NorthWestern (NWE) 10-Q26 Oct 232023 Q3 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information Document - shares	9 Months Ended
Document and Entity Information Document - shares	Sep. 30, 2023	Oct. 20, 2023
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2023
Entity Registrant Name	NORTHWESTERN CORP
Entity File Number	000-56598
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	93-2020320
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		61,242,238
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Central Index Key	0000073088
Northwestern Corporation [Member]
Entity Information [Line Items]
Document Quarterly Report	true
Entity File Number	1-10499
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-0172280
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
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false
Northwestern Energy Group
Entity Information [Line Items]
Entity Registrant Name	NORTHWESTERN ENERGY GROUP, INC.
Entity Central Index Key	0001993004

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues
Electric	$ 280,030	$ 292,270	$ 804,604	$ 807,415
Gas	41,060	42,798	261,530	245,139
Total Revenues	321,090	335,068	1,066,134	1,052,554
Operating expenses
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	88,943	108,920	322,013	338,994
Operating and maintenance	53,240	54,654	163,941	160,785
Administrative and general	29,355	28,146	94,058	87,010
Property and other taxes	41,763	46,466	131,043	140,209
Depreciation and depletion	52,159	48,588	157,787	145,705
Total Operating Expenses	265,460	286,774	868,842	872,703
Operating income	55,630	48,294	197,292	179,851
Interest expense, net	(28,725)	(25,332)	(85,144)	(73,081)
Other income, net	4,127	4,157	12,926	11,791
Income before income taxes	31,032	27,119	125,074	118,561
Income tax (expense) benefit	(1,697)	249	(14,085)	(2,297)
Net Income	$ 29,335	$ 27,368	$ 110,989	$ 116,264
Average Common Shares Outstanding	60,442,164	56,310,526	60,010,609	54,901,161
Basic Earnings per Average Common Share	$ 0.48	$ 0.48	$ 1.85	$ 2.12
Diluted Earnings per Average Common Share	0.48	0.47	1.85	2.09
Dividends Declared per Common Share	$ 0.640	$ 0.63	$ 1.92	$ 1.89

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Comprehensive Income (Loss)
Net Income	$ 29,335	$ 27,368	$ 110,989	$ 116,264
Other comprehensive income, net of tax:
Foreign currency translation adjustment	(7)	(4)	(10)	(5)
Postretirement medical liability adjustment	(168)	(158)	(502)	(474)
Reclassification of net losses on derivative instruments	113	113	339	339
Total Other Comprehensive Loss	(62)	(49)	(173)	(140)
Comprehensive Income	$ 29,273	$ 27,319	$ 110,816	$ 116,124

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEET - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current Assets:
Cash and cash equivalents	$ 5,091	$ 8,489
Restricted cash	16,549	13,974
Accounts receivable, net	148,043	244,952
Inventories	119,080	107,359
Regulatory assets	41,940	136,009
Prepaid expenses and other	27,651	28,041
Total current assets	358,354	538,824
Property, plant, and equipment, net	5,932,179	5,657,480
Goodwill	357,586	357,586
Regulatory assets	731,373	716,570
Other noncurrent assets	50,007	47,323
Total Assets	7,429,499	7,317,783
Current Liabilities:
Current maturities of finance leases	3,275	3,098
Current portion of long-term debt	99,900	144,525
Accounts payable	119,315	201,498
Accrued expenses and other	315,291	250,579
Regulatory liabilities	31,733	21,145
Total current liabilities	569,514	620,845
Long-term finance leases	6,327	8,799
Long-term debt	2,544,522	2,474,357
Deferred income taxes	551,221	538,983
Noncurrent regulatory liabilities	671,831	654,213
Other noncurrent liabilities	345,670	355,403
Total Liabilities	4,689,085	4,652,600
Commitments and Contingencies (Note 10)
Shareholders' Equity:
Common Stock, Value, Issued	648	633
Treasury stock at cost	(98,122)	(98,392)
Paid-in capital	2,078,554	1,999,376
Retained earnings	767,355	771,414
Accumulated other comprehensive loss	(8,021)	(7,848)
Total Shareholders' Equity	2,740,414	2,665,183
Total Liabilities and Shareholders' Equity	$ 7,429,499	$ 7,317,783
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	64,761,918
Common Stock, Shares, Outstanding	61,241,779
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, 2023	Sep. 30, 2022
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	$ 110,989	$ 116,264
Items not affecting cash:
Depreciation and depletion	157,787	145,705
Amortization of debt issuance costs, discount and deferred hedge gain	3,997	4,044
Stock-based compensation costs	5,119	4,324
Equity portion of allowance for funds used during construction	(12,530)	(9,983)
(Gain) loss on disposition of assets	(27)	524
Deferred income taxes	(13,281)	(12,127)
Changes in current assets and liabilities:
Accounts receivable	96,910	49,522
Inventories	(11,721)	(48,639)
Other current assets	389	(5,139)
Accounts payable	(60,815)	36,064
Accrued expenses and other	65,058	67,636
Regulatory assets	94,069	(20,788)
Regulatory liabilities	10,588	(6,398)
Other noncurrent assets	1,981	8,968
Other noncurrent liabilities	(21,591)	(20,707)
Cash Provided by Operating Activities	426,922	309,270
Net Cash Provided by (Used in) Investing Activities [Abstract]
Property, plant, and equipment additions	(407,170)	(386,339)
Investment in equity securities	(3,804)	(914)
Cash Used in Investing Activities	(410,974)	(387,253)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Proceeds from issuance of common stock, net	73,613	179,903
Dividends on common stock	(115,048)	(102,980)
Issuance of long-term debt	300,000	0
Line of credit (repayments) borrowings, net	(273,000)	12,000
Other financing activities, net	(2,336)	(977)
Cash (Used in) Provided by Financing Activities	(16,771)	87,946
(Decrease) Increase in Cash, Cash Equivalents, and Restricted Cash	(823)	9,963
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Beginning Balance	22,463	18,762
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Ending Balance	21,640	28,725
Cash Paid [Abstract]
Income Taxes Paid, Net	3,204	9,060
Interest Paid, Excluding Capitalized Interest, Operating Activities	64,533	60,610
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital expenditures included in accounts payable	43,389	26,184
Refinancing of Pollution Control Revenue Refunding Bonds	$ 144,660	$ 0

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Treasury Stock, Common	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance, shares at Dec. 31, 2021		57,606	3,546
Balance, beginning of period at Dec. 31, 2021	$ 2,339,713	$ 576	$ (98,248)	$ 1,716,227	$ 728,468	$ (7,310)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	116,264	0	0	0	116,264	0
Foreign currency translation adjustment	5	0	0	0	0	(5)
Reclassification of net losses on derivative instruments	339	0	0	0	0	339
Postretirement medical liability adjustment	(474)	$ 0	$ 0	0	0	(474)
Stock based compensation, shares		87	16
Stock based compensation, value	5,146	$ 1	$ (911)	6,056	0	0
Issuance of shares		3,625
Issuance of shares, treasury stock			(21)
Issuance of shares, value	179,326	$ 36	$ 581	178,709	0	0
Dividends on common stock	$ (102,980)	$ 0	$ 0	0	(102,980)	0
Dividends per share	$ 1.89
Balance, shares at Sep. 30, 2022		61,318	3,541
Balance, end of period at Sep. 30, 2022	$ 2,537,329	$ 613	$ (98,578)	1,900,992	741,752	(7,450)
Balance, shares at Jun. 30, 2022		59,697	3,548
Balance, beginning of period at Jun. 30, 2022	2,464,520	$ 597	$ (98,765)	1,820,531	749,558	(7,401)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	27,368	0	0	0	27,368	0
Foreign currency translation adjustment	4	0	0	0	0	4
Reclassification of net losses on derivative instruments	113	0	0	0	0	113
Postretirement medical liability adjustment	(158)	$ 0	$ 0	0	0	(158)
Stock based compensation, shares		0	0
Stock based compensation, value	2,080	$ 0	$ 0	2,080	0	0
Issuance of shares		1,621
Issuance of shares, treasury stock			(7)
Stock Issued During Period, Value, Treasury Stock Reissued			$ 187
Issuance of shares, value	78,584	$ 16		78,381	0	0
Dividends on common stock	$ (35,174)	$ 0	$ 0	0	(35,174)	0
Dividends per share	$ 0.63
Balance, shares at Sep. 30, 2022		61,318	3,541
Balance, end of period at Sep. 30, 2022	$ 2,537,329	$ 613	$ (98,578)	1,900,992	741,752	(7,450)
Balance, shares at Dec. 31, 2022		63,278	3,534
Balance, beginning of period at Dec. 31, 2022	2,665,183	$ 633	$ (98,392)	1,999,376	771,414	(7,848)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	110,989	0	0	0	110,989	0
Foreign currency translation adjustment	10	0	0	0	0	10
Reclassification of net losses on derivative instruments	339	0	0	0	0	339
Postretirement medical liability adjustment	(502)	$ 0	$ 0	0	0	(502)
Stock based compensation, shares		51	0
Stock based compensation, value	4,911	$ 0	$ 0	4,911	0	0
Issuance of shares		1,433
Issuance of shares, treasury stock			(14)
Issuance of shares, value	74,552	$ 15	$ 270	74,267	0	0
Dividends on common stock	$ (115,048)	$ 0	$ 0	0	(115,048)	0
Dividends per share	$ 1.92
Balance, shares at Sep. 30, 2023		64,762	3,520
Balance, end of period at Sep. 30, 2023	$ 2,740,414	$ 648	$ (98,122)	2,078,554	767,355	(8,021)
Balance, shares at Jun. 30, 2023		63,518	3,527
Balance, beginning of period at Jun. 30, 2023	2,686,724	$ 635	$ (98,302)	2,015,367	776,983	(7,959)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	29,335	0	0	0	29,335	0
Foreign currency translation adjustment	7	0	0	0	0	7
Reclassification of net losses on derivative instruments	113	0	0	0	0	113
Postretirement medical liability adjustment	(168)	$ 0	$ 0	0	0	(168)
Stock based compensation, shares		0	0
Stock based compensation, value	239	$ 0	$ 0	239	0	0
Issuance of shares		1,244
Issuance of shares, treasury stock			(7)
Stock Issued During Period, Value, Treasury Stock Reissued			$ 180
Issuance of shares, value	63,141	$ 13		62,948	0	0
Dividends on common stock	$ (38,963)	$ 0	$ 0	0	(38,963)	0
Dividends per share	$ 0.640
Balance, shares at Sep. 30, 2023		64,762	3,520
Balance, end of period at Sep. 30, 2023	$ 2,740,414	$ 648	$ (98,122)	$ 2,078,554	$ 767,355	$ (8,021)

Nature of Operations and Basis

Nature of Operations and Basis of Consolidation	9 Months Ended
Nature of Operations and Basis of Consolidation	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure	Nature of Operations and Basis of Consolidation NorthWestern Energy Group, doing business as NorthWestern Energy, provides electricity and/or natural gas to approximately 764,200 customers in Montana, South Dakota, Nebraska and Yellowstone National Park. We have generated and distributed electricity in South Dakota and distributed natural gas in South Dakota and Nebraska since 1923 and have generated and distributed electricity and distributed natural gas in Montana since 2002. The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires us 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 our opinion, 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, 2023 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, we believe that the condensed disclosures provided are adequate to make the information presented not misleading. We recommend that these Financial Statements be read in conjunction with the audited financial statements and related footnotes included in the NorthWestern Corporation Annual Report on Form 10-K for the year ended December 31, 2022 . Holding Company Reorganization On October 2, 2023, NorthWestern Corporation and NorthWestern Energy Group completed the reorganization into a holding company structure. In this reorganization, shareholders of Northwestern Corporation (the predecessor publicly held parent company) became shareholders of Northwestern Energy Group, maintaining the same number of shares and ownership percentage as held in Northwestern Corporation immediately prior to the reorganization. Northwestern Corporation became a wholly-owned subsidiary of Northwestern Energy Group. The transaction was effected pursuant to a merger pursuant to Section 251(g) of the General Corporation Law of the State of Delaware, which provides for the formation of a holding company without a vote of the shareholders of the constituent corporation. Immediately after consummation of the reorganization, NorthWestern Energy Group had, on a consolidated basis, the same assets, businesses and operations as NorthWestern Corporation had immediately prior to the consummation of the reorganization. As a result of the reorganization, NorthWestern Energy Group became the successor issuer to NorthWestern Corporation pursuant to Rule 12g-3(a) of the Securities Exchange Act of 1934, and as a result, NorthWestern Energy Group's common stock was deemed registered under Section 12(b) of the Securities Exchange Act of 1934. In the early part of 2024, we intend to complete the second and final phase of the holding company reorganization which will result in the South Dakota and Nebraska regulated utilities business becoming a separate direct subsidiary of NorthWestern Energy Group. This is planned to be accomplished through Northwestern Corporation contributing the assets and liabilities of its South Dakota and Nebraska regulated utilities to its direct subsidiary, Northwestern Energy Public Service Corporation (NPS), and then distributing its equity interest in NPS and certain other subsidiaries to Northwestern Energy Group, resulting in Northwestern Corporation owning and operating only the Montana regulated utility and NPS owning and operating the Nebraska and South Dakota utilities, each as a direct subsidiary of Northwestern Energy Group. The accompanying consolidated financial statements represent the consolidated results of NorthWestern Corporation and all companies NorthWestern Corporation directly or indirectly controlled, either through majority ownership or otherwise as of September 30, 2023. 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, 2023 2022 2022 2021 Cash and cash equivalents $ 5,091 $ 8,489 $ 9,069 $ 2,820 Restricted cash 16,549 13,974 19,656 15,942 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 21,640 $ 22,463 $ 28,725 $ 18,762 Goodwill

Regulatory Matters

Regulatory Matters	9 Months Ended
Regulatory Matters	Sep. 30, 2023
Regulated Operations [Abstract]
Public Utilities Disclosure [Text Block]	Regulatory Matters Except as set forth below, the circumstances set forth in Note 3 - Regulatory Matters to the financial statements included in the NorthWestern Corporation Annual Report on the Form 10-K for the year ended December 31, 2022 appropriately represent, in all material respects, the current status of our regulatory matters. Montana Rate Review On August 8, 2022, we filed a Montana electric and natural gas rate review with the Montana Public Service Commission (MPSC) under Docket 2022.07.78 requesting an annual increase to electric and natural gas utility rates. On October 25, 2023, the MPSC held a work session and approved the settlement agreement filed April 3, 2023. We expect final rates, adjusting from interim to settled rates, to be effective November 1, 2023. The details of our settlement agreement are set forth below: Returns, Capital Structure & Revenue Increase Resulting From Approved Settlement Agreement ($ in millions) Electric Natural Gas Return on Equity (ROE) 9.65% 9.55% Equity Capital Structure 48.02% 48.02% Base Rates $67.4 $14.1 Power Cost & Credit Mechanism (PCCAM) (1) $69.7 n/a Property Tax (tracker base adjustment) (1) $14.5 $4.2 Total Revenue Increase Through Approved Settlement Agreement $151.6 $18.3 (1) These items are flow-through costs. PCCAM reflects our fuel and purchased power costs. The approved settlement includes, among other things, agreement on electric and natural gas base revenue increases, allocated cost of service, rate design, updates to the base amount of revenues associated with property taxes and electric supply costs, and regulatory policy issues related to requested changes in regulatory mechanisms. The approved settlement agreement provides for an update to the PCCAM by adjusting the base costs from $138.7 million to $208.4 million and providing for more timely quarterly recovery of deferred balances instead of annual recovery. It also addresses the potential for future recovery of certain operating costs associated with the Yellowstone County Generating Station and provides for the deferral of incremental operating costs related to our Enhanced Wildfire Mitigation Plan. The settling parties agreed to terminate the pilot decoupling program (Fixed Cost Recovery Mechanism) and that the proposed business technology rider will not be implemented. South Dakota Electric Rate Review On June 15, 2023, we filed a South Dakota electric rate review filing (2022 test year) under Docket EL23-016 for an annual increase to electric rates totaling approximately $30.9 million. Our request was based on a ROE of 10.7 percent, a capital structure including 50.5 percent equity, and rate base of $787.3 million .

Income Taxes

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2023
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, 2023 2022 Income before income taxes $ 31,032 $ 27,119 Income tax calculated at federal statutory rate 6,516 21.0 % 5,697 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 121 0.4 145 0.5 Flow-through repairs deductions (4,189) (13.5) (3,374) (12.4) Production tax credits (1,261) (4.1) (1,668) (6.2) Amortization of excess deferred income tax (323) (1.0) (246) (0.9) Income tax return to accrual adjustment 411 1.3 (926) (3.4) Plant and depreciation flow-through items 358 1.2 266 1.0 Other, net 64 0.2 (143) (0.5) (4,819) (15.5) (5,946) (21.9) Income tax expense (benefit) $ 1,697 5.5 % $ (249) (0.9) % Nine Months Ended September 30, 2023 2022 Income before income taxes $ 125,074 $ 118,561 Income tax calculated at federal statutory rate 26,265 21.0 % 24,897 21.0 % Permanent or flow through adjustments: State income, net of federal provisions 1,353 1.1 976 0.8 Flow-through repairs deductions (11,742) (9.4) (13,488) (11.4) Production tax credits (5,607) (4.5) (8,050) (6.8) Amortization of excess deferred income tax (1,355) (1.1) (819) (0.7) Reduction to previously claimed alternative minimum tax credit 3,186 2.5 — — Plant and depreciation flow through items 1,247 1.0 409 0.3 Income tax return to accrual adjustment 411 0.3 (926) (0.8) Share-based compensation 388 0.3 (253) (0.2) Other, net (61) 0.1 (449) (0.3) (12,180) (9.7) (22,600) (19.1) Income tax expense $ 14,085 11.3 % $ 2,297 1.9 % 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 had unrecognized tax benefits of approximately $29.1 million as of September 30, 2023, including approximately $27.8 million that, if recognized, would impact our effective tax rate. On April 14, 2023, the Internal Revenue Service (IRS) issued Revenue Procedure 2023-15, which provides a safe harbor method of accounting for gas repairs expenditures. We are currently evaluating the safe harbor and, if adopted, would decrease our total unrecognized tax benefits by $0.5 million and recognize an income tax benefit of approximately $3.2 million for previously unrecognized tax benefits in the fourth quarter of 2023. Inclusive of the safe harbor impacts, we anticipate that by the end of 2024, total unrecognized tax benefits will decrease by approximately $17.4 million and that we will recognize an income tax benefit of approximately $20.1 million. Our policy is to recognize interest and penalties related to uncertain tax positions in income tax expense. As of September 30, 2023, we have accrued $2.4 million for the payment of interest and penalties on the Condensed Consolidated Balance Sheets. As of December 31, 2022, we had accrued $1.4 million for the payment of interest and penalties on the Condensed Consolidated Balance Sheets. Tax years 2019 and forward remain subject to examination by the IRS and state taxing authorities. During the first quarter of 2023 the IRS commenced and concluded a limited scope examination of our 2019 amended federal income tax return. This examination resulted in a reduction to our previously claimed alternative minimum tax credit refund that is reflected in the table above.

Comprehensive Income (Loss)

Comprehensive Income (Loss)	9 Months Ended
Comprehensive Income (Loss)	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Comprehensive (Loss) Income The following tables display the components of Other Comprehensive (Loss) Income, after-tax, and the related tax effects (in thousands): Three Months Ended September 30, 2023 September 30, 2022 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (7) $ — $ (7) $ (4) $ — $ (4) Reclassification of net income on derivative instruments 153 (40) 113 153 (40) 113 Postretirement medical liability adjustment (212) 44 (168) (212) 54 (158) Other comprehensive (loss) income $ (66) $ 4 $ (62) $ (63) $ 14 $ (49) Nine Months Ended September 30, 2023 September 30, 2022 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (10) $ — $ (10) $ (5) $ — $ (5) Reclassification of net income on derivative instruments 459 (120) 339 459 (120) 339 Postretirement medical liability adjustment (636) 134 (502) (636) 162 (474) Other comprehensive (loss) income $ (187) $ 14 $ (173) $ (182) $ 42 $ (140) 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, 2023 December 31, 2022 Foreign currency translation $ 1,425 $ 1,435 Derivative instruments designated as cash flow hedges (9,486) (9,825) Postretirement medical plans 40 542 Accumulated other comprehensive loss $ (8,021) $ (7,848) The following tables display the changes in AOCL by component, net of tax (in thousands): Three Months Ended September 30, 2023 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (9,599) $ 208 $ 1,432 $ (7,959) Other comprehensive loss before reclassifications — — (7) (7) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (168) — (168) Net current-period other comprehensive income (loss) 113 (168) (7) (62) Ending balance $ (9,486) $ 40 $ 1,425 $ (8,021) Three Months Ended September 30, 2022 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (10,051) $ 1,208 $ 1,442 $ (7,401) Other comprehensive loss before reclassifications — — (4) (4) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (158) — (158) Net current-period other comprehensive income (loss) 113 (158) (4) (49) Ending balance $ (9,938) $ 1,050 $ 1,438 $ (7,450) Nine Months Ended September 30, 2023 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 $ (9,825) $ 542 $ 1,435 $ (7,848) Other comprehensive loss before reclassifications — — (10) (10) Amounts reclassified from AOCL Interest Expense 339 — — 339 Amounts reclassified from AOCL — (502) — (502) Net current-period other comprehensive income (loss) 339 (502) (10) (173) Ending balance $ (9,486) $ 40 $ 1,425 $ (8,021) Nine Months Ended September 30, 2022 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 $ (10,277) $ 1,524 $ 1,443 $ (7,310) Other comprehensive loss before reclassifications — — (5) (5) Amounts reclassified from AOCL Interest Expense 339 — — 339 Amounts reclassified from AOCL — (474) — (474) Net current-period other comprehensive income (loss) 339 (474) (5) (140) Ending balance $ (9,938) $ 1,050 $ 1,438 $ (7,450)

Financing Activities

Financing Activities	9 Months Ended
Financing Activities	Sep. 30, 2023
Financing Activities [Abstract]
Financing Activities	Financing Activities On March 30, 2023, we issued and sold $239.0 million aggregate principal amount of Montana First Mortgage Bonds at a fixed interest rate of 5.57 percent maturing on March 30, 2033. On this same day, we issued and sold $31.0 million aggregate principal amount of South Dakota First Mortgage Bonds at a fixed interest rate of 5.57 percent maturing on March 30, 2033. On May 1, 2023, we issued and sold an additional $30.0 million aggregate principal amount of South Dakota First Mortgage Bonds at a fixed interest rate of 5.42 percent maturing on May 1, 2033. These bonds were issued in transactions 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. Pursuant to the NorthWestern Corporation Equity Distribution Agreement we have offered and sold shares of our common stock through an At-the-Market (ATM) offering program. During the three months ended September 30, 2023, we issued 1,244,056 shares of common stock under the ATM program at an average price of $51.14 per share, for net proceeds of $62.8 million which is net of sales commissions and other fees paid of approximately $0.8 million. During the nine months ended September 30, 2023, we issued 1,432,738 shares of common stock under the ATM program at an average price of $52.02 per share, for net proceeds of $73.6 million which is net of sales commissions and other fees paid of approximately $0.9 million. As of September 30, 2023, we have completed the ATM offering program under this Equity Distribution Agreement.

Segment Information

Segment Information	9 Months Ended
Segment Information	Sep. 30, 2023
Segment Reporting [Abstract]
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 utility 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 us 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, 2023 Electric Gas Other Eliminations Total Operating revenues $ 280,030 $ 41,060 $ — $ — $ 321,090 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 77,995 10,948 — — 88,943 Utility margin 202,035 30,112 — — 232,147 Operating and maintenance 39,990 13,250 — — 53,240 Administrative and general 20,682 8,249 424 — 29,355 Property and other taxes 33,740 9,574 (1,551) — 41,763 Depreciation and depletion 43,230 8,929 — — 52,159 Operating income (loss) 64,393 (9,890) 1,127 — 55,630 Interest expense, net (21,300) (4,426) (2,999) — (28,725) Other income (expense), net 3,380 1,328 (581) — 4,127 Income tax (expense) benefit (3,223) (41) 1,567 — (1,697) Net income (loss) $ 43,250 $ (13,029) $ (886) $ — $ 29,335 Total assets $ 5,963,950 $ 1,454,445 $ 11,104 $ — $ 7,429,499 Capital expenditures $ 110,804 $ 46,359 $ — $ — $ 157,163 Three Months Ended September 30, 2022 Electric Gas Other Eliminations Total Operating revenues $ 292,270 $ 42,798 $ — $ — $ 335,068 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 95,553 13,367 — — 108,920 Utility margin 196,717 29,431 — — 226,148 Operating and maintenance 40,914 13,740 — — 54,654 Administrative and general 20,739 7,934 (527) — 28,146 Property and other taxes 36,353 10,110 3 — 46,466 Depreciation and depletion 40,647 7,941 — — 48,588 Operating income 58,064 (10,294) 524 — 48,294 Interest expense, net (18,225) (3,238) (3,869) — (25,332) Other income (expense), net 2,944 1,727 (514) — 4,157 Income tax (expense) benefit (1,006) 1,119 136 — 249 Net income (loss) $ 41,777 $ (10,686) $ (3,723) $ — $ 27,368 Total assets $ 5,741,879 $ 1,365,896 $ 6,438 $ — $ 7,114,213 Capital expenditures $ 122,522 $ 29,379 $ — $ — $ 151,901 Nine Months Ended September 30, 2023 Electric Gas Other Eliminations Total Operating revenues $ 804,604 $ 261,530 $ — $ — $ 1,066,134 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 198,492 123,521 — — 322,013 Utility margin 606,112 138,009 — — 744,121 Operating and maintenance 123,771 40,170 — — 163,941 Administrative and general 67,285 26,336 437 — 94,058 Property and other taxes 103,013 29,576 (1,546) — 131,043 Depreciation and depletion 130,447 27,340 — — 157,787 Operating income 181,596 14,587 1,109 — 197,292 Interest expense, net (61,584) (12,167) (11,393) — (85,144) Other income (expense), net 9,700 3,887 (661) — 12,926 Income tax expense (13,366) (180) (539) — (14,085) Net income (loss) $ 116,346 $ 6,127 $ (11,484) $ — $ 110,989 Total assets $ 5,963,950 $ 1,454,445 $ 11,104 $ — $ 7,429,499 Capital expenditures $ 326,313 $ 94,212 $ — $ — $ 420,525 Nine Months Ended September 30, 2022 Electric Gas Other Eliminations Total Operating revenues $ 807,415 $ 245,139 $ — $ — $ 1,052,554 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 230,872 108,122 — — 338,994 Utility margin 576,543 137,017 — — 713,560 Operating and maintenance 121,237 39,548 — — 160,785 Administrative and general 63,591 23,757 (338) — 87,010 Property and other taxes 109,204 30,998 7 — 140,209 Depreciation and depletion 121,256 24,449 — — 145,705 Operating income 161,255 18,265 331 — 179,851 Interest expense, net (56,031) (9,951) (7,099) — (73,081) Other income (expense), net 7,245 4,669 (123) — 11,791 Income tax (expense) benefit (2,790) (1,263) 1,756 — (2,297) Net income (loss) $ 109,679 $ 11,720 $ (5,135) $ — $ 116,264 Total assets $ 5,741,879 $ 1,365,896 $ 6,438 $ — $ 7,114,213 Capital expenditures $ 312,804 $ 73,535 $ — $ — $ 386,339

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
Revenue from Contracts with Customers	Sep. 30, 2023
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 largest customer class consists of residential customers, which includes 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, 2023 September 30, 2022 Electric Natural Gas Total Electric Natural Gas Total Montana $ 96.8 $ 9.6 $ 106.4 $ 85.2 $ 10.8 $ 96.0 South Dakota 18.0 2.0 20.0 19.0 2.4 21.4 Nebraska — 2.2 2.2 — 3.2 3.2 Residential 114.8 13.8 128.6 104.2 16.4 120.6 Montana 110.1 6.1 116.2 92.6 7.1 99.7 South Dakota 27.5 1.5 29.0 29.1 2.1 31.2 Nebraska — 1.3 1.3 — 2.3 2.3 Commercial 137.6 8.9 146.5 121.7 11.5 133.2 Industrial 11.4 0.1 11.5 9.7 0.1 9.8 Lighting, governmental, irrigation, and interdepartmental 13.2 0.2 13.4 12.6 0.2 12.8 Total Customer Revenues 277.0 23.0 300.0 248.2 28.2 276.4 Other tariff and contract based revenues 22.1 10.2 32.3 22.3 8.6 30.9 Total Revenue from Contracts with Customers 299.1 33.2 332.3 270.5 36.8 307.3 Regulatory amortization and other (19.1) 7.9 (11.2) 21.8 6.0 27.8 Total Revenues $ 280.0 $ 41.1 $ 321.1 $ 292.3 $ 42.8 $ 335.1 Nine Months Ended September 30, 2023 September 30, 2022 Electric Natural Gas Total Electric Natural Gas Total Montana $ 306.1 $ 94.1 $ 400.2 $ 252.9 $ 91.7 $ 344.6 South Dakota 53.4 30.3 83.7 55.0 31.7 86.7 Nebraska — 30.2 30.2 — 26.0 26.0 Residential 359.5 154.6 514.1 307.9 149.4 457.3 Montana 324.6 52.4 377.0 263.4 48.9 312.3 South Dakota 77.8 21.3 99.1 83.2 23.0 106.2 Nebraska — 19.1 19.1 — 16.0 16.0 Commercial 402.4 92.8 495.2 346.6 87.9 434.5 Industrial 34.0 1.0 35.0 28.4 0.9 29.3 Lighting, governmental, irrigation, and interdepartmental 27.2 1.3 28.5 25.4 1.4 26.8 Total Customer Revenues 823.1 249.7 1,072.8 708.3 239.6 947.9 Other tariff and contract based revenues 63.5 33.1 96.6 64.0 27.8 91.8 Total Revenue from Contracts with Customers 886.6 282.8 1,169.4 772.3 267.4 1,039.7 Regulatory amortization and other (82.0) (21.3) (103.3) 35.1 (22.2) 12.9 Total Revenues $ 804.6 $ 261.5 $ 1,066.1 $ 807.4 $ 245.2 $ 1,052.6

Earnings Per Share

Earnings Per Share	3 Months Ended
Earnings Per Share	Sep. 30, 2023
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 and forward equity sale. Average shares used in computing the basic and diluted earnings per share are as follows: Three Months Ended September 30, 2023 September 30, 2022 Basic computation 60,442,164 56,310,526 Dilutive effect of: Performance share awards (1) 35,533 14,306 Forward equity sale (2) — 312,572 Diluted computation 60,477,697 56,637,404 Nine Months Ended September 30, 2023 September 30, 2022 Basic computation 60,010,609 54,901,161 Dilutive effect of: Performance share awards (1) 31,311 20,150 Forward equity sale (2) — 619,361 Diluted computation 60,041,920 55,540,672 (1) Performance share awards are included in diluted weighted average number of shares outstanding based upon what would be issued if the end of the most recent reporting period was the end of the term of the award. (2) Forward equity shares are included in diluted weighted average number of shares outstanding based upon what would be issued if the end of the most recent reporting period was the end of the term of the forward sale agreement.

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
Employee Benefit Plans	Sep. 30, 2023
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, 2023 2022 2023 2022 Components of Net Periodic Benefit Cost (Credit) Service cost $ 1,459 $ 2,555 $ 84 $ 88 Interest cost 6,524 4,697 168 90 Expected return on plan assets (6,679) (6,043) (274) (262) Amortization of prior service credit — — 29 (472) Recognized actuarial (gain) loss 68 96 18 (13) Net periodic benefit cost (credit) $ 1,372 $ 1,305 $ 25 $ (569) Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Components of Net Periodic Benefit Cost (Credit) Service cost $ 4,375 $ 7,667 $ 250 $ 263 Interest cost 19,571 14,090 505 269 Expected return on plan assets (20,036) (18,129) (822) (785) Amortization of prior service credit — — 87 (1,418) Recognized actuarial loss (gain) 205 287 54 (37) Net periodic benefit cost (credit) $ 4,115 $ 3,915 $ 74 $ (1,708)

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies Except as set forth below and in Note 2 - Regulatory Matters above, the circumstances set forth in Note 18 - Commitments and Contingencies to the financial statements included in the NorthWestern Corporation Annual Report on Form 10-K for the year ended December 31, 2022 appropriately represent, in all material respects, the current status of our material commitments and contingent liabilities. 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 or for which we are responsible, is estimated to range between $20.4 million to $31.5 million. As of September 30, 2023, we had a reserve of approximately $25.2 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. 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 ) and methane emissions from natural gas. These actions include legislative proposals, Executive, Congressional and Environmental Protection Agency (EPA) actions at the federal level, state level activity, investor activism and private party litigation relating to emissions. Coal-fired plants have come under particular scrutiny due to their level of 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. Proposed EPA Rules - Congress has not passed any federal climate change legislation regarding GHG emissions from coal fired plants, and we cannot predict the timing or form of any potential legislation. Section 111(d) of the Clean Air Act (CAA) confers authority on EPA and the states to regulate emissions, including GHGs, from existing stationary sources. In May 2023, EPA proposed new GHG emissions standards for coal and natural gas-fired plants. In particular, the proposed rules would (i) strengthen the current New Source Performance Standards for newly built fossil fuel-fired stationary combustion turbines (generally natural gas-fired); (ii) establish emission guidelines for states to follow in limiting carbon pollution from existing fossil fuel-fired steam generating electric generating units (including coal, oil and natural gas-fired units); and (iii) establish emission guidelines for large, frequently used existing fossil fuel-fired stationary combustion turbines (generally natural gas-fired). In addition, in April 2023, EPA proposed to amend the Mercury Air Toxics Standard (MATS). Among other things, MATS currently sets stringent emission limits for acid gases, mercury, and other hazardous air pollutants from new and existing electric generating units. We are in compliance with existing MATS requirements. The proposed amendment of the MATS would strengthen the MATS requirements, and if adopted as written, both the GHG and MATS proposed rules could have a material negative impact on our coal-fired plants, including requiring potentially expensive upgrades or the early retirement of Colstrip Unit's 3 and 4 due to the rules making the facility uneconomic. Previous efforts by the EPA were met with extensive litigation and we anticipate a similar response if the proposed rules are adopted. As MATS and GHG regulations are implemented, it could result in additional material compliance costs. We will continue working with federal and state regulatory authorities, other utilities, and stakeholders to seek relief from any MATS or GHG regulations that, in our view, disproportionately impact customers in our region. Future additional environmental requirements - federal or state - 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 or hazardous air pollutants may not be available within a timeframe consistent with the implementation of any such requirements. LEGAL PROCEEDINGS 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 state and federal court, including before the United States Supreme Court, as detailed in Note 18 - Commitments and Contingencies to the financial statements included in the NorthWestern Corporation Annual Report on Form 10-K for the year ended December 31, 2022 . 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). On August 1, 2018, the Federal District Court granted our and Talen’s motions to dismiss the State’s Complaint as it pertains to the navigability of the riverbeds associated with four of our hydroelectric facilities near Great Falls. A bench trial before the Federal District Court commenced January 4, 2022, and concluded on January 18, 2022, which addressed the issue of navigability concerning our other six facilities. On August 25, 2023, the Federal District Court issued its Findings of Fact, Conclusions of Law and Order (the "Order"), which found all but one of the segments of the riverbeds in dispute not navigable, and thus not owned by the State of Montana. The one segment found navigable, and thus owned by the State, was the segment on which the Black Eagle development was located. The State has filed a motion to pursue an interlocutory appeal of the Order. Damages were bifurcated by agreement and will be tried separately for the Black Eagle segment, and any other segments navigable should an appeal be granted and other segments found navigable. We dispute the State’s claims and intend to continue to vigorously defend the lawsuit. If the Federal District Court calculates damages as the State District Court did in 2008, we do not anticipate the resulting annual rent for the Black Eagle segment would have a material impact to our financial position or results of operations. 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. Colstrip Arbitration The remaining depreciable life of our investment in Colstrip Unit 4 is through 2042. The six owners of Colstrip Units 3 and 4 currently share the operating costs pursuant to the terms of an Ownership and Operation Agreement (O&O Agreement). However, several of the owners are mandated by Washington and Oregon law to eliminate coal-fired resources in 2025 and 2029, respectively. As a result of the mandate, the owners have disagreed on various operational funding decisions, including whether closure requires each owner’s consent under the O&O Agreement. On March 12, 2021, we initiated an arbitration under the O&O Agreement (the “Arbitration”), to resolve the issues of whether closure requires each owner's consent and to clarify each owner's obligations to continue to fund operations until all joint owners agree on closure. The owners previously initiated efforts to identify arbitrators and have agreed to stay the Arbitration through January 12, 2024, while they explore a potential resolution to their disagreements. Colstrip Coal Dust Litigation On December 14, 2020, a claim was filed against Talen in the Montana Sixteenth Judicial District Court, Rosebud County, Cause No. CV-20-58. Talen is one of the co-owners of Colstrip Unit 3, and the operator of Units 3 and 4. The plaintiffs allege they have suffered adverse effects from coal dust generated during operations associated with Colstrip. On August 26, 2021, the claim was amended to add in excess of 100 plaintiffs. It also added NorthWestern, the other owners of Colstrip, and Westmoreland Rosebud Mining LLC, as defendants. Plaintiffs are seeking economic damages, costs and disbursements, punitive damages, attorneys’ fees, and an injunction prohibiting defendants from allowing coal dust to blow onto plaintiffs’ properties. Since this lawsuit remains in its discovery stages, we are unable to predict outcomes or estimate a range of reasonably possible losses. BNSF Demands for Indemnity and Remediation Costs NorthWestern has received a demand for indemnity from BNSF Railway Company (BNSF) for past and future environmental investigation and remediation costs incurred by BNSF at one of the three operable units at the Anaconda Copper Mining (ACM) Smelter and Refinery Superfund Site, located near Great Falls, Montana. Smelter and refining operations at the site commenced in 1893 and continued until 1980. According to EPA, the smelter and refining operations have contaminated soil, groundwater and surface water resources around the site with lead, arsenic and other metal wastes. ARCO (Atlantic Richfield Company) initiated reclamation and maintenance activities in the 1980s and 1990s. Between 2002 and 2008, the EPA conducted several site investigations. In March 2011, the EPA placed the ACM Smelter and Refinery Site on the Superfund program’s National Priority List. The Superfund Site is 427 acres and contains three operable units: Operable Unit 1 (consisting of five subsections including the Railroad Corridor and four other “areas of interest”), Operable Unit 2 (the former smelter and refinery site), and Operable Unit 3 (the Missouri River that flows along the south sides of Operable Units 1 and 2). NorthWestern owns property in the Railroad Corridor sub-section of Operable Unit 1. BNSF claims it is entitled to indemnity and contribution from NorthWestern for the costs it has and will incur to investigate and remediate contamination in Operable Unit 1. BNSF reports it has incurred in excess of $4.4 million, pending final resolution, of response and oversight costs incurred by government agencies (EPA and Montana DEQ), in investigative and other response costs associated with Operable Unit 1, and that in the future it will incur additional costs to implement the final remedy for Operable Unit 1. In the Record of Decision (ROD) for Operable Unit 1 issued on August 21, 2021, the EPA estimated the costs to implement the selected remedies for the Railroad Corridor will be approximately $4.1 million. In the ROD, the EPA also estimated the costs to implement the selected remedy (including institutional controls) for the four “areas of interest” in Operable Unit 1 would be approximately $1.8 million, with annual operating costs of ten thousand dollars. We are evaluating BNSF’s claim and are unable at this time to predict outcomes or estimate a range of reasonably possible losses. Yellowstone County Generating Station Air Permit On October 21, 2021, the Montana Environmental Information Center (MEIC) and the Sierra Club filed a lawsuit in Montana State District Court, against the Montana Department of Environmental Quality (MDEQ) and NorthWestern, alleging that the environmental analysis conducted by MDEQ prior to issuance of the Yellowstone County Generating Station's air quality construction permit was inadequate. On April 4, 2023, the Montana District Court issued an order finding MDEQ's environmental analysis was deficient in not addressing exterior lighting and greenhouse gases and remanded it back to MDEQ to address the deficiencies and vacated the air quality permit pending that remand. As a result of the vacatur of the permit, we paused construction. On June 8, 2023, the Montana District Court granted our motion to stay the order vacating the air quality permit pending the outcome of our notice of appeal with the Montana Supreme Court. We recommenced construction in June 2023 and expect the plant to be operational by the end of the third quarter 2024. On May 10, 2023, Montana House Bill 971 was signed into law, preventing the MDEQ from, except under certain exceptions, evaluating greenhouse gas emissions and corresponding impacts to the climate in environmental reviews of large projects such as coal mines and power plants. On June 1, 2023, the MDEQ issued its supplemental environmental assessment that contained the updated exterior lighting analysis, and the MDEQ indicated that no other analysis was necessary. The comment period concerning the MDEQ’s supplemental air quality permit ended on July 3, 2023. On August 4, 2023, the Montana First Judicial District Court in Held v. State of Montana, issued its order finding House Bill 971 unconstitutional. The Held case has delayed MDEQ's issuance of an updated air quality permit. The lawsuit challenging the Yellowstone County Generating Station air quality permit, as well as additional related legal challenges and construction challenges, could delay the project timing and increase costs. 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 our opinion, the amount of ultimate liability with respect to these other actions will not materially affect our financial position, results of operations, or cash flows.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net Income	$ 29,335	$ 27,368	$ 110,989	$ 116,264

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Sep. 30, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Organization, Consolidation and

Organization, Consolidation and Presentation of Financial Statements (Tables)	9 Months Ended
	Sep. 30, 2023
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, 2023 2022 2022 2021 Cash and cash equivalents $ 5,091 $ 8,489 $ 9,069 $ 2,820 Restricted cash 16,549 13,974 19,656 15,942 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 21,640 $ 22,463 $ 28,725 $ 18,762

Regulated Operations (Tables)

Regulated Operations (Tables)	9 Months Ended
Regulated Operations (Tables)	Sep. 30, 2023
Regulated Operations [Abstract]
Montana Rate Review	On August 8, 2022, we filed a Montana electric and natural gas rate review with the Montana Public Service Commission (MPSC) under Docket 2022.07.78 requesting an annual increase to electric and natural gas utility rates. On October 25, 2023, the MPSC held a work session and approved the settlement agreement filed April 3, 2023. We expect final rates, adjusting from interim to settled rates, to be effective November 1, 2023. The details of our settlement agreement are set forth below: Returns, Capital Structure & Revenue Increase Resulting From Approved Settlement Agreement ($ in millions) Electric Natural Gas Return on Equity (ROE) 9.65% 9.55% Equity Capital Structure 48.02% 48.02% Base Rates $67.4 $14.1 Power Cost & Credit Mechanism (PCCAM) (1) $69.7 n/a Property Tax (tracker base adjustment) (1) $14.5 $4.2 Total Revenue Increase Through Approved Settlement Agreement $151.6 $18.3 (1) These items are flow-through costs. PCCAM reflects our fuel and purchased power costs.

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
Income Taxes (Tables)	Sep. 30, 2023
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, 2023 2022 Income before income taxes $ 31,032 $ 27,119 Income tax calculated at federal statutory rate 6,516 21.0 % 5,697 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 121 0.4 145 0.5 Flow-through repairs deductions (4,189) (13.5) (3,374) (12.4) Production tax credits (1,261) (4.1) (1,668) (6.2) Amortization of excess deferred income tax (323) (1.0) (246) (0.9) Income tax return to accrual adjustment 411 1.3 (926) (3.4) Plant and depreciation flow-through items 358 1.2 266 1.0 Other, net 64 0.2 (143) (0.5) (4,819) (15.5) (5,946) (21.9) Income tax expense (benefit) $ 1,697 5.5 % $ (249) (0.9) % Nine Months Ended September 30, 2023 2022 Income before income taxes $ 125,074 $ 118,561 Income tax calculated at federal statutory rate 26,265 21.0 % 24,897 21.0 % Permanent or flow through adjustments: State income, net of federal provisions 1,353 1.1 976 0.8 Flow-through repairs deductions (11,742) (9.4) (13,488) (11.4) Production tax credits (5,607) (4.5) (8,050) (6.8) Amortization of excess deferred income tax (1,355) (1.1) (819) (0.7) Reduction to previously claimed alternative minimum tax credit 3,186 2.5 — — Plant and depreciation flow through items 1,247 1.0 409 0.3 Income tax return to accrual adjustment 411 0.3 (926) (0.8) Share-based compensation 388 0.3 (253) (0.2) Other, net (61) 0.1 (449) (0.3) (12,180) (9.7) (22,600) (19.1) Income tax expense $ 14,085 11.3 % $ 2,297 1.9 %

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Income) Loss (Tables)	9 Months Ended
Accumulated Other Comprehensive (Income) Loss (Tables)	Sep. 30, 2023
Statement of Financial Position [Abstract]
Comprehensive Income (Loss) [Table Text Block]	The following tables display the components of Other Comprehensive (Loss) Income, after-tax, and the related tax effects (in thousands): Three Months Ended September 30, 2023 September 30, 2022 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (7) $ — $ (7) $ (4) $ — $ (4) Reclassification of net income on derivative instruments 153 (40) 113 153 (40) 113 Postretirement medical liability adjustment (212) 44 (168) (212) 54 (158) Other comprehensive (loss) income $ (66) $ 4 $ (62) $ (63) $ 14 $ (49) Nine Months Ended September 30, 2023 September 30, 2022 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (10) $ — $ (10) $ (5) $ — $ (5) Reclassification of net income on derivative instruments 459 (120) 339 459 (120) 339 Postretirement medical liability adjustment (636) 134 (502) (636) 162 (474) Other comprehensive (loss) income $ (187) $ 14 $ (173) $ (182) $ 42 $ (140)
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, 2023 December 31, 2022 Foreign currency translation $ 1,425 $ 1,435 Derivative instruments designated as cash flow hedges (9,486) (9,825) Postretirement medical plans 40 542 Accumulated other comprehensive loss $ (8,021) $ (7,848)
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, 2023 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (9,599) $ 208 $ 1,432 $ (7,959) Other comprehensive loss before reclassifications — — (7) (7) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (168) — (168) Net current-period other comprehensive income (loss) 113 (168) (7) (62) Ending balance $ (9,486) $ 40 $ 1,425 $ (8,021) Three Months Ended September 30, 2022 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (10,051) $ 1,208 $ 1,442 $ (7,401) Other comprehensive loss before reclassifications — — (4) (4) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (158) — (158) Net current-period other comprehensive income (loss) 113 (158) (4) (49) Ending balance $ (9,938) $ 1,050 $ 1,438 $ (7,450) Nine Months Ended September 30, 2023 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 $ (9,825) $ 542 $ 1,435 $ (7,848) Other comprehensive loss before reclassifications — — (10) (10) Amounts reclassified from AOCL Interest Expense 339 — — 339 Amounts reclassified from AOCL — (502) — (502) Net current-period other comprehensive income (loss) 339 (502) (10) (173) Ending balance $ (9,486) $ 40 $ 1,425 $ (8,021) Nine Months Ended September 30, 2022 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 $ (10,277) $ 1,524 $ 1,443 $ (7,310) Other comprehensive loss before reclassifications — — (5) (5) Amounts reclassified from AOCL Interest Expense 339 — — 339 Amounts reclassified from AOCL — (474) — (474) Net current-period other comprehensive income (loss) 339 (474) (5) (140) Ending balance $ (9,938) $ 1,050 $ 1,438 $ (7,450)

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
Segment Information (Tables)	Sep. 30, 2023
Segment Reporting [Abstract]
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, 2023 Electric Gas Other Eliminations Total Operating revenues $ 280,030 $ 41,060 $ — $ — $ 321,090 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 77,995 10,948 — — 88,943 Utility margin 202,035 30,112 — — 232,147 Operating and maintenance 39,990 13,250 — — 53,240 Administrative and general 20,682 8,249 424 — 29,355 Property and other taxes 33,740 9,574 (1,551) — 41,763 Depreciation and depletion 43,230 8,929 — — 52,159 Operating income (loss) 64,393 (9,890) 1,127 — 55,630 Interest expense, net (21,300) (4,426) (2,999) — (28,725) Other income (expense), net 3,380 1,328 (581) — 4,127 Income tax (expense) benefit (3,223) (41) 1,567 — (1,697) Net income (loss) $ 43,250 $ (13,029) $ (886) $ — $ 29,335 Total assets $ 5,963,950 $ 1,454,445 $ 11,104 $ — $ 7,429,499 Capital expenditures $ 110,804 $ 46,359 $ — $ — $ 157,163 Three Months Ended September 30, 2022 Electric Gas Other Eliminations Total Operating revenues $ 292,270 $ 42,798 $ — $ — $ 335,068 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 95,553 13,367 — — 108,920 Utility margin 196,717 29,431 — — 226,148 Operating and maintenance 40,914 13,740 — — 54,654 Administrative and general 20,739 7,934 (527) — 28,146 Property and other taxes 36,353 10,110 3 — 46,466 Depreciation and depletion 40,647 7,941 — — 48,588 Operating income 58,064 (10,294) 524 — 48,294 Interest expense, net (18,225) (3,238) (3,869) — (25,332) Other income (expense), net 2,944 1,727 (514) — 4,157 Income tax (expense) benefit (1,006) 1,119 136 — 249 Net income (loss) $ 41,777 $ (10,686) $ (3,723) $ — $ 27,368 Total assets $ 5,741,879 $ 1,365,896 $ 6,438 $ — $ 7,114,213 Capital expenditures $ 122,522 $ 29,379 $ — $ — $ 151,901 Nine Months Ended September 30, 2023 Electric Gas Other Eliminations Total Operating revenues $ 804,604 $ 261,530 $ — $ — $ 1,066,134 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 198,492 123,521 — — 322,013 Utility margin 606,112 138,009 — — 744,121 Operating and maintenance 123,771 40,170 — — 163,941 Administrative and general 67,285 26,336 437 — 94,058 Property and other taxes 103,013 29,576 (1,546) — 131,043 Depreciation and depletion 130,447 27,340 — — 157,787 Operating income 181,596 14,587 1,109 — 197,292 Interest expense, net (61,584) (12,167) (11,393) — (85,144) Other income (expense), net 9,700 3,887 (661) — 12,926 Income tax expense (13,366) (180) (539) — (14,085) Net income (loss) $ 116,346 $ 6,127 $ (11,484) $ — $ 110,989 Total assets $ 5,963,950 $ 1,454,445 $ 11,104 $ — $ 7,429,499 Capital expenditures $ 326,313 $ 94,212 $ — $ — $ 420,525 Nine Months Ended September 30, 2022 Electric Gas Other Eliminations Total Operating revenues $ 807,415 $ 245,139 $ — $ — $ 1,052,554 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 230,872 108,122 — — 338,994 Utility margin 576,543 137,017 — — 713,560 Operating and maintenance 121,237 39,548 — — 160,785 Administrative and general 63,591 23,757 (338) — 87,010 Property and other taxes 109,204 30,998 7 — 140,209 Depreciation and depletion 121,256 24,449 — — 145,705 Operating income 161,255 18,265 331 — 179,851 Interest expense, net (56,031) (9,951) (7,099) — (73,081) Other income (expense), net 7,245 4,669 (123) — 11,791 Income tax (expense) benefit (2,790) (1,263) 1,756 — (2,297) Net income (loss) $ 109,679 $ 11,720 $ (5,135) $ — $ 116,264 Total assets $ 5,741,879 $ 1,365,896 $ 6,438 $ — $ 7,114,213 Capital expenditures $ 312,804 $ 73,535 $ — $ — $ 386,339

Revenue from Contracts with C_2

Revenue from Contracts with Customers Disaggregation of Revenue (Tables)	9 Months Ended
	Sep. 30, 2023
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, 2023 September 30, 2022 Electric Natural Gas Total Electric Natural Gas Total Montana $ 96.8 $ 9.6 $ 106.4 $ 85.2 $ 10.8 $ 96.0 South Dakota 18.0 2.0 20.0 19.0 2.4 21.4 Nebraska — 2.2 2.2 — 3.2 3.2 Residential 114.8 13.8 128.6 104.2 16.4 120.6 Montana 110.1 6.1 116.2 92.6 7.1 99.7 South Dakota 27.5 1.5 29.0 29.1 2.1 31.2 Nebraska — 1.3 1.3 — 2.3 2.3 Commercial 137.6 8.9 146.5 121.7 11.5 133.2 Industrial 11.4 0.1 11.5 9.7 0.1 9.8 Lighting, governmental, irrigation, and interdepartmental 13.2 0.2 13.4 12.6 0.2 12.8 Total Customer Revenues 277.0 23.0 300.0 248.2 28.2 276.4 Other tariff and contract based revenues 22.1 10.2 32.3 22.3 8.6 30.9 Total Revenue from Contracts with Customers 299.1 33.2 332.3 270.5 36.8 307.3 Regulatory amortization and other (19.1) 7.9 (11.2) 21.8 6.0 27.8 Total Revenues $ 280.0 $ 41.1 $ 321.1 $ 292.3 $ 42.8 $ 335.1 Nine Months Ended September 30, 2023 September 30, 2022 Electric Natural Gas Total Electric Natural Gas Total Montana $ 306.1 $ 94.1 $ 400.2 $ 252.9 $ 91.7 $ 344.6 South Dakota 53.4 30.3 83.7 55.0 31.7 86.7 Nebraska — 30.2 30.2 — 26.0 26.0 Residential 359.5 154.6 514.1 307.9 149.4 457.3 Montana 324.6 52.4 377.0 263.4 48.9 312.3 South Dakota 77.8 21.3 99.1 83.2 23.0 106.2 Nebraska — 19.1 19.1 — 16.0 16.0 Commercial 402.4 92.8 495.2 346.6 87.9 434.5 Industrial 34.0 1.0 35.0 28.4 0.9 29.3 Lighting, governmental, irrigation, and interdepartmental 27.2 1.3 28.5 25.4 1.4 26.8 Total Customer Revenues 823.1 249.7 1,072.8 708.3 239.6 947.9 Other tariff and contract based revenues 63.5 33.1 96.6 64.0 27.8 91.8 Total Revenue from Contracts with Customers 886.6 282.8 1,169.4 772.3 267.4 1,039.7 Regulatory amortization and other (82.0) (21.3) (103.3) 35.1 (22.2) 12.9 Total Revenues $ 804.6 $ 261.5 $ 1,066.1 $ 807.4 $ 245.2 $ 1,052.6

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
Earnings Per Share (Tables)	Sep. 30, 2023
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, 2023 September 30, 2022 Basic computation 60,442,164 56,310,526 Dilutive effect of: Performance share awards (1) 35,533 14,306 Forward equity sale (2) — 312,572 Diluted computation 60,477,697 56,637,404 Nine Months Ended September 30, 2023 September 30, 2022 Basic computation 60,010,609 54,901,161 Dilutive effect of: Performance share awards (1) 31,311 20,150 Forward equity sale (2) — 619,361 Diluted computation 60,041,920 55,540,672 (1) Performance share awards are included in diluted weighted average number of shares outstanding based upon what would be issued if the end of the most recent reporting period was the end of the term of the award. (2) Forward equity shares are included in diluted weighted average number of shares outstanding based upon what would be issued if the end of the most recent reporting period was the end of the term of the forward sale agreement.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	9 Months Ended
Employee Benefit Plans (Tables)	Sep. 30, 2023
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, 2023 2022 2023 2022 Components of Net Periodic Benefit Cost (Credit) Service cost $ 1,459 $ 2,555 $ 84 $ 88 Interest cost 6,524 4,697 168 90 Expected return on plan assets (6,679) (6,043) (274) (262) Amortization of prior service credit — — 29 (472) Recognized actuarial (gain) loss 68 96 18 (13) Net periodic benefit cost (credit) $ 1,372 $ 1,305 $ 25 $ (569) Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Components of Net Periodic Benefit Cost (Credit) Service cost $ 4,375 $ 7,667 $ 250 $ 263 Interest cost 19,571 14,090 505 269 Expected return on plan assets (20,036) (18,129) (822) (785) Amortization of prior service credit — — 87 (1,418) Recognized actuarial loss (gain) 205 287 54 (37) Net periodic benefit cost (credit) $ 4,115 $ 3,915 $ 74 $ (1,708)

Nature of Operations and Basi_2

Nature of Operations and Basis of Consolidation (Details)	Dec. 31, 2022 customers
Number of customers	764,200

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, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Cash, Cash Equivalents, and Restricted Cash [Abstract]
Cash and cash equivalents	$ 5,091	$ 8,489	$ 9,069	$ 2,820
Restricted cash	16,549	13,974	19,656	15,942
Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows	$ 21,640	$ 22,463	$ 28,725	$ 18,762

Regulatory Matters (Details)

Regulatory Matters (Details) $ in Millions	9 Months Ended
Regulatory Matters (Details) $ in Millions	Sep. 30, 2023 USD ($) Rate
Montana \| Electricity, US Regulated
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	9.65%
Public Utilities, Approved Equity Capital Structure, Percentage \| Rate	48.02%
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 151.6
PCCAM base cost amount	138.7
Public Utilities, PCCAM base costs approved through settlement agreement	208.4
Montana \| Electricity, US Regulated \| Base electric rate
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	67.4
Montana \| Electricity, US Regulated \| PCCAM base amount
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	69.7
Montana \| Electricity, US Regulated \| Electric property tax tracker true-up
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 14.5
Montana \| Natural Gas, US Regulated
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	9.55%
Public Utilities, Approved Equity Capital Structure, Percentage \| Rate	48.02%
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 18.3
Montana \| Natural Gas, US Regulated \| Base gas rate
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	14.1
Montana \| Natural Gas, US Regulated \| Gas property tax tracker true-up
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	4.2
South Dakota
Public Utilities, General Disclosures [Line Items]
Rate base	$ 787.3
South Dakota \| Electricity, US Regulated
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage	10.70%
Public Utilities, Requested Equity Capital Structure, Percentage \| Rate	50.50%
South Dakota \| Electricity, US Regulated \| Base electric rate
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease), amount	$ 30.9

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	9 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Income Tax Contingency [Line Items]
Unrecognized tax benefit more likely than not percentage threshold	50%
Unrecognized tax benefits	$ 29.1
Unrecognized tax benefits that would impact effective tax rate	27.8
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	2.4	$ 1.4
Decrease in Unrecognized Tax Benefits is Reasonably Possible	17.4
Income Tax Benefit From Decrease in Unrecognized Tax Benefits Reasonably Possible by 2024	20.1
IRS Revenue Procedure 2023-15 - safe harbor method of accounting for gas repairs expenditures
Income Tax Contingency [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	0.5
Income Tax Benefit From Decrease in Unrecognized Tax Benefits Reasonably Possible by Fourth Quarter 2023	$ 3.2
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2019

Income Taxes Effective Tax Rate

Income Taxes Effective Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Effective tax rate reconciliation
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	$ 31,032	$ 27,119	$ 125,074	$ 118,561
Income tax calculated at federal statutory rate	6,516	5,697	26,265	24,897
State income tax, net of federal provisions	121	145	1,353	976
Flow-through repairs deductions	(4,189)	(3,374)	(11,742)	(13,488)
Production tax credits	(1,261)	(1,668)	(5,607)	(8,050)
Amortization of excess deferred income tax	(323)	(246)	(1,355)	(819)
Reduction to previously claimed alternative minimum tax credit			3,186	0
Plant and depreciation flow-through items	358	266	1,247	409
Income tax return to accrual adjustment	411	(926)	411	(926)
Share-based compensation			388	(253)
Other, net	64	(143)	(61)	(449)
Total Other Reconciling Items	(4,819)	(5,946)	(12,180)	(22,600)
Income tax expense	$ 1,697	$ (249)	$ 14,085	$ 2,297
Income tax calculated at federal statutory rate	21%	21%	21%	21%
State income tax, net of federal provisions	0.40%	0.50%	1.10%	0.80%
Flow-through repairs deductions	(13.50%)	(12.40%)	(9.40%)	(11.40%)
Production tax credits	(4.10%)	(6.20%)	(4.50%)	(6.80%)
Amortization of excess deferred income tax	(1.00%)	(0.90%)	(1.10%)	(0.70%)
Reduction to previously claimed alternative minimum tax credit			2.50%	0%
Plant and depreciation flow-through items	1.20%	1%	1%	0.30%
Income tax return to accrual adjustment	1.30%	(3.40%)	0.30%	(0.80%)
Share-based compensation			0.30%	(0.20%)
Other, net	0.20%	(0.50%)	0.10%	(0.30%)
Total Other Reconciling Items	(15.50%)	(21.90%)	(9.70%)	(19.10%)
Income tax expense	5.50%	(0.90%)	11.30%	1.90%
Income Tax Benefit From Decrease in Unrecognized Tax Benefits Reasonably Possible by 2024	$ 20,100		$ 20,100

Comprehensive Income (Loss) (De

Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Other Comprehensive Income (Loss), before Tax [Abstract]
Foreign currency translation adjustment	$ (7)	$ (4)	$ (10)	$ (5)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(153)	(153)	(459)	(459)
Postretirement medical liability adjustment	(212)	(212)	(636)	(636)
Other Comprehensive Income (Loss), before Tax	(66)	(63)	(187)	(182)
Other Comprehensive Income (Loss), Tax [Abstract]
Foreign currency translation adjustment	0	0	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	(40)	(40)	(120)	(120)
Postretirement medical liability adjustment	44	54	134	162
Other Comprehensive Income (Loss), Tax	4	14	14	42
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	(7)	(4)	(10)	(5)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(113)	(113)	(339)	(339)
Postretirement medical liability adjustment	(168)	(158)	(502)	(474)
Total Other Comprehensive Loss	$ (62)	$ (49)	$ (173)	$ (140)

Classification within AOCL on t

Classification within AOCL on the Condenced Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Foreign currency translation	$ 1,425		$ 1,435
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(9,486)		(9,825)
Postretirement medical plans	40		542
Accumulated other comprehensive loss	$ (8,021)	$ (7,959)	$ (7,848)	$ (7,450)	$ (7,401)	$ (7,310)

Changes in AOCI by Component (D

Changes in AOCI by Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (7,959)	$ (7,401)	$ (7,848)	$ (7,310)
Other comprehensive loss before reclassifications	(7)	(4)	(10)	(5)
Amounts reclassified from AOCL	113	113	339	339
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(168)	(158)	(502)	(474)
Total Other Comprehensive Loss	(62)	(49)	(173)	(140)
Ending balance	(8,021)	(7,450)	(8,021)	(7,450)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(9,599)	(10,051)	(9,825)	(10,277)
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from AOCL	113	113	339
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0			0
Total Other Comprehensive Loss	113	113	339	339
Ending balance	(9,486)	(9,938)	(9,486)	(9,938)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,432	1,442	1,435	1,443
Other comprehensive loss before reclassifications	(7)	(4)	(10)	(5)
Amounts reclassified from AOCL	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	0	0
Total Other Comprehensive Loss	(7)	(4)	(10)	(5)
Ending balance	1,425	1,438	1,425	1,438
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	208	1,208	542	1,524
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from AOCL	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(168)	(158)	(502)	(474)
Total Other Comprehensive Loss	(168)	(158)	(502)	(474)
Ending balance	$ 40	$ 1,050	$ 40	$ 1,050

Financing Activities (Details)

Financing Activities (Details) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares
Equity Distribution Agreement
Debt Instrument [Line Items]
Issuance of shares \| shares	1,244,056	1,432,738
Common Stock Average Price \| $ / shares	$ 51.14	$ 52.02
Stock Issued, Value, Net of Fees	$ 62.8	$ 73.6
Investment Banking, Advisory, Brokerage, and Underwriting Fees and Commissions	0.8	0.9
Montana First Mortgage Bonds Due 2033
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 239	$ 239
Debt Instrument, Interest Rate, Stated Percentage	5.57%	5.57%
Long-term Debt, Maturity Date	Mar. 30, 2033	Mar. 30, 2033
South Dakota First Mortgage Bonds Due 2033
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 31	$ 31
Debt Instrument, Interest Rate, Stated Percentage	5.57%	5.57%
Long-term Debt, Maturity Date	Mar. 30, 2033	Mar. 30, 2033
South Dakota First Mortgage Bonds Due 2033, To Be Issued May 2023
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 30	$ 30
Montana First Mortgage Bonds Due May 1, 2033
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.42%	5.42%
Long-term Debt, Maturity Date	May 01, 2033	May 01, 2033
Secured Debt Montana 2.00% Due 2023
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 144.7	$ 144.7
Debt Instrument, Interest Rate, Stated Percentage	3.88%	3.88%
Long-term Debt, Maturity Date	Jul. 01, 2028	Jul. 01, 2028
Secured Debt Montana 2.00% Due 2023
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 144.7	$ 144.7
Debt Instrument, Interest Rate, Stated Percentage	2%	2%

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Segment Information (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Operating revenues	$ 321,090	$ 335,068	$ 1,066,134	$ 1,052,554
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	88,943	108,920	322,013	338,994
Utility margin	232,147	226,148	744,121	713,560
Operating and maintenance	53,240	54,654	163,941	160,785
Administrative and general	29,355	28,146	94,058	87,010
Property and other taxes	41,763	46,466	131,043	140,209
Depreciation and depletion	52,159	48,588	157,787	145,705
Operating income (loss)	55,630	48,294	197,292	179,851
Interest expense, net	(28,725)	(25,332)	(85,144)	(73,081)
Other income (expense), net	4,127	4,157	12,926	11,791
Income tax (expense) benefit	1,697	(249)	14,085	2,297
Net Income	29,335	27,368	110,989	116,264
Total assets	7,429,499	7,114,213	7,429,499	7,114,213	$ 7,317,783
Capital expenditures	157,163	151,901	420,525	386,339
Operating Segments \| Electricity, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	280,030	292,270	804,604	807,415
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	77,995	95,553	198,492	230,872
Utility margin	202,035	196,717	606,112	576,543
Operating and maintenance	39,990	40,914	123,771	121,237
Administrative and general	20,682	20,739	67,285	63,591
Property and other taxes	33,740	36,353	103,013	109,204
Depreciation and depletion	43,230	40,647	130,447	121,256
Operating income (loss)	64,393	58,064	181,596	161,255
Interest expense, net	(21,300)	(18,225)	(61,584)	(56,031)
Other income (expense), net	3,380	2,944	9,700	7,245
Income tax (expense) benefit	3,223	1,006	13,366	2,790
Net Income	43,250	41,777	116,346	109,679
Total assets	5,963,950	5,741,879	5,963,950	5,741,879
Capital expenditures	110,804	122,522	326,313	312,804
Operating Segments \| Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	41,060	42,798	261,530	245,139
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	10,948	13,367	123,521	108,122
Utility margin	30,112	29,431	138,009	137,017
Operating and maintenance	13,250	13,740	40,170	39,548
Administrative and general	8,249	7,934	26,336	23,757
Property and other taxes	9,574	10,110	29,576	30,998
Depreciation and depletion	8,929	7,941	27,340	24,449
Operating income (loss)	(9,890)	(10,294)	14,587	18,265
Interest expense, net	(4,426)	(3,238)	(12,167)	(9,951)
Other income (expense), net	1,328	1,727	3,887	4,669
Income tax (expense) benefit	41	(1,119)	180	1,263
Net Income	(13,029)	(10,686)	6,127	11,720
Total assets	1,454,445	1,365,896	1,454,445	1,365,896
Capital expenditures	46,359	29,379	94,212	73,535
Operating Segments \| Product and Service, Other
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0	0	0
Utility margin	0	0	0	0
Operating and maintenance	0	0	0	0
Administrative and general	424	(527)	437	(338)
Property and other taxes	(1,551)	3	(1,546)	7
Depreciation and depletion	0	0	0	0
Operating income (loss)	1,127	524	1,109	331
Interest expense, net	(2,999)	(3,869)	(11,393)	(7,099)
Other income (expense), net	(581)	(514)	(661)	(123)
Income tax (expense) benefit	1,567	(136)	539	(1,756)
Net Income	(886)	(3,723)	(11,484)	(5,135)
Total assets	11,104	6,438	11,104	6,438
Capital expenditures	0	0	0	0
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0	0	0
Utility margin	0	0	0	0
Operating and maintenance	0	0	0	0
Administrative and general	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 (expense) benefit	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, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 332,300	$ 307,300	$ 1,169,400	$ 1,039,700
Total Revenues	321,090	335,068	1,066,134	1,052,554
Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	128,600	120,600	514,100	457,300
Residential \| Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	106,400	96,000	400,200	344,600
Residential \| South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	20,000	21,400	83,700	86,700
Residential \| Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,200	3,200	30,200	26,000
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	146,500	133,200	495,200	434,500
Commercial \| Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	116,200	99,700	377,000	312,300
Commercial \| South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	29,000	31,200	99,100	106,200
Commercial \| Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,300	2,300	19,100	16,000
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	11,500	9,800	35,000	29,300
Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	13,400	12,800	28,500	26,800
Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	300,000	276,400	1,072,800	947,900
Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	32,300	30,900	96,600	91,800
Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	(11,200)	27,800	(103,300)	12,900
Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	321,100	335,100	1,066,100	1,052,600
Electric Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	299,100	270,500	886,600	772,300
Electric Domestic Regulated [Member] \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	114,800	104,200	359,500	307,900
Electric Domestic Regulated [Member] \| Residential \| Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	96,800	85,200	306,100	252,900
Electric Domestic Regulated [Member] \| Residential \| South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	18,000	19,000	53,400	55,000
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	137,600	121,700	402,400	346,600
Electric Domestic Regulated [Member] \| Commercial \| Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	110,100	92,600	324,600	263,400
Electric Domestic Regulated [Member] \| Commercial \| South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	27,500	29,100	77,800	83,200
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	11,400	9,700	34,000	28,400
Electric Domestic Regulated [Member] \| Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	13,200	12,600	27,200	25,400
Electric Domestic Regulated [Member] \| Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	277,000	248,200	823,100	708,300
Electric Domestic Regulated [Member] \| Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	22,100	22,300	63,500	64,000
Electric Domestic Regulated [Member] \| Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	(19,100)	21,800	(82,000)	35,100
Electric Domestic Regulated [Member] \| Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	280,000	292,300	804,600	807,400
Gas Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	33,200	36,800	282,800	267,400
Gas Domestic Regulated [Member] \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	13,800	16,400	154,600	149,400
Gas Domestic Regulated [Member] \| Residential \| Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9,600	10,800	94,100	91,700
Gas Domestic Regulated [Member] \| Residential \| South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,000	2,400	30,300	31,700
Gas Domestic Regulated [Member] \| Residential \| Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,200	3,200	30,200	26,000
Gas Domestic Regulated [Member] \| Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	8,900	11,500	92,800	87,900
Gas Domestic Regulated [Member] \| Commercial \| Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	6,100	7,100	52,400	48,900
Gas Domestic Regulated [Member] \| Commercial \| South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,500	2,100	21,300	23,000
Gas Domestic Regulated [Member] \| Commercial \| Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,300	2,300	19,100	16,000
Gas Domestic Regulated [Member] \| Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	100	100	1,000	900
Gas Domestic Regulated [Member] \| Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	200	200	1,300	1,400
Gas Domestic Regulated [Member] \| Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	23,000	28,200	249,700	239,600
Gas Domestic Regulated [Member] \| Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	10,200	8,600	33,100	27,800
Gas Domestic Regulated [Member] \| Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	7,900	6,000	(21,300)	(22,200)
Gas Domestic Regulated [Member] \| Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	$ 41,100	$ 42,800	$ 261,500	$ 245,200

Earnings Per Share (Details)

Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
Earnings Per Share (Details) - shares	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Basic computation	60,442,164	56,310,526	60,010,609	54,901,161
Performance share awards(1)	35,533	14,306	31,311	20,150
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements	0	312,572	0	619,361
Diluted computation	60,477,697	56,637,404	60,041,920	55,540,672
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	32,649			51,829

Employee Benefit Plans Net Peri

Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Components of Net Periodic Benefit Cost (Income) [Abstract]
Minimum Expected Future Employer Pension Contributions, Remainder of Fiscal Year	$ 3,000		$ 3,000
Payment for pension benefits			8,200
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	1,459	$ 2,555	4,375	$ 7,667
Interest cost	6,524	4,697	19,571	14,090
Expected return on plan assets	(6,679)	(6,043)	(20,036)	(18,129)
Amortization of prior service credit	0	0	0	0
Recognized actuarial (gain) loss	68	96	205	287
Net periodic benefit cost (credit)	1,372	1,305	4,115	3,915
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	84	88	250	263
Interest cost	168	90	505	269
Expected return on plan assets	(274)	(262)	(822)	(785)
Amortization of prior service credit	29	(472)	87	(1,418)
Recognized actuarial (gain) loss	18	(13)	54	(37)
Net periodic benefit cost (credit)	$ 25	$ (569)	$ 74	$ (1,708)

Commitments and Contingencies E

Commitments and Contingencies Environmental (Details) - Environmental remediation obligations [Member] $ in Millions	Sep. 30, 2023 USD ($)
Environmental remediation obligation, minimum	$ 20.4
Environmental remediation obligation, maximum	31.5
Accrual for Environmental Loss Contingencies, Gross	$ 25.2

Commitments and Contingencies L

Commitments and Contingencies Litigation (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
BNSF Railway Company
Loss Contingencies [Line Items]
Damages sought	$ 4.4
EPA estimated costs to implement selected remedies
Loss Contingencies [Line Items]
Site Contingency, Loss Exposure Not Accrued, Best Estimate	4.1
EPA estimated costs to implement selected remedies for areas of interest in Operable Unit 1
Loss Contingencies [Line Items]
Site Contingency, Loss Exposure Not Accrued, Best Estimate	$ 1.8