	0
Gross margin	0	0	0	0
Operating, general and administrative	(1,104)	735	(4,160)	3,569
Property and other taxes	2	3	7	7
Depreciation and depletion	0	0	0	0
Operating income (loss)	1,102	(738)	4,153	(3,576)
Interest expense, net	(817)	(2,653)	(3,889)	(8,123)
Other income (expense), net	(1,233)	612	(4,967)	3,196
Income Tax Benefit (Expense)	899	1,092	3,085	24,542
Net Income	(49)	(1,687)	(1,618)	16,039
Total assets	10,754	4,590	10,754	4,590
Capital expenditures	0	0	0	0
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Cost of sales	0	0	0	0
Gross margin	0	0	0	0
Operating, general and administrative	0	0	0	0
Property and other taxes	0	0	0	0
Depreciation and depletion	0	0	0	0
Operating income (loss)	0	0	0	0
Interest expense, net	0	0	0	0
Other income (expense), net	0	0	0	0
Income Tax Benefit (Expense)	0	0	0	0
Net Income	0	0	0	0
Total assets	0	0	0	0
Capital expenditures	$ 0	$ 0	$ 0	$ 0

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 279,000	$ 264,700	$ 890,800	$ 903,100
Total Revenues	280,610	274,836	885,225	929,775
Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	110,700	96,800	385,400	382,200
Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	88,400	77,300	303,400	298,700
Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	20,600	17,700	69,100	67,800
Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,700	1,800	12,900	15,700
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	123,800	121,700	380,000	388,900
Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	94,700	93,200	285,500	295,300
Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	28,400	27,600	88,300	85,300
Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	700	900	6,200	8,300
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9,300	10,700	27,700	33,100
Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	12,000	12,500	27,100	25,800
Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	255,800	241,700	820,200	830,000
Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	23,200	23,000	70,600	73,100
Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	1,700	10,100	(5,600)	26,600
Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	280,700	274,800	885,200	929,700
Electric Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	249,900	236,700	717,400	705,400
Total Revenues	244,155	241,237	706,718	733,933
Electric Domestic Regulated [Member] | Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	97,400	84,400	290,100	272,800
Electric Domestic Regulated [Member] | Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	78,500	68,400	237,700	225,400
Electric Domestic Regulated [Member] | Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	18,900	16,000	52,400	47,400
Electric Domestic Regulated [Member] | Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Electric Domestic Regulated [Member] | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	116,500	114,000	329,600	328,500
Electric Domestic Regulated [Member] | Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	89,100	87,700	252,500	257,300
Electric Domestic Regulated [Member] | Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	27,400	26,300	77,100	71,200
Electric Domestic Regulated [Member] | Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Electric Domestic Regulated [Member] | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9,200	10,600	27,200	32,400
Electric Domestic Regulated [Member] | Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	11,900	12,400	26,400	25,200
Electric Domestic Regulated [Member] | Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	235,000	221,400	673,300	658,900
Electric Domestic Regulated [Member] | Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	14,900	15,300	44,100	46,500
Electric Domestic Regulated [Member] | Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	(5,700)	4,500	(10,700)	28,500
Electric Domestic Regulated [Member] | Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	244,200	241,200	706,700	733,900
Gas Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	29,100	28,000	173,400	197,700
Total Revenues	36,455	33,599	178,507	195,842
Gas Domestic Regulated [Member] | Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	13,300	12,400	95,300	109,400
Gas Domestic Regulated [Member] | Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9,900	8,900	65,700	73,300
Gas Domestic Regulated [Member] | Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,700	1,700	16,700	20,400
Gas Domestic Regulated [Member] | Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,700	1,800	12,900	15,700
Gas Domestic Regulated [Member] | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	7,300	7,700	50,400	60,400
Gas Domestic Regulated [Member] | Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	5,600	5,500	33,000	38,000
Gas Domestic Regulated [Member] | Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,000	1,300	11,200	14,100
Gas Domestic Regulated [Member] | Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	700	900	6,200	8,300
Gas Domestic Regulated [Member] | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	100	100	500	700
Gas Domestic Regulated [Member] | Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	100	100	700	600
Gas Domestic Regulated [Member] | Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	20,800	20,300	146,900	171,100
Gas Domestic Regulated [Member] | Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	8,300	7,700	26,500	26,600
Gas Domestic Regulated [Member] | Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	7,400	5,600	5,100	(1,900)
Gas Domestic Regulated [Member] | Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	$ 36,500	$ 33,600	$ 178,500	$ 195,800

Earnings Per Share (Details)

Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic computation	50,576,564	50,443,866	50,551,121	50,422,028
Performance share awards (1)	97,529	335,371	105,395	334,002
Diluted computation	50,674,093	50,779,237	50,656,516	50,756,030

Employee Benefit Plans Net Peri

Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Components of Net Periodic Benefit Cost (Income) [Abstract]
Payment for pension benefits			$ 11,400
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	$ 2,779	$ 2,409	8,337	$ 7,228
Interest cost	5,710	6,622	17,130	19,866
Expected return on plan assets	(6,541)	(6,360)	(19,622)	(19,082)
Amortization of prior service cost (credit)	0	1,636	0	4,908
Recognized actuarial loss (gain)	1,257	0	3,771	0
Plan settlements	0	715	0	715
Net periodic benefit cost (credit)	3,205	5,022	9,616	13,635
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	93	82	278	248
Interest cost	123	152	369	457
Expected return on plan assets	(246)	(217)	(738)	(652)
Amortization of prior service cost (credit)	(471)	(471)	(1,412)	(1,412)
Recognized actuarial loss (gain)	(15)	(24)	(45)	(72)
Plan settlements	0	0	0	0
Net periodic benefit cost (credit)	$ (516)	$ (478)	$ (1,548)	$ (1,431)

Commitments and Contingencies E

Commitments and Contingencies Environmental (Details) $ in Millions	Sep. 30, 2020USD ($)
Environmental remediation obligations [Member]
Environmental remediation obligation, minimum	$ 27.8
Environmental remediation obligation, maximum	30.5
Accrual for environmental loss contingencies	28.8
Combined Manufacturing Sites [Member] | Manufactured Gas Plants [Member]
Accrual for environmental loss contingencies	22.6
Aberdeen South Dakota Site [Member] | Manufactured Gas Plants [Member]
Accrual for environmental loss contingencies	7.8
Environmental remediation obligation through 2024	$ 2.4

Commitments and Contingencies L

Commitments and Contingencies Litigation (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Pacific Northwest Solar, LLC (PNWS) [Member]
Loss Contingencies [Line Items]
Damages sought	$ 8
Riverbed Rents [Member]
Loss Contingencies [Line Items]
Annual riverbed rent exposure	$ 3.8