0001193125-26-283163 | 11-K | XBRL Viewer

Plan Termination	12 Months Ended
Dec. 31, 2025
EBP 003
EBP, Description of Plan [Line Items]
Plan Termination	NOTE 6. PLAN TERMINATION Although it has not expressed any intent to do so, the Company has the right under the Plan to discontinue contributions at any time and to terminate the Plan subject to the provisions of ERISA. In the event of Plan termination, the participants would become 100% vested in their Company contributions.

Risks and Uncertainties	12 Months Ended
Dec. 31, 2025
EBP 003
EBP, Risk and Uncertainty [Line Items]
Risks and Uncertainties	NOTE 5. RISKS AND UNCERTAINTIES The Plan invests in various investment securities. Investment securities are exposed to various risks such as interest rate, market, and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of the investment securities will occur in the near term and such changes could materially affect participants’ account balances and the amounts reported in the statements of net assets available for benefits.

Plan Tax Status	12 Months Ended
Dec. 31, 2025
EBP 003
EBP, Tax Status [Line Items]
Plan Tax Status	NOTE 7. PLAN TAX STATUS The Plan relies on an opinion letter dated May 12, 2017, received from the IRS indicating the Plan is qualified under Section 401 of the IRC and is therefore not subject to tax under current income tax law. Although the Plan has been amended and restated since the date of the opinion letter, the Plan administrator believes the Plan is designed and is currently being operated in compliance with the applicable requirements of the IRC. Accounting principles generally accepted in the United States of America require Plan management to evaluate tax positions taken by the Plan and recognize a tax liability (or asset) if the Plan has taken an uncertain position that more likely than not would not be sustained upon examination by the IRS. The Plan administrator has analyzed the tax positions taken by the Plan, and concluded that as of December 31, 2025, there are no uncertain positions taken or expected to be taken that would require recognition of a liability (or asset) or disclosure in the financial statements. The Plan is subject to audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress.

Description of the Plan - Additional Information (Details) - EBP 003		12 Months Ended
	Dec. 16, 2024 Chapter	Dec. 31, 2025 USD ($) Chapter	Dec. 31, 2024 USD ($)
EBP, Description of Plan [Line Items]
Percentage of before-tax contributions of eligible compensation		1.00%
Employee's annual before-tax contribution limitation amount \| $		$ 23,500	$ 23,000
Employee benefit plan, IBEW chapter	77
Employer non-elective contribution of eligible compensation	5.00%
Vesting percentage		100.00%
Employee benefit plan, employer contribution, participant compensation matched, vesting percentage		100.00%
Employee benefit plan, non-elective employer contribution, participant compensation matched, vesting percentage		100.00%
Employee benefit plan notes receivable from participants interest rate of prime rate plus percentage		1.00%
Employee benefit plan contribution vesting description		Participant contributions are 100% vested at all times. Participants vest 100% in the Company matching contribution after one year of service or upon death, disability or reaching normal retirement age. Participants vest 100% in the non-elective employer contribution after three years of service or upon death, disability or reaching normal retirement age.
Employee benefit plan, notes receivable from participant, minimum loan, amount \| $		$ 1,000
Employee benefit plan, notes receivable from participant, account, maximum borrowing, amount \| $		$ 50,000
Employee benefit plan, note receivable from participant, account, maximum borrowing, to total account, percentage		50.00%
Employee benefit plan, notes receivable from participants general loan		5 years
Employee benefit plan, notes receivable from participants primary residence loan term		10 years
Employee benefit plan participant loan maturity year		2034
Employee benefit plan, unused forfeited balances \| $		$ 86,951	296,568
Employee benefit plan forfeited balance used to reduce Company contribution \| $		$ 165,027	$ 1,752
Plan Participants Hired Prior to April 1, 2022
EBP, Description of Plan [Line Items]
Percentage of participants contribution		3.00%
Plan Participants Hired on or After April 1, 2022
EBP, Description of Plan [Line Items]
Percentage of participants contribution		6.00%
75% Employee Contributions
EBP, Description of Plan [Line Items]
Matching contribution percentage		75.00%
Percentage on employee eligible compensation		6.00%
Employees Hired Prior to January 1, 2006
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		659
Employees Hired Prior to January 1, 2011
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		77
Employees Hired on or After January 1, 2006
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		659
Employees Hired on or After January 1, 2011
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		77
100% Employee Contributions
EBP, Description of Plan [Line Items]
Matching contribution percentage		100.00%
Percentage on employee eligible compensation		6.00%
Employees Hired on or After January 1, 2014
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		77
Employees Hired on or After April 1, 2014
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		659
Employees Hired on or after April 1, 2017
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		77
Members Hired on or After January 1, 2024
EBP, Description of Plan [Line Items]
Employee benefit plan, IBEW chapter		77
Employer non-elective contribution of eligible compensation		5.00%
Minimum
EBP, Description of Plan [Line Items]
Employee benefit plan, interest rate		4.25%
Employee benefit plan participant consent required for vested interest distribution \| $		$ 1,000
Minimum \| Plan Participants Hired Prior to April 1, 2022
EBP, Description of Plan [Line Items]
Percentage of increase in plan participants contribution per year		1.00%
Minimum \| Plan Participants Hired on or After April 1, 2022
EBP, Description of Plan [Line Items]
Percentage of increase in plan participants contribution per year		1.00%
Maximum
EBP, Description of Plan [Line Items]
Employee benefit plan, interest rate		9.50%
Employee benefit plan vested interest distribution period		3 years
Employee benefit plan vested interest distribution monthly installments period		15 years
Employee benefit plan vested interest distribution lump-sum payment \| $		$ 1,000
Maximum \| Plan Participants Hired Prior to April 1, 2022
EBP, Description of Plan [Line Items]
Percentage of increase in plan participants contribution per year		15.00%
Maximum \| Plan Participants Hired on or After April 1, 2022
EBP, Description of Plan [Line Items]
Percentage of increase in plan participants contribution per year		15.00%

Investments - Additional Information (Details) - EBP 003 - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
EBP, Master Trust [Line Items]
Stock Fund held in cash	$ 40,320	$ 35,564
Share price per share	$ 38.54	$ 36.63
Plan investments in the stock fund of total plan assets	1.98%	2.00%
Net appreciation in fair value of Plan assets	$ 1,013,000	$ 511,000
Common Stock
EBP, Master Trust [Line Items]
Number of shares purchased	494,358	460,288
Investments fair value	$ 19,052,557	$ 16,860,349

- Definition

Fair value of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Includes, but is not limited to, derivative, investment measured at net asset value per share as practical expedient, and insurance contract not meeting fully-benefit responsive investment criteria.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reference 29: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 50
-Paragraph 8C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477783/962-325-50-8C

+ Details

Schedule H, Line 4i - Schedule of Assets (Held at End of Year) (Details) - EBP 003	12 Months Ended
	Dec. 31, 2025 USD ($)
EBP, Schedule of Asset Held for Investment [Line Items]
Entity Tax Identification Number	91-0462470
EBP, Plan Number	003
Notes receivable from participants	$ 8,209,697
Total assets held for investment purposes	963,468,337
Investment, Identifier [Axis]: Avista Corporation Company Stock Fund
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 19,092,877
EBP, Investment, Issuer Name [Extensible Enumeration]	Avista Corporation [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	us-gaap:CommonStockMember
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
EBP, Asset Held for Investment, Party-in-Interest [true false]	true
Investment, Identifier [Axis]: Baird Core Plus Bond Fund Instl Class Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 14,139,290
EBP, Investment, Issuer Name [Extensible Enumeration]	Baird Core Plus Bond Fund Instl Class [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: MFS Growth Fund Class R6 Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 44,634,607
EBP, Investment, Issuer Name [Extensible Enumeration]	MFS Growth Fund Class R6 [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Self-Directed Brokerage Fund Self-Directed Brokerage Fund
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 17,395,322
EBP, Investment, Issuer Name [Extensible Enumeration]	Self-Directed Brokerage Fund [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	EBP, Self-Directed Brokerage Account [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: T. Rowe Price Inst'l Large Cap Value Fd C Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 19,010,651
EBP, Investment, Issuer Name [Extensible Enumeration]	T. Rowe Price Inst'l Large Cap Value Fd C [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: T. Rowe Price QM US Sm-Cap Grwth Eqty Fd I Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 4,896,185
EBP, Investment, Issuer Name [Extensible Enumeration]	T. Rowe Price QM US Sm-Cap Grwth Eqty Fd I [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Total Mutual Funds
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 885,418,068
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Transamerica International Equity R6 Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 6,922,085
EBP, Investment, Issuer Name [Extensible Enumeration]	Transamerica International Equity R6 [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Federal Money Market Fund Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 15,642,885
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Federal Money Market Fund [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Infla-Prot Securities Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 7,443,506
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Infla-Prot Securities [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Institutional Index Fund Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 200,479,375
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Institutional Index Fund [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Intl Growth Fund Admiral Shares Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 8,155,840
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Intl Growth Fund Admiral Shares [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Mid-Cap Index Fund Instl Shares Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 46,390,131
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Mid-Cap Index Fund Instl Shares [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Retirement Savings Trust III Collective Trust
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 33,352,373
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Retirement Savings Trust III [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Common Collective Trust [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Sm-Cap Growth Index Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 29,306,757
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Sm-Cap Growth Index [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Sm-Cap Value Index Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 14,328,793
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Sm-Cap Value Index [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2020 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 4,708,971
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2020 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2025 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 10,547,111
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2025 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2030 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 15,707,910
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2030 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2035 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 12,369,732
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2035 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2040 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 15,477,161
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2040 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2045 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 22,906,814
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2045 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2050 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 29,462,450
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2050 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2055 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 24,697,621
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2055 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2060 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 16,911,710
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2060 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2065 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 3,854,155
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2065 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret 2070 Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 863,002
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret 2070 Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret Income & Grwoth Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 296,440
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret Income & Growth Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Target Ret Income Trust II Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 4,670,173
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Target Ret Income Trust II [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Total Bd Mkt Indx Inv Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 64,838,493
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Total Bd Mkt Indx Inv [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Total Int'l Stock Idx Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 82,961,262
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Total Int'l Stock Idx [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Vanguard Wellington Fund Admiral Shares Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 161,768,149
EBP, Investment, Issuer Name [Extensible Enumeration]	Vanguard Wellington Fund Admiral Shares [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration]	us-gaap-ebp:EmployeeBenefitPlanParticipantDirectedMember
Investment, Identifier [Axis]: Victory Sycamore Sm Co Opportunity Fd R6 Registered Investment Company
EBP, Schedule of Asset Held for Investment [Line Items]
Current Value	$ 2,026,809
EBP, Investment, Issuer Name [Extensible Enumeration]	Victory Sycamore Sm Co Opportunity Fd R6 [Member]
EBP, Investment, Current Value, Type [Extensible Enumeration]	Mutual Fund [Member]
Minimum
EBP, Schedule of Asset Held for Investment [Line Items]
Employee benefit plan, asset held for investment, participant loan, interest rate	4.25%
Maximum
EBP, Schedule of Asset Held for Investment [Line Items]
Employee benefit plan, asset held for investment, participant loan, interest rate	9.50%

Schedule of Assets (Held at End of Year)

12 Months Ended

Dec. 31, 2025

EBP 003

EBP, Schedule of Asset Held for Investment [Line Items]

Schedule of Assets (Held at End of Year)

THE INVESTMENT AND EMPLOYEE STOCK OWNERSHIP PLAN

OF AVISTA CORPORATION

E.I.N. 91-0462470 PLAN NO. 003

SCHEDULE H, LINE 4i -- SCHEDULE OF ASSETS (HELD AT END OF YEAR)

DECEMBER 31, 2025

       (a)

       (b)

       (c)

       (d)

       (e)

        
       Current

        
       Identity of Issue

       Description of Investment

       Cost**

       Value

        
       Common Stock:

*

Avista Corporation

Company Stock Fund

19,092,877

        
       Self-Directed Securities:

*

Self-Directed Brokerage Fund

Self-Directed Brokerage Fund

17,395,322

        
       Mutual Funds:

Baird Core Plus Bond Fund Instl Class

Registered Investment Company

14,139,290

MFS Growth Fund Class R6

Registered Investment Company

44,634,607

T. Rowe Price Inst'l Large Cap Value Fd C

Registered Investment Company

19,010,651

T. Rowe Price QM US Sm-Cap Grwth Eqty Fd I

Registered Investment Company

4,896,185

Transamerica International Equity R6

Registered Investment Company

6,922,085

*

Vanguard Federal Money Market Fund

Registered Investment Company

15,642,885

*

Vanguard Infla-Prot Securities

Registered Investment Company

7,443,506

*

Vanguard Institutional Index Fund

Registered Investment Company

200,479,375

*

Vanguard Target Ret 2020 Trust II

Registered Investment Company

4,708,971

*

Vanguard Target Ret 2025 Trust II

Registered Investment Company

10,547,111

*

Vanguard Target Ret 2030 Trust II

Registered Investment Company

15,707,910

*

Vanguard Target Ret 2035 Trust II

Registered Investment Company

12,369,732

*

Vanguard Target Ret 2040 Trust II

Registered Investment Company

15,477,161

*

Vanguard Target Ret 2045 Trust II

Registered Investment Company

22,906,814

*

Vanguard Target Ret 2050 Trust II

Registered Investment Company

29,462,450

*

Vanguard Target Ret 2055 Trust II

Registered Investment Company

24,697,621

*

Vanguard Target Ret 2060 Trust II

Registered Investment Company

16,911,710

*

Vanguard Target Ret 2065 Trust II

Registered Investment Company

3,854,155

*

Vanguard Target Ret 2070 Trust II

Registered Investment Company

863,002

*

Vanguard Target Ret Income Trust II

Registered Investment Company

4,670,173

*

Vanguard Target Ret Income & Growth Trust II

Registered Investment Company

296,440

*

Vanguard Intl Growth Fund Admiral Shares

Registered Investment Company

8,155,840

*

Vanguard Mid-Cap Index Fund Instl Shares

Registered Investment Company

46,390,131

*

Vanguard Sm-Cap Growth Index

Registered Investment Company

29,306,757

*

Vanguard Sm-Cap Value Index

Registered Investment Company

14,328,793

*

Vanguard Total Bd Mkt Indx Inv

Registered Investment Company

64,838,493

*

Vanguard Total Int'l Stock Idx

Registered Investment Company

82,961,262

*

Vanguard Wellington Fund Admiral Shares

Registered Investment Company

161,768,149

Victory Sycamore Sm Co Opportunity Fd R6

Registered Investment Company

2,026,809

Total Mutual Funds

885,418,068

        
       Collective Trust:

*

Vanguard Retirement Savings Trust III

Collective Trust

33,352,373

       *

       Participant Loans

       Interest Rates 4.25% - 9.5%

Loan Fund

—

8,209,697

963,468,337

* Designates party-in-interest.

** Cost omitted for participant-directed investments.

STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS - EBP 003 - USD ($)	Dec. 31, 2025	Dec. 31, 2024
Investments (at Fair Value):
Total Investments (at Fair Value)	$ 955,258,640	$ 835,074,668
Receivables:
Employer Contributions	963,472	674,464
Notes receivable from participants	8,209,697	7,717,655
Total Receivables	9,173,169	8,392,119
Net Assets Available for Benefits	964,431,809	843,466,787
Avista Corp. Company Stock Fund
Investments (at Fair Value):
Total Investments (at Fair Value)	19,092,877	16,899,724
Self-Directed Securities
Investments (at Fair Value):
Total Investments (at Fair Value)	17,395,322	14,943,677
Collective Trust
Investments (at Fair Value):
Total Investments (at Fair Value)	33,352,373	37,524,876
Mutual Funds
Investments (at Fair Value):
Total Investments (at Fair Value)	$ 885,418,068	$ 765,706,391

Description of the Plan

12 Months Ended

Dec. 31, 2025

EBP 003

EBP, Description of Plan [Line Items]

Description of the Plan

NOTE 1. DESCRIPTION OF THE PLAN

The following description of The Investment and Employee Stock Ownership Plan of Avista Corporation (the Plan) provides only general information. Participants should refer to the Plan document for a more complete description of the Plan’s provisions.

General

Effective January 1, 1984, Avista Corporation (Corporation, Company or Avista) established an Employee Investment Plan under Section 401(k) of the Internal Revenue Code (IRC). The Plan, which was restated effective January 1, 2016, and most recently amended effective December 16, 2024, is a defined contribution plan which is subject to the provisions of the Employee Retirement Income Security Act of 1974 (ERISA) and all statutory revisions thereto. The purpose of the Plan, in which participation is voluntary, is to encourage employees to systematically save a portion of their compensation and to supplement their savings with contributions from Avista. All employees of Avista are eligible to participate in the Plan after their first pay period following employment. Students, leased employees, and collectively bargained employees (other than collectively bargained employees whose employment is subject to the terms of a collective bargaining agreement which provides for participation in the Plan) are ineligible to participate in the Plan.

Contributions

Plan participants may make contributions during any payroll period for which they receive earnings as eligible employees in an amount at least equal to 1% of their earnings. A participating employee’s annual before-tax contribution was subject to IRC limitations of $23,500 in 2025 and $23,000 in 2024. Participants who have attained age 50 before the end of the Plan year are eligible to make catch-up contributions. Participants may also contribute amounts representing distributions from other qualified defined benefit or defined contribution plans, subject to IRC limits. Employee contributions represent tax-deferred compensation and Roth 401(k) after tax compensation and may be invested in the employee’s choice of various fund options (each with a different investment objective and risk) in the combination specified by the employee. Employee contributions are made by payroll deduction and transferred to the Plan Trustee as soon as practicable following the payroll period in which such amounts are withheld.

Plan participants hired prior to April 1, 2022 are automatically enrolled in the Plan upon eligibility at a 3% deferral rate, with an automatic increase of 1% each year up to 15%.

Plan participants hired on or after April 1, 2022 are automatically enrolled in the Plan upon eligibility at a 6% deferral rate, with an automatic increase of 1% each year up to 15%.

Participants can opt out of the Plan at any time. Participants can change their deferral rate at any time.

Plan participants may transfer balances from other qualified defined benefit or defined contribution plans, and certain eligible retirement plans and accounts to the Plan.

Avista has an obligation to the trust fund for an amount equal to a percentage of employee contributions determined by the hire date of the employee.

All non-collectively bargained employees and Local 659 employees hired prior to January 1, 2006, and Local 77 employees hired prior to January 1, 2011, receive a matching contribution of 75% of employee contributions that does not exceed 6% of the employee’s salary.

All non-collectively bargained employees and Local 659 employees hired on or after January 1, 2006, and Local 77 employees hired on or after January 1, 2011, receive a matching contribution of 100% of employee contributions that does not exceed 6% of the employee’s salary.

Further, all non-collectively bargained employees hired on or after January 1, 2014, Local 659 employees hired on or after April 1, 2014, Local 77 employees hired on or after April 1, 2017 as a Distribution Dispatcher or Gas Controller from outside Avista or who is ineligible to participate in the Retirement Plan for Employees of Avista Corporation, Local 77 members hired on or after January 1, 2024, and any participant who elected to waive participation in the Retirement Plan for Employees of Avista Corporation as of July 1, 2024, receive an additional non-elective employer contribution based on the employee’s age. The table below illustrates the non-elective contribution rate assigned to the established age groups.


Age		Contribution as a Percentage of Eligible Pay
Younger than 40		3%
40-49		4%
50 or Older		5%

Local 77 members hired on or after January 1, 2024, or who waived participation in the Retirement Plan for Employees of Avista Corporation who are not Distribution Operators, Gas Controllers, or non-collectively bargained employees are also eligible for an additional Employer non-elective contribution equal to 5% of eligible compensation. Remaining Local 77 employees are eligible for the additional non-elective contribution equal to 5% of eligible compensation as of December 16, 2024.

The Company matching contributions are made in the form of cash that is invested as directed by participants from among the investment options offered under the Plan.

Any employees who transfer or have transferred from a Local 77 employee directly to non-Local 77 employee on or after January 1, 2014, other than those Local 77 employees hired on or after April 1, 2017 as a Distribution Dispatcher or Gas Controller from outside Avista or who is ineligible to participate in the Retirement Plan for Employees of Avista Corporation, are not eligible for the additional non-elective employer contributions.

Participant Accounts

Each participant’s account is credited with the participant’s contribution and allocations of (a) the Company’s contribution and (b) Plan earnings or losses, and charged with an allocation of administrative expenses. Allocations are based on participant earnings or account balances, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant’s vested account.

Vesting

Participant contributions are 100% vested at all times. Participants vest 100% in the Company matching contribution after one year of service or upon death, disability or reaching normal retirement age. Participants vest 100% in the non-elective employer contribution after three years of service or upon death, disability or reaching normal retirement age.

Notes Receivable from Participants

Participants may borrow from their fund accounts a minimum of $1,000 up to a maximum equal to the lesser of $50,000 or 50% of their vested account balance. Principal and interest is paid ratably through payroll deductions. The notes are secured by the balance in the participant’s account and bear interest at a rate of prime rate plus 1%. The maximum term of a general loan is five years, and the maximum term of a primary residence loan is 10 years. Interest rates ranged from 4.25% to 9.50% at December 31, 2025, for loans maturing through 2034.

Payment of Benefits

Distributions to participants are permitted for termination, retirement, death, disability, or financial hardship. A participant with a financial hardship which imposes an immediate and heavy financial need that cannot be reasonably met by other sources may withdraw a portion of their account balance subject to provisions of the Plan. Distributions due to termination shall commence as soon as administratively feasible following the date a participant terminates employment. Distributions may be made in a lump sum, partial lump sum, equal annual installments over a period not to exceed 3 years, or monthly installments over not more than 15 years. If the vested amount is less than $1,000, the account is paid in a lump-sum payment to the participant within a reasonable time frame. If the vested amount is more than $1,000, the participant must consent to the distribution before it may be made.

Forfeited Accounts

At December 31, 2025 and 2024, forfeited non-vested accounts totaled $86,951 and $296,568, respectively. These accounts are used first to restore accounts for returning participants, and then are used to reduce the Company’s obligations to make contributions under the Plan. If there are any excess forfeitures after the Company makes matching contributions, the excess amount may be used to pay administrative expenses under the Plan. In 2025 and 2024, forfeitures in the amount of $165,027 and $1,752 were used to reduce employer contributions.

Voting Rights

Each participant is entitled to exercise voting rights attributable to the shares allocated to their account and is notified by the Trustee prior to the time such rights are to be exercised. The Trustee will vote any shares on which such instructions have not been received, as well as unallocated shares, proportionately in the same manner as Avista Corporation Common Stock for which the Trustee received voting instructions, unless the Trustee determines that to do so would not be consistent with ERISA or a voting participant elects not to have their vote be used in this manner, in which case the Trustee will vote the non-voted or unallocated Avista Corporation Common Stock in a manner consistent with ERISA. Fractional shares will be combined to the largest number of whole shares and voted by the Trustee to the extent possible to reflect the voting direction of whole shares by the participants holding fractional shares.

Diversification

Diversification is offered to participants to provide the opportunity to move the value of their investment in the Avista Corporation Common Stock into investments which are more diversified. Participants are entitled to make an election to diversify up to 100% of the value of the Avista Corporation Common Stock held in their Employee Stock Ownership Plan (ESOP) account.

Employee Stock Ownership Plan (ESOP)

Effective January 1, 2006, the Avista Corporation Company Stock Fund was designated an ESOP. Employer and employee contributions into Avista Corporation Common Stock are classified as ESOP contributions.

Fair Value of Measurements (Tables)

12 Months Ended

Dec. 31, 2025

EBP 003

EBP, Investment, Fair Value and NAV [Line Items]

Summary of Fair Value of Plan Assets by Level within Fair Value Hierarchy

The following tables set forth by level, within the fair value hierarchy, the Plan’s assets at fair value as of December 31:


	2025
	Level 1		Level 2		Level 3		Total
Avista Corp. Company Stock Fund	$	19,092,877	$	—	$	—	$	19,092,877
Self-Directed Securities		17,395,322		—		—		17,395,322
Mutual Funds		885,418,068		—		—		885,418,068
Collective Trust		—		33,352,373		—		33,352,373
Total Investments at Fair Value	$	921,906,267	$	33,352,373	$	—	$	955,258,640

	2024
	Level 1		Level 2		Level 3		Total
Avista Corp. Company Stock Fund	$	16,899,724	$	—	$	—	$	16,899,724
Self-Directed Securities		14,943,677		—		—		14,943,677
Mutual Funds		765,706,391		—		—		765,706,391
Collective Trust		—		37,524,876		—		37,524,876
Total Investments at Fair Value	$	797,549,792	$	37,524,876	$	—	$	835,074,668

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Tabular disclosure of fair value of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), including, but not limited to, fair value measured at net asset value per share as practical expedient (NAV).

+ References

+ Details

Summary of Significant Accounting Policies (Policies) - EBP 003	12 Months Ended
	Dec. 31, 2025
EBP, Accounting Policy [Line Items]
Basis of Accounting	Basis of Accounting The accounting records of the Plan are maintained on the accrual basis of accounting in accordance with accounting principles generally accepted in the United States of America.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and changes therein, and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates.
Investment Valuation and Income Recognition	Investment Valuation and Income Recognition The Plan’s investments are reported at fair value. Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Plan’s Benefit Plan Administration Committee determines the Plan’s valuation policies utilizing information provided by the investment advisors and custodian. See Note 3 for discussion of fair value measurements. Purchases and sales are recorded on a trade-date basis. Interest income is recorded on the accrual basis. Dividends are recorded on the ex-dividend date. Net appreciation and depreciation includes the Plan’s realized gains and losses and the unrealized appreciation and depreciation of investments.
Benefit Payments	Benefit Payments Benefits are recorded when paid.
Notes Receivable From Participants	Notes Receivable from Participants Notes receivable from participants are measured at their unpaid principal balance plus any accrued but unpaid interest. Interest income is recorded on the accrual basis. Related fees are recorded as administrative expenses and are expensed when they are incurred. No allowance for credit losses was recorded as of December 31, 2025 or 2024. If a participant ceases to make note repayments and the Plan administrator deems the participant note to be in default, the participant note balance is reduced and a benefit payment is recorded based on the terms of the Plan document.
Administrative Expenses	Administrative Expenses The Plan’s expenses are paid either by the Plan or the Company, as provided by the Plan document. Expenses paid by the Company are excluded from these financial statements. Certain expenses incurred in connection with the general administration of the Plan paid by the Plan are recorded as deductions in the accompanying statements of changes in net assets available for benefits. Fees related to the administration of notes receivable from participants and benefit payments are charged directly to the participant’s account and are included in administrative expense.
Subsequent Events	Subsequent Events On August 12, 2025, the Plan amended provisions to allow for Roth in-plan conversions, traditional after-tax contributions, and Qualified Disaster Recovery Distributions, effective January 1, 2026. Other than the amendment disclosed above, the plan administrator evaluated events and transactions occurring after the date of the statement of net assets through the date the financial statements were issued, and noted no events subject to recognition or disclosure.

- Definition

Disclosure of accounting policy for use of estimate in preparation of financial statement of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References + Details

Fair Value of Measurements

12 Months Ended

Dec. 31, 2025

EBP 003

EBP, Investment, Fair Value and NAV [Line Items]

Fair Value Measurements

NOTE 3. FAIR VALUE OF INVESTMENTS

The framework for measuring fair value provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy are described as follows:

Level 1: Inputs to the valuation methodology are unadjusted quoted prices for identical assets or liabilities in active markets the Plan can access.

Level 2: Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly, such as:

•

quoted prices for similar assets or liabilities in active markets;

•

quoted prices for identical or similar assets or liabilities in inactive markets;

•

inputs other than quoted prices observable for the asset or liability;

•

inputs derived principally from or corroborated by observable market data by correlation or other means.

If the asset or liability has a specified (contractual) term, the Level 2 input must be observable for substantially the full term of the asset or liability.

Level 3: Inputs to the valuation methodology are unobservable and significant to the fair value measurement.

The asset's or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques maximize the use of relevant observable inputs and minimize the use of unobservable inputs.

Following is a description of the valuation methodologies used for assets measured at fair value. There were no changes in the valuation methodologies used at December 31, 2025 and 2024.

Mutual Funds: Valued at the daily closing price as reported by the fund. Mutual funds held by the Plan are open-end mutual funds registered with the Securities and Exchange Commission. These funds are required to publish their daily net asset value (NAV) and to transact at that price. The mutual funds held by the Plan are actively traded.

Collective Trust: Valued at the NAV of units of a collective trust. NAV is a readily-determinable fair value and is the price which participants are able to transact under the terms of the Plan. Participant transactions (purchases and sales) may occur daily. If the Plan initiates a full redemption of the collective trust, the issuer reserves the right to temporarily delay withdrawal from the trust in order to ensure securities liquidations will be carried out in an orderly business manner.

Common Stock: Valued at the closing price reported on the active market on which the individual securities are traded.

Avista Corporation Company Stock Fund: Includes shares of Avista Corporation and cash, and is reported based on unitized value.

Self-Directed Securities: Self-Directed Securities consist of mutual funds and common stocks and interest bearing cash that are valued on the basis of readily determinable market prices.

The following tables set forth by level, within the fair value hierarchy, the Plan’s assets at fair value as of December 31:


	2025
	Level 1		Level 2		Level 3		Total
Avista Corp. Company Stock Fund	$	19,092,877	$	—	$	—	$	19,092,877
Self-Directed Securities		17,395,322		—		—		17,395,322
Mutual Funds		885,418,068		—		—		885,418,068
Collective Trust		—		33,352,373		—		33,352,373
Total Investments at Fair Value	$	921,906,267	$	33,352,373	$	—	$	955,258,640

	2024
	Level 1		Level 2		Level 3		Total
Avista Corp. Company Stock Fund	$	16,899,724	$	—	$	—	$	16,899,724
Self-Directed Securities		14,943,677		—		—		14,943,677
Mutual Funds		765,706,391		—		—		765,706,391
Collective Trust		—		37,524,876		—		37,524,876
Total Investments at Fair Value	$	797,549,792	$	37,524,876	$	—	$	835,074,668

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The entire disclosure for fair value of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), including, but not limited to, fair value measured at net asset value per share as practical expedient (NAV).

+ References

+ Details

STATEMENTS OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS - EBP 003 - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Investment income:
Interest and Dividend Income	$ 40,389,472	$ 35,028,025
Net Appreciation in Fair Value of Investments	91,286,941	68,868,128
Total Investment Income	131,676,413	103,896,153
Interest Income on Notes Receivable from Participants	650,757	551,067
Contributions:
Employee	27,737,086	25,412,578
Employer	18,503,798	15,914,137
Rollover	3,836,110	2,041,150
Total Contributions	50,076,994	43,367,865
Deductions:
Benefits Paid to Participants	60,598,545	54,894,454
Administrative Expenses	840,597	784,281
Total Deductions	61,439,142	55,678,735
INCREASE IN NET ASSETS	120,965,022	92,136,350
Net Assets Available for Benefits
Beginning of Year	843,466,787	751,330,437
End of Year	$ 964,431,809	$ 843,466,787

Fair Value Measurements - Summary of Fair Value of Plan Assets by Level within Fair Value Hierarchy (Details) - EBP 003 - USD ($)	Dec. 31, 2025	Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	$ 955,258,640	$ 835,074,668
Avista Corp. Company Stock Fund
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	19,092,877	16,899,724
Self-Directed Securities
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	17,395,322	14,943,677
Mutual Funds
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	885,418,068	765,706,391
Collective Trust
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	33,352,373	37,524,876
Level 1
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	921,906,267	797,549,792
Level 1 \| Avista Corp. Company Stock Fund
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	19,092,877	16,899,724
Level 1 \| Self-Directed Securities
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	17,395,322	14,943,677
Level 1 \| Mutual Funds
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	885,418,068	765,706,391
Level 1 \| Collective Trust
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 2
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	33,352,373	37,524,876
Level 2 \| Avista Corp. Company Stock Fund
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 2 \| Self-Directed Securities
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 2 \| Mutual Funds
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 2 \| Collective Trust
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	33,352,373	37,524,876
Level 3
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 3 \| Avista Corp. Company Stock Fund
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 3 \| Self-Directed Securities
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 3 \| Mutual Funds
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	0	0
Level 3 \| Collective Trust
EBP, Investment, Fair Value and NAV [Line Items]
Total Investments at Fair Value	$ 0	$ 0

Document and Entity Information	12 Months Ended
Document and Entity Information	Dec. 31, 2025
Document Information [Line Items]
Document Type	11-K
Entity Central Index Key	0000104918
Entity Registrant Name	AVISTA CORPORATION
Amendment Flag	false
EBP 003 [Member]
Document Information [Line Items]
Document Type	11-K
Document Period End Date	Dec. 31, 2025
Document Fiscal Year Focus	2025
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0000104918
Entity Registrant Name	AVISTA CORPORATION
Amendment Flag	false
Document Fiscal Period Focus	FY

Party-in-Interest Transactions - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
EBP 003 \| Common Stock
EBP, Related Party and Party-in-Interest Transactions [Line Items]
Employee benefit plan, Dividends received	$ 941,542	$ 933,889

Party-in-Interest Transactions	12 Months Ended
Party-in-Interest Transactions	Dec. 31, 2025
EBP 003
EBP, Related Party and Party-in-Interest Transactions [Line Items]
Party-in-Interest Transactions	NOTE 8. PARTY-IN-INTEREST TRANSACTIONS The Plan investments are managed by Vanguard Fiduciary Trust Company (Vanguard). Vanguard is the Trustee as defined by the Plan, and therefore, the investment transactions qualify as party-in-interest transactions. SageView is the investment advisor for the Plan, and fees paid for investment advisory services qualify as party-in-interest transactions. Dividends received from Avista Corporation common stock totaled $941,542 and $933,889 for the years ended December 31, 2025 and 2024, respectively, and qualify as party-in-interest transactions. These party-in-interest transactions are exempt from the prohibited transaction rules of ERISA. Fees incurred by the Plan for investment management services and investment advisory services are included in administrative expenses. Certain other expenses of the Plan for recordkeeping, legal and accounting fees are included in administrative expenses. Expenses paid by the Company are not included in the statements of changes in net assets available for benefits.

Description of the Plan - Summary of Percentage of Compensation the Company Contributes (Details) - EBP 003		12 Months Ended
	Dec. 16, 2024	Dec. 31, 2025
EBP, Description of Plan [Line Items]
Contribution percentage	5.00%
Younger than 40
EBP, Description of Plan [Line Items]
Contribution percentage		3.00%
40-49
EBP, Description of Plan [Line Items]
Contribution percentage		4.00%
50 or Older
EBP, Description of Plan [Line Items]
Contribution percentage		5.00%

Plan Termination - Additional Information (Details)	12 Months Ended
Plan Termination - Additional Information (Details)	Dec. 31, 2025
EBP 003
EBP, Description of Plan [Line Items]
Employee benefit plan termination participants employer contributions vested percentage	100.00%

Investments	12 Months Ended
Investments	Dec. 31, 2025
EBP 003
EBP, Fully Benefit-Responsive Investment Contract [Line Items]
Investments	NOTE 4. INVESTMENTS Participants of the Plan can invest in the Avista Corporation Company Stock Fund (Stock Fund). NAV is based on the fair value of the underlying Avista Corporation common stock and money market fund owned by the Stock Fund and then divided by the number of units outstanding. The Stock Fund consists of Avista Corporation common stock and Northern Trust Money Market Fund. The money market fund and common stock are valued as described in the previous paragraphs. At December 31, 2025, the Stock Fund held $40,320 of cash and 494,358 shares of the Company’s common stock with a value of $19,052,557, which is based on a price per share of $38.54. At December 31, 2024, the Stock Fund held $35,564 of cash and 460,288 shares of the Company’s common stock with a value of $16,860,349, which is based on a price per share of $36.63. Plan investments in the Stock Fund represented 1.98% and 2.00% of total Plan assets at December 31, 2025 and 2024, respectively. For the year ended December 31, 2025, the Plan's investment in the Stock Fund experienced net appreciation in fair value of approximately $1,013,000 compared to the net appreciation of approximately $511,000 experienced in 2024.

Plan Tax Status - Additional Information (Details) - EBP 003	12 Months Ended
	Dec. 31, 2025
EBP, Tax Status [Line Items]
Tax determination letter, obtained	true
Tax determination letter, date	May 12, 2017
EBP, Tax Qualification Status [Extensible Enumeration]	us-gaap:QualifiedPlanMember