NorthWestern Energy 10-Q 30 Jul 24 2024 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information Document - shares	6 Months Ended
	Jun. 30, 2024	Jul. 26, 2024
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 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		61,300,497
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Central Index Key	0001993004

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues
Electric	$ 260,134	$ 229,266	$ 603,320	$ 524,574
Gas	59,795	61,236	191,951	220,470
Total Revenues	319,929	290,502	795,271	745,044
Operating expenses
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	76,480	67,578	251,201	233,070
Operating and maintenance	57,367	54,840	111,549	110,701
Administrative and general	31,281	29,955	71,726	64,703
Property and other taxes	36,256	40,129	83,427	89,280
Depreciation and depletion	56,933	52,380	113,676	105,628
Total Operating Expenses	258,317	244,882	631,579	603,382
Operating income	61,612	45,620	163,692	141,662
Interest expense, net	(31,875)	(28,411)	(62,854)	(56,419)
Other income, net	6,160	4,062	10,479	8,799
Income before income taxes	35,897	21,271	111,317	94,042
Income tax expense	(4,243)	(2,147)	(14,577)	(12,388)
Net Income	$ 31,654	$ 19,124	$ 96,740	$ 81,654
Average Common Shares Outstanding	61,288,870	59,804,283	61,277,418	59,790,316
Basic Earnings per Average Common Share	$ 0.52	$ 0.32	$ 1.58	$ 1.37
Diluted Earnings per Average Common Share	0.52	0.32	1.58	1.37
Dividends Declared per Common Share	$ 0.650	$ 0.640	$ 1.30	$ 1.28

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Comprehensive Income (Loss)
Net Income	$ 31,654	$ 19,124	$ 96,740	$ 81,654
Other comprehensive income, net of tax:
Foreign currency translation adjustment	(1)	(1)	(2)	(3)
Defined benefit pension plan and postretirement medical liability adjustment	0	(167)	0	(334)
Reclassification of net losses on derivative instruments	113	113	226	226
Total Other Comprehensive Income (Loss)	112	(55)	224	(111)
Comprehensive Income	$ 31,766	$ 19,069	$ 96,964	$ 81,543

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEET - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Current Assets:
Cash and cash equivalents	$ 6,398	$ 9,164
Restricted cash	24,640	16,023
Accounts receivable, net	149,500	212,257
Inventories	114,956	114,539
Regulatory assets	42,024	29,626
Prepaid expenses and other	26,527	25,397
Total current assets	364,045	407,006
Property, plant, and equipment, net	6,193,234	6,039,801
Goodwill	357,586	357,586
Regulatory assets	748,857	743,945
Other noncurrent assets	50,097	52,314
Total Assets	7,713,819	7,600,652
Current Liabilities:
Current maturities of finance leases	3,462	3,338
Current portion of long-term debt	224,926	99,950
Short-Term Debt	100,000
Accounts payable	91,258	124,340
Accrued expenses and other	244,000	246,167
Regulatory liabilities	36,164	61,103
Total current liabilities	699,810	534,898
Long-term finance leases	3,730	5,461
Long-term debt	2,569,553	2,684,635
Deferred income taxes	629,311	600,520
Noncurrent regulatory liabilities	658,857	657,452
Other noncurrent liabilities	345,301	332,372
Total Liabilities	4,906,562	4,815,338
Commitments and Contingencies (Note 10)
Shareholders' Equity:
Common Stock, Value, Issued	648	648
Treasury stock at cost	(97,776)	(97,926)
Paid-in capital	2,082,857	2,078,753
Retained earnings	828,960	811,495
Accumulated other comprehensive loss	(7,432)	(7,656)
Total Shareholders' Equity	2,807,257	2,785,314
Total Liabilities and Shareholders' Equity	$ 7,713,819	$ 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	64,803,261
Common Stock, Shares, Outstanding	61,299,477
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	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	$ 96,740	$ 81,654
Items not affecting cash:
Depreciation and depletion	113,676	105,628
Amortization of debt issuance costs, discount and deferred hedge gain	2,337	2,636
Stock-based compensation costs	3,797	4,868
Equity portion of allowance for funds used during construction	(9,397)	(7,812)
Loss (gain) on disposition of assets	21	(20)
Other Noncash Expense	4,659	0
Deferred income taxes	12,953	(10,005)
Changes in current assets and liabilities:
Accounts receivable	62,757	97,779
Inventories	(417)	(218)
Other current assets	(1,130)	2,474
Accounts payable	(20,693)	(63,127)
Accrued expenses and other	(2,157)	(3,029)
Regulatory assets	(12,398)	83,139
Regulatory liabilities	(24,939)	7,299
Other noncurrent assets and liabilities	(1,866)	(7,201)
Cash Provided by Operating Activities	223,943	294,065
Net Cash Provided by (Used in) Investing Activities [Abstract]
Property, plant, and equipment additions	(247,361)	(263,362)
Investment in equity securities	(917)	(2,426)
Cash Used in Investing Activities	(248,278)	(265,788)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Dividends on common stock	(79,275)	(76,085)
Issuance of long-term debt	215,000	300,000
Proceeds from (Repayments of) Short-Term Debt, Maturing in More than Three Months	100,000	0
Repayments of Long-Term Debt	100,000	0
Line of credit repayments, net	(105,000)	(259,000)
Other financing activities, net	(539)	(2,437)
Cash Provided by (Used in) Financing Activities	30,186	(26,720)
Increase in Cash, Cash Equivalents, and Restricted Cash	5,851	1,557
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	31,038	24,020
Cash Paid [Abstract]
Income Taxes Paid, Net	(4,669)	3,204
Interest Paid, Excluding Capitalized Interest, Operating Activities	59,995	51,047
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital expenditures included in accounts payable	27,144	20,938
Notes Issued	0	144,660
Proceeds from Issuance of Common Stock	$ 0	$ 10,802

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	81,654	0	0	0	81,654	0
Foreign currency translation adjustment	3	0	0	0	0	(3)
Reclassification of net losses on derivative instruments	226	0	0	0	0	226
Defined benefit pension plan and postretirement medical liability adjustment	(334)	$ 0	$ 0	0	0	(334)
Stock based compensation, shares		51	0
Stock based compensation, value	4,672	$ 0	$ 0	4,672	0	0
Issuance of shares		189
Issuance of shares, treasury stock			(7)
Stock Issued During Period, Value, Treasury Stock Reissued			$ 90
Issuance of shares, value	11,411	$ 2		11,319	0	0
Dividends on common stock	$ (76,085)	$ 0	$ 0	0	(76,085)	0
Dividends per share	$ 1.28
Balance, shares at Jun. 30, 2023		63,518	3,527
Balance, end of period at Jun. 30, 2023	$ 2,686,724	$ 635	$ (98,302)	2,015,367	776,983	(7,959)
Balance, shares at Mar. 31, 2023		63,326	3,533
Balance, beginning of period at Mar. 31, 2023	2,693,000	$ 633	$ (98,471)	2,002,839	795,903	(7,904)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	19,124	0	0	0	19,124	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	(167)	$ 0	$ 0	0	0	(167)
Stock based compensation, shares		3	0
Stock based compensation, value	1,378	$ 0	$ 0	1,378	0	0
Issuance of shares		189
Issuance of shares, treasury stock			(6)
Stock Issued During Period, Value, Treasury Stock Reissued			$ 169
Issuance of shares, value	11,321	$ 2		11,150	0	0
Dividends on common stock	$ (38,044)	$ 0	$ 0	0	(38,044)	0
Dividends per share	$ 0.640
Balance, shares at Jun. 30, 2023		63,518	3,527
Balance, end of period at Jun. 30, 2023	$ 2,686,724	$ 635	$ (98,302)	2,015,367	776,983	(7,959)
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	96,740	0	0	0	96,740	0
Foreign currency translation adjustment	2	0	0	0	0	2
Reclassification of net losses on derivative instruments	226	0	0	0	0	226
Defined benefit pension plan and postretirement medical liability adjustment	0	$ 0	$ 0	0	0	0
Stock based compensation, shares		41	0
Stock based compensation, value	3,499	$ 0	$ (272)	3,771	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(9)
Stock Issued During Period, Value, Treasury Stock Reissued			$ 422
Issuance of shares, value	755	$ 0		333	0	0
Dividends on common stock	$ (79,275)	$ 0	$ 0	0	(79,275)	0
Dividends per share	$ 1.30
Balance, shares at Jun. 30, 2024		64,803	3,504
Balance, end of period at Jun. 30, 2024	$ 2,807,257	$ 648	$ (97,776)	2,082,857	828,960	(7,432)
Balance, shares at Mar. 31, 2024		64,798	3,515
Balance, beginning of period at Mar. 31, 2024	2,813,018	$ 648	$ (97,990)	2,080,953	836,951	(7,544)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	31,654	0	0	0	31,654	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		5	0
Stock based compensation, value	1,732	$ 0	$ 0	1,732	0	0
Issuance of shares		0
Issuance of shares, treasury stock			(11)
Stock Issued During Period, Value, Treasury Stock Reissued			$ 214
Issuance of shares, value	386	$ 0		172	0	0
Dividends on common stock	$ (39,645)	$ 0	$ 0	0	(39,645)	0
Dividends per share	$ 0.650
Balance, shares at Jun. 30, 2024		64,803	3,504
Balance, end of period at Jun. 30, 2024	$ 2,807,257	$ 648	$ (97,776)	$ 2,082,857	$ 828,960	$ (7,432)

Nature of Operations and Basis

Nature of Operations and Basis of Consolidation	6 Months Ended
	Jun. 30, 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 June 30, 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): June 30, December 31, June 30, December 31, 2024 2023 2023 2022 Cash and cash equivalents $ 6,398 $ 9,164 $ 7,757 $ 8,489 Restricted cash 24,640 16,023 16,263 13,974 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 31,038 $ 25,187 $ 24,020 $ 22,463 Goodwill We completed our annual goodwill impairment test as of April 1, 2024, and no impairment was identified. We calculate the fair value of our reporting units by considering various factors, including valuation studies based primarily on a discounted cash flow analysis, with published industry valuations and market data as supporting information. Key assumptions in the determination of fair value include the use of an appropriate discount rate and estimated future cash flows. In estimating cash

Regulatory Matters

Regulatory Matters	6 Months Ended
	Jun. 30, 2024
Regulated Operations [Abstract]
Public Utilities Disclosure [Text Block]	Regulatory Matters Montana Rate Review On July 10, 2024, we filed a Montana electric and natural gas rate review with the Montana Public Service Commission (MPSC). The filing requests a base rate annual revenue increase of $156.5 million ($69.4 million net with Property Tax and Power Cost and Credit Adjustment Mechanism (PCCAM) tracker adjustments) for electric and $28.6 million for natural gas. Our request is based on a return on equity of 10.80 percent with a capital structure including 46.81 percent equity, and forecasted 2024 electric and natural gas rate base of $3.45 billion and $731.9 million, respectively. The electric rate base investment includes the 175-megawatt natural gas-fired Yellowstone County Generating Station ("YCGS"), which is expected to be in service during the third quarter of 2024. We requested interim base rates to be effective October 1, 2024. South Dakota Natural Gas Rate Review On June 21, 2024, we filed a natural gas rate review (2023 test year) with the South Dakota Public Utilities Commission. The filing requests a base rate annual revenue increase of $6.0 million. Our request is based on a return on equity of 10.70 percent, a capital structure including 53.13 percent equity, and rate base of $95.6 million. If a final order is not received by December 21, 2024, interim base rates may go into effect. Nebraska Natural Gas Rate Review On June 6, 2024, we filed a natural gas rate review (2023 test year) with the Nebraska Public Service Commission. The filing requests a base rate annual revenue increase of $3.6 million. Our request is based on a return on equity of 10.70 percent, a capital structure including 53.13 percent equity, and rate base of $47.4 million. Interim base rates are not anticipated to be implemented prior to October 1, 2024.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 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 June 30, 2024 2023 Income before income taxes $ 35,897 $ 21,271 Income tax calculated at federal statutory rate 7,539 21.0 % 4,467 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 49 0.1 273 1.3 Flow-through repairs deductions (3,069) (8.5) (1,708) (8.0) Production tax credits (2,004) (5.6) (1,147) (5.4) Amortization of excess deferred income tax (196) (0.5) (233) (1.1) Plant and depreciation flow-through items 1,060 3.0 201 0.9 Other, net 864 2.3 294 1.4 (3,296) (9.2) (2,320) (10.9) Income tax expense $ 4,243 11.8 % $ 2,147 10.1 % Six Months Ended June 30, 2024 2023 Income before income taxes $ 111,317 $ 94,042 Income tax calculated at federal statutory rate 23,377 21.0 % 19,749 21.0 % Permanent or flow through adjustments: State income, net of federal provisions 688 0.6 1,232 1.3 Flow-through repairs deductions (9,243) (8.3) (7,553) (8.0) Production tax credits (4,987) (4.5) (4,346) (4.6) Amortization of excess deferred income tax (556) (0.5) (1,032) (1.1) Reduction to previously claimed alternative minimum tax credit — — 3,186 3.4 Plant and depreciation flow through items 4,139 3.7 889 0.9 Share-based compensation 298 0.3 388 0.4 Other, net 861 0.8 (125) (0.1) (8,800) (7.9) (7,361) (7.8) Income tax expense $ 14,577 13.1 % $ 12,388 13.2 % 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 $27.3 million as of June 30, 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 June 30, 2024, we have accrued $6.0 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)	6 Months Ended
	Jun. 30, 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 June 30, 2024 June 30, 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) $ (1) $ — $ (1) 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 $ (60) $ 5 $ (55) Six Months Ended June 30, 2024 June 30, 2023 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (2) $ — $ (2) $ (3) $ — $ (3) Reclassification of net income on derivative instruments 306 (80) 226 306 (80) 226 Defined benefit pension plan and postretirement medical liability adjustment — — — (424) 90 (334) Other comprehensive income (loss) $ 304 $ (80) $ 224 $ (121) $ 10 $ (111) Balances by classification included within accumulated other comprehensive loss (AOCL) on the Condensed Consolidated Balance Sheets are as follows, net of tax (in thousands): June 30, 2024 December 31, 2023 Foreign currency translation $ 1,435 $ 1,437 Derivative instruments designated as cash flow hedges (9,147) (9,373) Defined benefit pension plan 280 280 Accumulated other comprehensive loss $ (7,432) $ (7,656) The following tables display the changes in AOCL by component, net of tax (in thousands): Three Months Ended June 30, 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 $ (9,260) $ 280 $ 1,436 $ (7,544) Other comprehensive loss before reclassifications — — (1) (1) Amounts reclassified from AOCL Interest Expense 113 — — 113 Net current-period other comprehensive income (loss) 113 — (1) 112 Ending balance $ (9,147) $ 280 $ 1,435 $ (7,432) Three Months Ended June 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 $ (9,712) $ 375 $ 1,433 $ (7,904) Other comprehensive loss before reclassifications — — (1) (1) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (167) — (167) Net current-period other comprehensive income (loss) 113 (167) (1) (55) Ending balance $ (9,599) $ 208 $ 1,432 $ (7,959) Six Months Ended June 30, 2024 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 $ (9,373) $ 280 $ 1,437 $ (7,656) Other comprehensive loss before reclassifications — — (2) (2) Amounts reclassified from AOCL Interest Expense 226 — — 226 Net current-period other comprehensive income (loss) 226 — (2) 224 Ending balance $ (9,147) $ 280 $ 1,435 $ (7,432) Six Months Ended June 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 — — (3) (3) Amounts reclassified from AOCL Interest Expense 226 — — 226 Amounts reclassified from AOCL — (334) — (334) Net current-period other comprehensive income (loss) 226 (334) (3) (111) Ending balance $ (9,599) $ 208 $ 1,432 $ (7,959)

Financing Activities

Financing Activities	6 Months Ended
	Jun. 30, 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	6 Months Ended
	Jun. 30, 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 June 30, 2024 Electric Gas Other Eliminations Total Operating revenues $ 260,134 $ 59,795 $ — $ — $ 319,929 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 60,887 15,593 — — 76,480 Utility margin 199,247 44,202 — — 243,449 Operating and maintenance 43,467 13,900 — — 57,367 Administrative and general 23,294 7,821 166 — 31,281 Property and other taxes 28,006 8,251 (1) — 36,256 Depreciation and depletion 47,546 9,387 — — 56,933 Operating income (loss) 56,934 4,843 (165) — 61,612 Interest expense, net (23,298) (7,147) (1,430) — (31,875) Other income, net 4,031 927 1,202 — 6,160 Income tax (expense) benefit (3,891) 304 (656) — (4,243) Net income (loss) $ 33,776 $ (1,073) $ (1,049) $ — $ 31,654 Total assets $ 6,172,704 $ 1,525,851 $ 15,264 $ — $ 7,713,819 Capital expenditures $ 112,258 $ 26,349 $ — $ — $ 138,607 Three Months Ended June 30, 2023 Electric Gas Other Eliminations Total Operating revenues $ 229,266 $ 61,236 $ — $ — $ 290,502 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 42,363 25,215 — — 67,578 Utility margin 186,903 36,021 — — 222,924 Operating and maintenance 41,368 13,472 — — 54,840 Administrative and general 21,635 8,321 (1) — 29,955 Property and other taxes 31,022 9,104 3 — 40,129 Depreciation and depletion 43,319 9,061 — — 52,380 Operating income (loss) 49,559 (3,937) (2) — 45,620 Interest expense, net (21,724) (4,490) (2,197) — (28,411) Other income (expense), net 2,954 1,144 (36) — 4,062 Income tax (expense) benefit (3,515) (373) 1,741 — (2,147) Net income (loss) $ 27,274 $ (7,656) $ (494) $ — $ 19,124 Total assets $ 5,878,433 $ 1,406,068 $ 9,741 $ — $ 7,294,242 Capital expenditures $ 94,690 $ 32,068 $ — $ — $ 126,758 Six Months Ended June 30, 2024 Electric Gas Other Eliminations Total Operating revenues $ 603,320 $ 191,951 $ — $ — $ 795,271 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 176,228 74,973 — — 251,201 Utility margin 427,092 116,978 — — 544,070 Operating and maintenance 83,766 27,783 — — 111,549 Administrative and general 51,213 17,867 2,646 — 71,726 Property and other taxes 64,306 19,120 1 — 83,427 Depreciation and depletion 94,850 18,826 — — 113,676 Operating income (loss) 132,957 33,382 (2,647) — 163,692 Interest expense, net (47,955) (13,396) (1,503) — (62,854) Other income (expense), net 9,492 1,981 (994) — 10,479 Income tax expense (11,174) (2,869) (534) — (14,577) Net income (loss) $ 83,320 $ 19,098 $ (5,678) $ — $ 96,740 Total assets $ 6,172,704 $ 1,525,851 $ 15,264 $ — $ 7,713,819 Capital expenditures $ 202,848 $ 44,513 $ — $ — $ 247,361 Six Months Ended June 30, 2023 Electric Gas Other Eliminations Total Operating revenues $ 524,574 $ 220,470 $ — $ — $ 745,044 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 120,497 112,573 — — 233,070 Utility margin 404,077 107,897 — — 511,974 Operating and maintenance 83,781 26,920 — — 110,701 Administrative and general 46,603 18,087 13 — 64,703 Property and other taxes 69,273 20,002 5 — 89,280 Depreciation and depletion 87,217 18,411 — — 105,628 Operating income (loss) 117,203 24,477 (18) — 141,662 Interest expense, net (40,284) (7,741) (8,394) — (56,419) Other income (expense), net 6,320 2,559 (80) — 8,799 Income tax expense (10,143) (139) (2,106) — (12,388) Net income (loss) $ 73,096 $ 19,156 $ (10,598) $ — $ 81,654 Total assets $ 5,878,433 $ 1,406,068 $ 9,741 $ — $ 7,294,242 Capital expenditures $ 215,509 $ 47,853 $ — $ — $ 263,362

Revenue from Contracts with Cus

Revenue from Contracts with Customers	6 Months Ended
	Jun. 30, 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 June 30, 2024 June 30, 2023 Electric Natural Gas Total Electric Natural Gas Total Montana $ 86.0 $ 18.9 $ 104.9 $ 83.8 $ 17.6 $ 101.4 South Dakota 15.4 5.9 21.3 15.7 8.4 24.1 Nebraska — 3.8 3.8 — 7.4 7.4 Residential 101.4 28.6 130.0 99.5 33.4 132.9 Montana 99.7 10.7 110.4 101.9 9.9 111.8 South Dakota 26.3 3.7 30.0 25.1 5.5 30.6 Nebraska — 2.0 2.0 — 4.7 4.7 Commercial 126.0 16.4 142.4 127.0 20.1 147.1 Industrial 11.3 0.2 11.5 10.8 0.2 11.0 Lighting, governmental, irrigation, and interdepartmental 8.6 0.3 8.9 8.7 0.3 9.0 Total Customer Revenues 247.3 45.5 292.8 246.0 54.0 300.0 Other tariff and contract based revenues 24.2 10.6 34.8 20.0 10.6 30.6 Total Revenue from Contracts with Customers 271.5 56.1 327.6 266.0 64.6 330.6 Regulatory amortization and other (11.4) 3.7 (7.7) (36.7) (3.4) (40.1) Total Revenues $ 260.1 $ 59.8 $ 319.9 $ 229.3 $ 61.2 $ 290.5 Six Months Ended June 30, 2024 June 30, 2023 Electric Natural Gas Total Electric Natural Gas Total Montana $ 203.4 $ 67.5 $ 270.9 $ 209.3 $ 84.5 $ 293.8 South Dakota 34.7 19.5 54.2 35.5 28.3 63.8 Nebraska — 14.3 14.3 — 28.0 28.0 Residential 238.1 101.3 339.4 244.8 140.8 385.6 Montana 201.2 35.8 237.0 214.5 46.3 260.8 South Dakota 54.1 13.0 67.1 50.3 19.8 70.1 Nebraska — 8.2 8.2 — 17.8 17.8 Commercial 255.3 57.0 312.3 264.8 83.9 348.7 Industrial 23.0 0.6 23.6 22.6 0.9 23.5 Lighting, governmental, irrigation, and interdepartmental 13.3 0.9 14.2 13.9 1.0 14.9 Total Customer Revenues 529.7 159.8 689.5 546.1 226.6 772.7 Other tariff and contract based revenues 49.3 21.6 70.9 41.3 22.9 64.2 Total Revenue from Contracts with Customers 579.0 181.4 760.4 587.4 249.5 836.9 Regulatory amortization and other 24.3 10.6 34.9 (62.8) (29.1) (91.9) Total Revenues $ 603.3 $ 192.0 $ 795.3 $ 524.6 $ 220.4 $ 745.0

Earnings Per Share

Earnings Per Share	3 Months Ended
	Jun. 30, 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 June 30, 2024 June 30, 2023 Basic computation 61,288,870 59,804,283 Dilutive effect of: Performance share awards (1) 68,478 45,391 Diluted computation 61,357,348 59,849,674 Six Months Ended June 30, 2024 June 30, 2023 Basic computation 61,277,418 59,790,316 Dilutive effect of: Performance share awards (1) 56,065 29,200 Diluted computation 61,333,483 59,819,516 (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 June 30, 2024, there were 35,933 shares from performance and restricted share awards which were antidilutive and excluded from the earnings per share calculations, compared to 21,890 shares as of June 30, 2023.

Employee Benefit Plans

Employee Benefit Plans	6 Months Ended
	Jun. 30, 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 June 30, Three Months Ended June 30, 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (Credit) Service cost $ 1,378 $ 1,422 $ 74 $ 79 Interest cost 5,739 6,482 132 161 Expected return on plan assets (6,335) (6,671) (321) (273) Amortization of prior service credit — — — 29 Recognized actuarial loss (gain) 6 (3) (25) 5 Net periodic benefit cost (credit) $ 788 $ 1,230 $ (140) $ 1 Pension Benefits Other Postretirement Benefits Six Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (Credit) Service cost $ 2,796 $ 2,916 $ 154 $ 166 Interest cost 11,472 13,047 279 337 Expected return on plan assets (12,663) (13,357) (640) (548) Amortization of prior service credit — — — 58 Recognized actuarial loss (gain) 17 137 (37) 36 Net periodic benefit cost (credit) $ 1,622 $ 2,743 $ (244) $ 49

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 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 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). Compliance with the rules will require expensive upgrades at Colstrip Units 3 and 4 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. The final MATS and GHG Rules require compliance as early as 2027 and 2032, respectively. Previous efforts by the EPA were met with extensive litigation, and this time is no different. We, along with many other utilities, electric cooperatives, organizations, and states, have petitioned for judicial review of the GHG and MATS Rules with the U.S. Court of Appeals for the D.C. Circuit. We have further requested the court stay the implementation of the Rules pending review on the merits, but that judicial relief is discretionary. Briefing is underway for the requests to stay the MATS Rules. On July 19, 2024, the D.C. Circuit denied all consolidated motions to stay the GHG Rules, concluding the petitioners had not shown likelihood of success on the merits and irreparable harm from the GHG Rules' imposition. However, the court ordered the litigation parties to submit a proposed briefing schedule to ensure the case is argued and the GHG Rule is reviewed on the merits as soon as possible. If the MATS Rules and GHG Rules are implemented, it would 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 retaining an arbitrator 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; though the number of plaintiffs has since decreased to 57. 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 was held May 15, 2024. We recommenced construction in June 2023 and expect the plant to be in service during the third quarter of 2024. The ultimate resolution of the lawsuit challenging the Yellowstone County Generating Station air quality permit could impact our ability to operate the facility. 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 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 Montana Supreme Court heard oral argument on the Held appeal on July 10, 2024. 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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net Income	$ 31,654	$ 19,124	$ 96,740	$ 81,654

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 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)	6 Months Ended
	Jun. 30, 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): June 30, December 31, June 30, December 31, 2024 2023 2023 2022 Cash and cash equivalents $ 6,398 $ 9,164 $ 7,757 $ 8,489 Restricted cash 24,640 16,023 16,263 13,974 Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows $ 31,038 $ 25,187 $ 24,020 $ 22,463 Goodwill We completed our annual goodwill impairment test as of April 1, 2024, and no impairment was identified. We calculate the fair value of our reporting units by considering various factors, including valuation studies based primarily on a discounted cash flow analysis, with published industry valuations and market data as supporting information. Key assumptions in the determination of fair value include the use of an appropriate discount rate and estimated future cash flows. In estimating cash

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2024 2023 Income before income taxes $ 35,897 $ 21,271 Income tax calculated at federal statutory rate 7,539 21.0 % 4,467 21.0 % Permanent or flow-through adjustments: State income tax, net of federal provisions 49 0.1 273 1.3 Flow-through repairs deductions (3,069) (8.5) (1,708) (8.0) Production tax credits (2,004) (5.6) (1,147) (5.4) Amortization of excess deferred income tax (196) (0.5) (233) (1.1) Plant and depreciation flow-through items 1,060 3.0 201 0.9 Other, net 864 2.3 294 1.4 (3,296) (9.2) (2,320) (10.9) Income tax expense $ 4,243 11.8 % $ 2,147 10.1 % Six Months Ended June 30, 2024 2023 Income before income taxes $ 111,317 $ 94,042 Income tax calculated at federal statutory rate 23,377 21.0 % 19,749 21.0 % Permanent or flow through adjustments: State income, net of federal provisions 688 0.6 1,232 1.3 Flow-through repairs deductions (9,243) (8.3) (7,553) (8.0) Production tax credits (4,987) (4.5) (4,346) (4.6) Amortization of excess deferred income tax (556) (0.5) (1,032) (1.1) Reduction to previously claimed alternative minimum tax credit — — 3,186 3.4 Plant and depreciation flow through items 4,139 3.7 889 0.9 Share-based compensation 298 0.3 388 0.4 Other, net 861 0.8 (125) (0.1) (8,800) (7.9) (7,361) (7.8) Income tax expense $ 14,577 13.1 % $ 12,388 13.2 %

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Income) Loss (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2024 June 30, 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) $ (1) $ — $ (1) 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 $ (60) $ 5 $ (55) Six Months Ended June 30, 2024 June 30, 2023 Before-Tax Amount Tax Expense Net-of-Tax Amount Before-Tax Amount Tax Expense Net-of-Tax Amount Foreign currency translation adjustment $ (2) $ — $ (2) $ (3) $ — $ (3) Reclassification of net income on derivative instruments 306 (80) 226 306 (80) 226 Defined benefit pension plan and postretirement medical liability adjustment — — — (424) 90 (334) Other comprehensive income (loss) $ 304 $ (80) $ 224 $ (121) $ 10 $ (111)
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): June 30, 2024 December 31, 2023 Foreign currency translation $ 1,435 $ 1,437 Derivative instruments designated as cash flow hedges (9,147) (9,373) Defined benefit pension plan 280 280 Accumulated other comprehensive loss $ (7,432) $ (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 June 30, 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 $ (9,260) $ 280 $ 1,436 $ (7,544) Other comprehensive loss before reclassifications — — (1) (1) Amounts reclassified from AOCL Interest Expense 113 — — 113 Net current-period other comprehensive income (loss) 113 — (1) 112 Ending balance $ (9,147) $ 280 $ 1,435 $ (7,432) Three Months Ended June 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 $ (9,712) $ 375 $ 1,433 $ (7,904) Other comprehensive loss before reclassifications — — (1) (1) Amounts reclassified from AOCL Interest Expense 113 — — 113 Amounts reclassified from AOCL — (167) — (167) Net current-period other comprehensive income (loss) 113 (167) (1) (55) Ending balance $ (9,599) $ 208 $ 1,432 $ (7,959) Six Months Ended June 30, 2024 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 $ (9,373) $ 280 $ 1,437 $ (7,656) Other comprehensive loss before reclassifications — — (2) (2) Amounts reclassified from AOCL Interest Expense 226 — — 226 Net current-period other comprehensive income (loss) 226 — (2) 224 Ending balance $ (9,147) $ 280 $ 1,435 $ (7,432) Six Months Ended June 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 — — (3) (3) Amounts reclassified from AOCL Interest Expense 226 — — 226 Amounts reclassified from AOCL — (334) — (334) Net current-period other comprehensive income (loss) 226 (334) (3) (111) Ending balance $ (9,599) $ 208 $ 1,432 $ (7,959)

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2024 Electric Gas Other Eliminations Total Operating revenues $ 260,134 $ 59,795 $ — $ — $ 319,929 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 60,887 15,593 — — 76,480 Utility margin 199,247 44,202 — — 243,449 Operating and maintenance 43,467 13,900 — — 57,367 Administrative and general 23,294 7,821 166 — 31,281 Property and other taxes 28,006 8,251 (1) — 36,256 Depreciation and depletion 47,546 9,387 — — 56,933 Operating income (loss) 56,934 4,843 (165) — 61,612 Interest expense, net (23,298) (7,147) (1,430) — (31,875) Other income, net 4,031 927 1,202 — 6,160 Income tax (expense) benefit (3,891) 304 (656) — (4,243) Net income (loss) $ 33,776 $ (1,073) $ (1,049) $ — $ 31,654 Total assets $ 6,172,704 $ 1,525,851 $ 15,264 $ — $ 7,713,819 Capital expenditures $ 112,258 $ 26,349 $ — $ — $ 138,607 Three Months Ended June 30, 2023 Electric Gas Other Eliminations Total Operating revenues $ 229,266 $ 61,236 $ — $ — $ 290,502 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 42,363 25,215 — — 67,578 Utility margin 186,903 36,021 — — 222,924 Operating and maintenance 41,368 13,472 — — 54,840 Administrative and general 21,635 8,321 (1) — 29,955 Property and other taxes 31,022 9,104 3 — 40,129 Depreciation and depletion 43,319 9,061 — — 52,380 Operating income (loss) 49,559 (3,937) (2) — 45,620 Interest expense, net (21,724) (4,490) (2,197) — (28,411) Other income (expense), net 2,954 1,144 (36) — 4,062 Income tax (expense) benefit (3,515) (373) 1,741 — (2,147) Net income (loss) $ 27,274 $ (7,656) $ (494) $ — $ 19,124 Total assets $ 5,878,433 $ 1,406,068 $ 9,741 $ — $ 7,294,242 Capital expenditures $ 94,690 $ 32,068 $ — $ — $ 126,758 Six Months Ended June 30, 2024 Electric Gas Other Eliminations Total Operating revenues $ 603,320 $ 191,951 $ — $ — $ 795,271 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 176,228 74,973 — — 251,201 Utility margin 427,092 116,978 — — 544,070 Operating and maintenance 83,766 27,783 — — 111,549 Administrative and general 51,213 17,867 2,646 — 71,726 Property and other taxes 64,306 19,120 1 — 83,427 Depreciation and depletion 94,850 18,826 — — 113,676 Operating income (loss) 132,957 33,382 (2,647) — 163,692 Interest expense, net (47,955) (13,396) (1,503) — (62,854) Other income (expense), net 9,492 1,981 (994) — 10,479 Income tax expense (11,174) (2,869) (534) — (14,577) Net income (loss) $ 83,320 $ 19,098 $ (5,678) $ — $ 96,740 Total assets $ 6,172,704 $ 1,525,851 $ 15,264 $ — $ 7,713,819 Capital expenditures $ 202,848 $ 44,513 $ — $ — $ 247,361 Six Months Ended June 30, 2023 Electric Gas Other Eliminations Total Operating revenues $ 524,574 $ 220,470 $ — $ — $ 745,044 Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below) 120,497 112,573 — — 233,070 Utility margin 404,077 107,897 — — 511,974 Operating and maintenance 83,781 26,920 — — 110,701 Administrative and general 46,603 18,087 13 — 64,703 Property and other taxes 69,273 20,002 5 — 89,280 Depreciation and depletion 87,217 18,411 — — 105,628 Operating income (loss) 117,203 24,477 (18) — 141,662 Interest expense, net (40,284) (7,741) (8,394) — (56,419) Other income (expense), net 6,320 2,559 (80) — 8,799 Income tax expense (10,143) (139) (2,106) — (12,388) Net income (loss) $ 73,096 $ 19,156 $ (10,598) $ — $ 81,654 Total assets $ 5,878,433 $ 1,406,068 $ 9,741 $ — $ 7,294,242 Capital expenditures $ 215,509 $ 47,853 $ — $ — $ 263,362

Revenue from Contracts with C_2

Revenue from Contracts with Customers Disaggregation of Revenue (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2024 June 30, 2023 Electric Natural Gas Total Electric Natural Gas Total Montana $ 86.0 $ 18.9 $ 104.9 $ 83.8 $ 17.6 $ 101.4 South Dakota 15.4 5.9 21.3 15.7 8.4 24.1 Nebraska — 3.8 3.8 — 7.4 7.4 Residential 101.4 28.6 130.0 99.5 33.4 132.9 Montana 99.7 10.7 110.4 101.9 9.9 111.8 South Dakota 26.3 3.7 30.0 25.1 5.5 30.6 Nebraska — 2.0 2.0 — 4.7 4.7 Commercial 126.0 16.4 142.4 127.0 20.1 147.1 Industrial 11.3 0.2 11.5 10.8 0.2 11.0 Lighting, governmental, irrigation, and interdepartmental 8.6 0.3 8.9 8.7 0.3 9.0 Total Customer Revenues 247.3 45.5 292.8 246.0 54.0 300.0 Other tariff and contract based revenues 24.2 10.6 34.8 20.0 10.6 30.6 Total Revenue from Contracts with Customers 271.5 56.1 327.6 266.0 64.6 330.6 Regulatory amortization and other (11.4) 3.7 (7.7) (36.7) (3.4) (40.1) Total Revenues $ 260.1 $ 59.8 $ 319.9 $ 229.3 $ 61.2 $ 290.5 Six Months Ended June 30, 2024 June 30, 2023 Electric Natural Gas Total Electric Natural Gas Total Montana $ 203.4 $ 67.5 $ 270.9 $ 209.3 $ 84.5 $ 293.8 South Dakota 34.7 19.5 54.2 35.5 28.3 63.8 Nebraska — 14.3 14.3 — 28.0 28.0 Residential 238.1 101.3 339.4 244.8 140.8 385.6 Montana 201.2 35.8 237.0 214.5 46.3 260.8 South Dakota 54.1 13.0 67.1 50.3 19.8 70.1 Nebraska — 8.2 8.2 — 17.8 17.8 Commercial 255.3 57.0 312.3 264.8 83.9 348.7 Industrial 23.0 0.6 23.6 22.6 0.9 23.5 Lighting, governmental, irrigation, and interdepartmental 13.3 0.9 14.2 13.9 1.0 14.9 Total Customer Revenues 529.7 159.8 689.5 546.1 226.6 772.7 Other tariff and contract based revenues 49.3 21.6 70.9 41.3 22.9 64.2 Total Revenue from Contracts with Customers 579.0 181.4 760.4 587.4 249.5 836.9 Regulatory amortization and other 24.3 10.6 34.9 (62.8) (29.1) (91.9) Total Revenues $ 603.3 $ 192.0 $ 795.3 $ 524.6 $ 220.4 $ 745.0

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2024 June 30, 2023 Basic computation 61,288,870 59,804,283 Dilutive effect of: Performance share awards (1) 68,478 45,391 Diluted computation 61,357,348 59,849,674 Six Months Ended June 30, 2024 June 30, 2023 Basic computation 61,277,418 59,790,316 Dilutive effect of: Performance share awards (1) 56,065 29,200 Diluted computation 61,333,483 59,819,516 (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)	6 Months Ended
	Jun. 30, 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 June 30, Three Months Ended June 30, 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (Credit) Service cost $ 1,378 $ 1,422 $ 74 $ 79 Interest cost 5,739 6,482 132 161 Expected return on plan assets (6,335) (6,671) (321) (273) Amortization of prior service credit — — — 29 Recognized actuarial loss (gain) 6 (3) (25) 5 Net periodic benefit cost (credit) $ 788 $ 1,230 $ (140) $ 1 Pension Benefits Other Postretirement Benefits Six Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Components of Net Periodic Benefit Cost (Credit) Service cost $ 2,796 $ 2,916 $ 154 $ 166 Interest cost 11,472 13,047 279 337 Expected return on plan assets (12,663) (13,357) (640) (548) Amortization of prior service credit — — — 58 Recognized actuarial loss (gain) 17 137 (37) 36 Net periodic benefit cost (credit) $ 1,622 $ 2,743 $ (244) $ 49

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	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Cash, Cash Equivalents, and Restricted Cash [Abstract]
Cash and cash equivalents	$ 6,398	$ 9,164	$ 7,757	$ 8,489
Restricted cash	24,640	16,023	16,263	13,974
Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statements of Cash Flows	$ 31,038	$ 25,187	$ 24,020	$ 22,463

Regulatory Matters (Details)

Regulatory Matters (Details) $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($) Rate
Electricity, US Regulated | Montana
Schedule of Regulated Operations [Line Items]
Rate base	$ 3,450
Electricity, US Regulated | Base electric rate | Montana
Schedule of Regulated Operations [Line Items]
Requested rate increase (decrease), amount	156.5
Electricity, US Regulated | Base electric rate - net of PCCAM and Property Tax | Montana
Schedule of Regulated Operations [Line Items]
Requested rate increase (decrease), amount	$ 69.4
Natural Gas, US Regulated | Montana
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Return on Equity, Percentage | Rate	10.80%
Public Utilities, Requested Equity Capital Structure, Percentage | Rate	46.81%
Rate base	$ 731.9
Natural Gas, US Regulated | South Dakota
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Return on Equity, Percentage | Rate	10.70%
Public Utilities, Requested Equity Capital Structure, Percentage | Rate	53.13%
Rate base	$ 95.6
Natural Gas, US Regulated | Nebraska
Schedule of Regulated Operations [Line Items]
Public Utilities, Requested Return on Equity, Percentage | Rate	10.70%
Public Utilities, Requested Equity Capital Structure, Percentage | Rate	53.13%
Rate base	$ 47.4
Natural Gas, US Regulated | Base gas rate | Montana
Schedule of Regulated Operations [Line Items]
Requested rate increase (decrease), amount	28.6
Natural Gas, US Regulated | Base gas rate | South Dakota
Schedule of Regulated Operations [Line Items]
Requested rate increase (decrease), amount	6
Natural Gas, US Regulated | Base gas rate | Nebraska
Schedule of Regulated Operations [Line Items]
Requested rate increase (decrease), amount	$ 3.6

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Income Tax Contingency [Line Items]
Unrecognized tax benefit more likely than not percentage threshold	50%
Unrecognized tax benefits	$ 27.3
Unrecognized tax benefits that would impact effective tax rate	24.3
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	6	$ 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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Effective tax rate reconciliation
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	$ 35,897	$ 21,271	$ 111,317	$ 94,042
Income tax calculated at federal statutory rate	7,539	4,467	23,377	19,749
State income tax, net of federal provisions	49	273	688	1,232
Flow-through repairs deductions	(3,069)	(1,708)	(9,243)	(7,553)
Production tax credits	(2,004)	(1,147)	(4,987)	(4,346)
Amortization of excess deferred income tax	(196)	(233)	(556)	(1,032)
Plant and depreciation flow-through items	1,060	201	4,139	889
Reduction to previously claimed alternative minimum tax credit			0	3,186
Share-based compensation			298	388
Other, net	864	294	861	(125)
Effective Income Tax Rate Reconciliation, Total Reconciling Items, Amount	(3,296)	(2,320)	(8,800)	(7,361)
Income tax expense	$ 4,243	$ 2,147	$ 14,577	$ 12,388
Income tax calculated at federal statutory rate	21%	21%	21%	21%
State income tax, net of federal provisions	0.10%	1.30%	0.60%	1.30%
Flow-through repairs deductions	(8.50%)	(8.00%)	(8.30%)	(8.00%)
Production tax credits	(5.60%)	(5.40%)	(4.50%)	(4.60%)
Amortization of excess deferred income tax	(0.50%)	(1.10%)	(0.50%)	(1.10%)
Reduction to previously claimed alternative minimum tax credit			0%	3.40%
Plant and depreciation flow-through items	3%	0.90%	3.70%	0.90%
Share-based compensation			0.30%	0.40%
Other, net	2.30%	1.40%	0.80%	(0.10%)
Effective Income Tax Rate Reconciliation, Total Reconciling Items, Percent	(9.20%)	(10.90%)	(7.90%)	(7.80%)
Income tax expense	11.80%	10.10%	13.10%	13.20%

Comprehensive Income (Loss) (De

Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Other Comprehensive Income (Loss), before Tax [Abstract]
Foreign currency translation adjustment	$ (1)	$ (1)	$ (2)	$ (3)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(153)	(153)	(306)	(306)
Defined benefit pension plan and postretirement medical liability adjustment	0	(212)	0	(424)
Other Comprehensive Income (Loss), before Tax	152	(60)	304	(121)
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)	(80)	(80)
Defined benefit pension plan and postretirement medical liability adjustment	0	45	0	90
Other Comprehensive Income (Loss), Tax	(40)	5	(80)	10
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	(1)	(1)	(2)	(3)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(113)	(113)	(226)	(226)
Defined benefit pension plan and postretirement medical liability adjustment	0	(167)	0	(334)
Total Other Comprehensive Income (Loss)	$ 112	$ (55)	$ 224	$ (111)

Classification within AOCL on t

Classification within AOCL on the Condenced Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Foreign currency translation	$ 1,435		$ 1,437
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(9,147)		(9,373)
Defined benefit pension plan	280		280
Accumulated other comprehensive loss	$ (7,432)	$ (7,544)	$ (7,656)	$ (7,959)	$ (7,904)	$ (7,848)

Changes in AOCI by Component (D

Changes in AOCI by Component (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (7,544)	$ (7,904)	$ (7,656)	$ (7,848)
Other comprehensive loss before reclassifications	(1)	(1)	(2)	(3)
Amounts reclassified from AOCL	113	113	226	226
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(167)		(334)
Total Other Comprehensive Income (Loss)	112	(55)	224	(111)
Ending balance	(7,432)	(7,959)	(7,432)	(7,959)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(9,260)	(9,712)	(9,373)	(9,825)
Other comprehensive loss before reclassifications	0	0	0	0
Amounts reclassified from AOCL	113	113	226	226
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		0		0
Total Other Comprehensive Income (Loss)	113	113	226	226
Ending balance	(9,147)	(9,599)	(9,147)	(9,599)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,436	1,433	1,437	1,435
Other comprehensive loss before reclassifications	(1)	(1)	(2)	(3)
Amounts reclassified from AOCL	0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		0		0
Total Other Comprehensive Income (Loss)	(1)	(1)	(2)	(3)
Ending balance	1,435	1,432	1,435	1,432
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	280	375	280	542
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		(167)		(334)
Total Other Comprehensive Income (Loss)	0	(167)	0	(334)
Ending balance	$ 280	$ 208	$ 280	$ 208

Financing Activities (Details)

Financing Activities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Short-term Debt [Line Items]
Short-Term Debt	$ 100,000	$ 0
Term Loan Due 2025
Short-term Debt [Line Items]
Short-Term Debt	$ 100,000
Debt Instrument, Maturity Date	Apr. 11, 2025
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	$ 175,000
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	$ 33,000
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	$ 7,000
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	$ 100,000

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Operating revenues	$ 319,929	$ 290,502	$ 795,271	$ 745,044
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	76,480	67,578	251,201	233,070
Utility margin	243,449	222,924	544,070	511,974
Operating and maintenance	57,367	54,840	111,549	110,701
Administrative and general	31,281	29,955	71,726	64,703
Property and other taxes	36,256	40,129	83,427	89,280
Depreciation and depletion	56,933	52,380	113,676	105,628
Operating income (loss)	61,612	45,620	163,692	141,662
Interest expense, net	(31,875)	(28,411)	(62,854)	(56,419)
Other income, net	6,160	4,062	10,479	8,799
Income tax expense	(4,243)	(2,147)	(14,577)	(12,388)
Net Income	31,654	19,124	96,740	81,654
Total assets	7,713,819	7,294,242	7,713,819	7,294,242	$ 7,600,652
Capital expenditures	138,607	126,758	247,361	263,362
Operating Segments | Electricity, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	260,134	229,266	603,320	524,574
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	60,887	42,363	176,228	120,497
Utility margin	199,247	186,903	427,092	404,077
Operating and maintenance	43,467	41,368	83,766	83,781
Administrative and general	23,294	21,635	51,213	46,603
Property and other taxes	28,006	31,022	64,306	69,273
Depreciation and depletion	47,546	43,319	94,850	87,217
Operating income (loss)	56,934	49,559	132,957	117,203
Interest expense, net	(23,298)	(21,724)	(47,955)	(40,284)
Other income, net	4,031	2,954	9,492	6,320
Income tax expense	(3,891)	(3,515)	(11,174)	(10,143)
Net Income	33,776	27,274	83,320	73,096
Total assets	6,172,704	5,878,433	6,172,704	5,878,433
Capital expenditures	112,258	94,690	202,848	215,509
Operating Segments | Natural Gas, US Regulated
Segment Reporting Information [Line Items]
Operating revenues	59,795	61,236	191,951	220,470
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	15,593	25,215	74,973	112,573
Utility margin	44,202	36,021	116,978	107,897
Operating and maintenance	13,900	13,472	27,783	26,920
Administrative and general	7,821	8,321	17,867	18,087
Property and other taxes	8,251	9,104	19,120	20,002
Depreciation and depletion	9,387	9,061	18,826	18,411
Operating income (loss)	4,843	(3,937)	33,382	24,477
Interest expense, net	(7,147)	(4,490)	(13,396)	(7,741)
Other income, net	927	1,144	1,981	2,559
Income tax expense	304	(373)	(2,869)	(139)
Net Income	(1,073)	(7,656)	19,098	19,156
Total assets	1,525,851	1,406,068	1,525,851	1,406,068
Capital expenditures	26,349	32,068	44,513	47,853
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	166	(1)	2,646	13
Property and other taxes	(1)	3	1	5
Depreciation and depletion	0	0	0	0
Operating income (loss)	(165)	(2)	(2,647)	(18)
Interest expense, net	(1,430)	(2,197)	(1,503)	(8,394)
Other income, net	1,202	(36)	(994)	(80)
Income tax expense	(656)	1,741	(534)	(2,106)
Net Income	(1,049)	(494)	(5,678)	(10,598)
Total assets	15,264	9,741	15,264	9,741
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, net	0	0	0	0
Income tax expense	0	0	0	0
Net Income	0	0	0	0
Total assets	0	0	0	0
Capital expenditures	$ 0	$ 0	$ 0	$ 0

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 327,600	$ 330,600	$ 760,400	$ 836,900
Total Revenues	319,929	290,502	795,271	745,044
Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	130,000	132,900	339,400	385,600
Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	104,900	101,400	270,900	293,800
Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	21,300	24,100	54,200	63,800
Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3,800	7,400	14,300	28,000
Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	142,400	147,100	312,300	348,700
Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	110,400	111,800	237,000	260,800
Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	30,000	30,600	67,100	70,100
Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,000	4,700	8,200	17,800
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	11,500	11,000	23,600	23,500
Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	8,900	9,000	14,200	14,900
Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	292,800	300,000	689,500	772,700
Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	34,800	30,600	70,900	64,200
Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	(7,700)	(40,100)	34,900	(91,900)
Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	319,900	290,500	795,300	745,000
Electric Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	271,500	266,000	579,000	587,400
Electric Domestic Regulated [Member] | Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	101,400	99,500	238,100	244,800
Electric Domestic Regulated [Member] | Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	86,000	83,800	203,400	209,300
Electric Domestic Regulated [Member] | Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	15,400	15,700	34,700	35,500
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	126,000	127,000	255,300	264,800
Electric Domestic Regulated [Member] | Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	99,700	101,900	201,200	214,500
Electric Domestic Regulated [Member] | Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	26,300	25,100	54,100	50,300
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	11,300	10,800	23,000	22,600
Electric Domestic Regulated [Member] | Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	8,600	8,700	13,300	13,900
Electric Domestic Regulated [Member] | Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	247,300	246,000	529,700	546,100
Electric Domestic Regulated [Member] | Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	24,200	20,000	49,300	41,300
Electric Domestic Regulated [Member] | Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	(11,400)	(36,700)	24,300	(62,800)
Electric Domestic Regulated [Member] | Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	260,100	229,300	603,300	524,600
Gas Domestic Regulated [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	56,100	64,600	181,400	249,500
Gas Domestic Regulated [Member] | Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	28,600	33,400	101,300	140,800
Gas Domestic Regulated [Member] | Residential | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	18,900	17,600	67,500	84,500
Gas Domestic Regulated [Member] | Residential | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	5,900	8,400	19,500	28,300
Gas Domestic Regulated [Member] | Residential | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3,800	7,400	14,300	28,000
Gas Domestic Regulated [Member] | Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	16,400	20,100	57,000	83,900
Gas Domestic Regulated [Member] | Commercial | Montana
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	10,700	9,900	35,800	46,300
Gas Domestic Regulated [Member] | Commercial | South Dakota
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3,700	5,500	13,000	19,800
Gas Domestic Regulated [Member] | Commercial | Nebraska
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,000	4,700	8,200	17,800
Gas Domestic Regulated [Member] | Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	200	200	600	900
Gas Domestic Regulated [Member] | Other, Lighting, Governmental, Irrigation, and Interdepartmental
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	300	300	900	1,000
Gas Domestic Regulated [Member] | Total Customer Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	45,500	54,000	159,800	226,600
Gas Domestic Regulated [Member] | Other Tariff and Contract Based Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	10,600	10,600	21,600	22,900
Gas Domestic Regulated [Member] | Regulatory amortization
Disaggregation of Revenue [Line Items]
Regulatory amortization	3,700	(3,400)	10,600	(29,100)
Gas Domestic Regulated [Member] | Total Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	$ 59,800	$ 61,200	$ 192,000	$ 220,400

Earnings Per Share (Details)

Earnings Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Basic computation	61,288,870	59,804,283	61,277,418	59,790,316
Performance share awards(1)	68,478	45,391	56,065	29,200
Diluted computation	61,357,348	59,849,674	61,333,483	59,819,516
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	35,933			21,890

Employee Benefit Plans Net Peri

Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Components of Net Periodic Benefit Cost (Income) [Abstract]
Minimum Expected Future Employer Pension Contributions, Remainder of Fiscal Year	$ 8,000		$ 8,000
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	1,378	$ 1,422	2,796	$ 2,916
Interest cost	5,739	6,482	11,472	13,047
Expected return on plan assets	(6,335)	(6,671)	(12,663)	(13,357)
Amortization of prior service credit	0	0	0	0
Recognized actuarial loss (gain)	6	(3)	17	137
Net periodic benefit cost (credit)	788	1,230	1,622	2,743
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	74	79	154	166
Interest cost	132	161	279	337
Expected return on plan assets	(321)	(273)	(640)	(548)
Amortization of prior service credit	0	29	0	58
Recognized actuarial loss (gain)	(25)	5	(37)	36
Net periodic benefit cost (credit)	$ (140)	$ 1	$ (244)	$ 49