NorthWestern Energy (NWE) 10-Q 25 Apr 24 2024 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	3 Months Ended
	Mar. 31, 2024	Apr. 19, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2024
Entity Registrant Name	NORTHWESTERN ENERGY GROUP, INC.
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		61,286,398
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Central Index Key	0001993004

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenues
Electric	$ 343,186	$ 295,308
Gas	132,156	159,234
Total Revenues	475,342	454,542
Operating expenses
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	174,721	165,492
Operating and maintenance	54,182	55,861
Administrative and general	40,445	34,748
Property and other taxes	47,171	49,151
Depreciation and depletion	56,743	53,248
Total Operating Expenses	373,262	358,500
Operating income	102,080	96,042
Interest expense, net	(30,979)	(28,008)
Other income, net	4,319	4,737
Income before income taxes	75,420	72,771
Income tax expense	(10,334)	(10,241)
Net Income	$ 65,086	$ 62,530
Average Common Shares Outstanding	61,265,967	59,776,195
Basic Earnings per Average Common Share	$ 1.06	$ 1.05
Diluted Earnings per Average Common Share	1.06	1.05
Dividends Declared per Common Share	$ 0.650	$ 0.64

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Comprehensive Income (Loss)
Net Income	$ 65,086	$ 62,530
Other comprehensive income, net of tax:
Foreign currency translation adjustment	(1)	(2)
Defined benefit pension plan and postretirement medical liability adjustment	0	(167)
Reclassification of net losses on derivative instruments	113	113
Total Other Comprehensive Income (Loss)	112	(56)
Comprehensive Income	$ 65,198	$ 62,474

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEET - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current Assets:
Cash and cash equivalents	$ 4,150	$ 9,164
Restricted cash	16,232	16,023
Accounts receivable, net	186,927	212,257
Inventories	103,843	114,539
Regulatory assets	60,788	29,626
Prepaid expenses and other	24,896	25,397
Total current assets	396,836	407,006
Property, plant, and equipment, net	6,086,585	6,039,801
Goodwill	357,586	357,586
Regulatory assets	743,140	743,945
Other noncurrent assets	49,287	52,314
Total Assets	7,633,434	7,600,652
Current Liabilities:
Current maturities of finance leases	3,400	3,338
Current portion of long-term debt	0	99,950
Accounts payable	96,544	124,340
Accrued expenses and other	298,302	246,167
Regulatory liabilities	46,438	61,103
Total current liabilities	444,684	534,898
Long-term finance leases	4,596	5,461
Long-term debt	2,767,107	2,684,635
Deferred income taxes	619,744	600,520
Noncurrent regulatory liabilities	651,831	657,452
Other noncurrent liabilities	332,454	332,372
Total Liabilities	4,820,416	4,815,338
Commitments and Contingencies (Note 10)
Shareholders' Equity:
Common Stock, Value, Issued	648	648
Treasury stock at cost	(97,990)	(97,926)
Paid-in capital	2,080,953	2,078,753
Retained earnings	836,951	811,495
Accumulated other comprehensive loss	(7,544)	(7,656)
Total Shareholders' Equity	2,813,018	2,785,314
Total Liabilities and Shareholders' Equity	$ 7,633,434	$ 7,600,652
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	64,797,508
Common Stock, Shares, Outstanding	61,282,747
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	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	$ 65,086	$ 62,530
Items not affecting cash:
Depreciation and depletion	56,743	53,248
Amortization of debt issuance costs, discount and deferred hedge gain	1,186	1,349
Stock-based compensation costs	2,051	3,308
Equity portion of allowance for funds used during construction	(4,288)	(3,715)
Gain on disposition of assets	(1)	(18)
Other Noncash Expense	4,659	0
Deferred income taxes	9,035	(10,420)
Changes in current assets and liabilities:
Accounts receivable	25,330	26,208
Inventories	10,695	14,814
Other current assets	501	4,714
Accounts payable	(9,391)	(44,193)
Accrued expenses and other	52,132	58,236
Regulatory assets	(31,161)	49,391
Regulatory liabilities	(14,665)	(1,378)
Other noncurrent assets and liabilities	(6,235)	(375)
Cash Provided by Operating Activities	161,677	213,699
Net Cash Provided by (Used in) Investing Activities [Abstract]
Property, plant, and equipment additions	(108,754)	(136,604)
Investment in equity securities	(242)	0
Cash Used in Investing Activities	(108,996)	(136,604)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Dividends on common stock	(39,630)	(38,041)
Issuance of long-term debt	215,000	220,000
Repayments of Long-Term Debt	100,000	0
Line of credit repayments, net	(132,000)	(253,000)
Other financing activities, net	(856)	(1,415)
Cash Used in Financing Activities	(57,486)	(72,456)
(Decrease) Increase in Cash, Cash Equivalents, and Restricted Cash	(4,805)	4,639
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Beginning Balance	25,187	22,463
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Ending Balance	20,382	27,102
Cash Paid [Abstract]
Income Taxes Paid, Net	(4,810)	3,204
Interest Paid, Excluding Capitalized Interest, Operating Activities	18,128	18,196
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital expenditures included in accounts payable	$ 21,129	$ 12,209

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, 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	62,530	0	0	0	62,530	0
Foreign currency translation adjustment	2	0	0	0	0	2
Reclassification of net losses on derivative instruments	113	0	0	0	0	113
Defined benefit pension plan and postretirement medical liability adjustment	(167)	$ 0	$ 0	0	0	(167)
Stock based compensation, shares		48	0
Stock based compensation, value	3,215	$ 0	$ (79)	3,294	0	0
Issuance of shares		0
Issuance of shares, treasury stock			1
Stock Issued During Period, Value, Treasury Stock Reissued			$ 0
Issuance of shares, value	169	$ 0		169	0	0
Dividends on common stock	$ (38,041)	$ 0	$ 0	0	(38,041)	0
Dividends per share	$ 0.64
Balance, shares at Mar. 31, 2023		63,326	3,533
Balance, end of period at Mar. 31, 2023	$ 2,693,000	$ 633	$ (98,471)	2,002,839	795,903	(7,904)
Balance, shares at Dec. 31, 2023		64,762	3,513
Balance, beginning of period at Dec. 31, 2023	2,785,314	$ 648	$ (97,926)	2,078,753	811,495	(7,656)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	65,086	0	0	0	65,086	0
Foreign currency translation adjustment	1	0	0	0	0	1
Reclassification of net losses on derivative instruments	113	$ 0	$ 0	0	0	113
Defined benefit pension plan and postretirement medical liability adjustment	0
Stock based compensation, shares		36	0
Stock based compensation, value	1,767	$ 0	$ (272)	2,039	0	0
Issuance of shares		0
Issuance of shares, treasury stock			2
Stock Issued During Period, Value, Treasury Stock Reissued			$ 208
Issuance of shares, value	369	$ 0		161	0	0
Dividends on common stock	$ (39,630)	$ 0	$ 0	0	(39,630)	0
Dividends per share	$ 0.650
Balance, shares at Mar. 31, 2024		64,798	3,515
Balance, end of period at Mar. 31, 2024	$ 2,813,018	$ 648	$ (97,990)	$ 2,080,953	$ 836,951	$ (7,544)

Nature of Operations and Basis

Nature of Operations and Basis of Consolidation	3 Months Ended
	Mar. 31, 2024
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 775,300 customers in Montana, South Dakota, Nebraska and Yellowstone National Park, through its subsidiaries NorthWestern Corporation (NW Corp) and NorthWestern Energy Public Service Corporation (NWE Public Service). 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 March 31, 2024 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 Energy Group Annual Report on Form 10-K for the year ended December 31, 2023 . Holding Company Reorganization On January 1, 2024, we completed the second and final phase of our holding company reorganization. NW Corp contributed the assets and liabilities of its South Dakota and Nebraska regulated utilities to NWE Public Service, and then distributed its equity interest in NWE Public Service and certain other subsidiaries to NorthWestern Energy Group, resulting in NW Corp owning and operating the Montana regulated utility and NWE Public Service owning and operating the Nebraska and South Dakota utilities, each as a direct subsidiary of NorthWestern Energy Group. 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): March 31, December 31, March 31, December 31, 2024 2023 2023 2022 Cash and cash equivalents $ 4,150 $ 9,164 $ 10,730 $ 8,489 Restricted cash 16,232 16,023 16,372 13,974 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 20,382 $ 25,187 $ 27,102 $ 22,463

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2024
Regulated Operations [Abstract]
Public Utilities Disclosure [Text Block]	Regulatory Matters The circumstances set forth in Note 3 - Regulatory Matters to the financial statements included in the NorthWestern Energy Group Annual Report on the Form 10-K for the year ended December 31, 2023

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024 2023 Income before income taxes $ 75,420 $ 72,771 Income tax calculated at federal statutory rate 15,838 21.0 % 15,282 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 639 0.9 959 1.3 Flow-through repairs deductions (6,174) (8.2) (5,845) (8.0) Production tax credits (2,983) (4.0) (3,199) (4.4) Amortization of excess deferred income tax (360) (0.5) (799) (1.1) Plant and depreciation flow-through items 3,079 4.1 688 0.9 Share-based compensation 334 0.4 388 0.5 Reduction to previously claimed alternative minimum tax credit — — 3,186 4.4 Other, net (39) 0.0 (419) (0.5) (5,504) (7.3) (5,041) (6.9) Income tax expense $ 10,334 13.7 % $ 10,241 14.1 % 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 $27.7 million as of March 31, 2024, including approximately $24.3 million that, if recognized, would impact our effective tax rate. In the next twelve months we expect the statute of limitations to expire for certain uncertain tax benefits, which would result in a decrease to our total unrecognized tax benefits of approximately $16.9 million. Our policy is to recognize interest and penalties related to uncertain tax positions in income tax expense. As of March 31, 2024, we have accrued $5.3 million for the payment of interest and penalties on the Condensed Consolidated Balance Sheets. As of December 31, 2023, we had accrued $4.5 million for the payment of interest and penalties on the Condensed Consolidated Balance Sheets.

Comprehensive Income (Loss)

Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2024
Statement of Comprehensive Income [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Comprehensive (Loss) Income The following tables display the components of Other Comprehensive Income (Loss), after-tax, and the related tax effects (in thousands): Three Months Ended March 31, 2024 March 31, 2023 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (1) $ — $ (1) $ (2) $ — $ (2) Reclassification of net income on derivative instruments 153 (40) 113 153 (40) 113 Defined benefit pension plan and postretirement medical liability adjustment — — — (212) 45 (167) Other comprehensive income (loss) $ 152 $ (40) $ 112 $ (61) $ 5 $ (56) Balances by classification included within accumulated other comprehensive loss (AOCL) on the Condensed Consolidated Balance Sheets are as follows, net of tax (in thousands): March 31, 2024 December 31, 2023 Foreign currency translation $ 1,436 $ 1,437 Derivative instruments designated as cash flow hedges (9,260) (9,373) Defined benefit pension plan 280 280 Accumulated other comprehensive loss $ (7,544) $ (7,656) The following tables display the changes in AOCL by component, net of tax (in thousands): Three Months Ended March 31, 2024 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Defined Benefit Pension Plan Foreign Currency Translation Total Beginning balance $ (9,373) $ 280 $ 1,437 $ (7,656) Other comprehensive loss before reclassifications — — (1) (1) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — — — — Net current-period other comprehensive income (loss) 113 — (1) 112 Ending balance $ (9,260) $ 280 $ 1,436 $ (7,544) Three Months Ended March 31, 2023 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Defined Benefit Pension Plan and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (9,825) $ 542 $ 1,435 $ (7,848) Other comprehensive loss before reclassifications — — (2) (2) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (167) — (167) Net current-period other comprehensive income (loss) 113 (167) (2) (56) Ending balance $ (9,712) $ 375 $ 1,433 $ (7,904)

Financing Activities

Financing Activities	3 Months Ended
	Mar. 31, 2024
Financing Activities [Abstract]
Financing Activities	(5) Financing Activities On March 28, 2024, NW Corp issued and sold $175.0 million aggregate principal amount of Montana First Mortgage Bonds at a fixed interest rate of 5.56 percent maturing on March 28, 2031. These bonds were issued in transactions exempt from the registration requirements of the Securities Act of 1933. Proceeds were used to redeem NW Corp's $100.0 million of Montana First Mortgage Bonds due this year and for other general utility purposes. The bonds are secured by NW Corp's electric and natural gas assets associated with its Montana utility operations. On March 28, 2024, NWE Public Service issued and sold $33.0 million aggregate principal amount of South Dakota First Mortgage Bonds at a fixed interest rate of 5.55 percent maturing on March 28, 2029 and $7.0 million aggregate principal amount of South Dakota First Mortgage Bonds at a fixed interest rate of 5.75 percent maturing on March 28, 2034. These bonds were issued in transactions exempt from the registration requirements of the Securities Act of 1933. Proceeds were used for general utility purposes. The bonds are secured by NWE Public Service's electric and natural gas assets associated with its South Dakota and Nebraska utility operations. On April 12, 2024, NorthWestern Energy Group entered into a $100.0 million Term Loan Credit Agreement (Term Loan) with a maturity date of April 11, 2025. Borrowings may be made at a variable interest rate equal to the Secured Overnight Financing Rate plus an applicable margin as provided in the Term Loan. These proceeds were used to repay a portion of our outstanding revolving credit facility borrowings and for general corporate purposes. The Term Loan provides for prepayment of the principal and interest; however, amounts prepaid may not be reborrowed. The Term Loan requires us to maintain a consolidated indebtedness to total capitalization ratio of 65 percent or less. It also contains covenants which, among other things, limit our ability to engage in any consolidation or merger or otherwise liquidate or dissolve, dispose of property, and restricts certain affiliate transactions. A default on the South Dakota or Montana First Mortgage Bonds would trigger a cross default on the Term Loan; however a default on the Term Loan would not trigger a default on the South Dakota or Montana First Mortgage Bonds.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024 Electric Gas Other Eliminations Total Operating revenues $ 343,186 $ 132,156 $ — $ — $ 475,342 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 115,341 59,380 — — 174,721 Utility margin 227,845 72,776 — — 300,621 Operating and maintenance 40,299 13,883 — — 54,182 Administrative and general 27,919 10,046 2,480 — 40,445 Property and other taxes 36,300 10,869 2 — 47,171 Depreciation and depletion 47,304 9,439 — — 56,743 Operating income (loss) 76,023 28,539 (2,482) — 102,080 Interest expense, net (24,657) (6,249) (73) — (30,979) Other income (expense), net 5,461 1,054 (2,196) — 4,319 Income tax (expense) benefit (7,283) (3,173) 122 — (10,334) Net income (loss) $ 49,544 $ 20,171 $ (4,629) $ — $ 65,086 Total assets $ 6,107,575 $ 1,511,593 $ 14,266 $ — $ 7,633,434 Capital expenditures $ 90,590 $ 18,164 $ — $ — $ 108,754 Three Months Ended March 31, 2023 Electric Gas Other Eliminations Total Operating revenues $ 295,308 $ 159,234 $ — $ — $ 454,542 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 78,134 87,358 — — 165,492 Utility margin 217,174 71,876 — — 289,050 Operating and maintenance 42,413 13,448 — — 55,861 Administrative and general 24,968 9,766 14 — 34,748 Property and other taxes 38,251 10,898 2 — 49,151 Depreciation and depletion 43,898 9,350 — — 53,248 Operating income 67,644 28,414 (16) — 96,042 Interest expense, net (18,560) (3,251) (6,197) — (28,008) Other income (expense), net 3,366 1,415 (44) — 4,737 Income tax (expense) benefit (6,628) 234 (3,847) — (10,241) Net income (loss) $ 45,822 $ 26,812 $ (10,104) $ — $ 62,530 Total assets $ 5,874,061 $ 1,399,717 $ 7,216 $ — $ 7,280,994 Capital expenditures $ 120,819 $ 15,785 $ — $ — $ 136,604

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2024
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 0-30 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 0-30 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 March 31, 2024 March 31, 2023 Electric Natural Gas Total Electric Natural Gas Total Montana $ 117.4 $ 48.6 $ 166.0 $ 125.5 $ 66.9 $ 192.4 South Dakota 19.3 13.6 32.9 19.8 19.9 39.7 Nebraska — 10.5 10.5 — 20.5 20.5 Residential 136.7 72.7 209.4 145.3 107.3 252.6 Montana 101.5 25.1 126.6 112.6 36.3 148.9 South Dakota 27.8 9.3 37.1 25.1 14.3 39.4 Nebraska — 6.2 6.2 — 13.2 13.2 Commercial 129.3 40.6 169.9 137.7 63.8 201.5 Industrial 11.7 0.4 12.1 11.8 0.7 12.5 Lighting, governmental, irrigation, and interdepartmental 4.7 0.6 5.3 5.3 0.8 6.1 Total Customer Revenues 282.4 114.3 396.7 300.1 172.6 472.7 Other tariff and contract based revenues 25.2 10.9 36.1 21.4 12.3 33.7 Total Revenue from Contracts with Customers 307.6 125.2 432.8 321.5 184.9 506.4 Regulatory amortization and other 35.6 6.9 42.5 (26.2) (25.7) (51.9) Total Revenues $ 343.2 $ 132.1 $ 475.3 $ 295.3 $ 159.2 $ 454.5

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Earnings Per Share Basic earnings per share are computed by dividing earnings applicable to common stock by the weighted average number of common shares outstanding for the period. Diluted earnings per share reflect the potential dilution of common stock equivalent shares that could occur if unvested shares were to vest. Common stock equivalent shares are calculated using the treasury stock method, as applicable. The dilutive effect is computed by dividing earnings applicable to common stock by the weighted average number of common shares outstanding plus the effect of the outstanding unvested restricted stock and performance share awards. Average shares used in computing the basic and diluted earnings per share are as follows: Three Months Ended March 31, 2024 March 31, 2023 Basic computation 61,265,967 59,776,195 Dilutive effect of: Performance share awards (1) 43,652 13,009 Diluted computation 61,309,619 59,789,204 (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. As of March 31, 2024, there were 54,182 shares from performance and restricted share awards which were antidilutive and excluded from the earnings per share calculations, compared to 69,853 shares as of March 31, 2023.

Employee Benefit Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 2024
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 March 31, Three Months Ended March 31, 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (Credit) Service cost $ 1,418 $ 1,494 $ 80 $ 87 Interest cost 5,733 6,565 147 176 Expected return on plan assets (6,328) (6,686) (319) (275) Amortization of prior service credit — — — 29 Recognized actuarial (gain) loss 11 140 (12) 31 Net periodic benefit cost (credit) $ 834 $ 1,513 $ (104) $ 48

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies ENVIRONMENTAL LIABILITIES AND REGULATION Except as set forth below, the circumstances set forth in Note 18 - Commitments and Contingencies to the financial statements included in the NorthWestern Energy Group Annual Report on Form 10-K for the year ended December 31, 2023 appropriately represent, in all material respects, the current status of our environmental liabilities and regulation. Environmental Protection Agency (EPA) Rules As previously reported, draft Greenhouse Gas (GHG) emission standards for existing coal-fired facilities and new coal and natural gas-fired facilities, including enhanced Mercury Air Toxics Standard (MATS) rules, were released by the EPA in the second quarter of 2023. Our review of these draft rules indicated they would require potentially expensive upgrades at Colstrip Units 3 and 4 to comply, with proposed compliance dates that may not be achievable and / or require technology that is unproven, resulting in significant impacts to costs of the facilities. On April 25, 2024, the EPA released final rules related to GHG emission standards (GHG Rules) for existing coal-fired facilities and new coal and natural gas-fired facilities as well as final rules strengthening the MATS requirements (MATS Rules). The final MATS and GHG Rules will require compliance as early as 2028 and 2032, respectively. We are evaluating how the final MATS and GHG Rules may impact our coal-fired generation facilities and operations. Previous efforts by the EPA were met with extensive litigation and we anticipate a similar response to the new GHG Rules and MATS Rules. As the MATS Rules and GHG Rules 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 the MATS or GHG regulations that, in our view, disproportionately impact customers in our region. These GHG Rules and MATS Rules as well as 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 Energy Group Annual Report on Form 10-K for the year ended December 31, 2023 . 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 filed a motion to pursue an interlocutory appeal of the Order, and on January 2, 2024, the Federal District Court certified the Order for appeal to the 9th Circuit Court of Appeals. Briefing in the appeal is underway. Damages were bifurcated by agreement and will be tried separately for the Black Eagle segment, and any other segments found navigable should the State prevail on appeal. 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 Montana Public Service Commission (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 agreed to stay the Arbitration in an effort to work out a global resolution to the dispute, but that stay has now expired. The parties were not able to agree to continue the stay, and are presently in the process of identifying and retaining an arbitrator (or arbitrators) and are proceeding with the Arbitration. 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. We continue to evaluate a range of reasonably possible losses. Yellowstone County Generating Station Air Permit On October 21, 2021, the Montana Environmental Information Center 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 appeal to the Montana Supreme Court. Oral argument is presently scheduled for May 15, 2024, and a determination of the appeal will follow. We recommenced construction in June 2023 and expect the plant to be operational by the end of the third quarter 2024. The ultimate resolution of the lawsuit challenging the Yellowstone County Generating Station air quality permit could impact our ability to operate the facility and increase costs. During the litigation of the air permit, 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 draft 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 draft supplemental environmental assessment ended on July 3, 2023. On August 4, 2023, the Montana First Judicial District Court in Held v. State of Montana, a separate case by Montana youths alleging climate damages, issued its order finding House Bill 971 unconstitutional delaying the issuance of the revised Yellowstone County Generating Station's air permit. The Montana Supreme Court granted NorthWestern permission to participate as amicus in the Held appeal. The outcome of the Held case could pose additional delays and costs for the Yellowstone County Generating Station. 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
	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income	$ 65,086	$ 62,530

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
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)	3 Months Ended
	Mar. 31, 2024
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): March 31, December 31, March 31, December 31, 2024 2023 2023 2022 Cash and cash equivalents $ 4,150 $ 9,164 $ 10,730 $ 8,489 Restricted cash 16,232 16,023 16,372 13,974 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 20,382 $ 25,187 $ 27,102 $ 22,463

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024 2023 Income before income taxes $ 75,420 $ 72,771 Income tax calculated at federal statutory rate 15,838 21.0 % 15,282 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 639 0.9 959 1.3 Flow-through repairs deductions (6,174) (8.2) (5,845) (8.0) Production tax credits (2,983) (4.0) (3,199) (4.4) Amortization of excess deferred income tax (360) (0.5) (799) (1.1) Plant and depreciation flow-through items 3,079 4.1 688 0.9 Share-based compensation 334 0.4 388 0.5 Reduction to previously claimed alternative minimum tax credit — — 3,186 4.4 Other, net (39) 0.0 (419) (0.5) (5,504) (7.3) (5,041) (6.9) Income tax expense $ 10,334 13.7 % $ 10,241 14.1 %

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Income) Loss (Tables)	3 Months Ended
	Mar. 31, 2024
Statement of Financial Position [Abstract]
Comprehensive Income (Loss) [Table Text Block]	The following tables display the components of Other Comprehensive Income (Loss), after-tax, and the related tax effects (in thousands): Three Months Ended March 31, 2024 March 31, 2023 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (1) $ — $ (1) $ (2) $ — $ (2) Reclassification of net income on derivative instruments 153 (40) 113 153 (40) 113 Defined benefit pension plan and postretirement medical liability adjustment — — — (212) 45 (167) Other comprehensive income (loss) $ 152 $ (40) $ 112 $ (61) $ 5 $ (56)
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): March 31, 2024 December 31, 2023 Foreign currency translation $ 1,436 $ 1,437 Derivative instruments designated as cash flow hedges (9,260) (9,373) Defined benefit pension plan 280 280 Accumulated other comprehensive loss $ (7,544) $ (7,656)
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 March 31, 2024 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Defined Benefit Pension Plan Foreign Currency Translation Total Beginning balance $ (9,373) $ 280 $ 1,437 $ (7,656) Other comprehensive loss before reclassifications — — (1) (1) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — — — — Net current-period other comprehensive income (loss) 113 — (1) 112 Ending balance $ (9,260) $ 280 $ 1,436 $ (7,544) Three Months Ended March 31, 2023 Affected Line Item in the Condensed Consolidated Statements of Income Interest Rate Derivative Instruments Designated as Cash Flow Hedges Defined Benefit Pension Plan and Postretirement Medical Plans Foreign Currency Translation Total Beginning balance $ (9,825) $ 542 $ 1,435 $ (7,848) Other comprehensive loss before reclassifications — — (2) (2) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (167) — (167) Net current-period other comprehensive income (loss) 113 (167) (2) (56) Ending balance $ (9,712) $ 375 $ 1,433 $ (7,904)

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024 Electric Gas Other Eliminations Total Operating revenues $ 343,186 $ 132,156 $ — $ — $ 475,342 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 115,341 59,380 — — 174,721 Utility margin 227,845 72,776 — — 300,621 Operating and maintenance 40,299 13,883 — — 54,182 Administrative and general 27,919 10,046 2,480 — 40,445 Property and other taxes 36,300 10,869 2 — 47,171 Depreciation and depletion 47,304 9,439 — — 56,743 Operating income (loss) 76,023 28,539 (2,482) — 102,080 Interest expense, net (24,657) (6,249) (73) — (30,979) Other income (expense), net 5,461 1,054 (2,196) — 4,319 Income tax (expense) benefit (7,283) (3,173) 122 — (10,334) Net income (loss) $ 49,544 $ 20,171 $ (4,629) $ — $ 65,086 Total assets $ 6,107,575 $ 1,511,593 $ 14,266 $ — $ 7,633,434 Capital expenditures $ 90,590 $ 18,164 $ — $ — $ 108,754 Three Months Ended March 31, 2023 Electric Gas Other Eliminations Total Operating revenues $ 295,308 $ 159,234 $ — $ — $ 454,542 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 78,134 87,358 — — 165,492 Utility margin 217,174 71,876 — — 289,050 Operating and maintenance 42,413 13,448 — — 55,861 Administrative and general 24,968 9,766 14 — 34,748 Property and other taxes 38,251 10,898 2 — 49,151 Depreciation and depletion 43,898 9,350 — — 53,248 Operating income 67,644 28,414 (16) — 96,042 Interest expense, net (18,560) (3,251) (6,197) — (28,008) Other income (expense), net 3,366 1,415 (44) — 4,737 Income tax (expense) benefit (6,628) 234 (3,847) — (10,241) Net income (loss) $ 45,822 $ 26,812 $ (10,104) $ — $ 62,530 Total assets $ 5,874,061 $ 1,399,717 $ 7,216 $ — $ 7,280,994 Capital expenditures $ 120,819 $ 15,785 $ — $ — $ 136,604

Revenue from Contracts with C_2

Revenue from Contracts with Customers Disaggregation of Revenue (Tables)	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024 March 31, 2023 Electric Natural Gas Total Electric Natural Gas Total Montana $ 117.4 $ 48.6 $ 166.0 $ 125.5 $ 66.9 $ 192.4 South Dakota 19.3 13.6 32.9 19.8 19.9 39.7 Nebraska — 10.5 10.5 — 20.5 20.5 Residential 136.7 72.7 209.4 145.3 107.3 252.6 Montana 101.5 25.1 126.6 112.6 36.3 148.9 South Dakota 27.8 9.3 37.1 25.1 14.3 39.4 Nebraska — 6.2 6.2 — 13.2 13.2 Commercial 129.3 40.6 169.9 137.7 63.8 201.5 Industrial 11.7 0.4 12.1 11.8 0.7 12.5 Lighting, governmental, irrigation, and interdepartmental 4.7 0.6 5.3 5.3 0.8 6.1 Total Customer Revenues 282.4 114.3 396.7 300.1 172.6 472.7 Other tariff and contract based revenues 25.2 10.9 36.1 21.4 12.3 33.7 Total Revenue from Contracts with Customers 307.6 125.2 432.8 321.5 184.9 506.4 Regulatory amortization and other 35.6 6.9 42.5 (26.2) (25.7) (51.9) Total Revenues $ 343.2 $ 132.1 $ 475.3 $ 295.3 $ 159.2 $ 454.5

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2024
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 March 31, 2024 March 31, 2023 Basic computation 61,265,967 59,776,195 Dilutive effect of: Performance share awards (1) 43,652 13,009 Diluted computation 61,309,619 59,789,204 (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.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2024
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 March 31, Three Months Ended March 31, 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (Credit) Service cost $ 1,418 $ 1,494 $ 80 $ 87 Interest cost 5,733 6,565 147 176 Expected return on plan assets (6,328) (6,686) (319) (275) Amortization of prior service credit — — — 29 Recognized actuarial (gain) loss 11 140 (12) 31 Net periodic benefit cost (credit) $ 834 $ 1,513 $ (104) $ 48

Nature of Operations and Basi_2

Nature of Operations and Basis of Consolidation (Details)	Dec. 31, 2023 customers
Number of customers	775,300

Nature of Operations and Basi_3

Nature of Operations and Basis of Consolidation Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Cash, Cash Equivalents, and Restricted Cash [Abstract]
Cash and cash equivalents	$ 4,150	$ 9,164	$ 10,730	$ 8,489
Restricted cash	16,232	16,023	16,372	13,974
Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows	$ 20,382	$ 25,187	$ 27,102	$ 22,463

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Income Tax Contingency [Line Items]
Unrecognized tax benefit more likely than not percentage threshold	50%
Unrecognized tax benefits	$ 27.7
Unrecognized tax benefits that would impact effective tax rate	24.3
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	5.3	$ 4.5
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 16.9
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Open Tax Year	2020

Income Taxes Effective Tax Rate

Income Taxes Effective Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Effective tax rate reconciliation
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	$ 75,420	$ 72,771
Income tax calculated at federal statutory rate	15,838	15,282
State income tax, net of federal provisions	639	959
Flow-through repairs deductions	(6,174)	(5,845)
Production tax credits	(2,983)	(3,199)
Amortization of excess deferred income tax	(360)	(799)
Reduction to previously claimed alternative minimum tax credit	0	3,186
Plant and depreciation flow-through items	3,079	688
Share-based compensation	334	388
Other, net	(39)	(419)
Total Other Reconciling Items	(5,504)	(5,041)
Income tax expense	$ 10,334	$ 10,241
Income tax calculated at federal statutory rate	21%	21%
State income tax, net of federal provisions	0.90%	1.30%
Flow-through repairs deductions	(8.20%)	(8.00%)
Production tax credits	(4.00%)	(4.40%)
Amortization of excess deferred income tax	(0.50%)	(1.10%)
Reduction to previously claimed alternative minimum tax credit	0%	4.40%
Plant and depreciation flow-through items	4.10%	0.90%
Share-based compensation	0.40%	0.50%
Other, net	0%	(0.50%)
Total Other Reconciling Items	(7.30%)	(6.90%)
Income tax expense	13.70%	14.10%

Comprehensive Income (Loss) (De

Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other Comprehensive Income (Loss), before Tax [Abstract]
Foreign currency translation adjustment	$ (1)	$ (2)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(153)	(153)
Defined benefit pension plan and postretirement medical liability adjustment	0	(212)
Other Comprehensive Income (Loss), before Tax	152	(61)
Other Comprehensive Income (Loss), Tax [Abstract]
Foreign currency translation adjustment	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	(40)	(40)
Defined benefit pension plan and postretirement medical liability adjustment	0	45
Other Comprehensive Income (Loss), Tax	(40)	5
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	(1)	(2)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(113)	(113)
Defined benefit pension plan and postretirement medical liability adjustment	0	(167)
Total Other Comprehensive Income (Loss)	$ 112	$ (56)

Classification within AOCL on t

Classification within AOCL on the Condenced Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Foreign currency translation	$ 1,436	$ 1,437
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(9,260)	(9,373)
Defined benefit pension plan	280	280
Accumulated other comprehensive loss	$ (7,544)	$ (7,656)	$ (7,904)	$ (7,848)

Changes in AOCI by Component (D

Changes in AOCI by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (7,656)	$ (7,848)
Other comprehensive loss before reclassifications	(1)	(2)
Amounts reclassified from AOCL	113	113
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(167)
Total Other Comprehensive Income (Loss)	112	(56)
Ending balance	(7,544)	(7,904)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(9,373)	(9,825)
Other comprehensive loss before reclassifications	0	0
Amounts reclassified from AOCL	113	113
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Total Other Comprehensive Income (Loss)	113	113
Ending balance	(9,260)	(9,712)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,437	1,435
Other comprehensive loss before reclassifications	(1)	(2)
Amounts reclassified from AOCL	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Total Other Comprehensive Income (Loss)	(1)	(2)
Ending balance	1,436	1,433
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	280	542
Other comprehensive loss before reclassifications	0	0
Amounts reclassified from AOCL	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(167)
Total Other Comprehensive Income (Loss)	0	(167)
Ending balance	$ 280	$ 375

Financing Activities (Details)

Financing Activities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Debt Instrument [Line Items]
Long-term Debt, Maturity Date	Apr. 11, 2025
Term Loan Due 2025
Debt Instrument [Line Items]
Short-Term Debt	$ 100
Short-term Debt [Line Items]
Short-Term Debt	$ 100
Maximum Ratio Of Indebtedness To Net Capital Threshold Percentage	65%
Montana First Mortgage Bonds Due March 28, 2031
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 175
Debt Instrument, Interest Rate, Stated Percentage	5.56%
Long-term Debt, Maturity Date	Mar. 28, 2031
South Dakota First Mortgage Bonds Due 2031
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 33
Debt Instrument, Interest Rate, Stated Percentage	5.55%
Long-term Debt, Maturity Date	Mar. 28, 2029
South Dakota First Mortgage Bonds Due 2034
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 7
Debt Instrument, Interest Rate, Stated Percentage	5.75%
Long-term Debt, Maturity Date	Mar. 28, 2034
Montana First Mortgage Bonds Due 2024
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount	$ 100

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Operating revenues	$ 475,342	$ 454,542
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	174,721	165,492
Utility margin	300,621	289,050
Operating and maintenance	54,182	55,861
Administrative and general	40,445	34,748
Property and other taxes	47,171	49,151
Depreciation and depletion	56,743	53,248
Operating income (loss)	102,080	96,042
Interest expense, net	(30,979)	(28,008)
Other income (expense), net	4,319	4,737
Income tax expense	(10,334)	(10,241)
Net Income	65,086	62,530
Total assets	7,633,434	7,280,994	$ 7,600,652
Capital expenditures	108,754	136,604
Operating Segments | Electricity, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	343,186	295,308
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	115,341	78,134
Utility margin	227,845	217,174
Operating and maintenance	40,299	42,413
Administrative and general	27,919	24,968
Property and other taxes	36,300	38,251
Depreciation and depletion	47,304	43,898
Operating income (loss)	76,023	67,644
Interest expense, net	(24,657)	(18,560)
Other income (expense), net	5,461	3,366
Income tax expense	(7,283)	(6,628)
Net Income	49,544	45,822
Total assets	6,107,575	5,874,061
Capital expenditures	90,590	120,819
Operating Segments | Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	132,156	159,234
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	59,380	87,358
Utility margin	72,776	71,876
Operating and maintenance	13,883	13,448
Administrative and general	10,046	9,766
Property and other taxes	10,869	10,898
Depreciation and depletion	9,439	9,350
Operating income (loss)	28,539	28,414
Interest expense, net	(6,249)	(3,251)
Other income (expense), net	1,054	1,415
Income tax expense	(3,173)	234
Net Income	20,171	26,812
Total assets	1,511,593	1,399,717
Capital expenditures	18,164	15,785
Operating Segments | Product and Service, Other
Segment Reporting Information [Line Items]
Operating revenues	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0
Utility margin	0	0
Operating and maintenance	0	0
Administrative and general	2,480	14
Property and other taxes	2	2
Depreciation and depletion	0	0
Operating income (loss)	(2,482)	(16)
Interest expense, net	(73)	(6,197)
Other income (expense), net	(2,196)	(44)
Income tax expense	122	(3,847)
Net Income	(4,629)	(10,104)
Total assets	14,266	7,216
Capital expenditures	0	0
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	0	0
Utility margin	0	0
Operating and maintenance	0	0
Administrative and general	0	0
Property and other taxes	0	0
Depreciation and depletion	0	0
Operating income (loss)	0	0
Interest expense, net	0	0
Other income (expense), net	0	0
Income tax expense	0	0
Net Income	0	0
Total assets	0	0
Capital expenditures	$ 0	$ 0

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 432,800	$ 506,400
Total Revenues	475,342	454,542
Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	209,400	252,600
Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	166,000	192,400
Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	32,900	39,700
Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	10,500	20,500
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	169,900	201,500
Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	126,600	148,900
Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	37,100	39,400
Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	6,200	13,200
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	12,100	12,500
Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	5,300	6,100
Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	396,700	472,700
Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	36,100	33,700
Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	42,500	(51,900)
Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	475,300	454,500
Electric Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	307,600	321,500
Electric Domestic Regulated [Member] | Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	136,700	145,300
Electric Domestic Regulated [Member] | Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	117,400	125,500
Electric Domestic Regulated [Member] | Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	19,300	19,800
Electric Domestic Regulated [Member] | Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Electric Domestic Regulated [Member] | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	129,300	137,700
Electric Domestic Regulated [Member] | Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	101,500	112,600
Electric Domestic Regulated [Member] | Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	27,800	25,100
Electric Domestic Regulated [Member] | Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Electric Domestic Regulated [Member] | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	11,700	11,800
Electric Domestic Regulated [Member] | Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	4,700	5,300
Electric Domestic Regulated [Member] | Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	282,400	300,100
Electric Domestic Regulated [Member] | Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	25,200	21,400
Electric Domestic Regulated [Member] | Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	35,600	(26,200)
Electric Domestic Regulated [Member] | Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	343,200	295,300
Gas Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	125,200	184,900
Gas Domestic Regulated [Member] | Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	72,700	107,300
Gas Domestic Regulated [Member] | Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	48,600	66,900
Gas Domestic Regulated [Member] | Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	13,600	19,900
Gas Domestic Regulated [Member] | Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	10,500	20,500
Gas Domestic Regulated [Member] | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	40,600	63,800
Gas Domestic Regulated [Member] | Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	25,100	36,300
Gas Domestic Regulated [Member] | Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9,300	14,300
Gas Domestic Regulated [Member] | Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	6,200	13,200
Gas Domestic Regulated [Member] | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	400	700
Gas Domestic Regulated [Member] | Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	600	800
Gas Domestic Regulated [Member] | Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	114,300	172,600
Gas Domestic Regulated [Member] | Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	10,900	12,300
Gas Domestic Regulated [Member] | Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	6,900	(25,700)
Gas Domestic Regulated [Member] | Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	$ 132,100	$ 159,200

Earnings Per Share (Details)

Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Basic computation	61,265,967	59,776,195
Performance share awards(1)	43,652	13,009
Diluted computation	61,309,619	59,789,204
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	54,182	69,853

Employee Benefit Plans Net Peri

Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Components of Net Periodic Benefit Cost (Income) [Abstract]
Minimum Expected Future Employer Pension Contributions, Remainder of Fiscal Year	$ 11,200
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	1,418	$ 1,494
Interest cost	5,733	6,565
Expected return on plan assets	(6,328)	(6,686)
Amortization of prior service credit	0	0
Recognized actuarial (gain) loss	11	140
Net periodic benefit cost (credit)	834	1,513
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	80	87
Interest cost	147	176
Expected return on plan assets	(319)	(275)
Amortization of prior service credit	0	29
Recognized actuarial (gain) loss	(12)	31
Net periodic benefit cost (credit)	$ (104)	$ 48