Avista (AVA) 10-Q 2 Aug 17 2017 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Jul. 31, 2017
Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Trading Symbol	ava
Entity Registrant Name	AVISTA CORP
Entity Central Index Key	104,918
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		64,411,244

Consolidated Statements Of Inco

Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating Revenues:
Utility revenues	$ 308,729	$ 312,888	$ 739,266	$ 725,681
Other non-utility revenues	5,772	5,950	11,705	11,330
Total operating revenues	314,501	318,838	750,971	737,011
Utility operating expenses:
Resource costs	102,751	109,815	268,337	271,534
Other operating expenses	81,965	78,666	156,449	154,445
Depreciation and amortization	42,643	39,678	84,628	78,870
Taxes other than income taxes	23,802	22,615	56,464	52,000
Other non-utility operating expenses:
Other operating expenses	7,086	6,281	13,265	12,106
Depreciation and amortization	157	192	345	380
Total operating expenses	258,404	257,247	579,488	569,335
Income from operations	56,097	61,591	171,483	167,676
Interest expense	23,670	21,318	47,215	42,591
Interest expense to affiliated trusts	200	154	385	292
Capitalized interest	(890)	(837)	(1,614)	(1,751)
Other income-net	(1,656)	(3,041)	(4,757)	(5,463)
Income before income taxes	34,773	43,997	130,254	132,007
Income tax expense	13,051	16,710	46,395	47,055
Net income	21,722	27,287	83,859	84,952
Net income attributable to noncontrolling interests	49	(33)	28	(49)
Net income attributable to Avista Corporation shareholders	$ 21,771	$ 27,254	$ 83,887	$ 84,903
Weighted-average common shares outstanding (thousands), basic	64,401	63,386	64,382	62,995
Weighted-average common shares outstanding (thousands), diluted	64,553	63,783	64,511	63,368
Earnings per common share attributable to Avista Corporation shareholders:
Basic	$ 0.34	$ 0.43	$ 1.30	$ 1.35
Diluted	0.34	0.43	1.30	1.34
Common Stock, Dividends, Per Share, Cash Paid	$ 0.3575	$ 0.3425	$ 0.7150	$ 0.6850

Consolidated Statements Of Comp

Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 21,722	$ 27,287	$ 83,859	$ 84,952
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	183	140	366	(1,089)
Total other comprehensive loss	183	140	366	(1,089)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	21,905	27,427	84,225	83,863
Net income attributable to noncontrolling interests	49	(33)	28	(49)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 21,954	$ 27,394	$ 84,253	$ 83,814

Consolidated Statements Of Com4

Consolidated Statements Of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax	$ 99	$ 76	$ 197	$ (587)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 13,410	$ 8,507
Accounts and notes receivable-less allowances of $5,607 and $5,026, respectively	133,946	180,265
Regulatory asset for energy commodity derivatives	13,982	11,365
Materials and supplies, fuel stock and stored natural gas	61,187	53,314
Income taxes receivable	35,808	48,265
Other current assets	62,403	49,625
Total current assets	320,736	351,341
Net Utility Property:
Utility plant in service	5,617,233	5,506,499
Construction work in progress	169,000	150,474
Total	5,786,233	5,656,973
Less: Accumulated depreciation and amortization	1,558,773	1,509,473
Total net utility property	4,227,460	4,147,500
Other Non-current Assets:
Investment in affiliated trusts	11,547	11,547
Goodwill	57,672	57,672
Other property and investments-net	79,487	72,224
Total other non-current assets	148,706	141,443
Deferred Charges:
Regulatory assets for deferred income tax	118,984	109,853
Regulatory assets for pensions and other postretirement benefits	234,046	240,114
Other regulatory assets	134,533	135,751
Regulatory asset for interest rate swaps	168,084	161,508
Non-current regulatory asset for utility derivatives	15,023	16,919
Other deferred charges	5,432	5,326
Total deferred charges	676,102	669,471
Total assets	5,373,004	5,309,755
Current Liabilities:
Accounts payable	69,165	115,545
Current portion of long-term debt	277,814	3,287
Short-term borrowings	136,398	120,000
Utility energy commodity derivative liabilities	8,308	7,035
Accrued interest	16,128	15,869
Accrued taxes other than income taxes	33,169	33,374
Deferred natural gas costs	28,973	30,820
Current portion of pensions and other postretirement benefits	11,235	10,994
Current interest rate swap derivative liabilities	36,507	6,025
Other current liabilities	64,417	64,579
Total current liabilities	682,114	407,528
Long-term debt and capital leases	1,403,064	1,678,717
Long-term debt to affiliated trusts	51,547	51,547
Regulatory liability for utility plant retirement costs	280,580	273,983
Pensions and other postretirement benefits	219,584	226,552
Deferred income taxes	886,727	840,928
Non-current interest rate swap derivative liabilities	336	28,705
Other non-current liabilities and deferred credits	162,158	153,319
Total liabilities	3,686,110	3,661,279
Commitments and Contingencies (See Notes to Consolidated Financial Statements)
Avista Corporation Stockholders’ Equity:
Common stock, no par value; 200,000,000 shares authorized; 64,408,983 and 64,187,934 shares issued and outstanding as of June 30, 2017 and December 31, 2016, respectively	1,075,667	1,075,281
Accumulated other comprehensive loss	(7,202)	(7,568)
Retained earnings	618,708	581,014
Total Avista Corporation stockholders’ equity	1,687,173	1,648,727
Noncontrolling Interests	(279)	(251)
Total equity	1,686,894	1,648,476
Total liabilities and equity	$ 5,373,004	$ 5,309,755

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts and notes receivable, allowances	$ 5,607	$ 5,026
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares outstanding	64,408,983	64,187,934

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating Activities:
Net income	$ 83,859	$ 84,952
Non-cash items included in net income:
Depreciation and amortization	86,790	81,071
Provision for deferred income taxes	36,169	56,652
Power and natural gas cost amortizations (deferrals), net	6,366	9,958
Amortization of debt expense	1,627	1,742
Amortization of investment in exchange power	1,225	1,225
Stock-based compensation expense	2,643	4,236
Equity-related AFUDC	(3,292)	(4,368)
Pension and other postretirement benefit expense	18,539	19,315
Amortization of Spokane Energy contract	0	7,192
Other regulatory assets and liabilities and deferred debits and credits	(8,831)	(13,169)
Change in decoupling regulatory deferral	10,365	(24,787)
Other	420	5,032
Contributions to defined benefit pension plan	(14,800)	(8,000)
Changes in certain current assets and liabilities:
Accounts and notes receivable	45,375	50,062
Materials and supplies, fuel stock and natural gas stored	(7,879)	2,510
Collateral posted for derivative instruments	(5,460)	(83,499)
Income taxes receivable	12,457	(1,450)
Other current assets	(3,825)	(4,436)
Accounts payable	(29,435)	(31,484)
Other current liabilities	(3,787)	3,197
Net cash provided by operating activities	228,526	155,951
Investing Activities:
Utility property capital expenditures (excluding equity-related AFUDC)	(177,714)	(182,815)
Issuance of notes receivable at subsidiaries	(2,500)	(9,668)
Equity and property investments made by subsidiaries	(10,347)	(6,988)
Distributions received from investments	1,915	0
Other	(943)	(7,153)
Net cash used in investing activities	(189,589)	(206,624)
Financing Activities:
Net increase in short-term borrowings	16,000	55,000
Maturity of long-term debt and capital leases	(1,643)	(1,583)
Issuance of common stock	1,247	47,173
Cash dividends paid	(46,193)	(43,267)
Other	(3,445)	(3,612)
Net cash provided by (used in) financing activities	(34,034)	53,711
Net increase in cash and cash equivalents	4,903	3,038
Cash and cash equivalents at beginning of period	8,507	10,484
Cash and cash equivalents at end of period	$ 13,410	$ 13,522

Consolidated Statements Of Equi

Consolidated Statements Of Equity And Redeemable Noncontrolling Interests - USD ($) $ in Thousands	Total	Common Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Noncontrolling Interests [Member]
Beginning Balance (in shares) at Dec. 31, 2015		62,312,651
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued		1,391,644
Ending Balance (in shares) at Jun. 30, 2016		63,704,295
Beginning Balance at Dec. 31, 2015		$ 1,004,336	$ (6,650)	$ 530,940
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		3,708
Issuance of common stock, net of issuance costs		47,173
Payment of minimum tax withholdings for share-based payment awards		(3,027)
Other comprehensive income (loss)	$ (1,089)		(1,089)
Net income attributable to Avista Corporation shareholders	84,903			84,903
Cash dividends paid (common stock)				(43,267)
Ending Balance at Jun. 30, 2016	$ 1,617,027	$ 1,052,190	(7,739)	572,576
Beginning Balance Noncontrolling Interest at Dec. 31, 2015					$ (339)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					49
Ending Balance Noncontrolling Interest at Jun. 30, 2016					(290)
Beginning Balance (in shares) at Dec. 31, 2015		62,312,651
Ending Balance (in shares) at Dec. 31, 2016	64,187,934	64,187,934
Beginning Balance at Dec. 31, 2015		$ 1,004,336	(6,650)	530,940
Ending Balance at Dec. 31, 2016	$ 1,648,727	$ 1,075,281	(7,568)	581,014
Beginning Balance Noncontrolling Interest at Dec. 31, 2015					(339)
Ending Balance Noncontrolling Interest at Dec. 31, 2016	251				(251)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total equity	1,616,737
Total equity	$ 1,648,476
Shares issued		221,049
Ending Balance (in shares) at Jun. 30, 2017	64,408,983	64,408,983
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity compensation expense		$ 2,559
Issuance of common stock, net of issuance costs		1,247
Payment of minimum tax withholdings for share-based payment awards		(3,420)
Other comprehensive income (loss)	$ 366		366
Net income attributable to Avista Corporation shareholders	83,887			83,887
Cash dividends paid (common stock)				(46,193)
Ending Balance at Jun. 30, 2017	1,687,173	$ 1,075,667	$ (7,202)	$ 618,708
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Net income (loss) attributable to noncontrolling interests					(28)
Ending Balance Noncontrolling Interest at Jun. 30, 2017	279				$ (279)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Total equity	$ 1,686,894

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Business Avista Corp. is primarily an electric and natural gas utility with certain other business ventures. Avista Utilities is an operating division of Avista Corp., comprising the regulated utility operations in the Pacific Northwest. Avista Utilities provides electric distribution and transmission, and natural gas distribution services in parts of eastern Washington and northern Idaho. Avista Utilities also provides natural gas distribution service in parts of northeastern and southwestern Oregon. Avista Utilities has electric generating facilities in Washington, Idaho, Oregon and Montana. Avista Utilities also supplies electricity to a small number of customers in Montana, most of whom are employees who operate Avista Utilities' Noxon Rapids generating facility. Alaska Energy and Resources Company (AERC) is a wholly-owned subsidiary of Avista Corp. The primary subsidiary of AERC is Alaska Electric Light and Power Company (AEL&P), which comprises Avista Corp.'s regulated utility operations in Alaska. Avista Capital, Inc. (Avista Capital), a wholly owned non-regulated subsidiary of Avista Corp., is the parent company of all of the subsidiary companies in the non-utility businesses, with the exception of AJT Mining Properties, Inc., which is a subsidiary of AERC. Basis of Reporting The condensed consolidated financial statements include the assets, liabilities, revenues and expenses of the Company and its subsidiaries and other majority owned subsidiaries and variable interest entities for which the Company or its subsidiaries are the primary beneficiaries. Intercompany balances were eliminated in consolidation. The accompanying condensed consolidated financial statements include the Company’s proportionate share of utility plant and related operations resulting from its interests in jointly owned plants. Taxes Other Than Income Taxes Taxes other than income taxes include state excise taxes, city occupational and franchise taxes, real and personal property taxes and certain other taxes not based on income. These taxes are generally based on revenues or the value of property. Utility related taxes collected from customers (primarily state excise taxes and city utility taxes) are recorded as operating revenue and expense. Taxes other than income taxes consisted of the following items for the three and six months ended June 30 (dollars in thousands): Three months ended June 30, Six months ended June 30, 2017 2016 2017 2016 Utility related taxes $ 13,552 $ 12,573 $ 35,136 $ 30,938 Property taxes 9,432 9,290 19,838 19,710 Other taxes 818 752 1,490 1,352 Total $ 23,802 $ 22,615 $ 56,464 $ 52,000 Materials and Supplies, Fuel Stock and Stored Natural Gas Inventories of materials and supplies, fuel stock and stored natural gas are recorded at average cost for our regulated operations and the lower of cost or net realizable value for our non-regulated operations and consisted of the following as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Materials and supplies $ 41,492 $ 40,700 Fuel stock 5,921 4,585 Stored natural gas 13,774 8,029 Total $ 61,187 $ 53,314 Derivative Assets and Liabilities Derivatives are recorded as either assets or liabilities on the Condensed Consolidated Balance Sheets measured at estimated fair value. The Washington Utilities and Transportation Commission (UTC) and the Idaho Public Utilities Commission (IPUC) issued accounting orders authorizing Avista Corp. to offset energy commodity derivative assets or liabilities with a regulatory asset or liability. This accounting treatment is intended to defer the recognition of mark-to-market gains and losses on energy commodity transactions until the period of delivery. Realized benefits and costs result in adjustments to retail rates through purchased gas cost adjustments, the Energy Recovery Mechanism (ERM) in Washington, the Power Cost Adjustment (PCA) mechanism in Idaho, and periodic general rate cases. The resulting regulatory assets have been concluded to be probable of recovery through future rates. Substantially all forward contracts to purchase or sell power and natural gas are recorded as derivative assets or liabilities at estimated fair value with an offsetting regulatory asset or liability. Contracts that are not considered derivatives are accounted for on the accrual basis until they are settled or realized unless there is a decline in the fair value of the contract that is determined to be other-than-temporary. For interest rate swap derivatives, Avista Corp. records all mark-to-market gains and losses in each accounting period as assets and liabilities, as well as offsetting regulatory assets and liabilities, such that there is no income statement impact. The interest rate swap derivatives are risk management tools similar to energy commodity derivatives. Upon settlement of interest rate swap derivatives, the regulatory asset or liability is amortized as a component of interest expense over the term of the associated debt. The Company records an offset of interest rate swap derivative assets and liabilities with regulatory assets and liabilities, based on the prior practice of the commissions to provide recovery through the ratemaking process. As of June 30, 2017 , the Company has multiple master netting agreements with a variety of entities that allow for cross-commodity netting of derivative agreements with the same counterparty (i.e. power derivatives can be netted with natural gas derivatives). In addition, some master netting agreements allow for the netting of commodity derivatives and interest rate swap derivatives for the same counterparty. The Company does not have any agreements which allow for cross-affiliate netting among multiple affiliated legal entities. The Company nets all derivative instruments when allowed by the agreement for presentation in the Condensed Consolidated Balance Sheets. Fair Value Measurements Fair value represents the price that would be received when selling an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. Energy commodity derivative assets and liabilities, deferred compensation assets, as well as derivatives related to interest rate swaps and foreign currency exchange contracts, are reported at estimated fair value on the Condensed Consolidated Balance Sheets. See Note 8 for the Company’s fair value disclosures. Accumulated Other Comprehensive Loss Accumulated other comprehensive loss, net of tax, consisted of the following as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Unfunded benefit obligation for pensions and other postretirement benefit plans - net of taxes of $3,878 and $4,075, respectively $ 7,202 $ 7,568 The following table details the reclassifications out of accumulated other comprehensive loss by component for the three and six months ended June 30 (dollars in thousands). Amounts Reclassified from Accumulated Other Comprehensive Loss Three months ended June 30, Six months ended June 30, Details about Accumulated Other Comprehensive Loss Components 2017 2016 2017 2016 Affected Line Item in Statement of Income Amortization of defined benefit pension items Amortization of net prior service cost $ (299 ) $ (311 ) $ (598 ) $ (622 ) (a) Amortization of net loss 3,638 3,642 $ 7,276 $ 7,284 (a) Adjustment due to effects of regulation (3,057 ) (3,115 ) (6,115 ) (8,338 ) (a) (b) 282 216 563 (1,676 ) Total before tax (99 ) (76 ) (197 ) 587 Tax benefit (expense) $ 183 $ 140 $ 366 $ (1,089 ) Net of tax (a) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 4 for additional details). (b) The adjustment for the effects of regulation during the six months ended June 30, 2016 includes approximately $2.1 million related to the reclassification of a pension regulatory asset associated with one of our jurisdictions into accumulated other comprehensive loss. Contingencies The Company has unresolved regulatory, legal and tax issues which have inherently uncertain outcomes. The Company accrues a loss contingency if it is probable that a liability has been incurred and the amount of the loss or impairment can be reasonably estimated. The Company also discloses loss contingencies that do not meet these conditions for accrual if there is a reasonable possibility that a material loss may be incurred. As of June 30, 2017 , the Company has not recorded any significant amounts related to unresolved contingencies. See Note 11 for further discussion of the Company's commitments and contingencies.

New Accounting Standards

New Accounting Standards	6 Months Ended
	Jun. 30, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Standards	NEW ACCOUNTING STANDARDS ASU No. 2014-09, “Revenue from Contracts with Customers (Topic 606)” In May 2014, the FASB issued ASU No. 2014-09, which outlines a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The core principle of the revenue model is that an entity should identify the various performance obligations in a contract, allocate the transaction price among the performance obligations and recognize revenue when (or as) the entity satisfies each performance obligation. This ASU is effective for periods beginning after December 15, 2017. The Company has a revenue recognition standard implementation team that is working through implementation issues. The Company has evaluated this standard and is planning to adopt this standard in 2018 upon its effective date. The Company is expecting to use a modified retrospective method of adoption, which would require a cumulative adjustment to opening retained earnings, as opposed to a full retrospective application. Based on work performed to date, the Company has not identified any material cumulative adjustments necessary. Since the majority of Avista Corp.’s revenue is from rate-regulated sales of electricity and natural gas to retail customers and revenue is recognized as energy is delivered to these customers, the Company does not expect a significant change in operating revenues or net income. The Company is in the process of reviewing and analyzing certain contracts with customers (most of which are related to wholesale sales of power and natural gas) and has not yet identified any significant differences in revenue recognition between current GAAP and ASU No. 2014-09. During the implementation process, the Company has identified several issues, the most significant of which are as follows based on our current assessment: Contributions in Aid of Construction – There was the potential that contributions in aid of construction (CIAC) could be recognized as revenue upon the adoption of ASU No. 2014-09. Under current GAAP, CIACs are accounted for as an offset to the cost of utility plant in service. Current preliminary implementation guidance indicates that CIACs will continue to be accounted for as an offset to utility plant in service. Utility-Related Taxes Collected from Customers – There were questions on the presentation of utility related taxes collected from customers (primarily state excise taxes and city utility taxes) on a gross basis. Under current GAAP, the Company is allowed to record these utility related taxes on a gross basis in revenue when billed to customers with an offset included in taxes other than income taxes in operating expenses. The Company evaluated whether this gross presentation is appropriate under ASU 2014-09 and the Company's preliminary assessment indicates that there will be no material changes to current presentation. Collectibility - There were questions regarding the requirement that collection of a sale be probable and how, or if, utilities should consider bad debt collection mechanisms (riders, base rate adjustments, etc.) in assessing probability of collection on sales to low income customers. Current preliminary implementation guidance indicates that bad debt collection mechanisms should be considered; therefore, the Company does not expect a change to its current presentation going forward. The Company is monitoring utility industry implementation guidance as it relates to certain issues to determine if there will be an industry consensus regarding accounting and presentation of these items. In addition to the issues described above, the Company also expects significant changes to its revenue-related footnote disclosures. The Company continues to evaluate what information would be most useful for users of the financial statements, including information already provided elsewhere in the document outside the footnote disclosures. These additional disclosures could include the disaggregation of revenues by geographic location, type of service, source of revenue or customer class. Also, the Company expects enhanced disclosures regarding its revenue recognition policies and elections. ASU No. 2016-02 “Leases (Topic 842).” In February 2016, the FASB issued ASU No. 2016-02. This ASU introduces a new lessee model that requires most leases to be capitalized and shown on the balance sheet with corresponding lease assets and liabilities. The standard also aligns certain of the underlying principles of the new lessor model with those in Topic 606, the FASB’s new revenue recognition standard. Furthermore, this ASU addresses other issues that arise under the current lease model; for example, eliminating the required use of bright-line tests in current GAAP for determining lease classification (operating leases versus capital leases). This ASU also includes enhanced disclosures surrounding leases. This ASU is effective for periods beginning on or after December 15, 2018; however, early adoption is permitted. Upon adoption, this ASU must be applied using a modified retrospective approach to the earliest period presented, which will likely require restatements of previously issued financial statements. The modified retrospective approach includes a number of optional practical expedients that entities may elect to apply. The Company evaluated this standard and determined that it will most likely not early adopt this standard before its effective date in 2019. The Company has formed a lease standard implementation team that is working through the implementation process. The most significant implementation challenge identified thus far relates to identifying a complete population of leases and potential leases under the new lease standard. Also, the Company is monitoring utility industry implementation guidance as it relates to several unresolved issues to determine if there will be an industry consensus, including whether right-of-ways are considered leases. The Company has not yet estimated the potential impact on its future financial condition, results of operations and cash flows. ASU No. 2016-09 “Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting.” In March 2016, the FASB issued ASU No. 2016-09. This ASU simplified several aspects of the accounting for employee share-based payment transactions including: • allowing excess tax benefits or tax deficiencies to be recognized as income tax benefits or expenses in the Condensed Consolidated Statements of Income rather than in Additional Paid in Capital (APIC), • excess tax benefits no longer represent a financing cash inflow on the Condensed Consolidated Statements of Cash Flows and instead will be included as an operating activity, • requiring excess tax benefits and tax deficiencies to be excluded from the calculation of diluted earnings per share, whereas under previous accounting guidance, these amounts had to be estimated and included in the calculation, • allowing forfeitures to be accounted for as they occur, instead of estimating forfeitures, and • changing the statutory tax withholding requirements for share-based payments. The Company early adopted this standard during the second quarter of 2016, with a retrospective effective date of January 1, 2016. The adoption of this standard resulted in a recognized income tax benefit of $1.6 million in 2016 associated with excess tax benefits on settled share-based employee payments. Because this standard was adopted in the second quarter of 2016, but had a retrospective effective date of January 1, 2016, the effects from the adoption were reflected in the first quarter of 2016 and the Condensed Consolidated Financial Statements for that quarter were recast from those presented when the financial statements were originally issued. ASU No. 2017-07 “Compensation-Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” In March 2017, the FASB issued ASU No. 2017-07, which amends the income statement presentation of the components of net period benefit cost for an entity’s defined benefit pension and other postretirement plans. Under current GAAP, net benefit cost consists of several components that reflect different aspects of an employer’s financial arrangements as well as the cost of benefits earned by employees. These components are aggregated and reported net in the financial statements. ASU No. 2017-07 requires entities to (1) disaggregate the current service-cost component from the other components of net benefit cost (other components) and present it with other current compensation costs for related employees in the income statement and (2) present the other components elsewhere in the income statement and outside of income from operations. In addition, only the service-cost component of net benefit cost is eligible for capitalization (e.g., as part of utility plant). This is a change from current practice, under which entities capitalize the aggregate net benefit cost to utility plant when applicable, in accordance with Federal Energy and Regulatory Commission (FERC) accounting guidance. Avista Corp. is a rate-regulated entity and all components of net benefit cost are currently recovered from rate payers as a component of utility plant and under the new ASU these costs will continue to be recovered from rate payers in the same manner over the depreciable lives of utility plant. As all such costs are expected to continue to be recoverable, the components that are no longer eligible to be recorded as a component of plant for GAAP will be recorded as regulatory assets. This ASU is effective for periods beginning after December 15, 2017 and early adoption is permitted. Upon adoption, entities must use a retrospective transition method to adopt the requirement for separate presentation in the income statement and a prospective transition method to adopt the requirement to limit the capitalization of benefit costs to the service-cost component. The Company does not expect to early adopt this standard and does not expect a material impact on its future financial condition, results of operations or cash flows upon adoption of this standard.

Derivatives And Risk Management

Derivatives And Risk Management	6 Months Ended
	Jun. 30, 2017
Derivative Instruments and Hedges, Assets [Abstract]
Derivatives And Risk Management	DERIVATIVES AND RISK MANAGEMENT The disclosures below in Note 3 apply only to Avista Corp. and its operating division Avista Utilities; AERC and its primary subsidiary AEL&P do not enter into derivative instruments. Energy Commodity Derivatives Avista Corp. is exposed to market risks relating to changes in electricity and natural gas commodity prices and certain other fuel prices. Market risk is, in general, the risk of fluctuation in the market price of the commodity being traded and is influenced primarily by supply and demand. Market risk includes the fluctuation in the market price of associated derivative commodity instruments. Avista Corp. utilizes derivative instruments, such as forwards, futures, swap derivatives and options in order to manage the various risks relating to these commodity price exposures. Avista Corp. has an energy resources risk policy and control procedures to manage these risks. As part of Avista Corp.'s resource procurement and management operations in the electric business, Avista Corp. engages in an ongoing process of resource optimization, which involves the economic selection from available energy resources to serve Avista Corp.'s load obligations and the use of these resources to capture available economic value. Avista Corp. transacts in wholesale markets by selling and purchasing electric capacity and energy, fuel for electric generation, and derivative contracts related to capacity, energy and fuel. Such transactions are part of the process of matching resources with load obligations and hedging a portion of the related financial risks. These transactions range from terms of intra-hour up to multiple years. As part of its resource procurement and management of its natural gas business, Avista Corp. makes continuing projections of its natural gas loads and assesses available natural gas resources including natural gas storage availability. Natural gas resource planning typically includes peak requirements, low and average monthly requirements and delivery constraints from natural gas supply locations to Avista Corp.’s distribution system. However, daily variations in natural gas demand can be significantly different than monthly demand projections. On the basis of these projections, Avista Corp. plans and executes a series of transactions to hedge a portion of its projected natural gas requirements through forward market transactions and derivative instruments. These transactions may extend as much as four natural gas operating years (November through October) into the future. Avista Corp. also leaves a significant portion of its natural gas supply requirements unhedged for purchase in short-term and spot markets. Avista Corp. plans for sufficient natural gas delivery capacity to serve its retail customers for a theoretical peak day event. Avista Corp. generally has more pipeline and storage capacity than what is needed during periods other than a peak day. Avista Corp. optimizes its natural gas resources by using market opportunities to generate economic value that helps mitigate fixed costs. Avista Corp. also optimizes its natural gas storage capacity by purchasing and storing natural gas when prices are traditionally lower, typically in the summer, and withdrawing during higher priced months, typically during the winter. However, if market conditions and prices indicate that Avista Corp. should buy or sell natural gas at other times during the year, Avista Corp. engages in optimization transactions to capture value in the marketplace. Natural gas optimization activities include, but are not limited to, wholesale market sales of surplus natural gas supplies, purchases and sales of natural gas to optimize use of pipeline and storage capacity, and participation in the transportation capacity release market. The following table presents the underlying energy commodity derivative volumes as of June 30, 2017 that are expected to be delivered in each respective year (in thousands of MWhs and mmBTUs): Purchases Sales Electric Derivatives Gas Derivatives Electric Derivatives Gas Derivatives Year Physical (1) MWH Financial (1) MWH Physical (1) mmBTUs Financial (1) mmBTUs Physical (1) Financial (1) Physical (1) Financial (1) Remainder 2017 185 999 7,418 63,423 154 1,129 3,378 43,940 2018 397 307 — 78,488 254 1,244 1,360 46,805 2019 235 737 610 42,775 158 982 1,345 26,590 2020 — — 910 3,635 — — 1,430 — 2021 — — — — — — 1,049 — Thereafter — — — — — — — — The following table presents the underlying energy commodity derivative volumes as of December 31, 2016 that are expected to be delivered in each respective year (in thousands of MWhs and mmBTUs): Purchases Sales Electric Derivatives Gas Derivatives Electric Derivatives Gas Derivatives Year Physical (1) MWH Financial (1) MWH Physical (1) mmBTUs Financial (1) mmBTUs Physical (1) Financial (1) Physical (1) Financial (1) 2017 510 907 15,475 110,380 316 1,552 4,165 73,110 2018 397 — — 52,755 286 1,244 1,360 15,113 2019 235 — 610 29,475 158 982 1,345 4,020 2020 — — 910 2,725 — — 1,430 — 2021 — — — — — — 1,060 — Thereafter — — — — — — — — (1) Physical transactions represent commodity transactions in which Avista Corp. will take or make delivery of either electricity or natural gas; financial transactions represent derivative instruments with delivery of cash in the amount of the benefit or cost but with no physical delivery of the commodity, such as futures, swap derivatives, options, or forward contracts. The electric and natural gas derivative contracts above will be included in either power supply costs or natural gas supply costs during the period they are delivered and will be included in the various recovery mechanisms (ERM, PCA, and Purchased Gas Adjustments (PGA)), or in the general rate case process, and are expected to be collected through retail rates from customers. Foreign Currency Exchange Derivatives A significant portion of Avista Corp.’s natural gas supply (including fuel for power generation) is obtained from Canadian sources. Most of those transactions are executed in U.S. dollars, which avoids foreign currency risk. A portion of Avista Corp.’s short-term natural gas transactions and long-term Canadian transportation contracts are committed based on Canadian currency prices and settled within 60 days with U.S. dollars. Avista Corp. hedges a portion of the foreign currency risk by purchasing Canadian currency exchange derivatives when such commodity transactions are initiated. The foreign currency exchange derivatives and the unhedged foreign currency risk have not had a material effect on Avista Corp.’s financial condition, results of operations or cash flows and these differences in cost related to currency fluctuations are included with natural gas supply costs for ratemaking. The following table summarizes the foreign currency exchange derivatives that Avista Corp. has outstanding as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Number of contracts 24 21 Notional amount (in United States dollars) $ 7,588 $ 2,819 Notional amount (in Canadian dollars) 10,075 3,754 Interest Rate Derivatives Avista Corp. is affected by fluctuating interest rates related to a portion of its existing debt, and future borrowing requirements. Avista Corp. hedges a portion of its interest rate risk with financial derivative instruments, which may include interest rate swap derivatives and U.S. Treasury lock agreements. These interest rate swap derivatives and U.S. Treasury lock agreements are considered economic hedges against fluctuations in future cash flows associated with anticipated debt issuances. The following table summarizes the unsettled interest rate swap derivatives that Avista Corp. has outstanding as of June 30, 2017 and December 31, 2016 (dollars in thousands): Balance Sheet Date Number of Contracts Notional Amount Mandatory Cash Settlement Date June 30, 2017 6 $ 75,000 2017 14 275,000 2018 6 70,000 2019 3 30,000 2020 5 60,000 2022 December 31, 2016 6 $ 75,000 2017 14 275,000 2018 6 70,000 2019 2 20,000 2020 5 60,000 2022 The fair value of outstanding interest rate swap derivatives can vary significantly from period to period depending on the total notional amount of swap derivatives outstanding and fluctuations in market interest rates compared to the interest rates fixed by the swaps. Avista Corp. is required to make cash payments to settle the interest rate swap derivatives when the fixed rates are higher than prevailing market rates at the date of settlement. Conversely, Avista Corp. receives cash to settle its interest rate swap derivatives when prevailing market rates at the time of settlement exceed the fixed swap rates. Upon settlement of interest rate swaps, the cash payments made or received are recorded as a regulatory asset or liability and are amortized as a component of interest expense over the life of the associated debt. The settled interest rate swaps are also included as a part of the Company's cost of debt calculation for ratemaking purposes. Summary of Outstanding Derivative Instruments The amounts recorded on the Condensed Consolidated Balance Sheet as of June 30, 2017 and December 31, 2016 reflect the offsetting of derivative assets and liabilities where a legal right of offset exists. The following table presents the fair values and locations of derivative instruments recorded on the Condensed Consolidated Balance Sheet as of June 30, 2017 (in thousands): Fair Value as of June 30, 2017 Derivative and Balance Sheet Location Gross Asset Gross Liability Collateral Netted Net Asset (Liability) on Balance Sheet Foreign currency exchange derivatives Other current assets $ 187 $ — $ — $ 187 Interest rate swap derivatives Other current assets 5,626 (208 ) — 5,418 Other property and investments-net and other non-current assets 5,676 (1,645 ) — 4,031 Current interest rate swap derivative liabilities — (78,077 ) 41,570 (36,507 ) Non-current interest rate swap derivative liabilities — (336 ) — (336 ) Energy commodity derivatives Other current assets 168 (11 ) — 157 Current energy commodity derivative liabilities 22,577 (36,716 ) 5,831 (8,308 ) Other non-current liabilities, regulatory liabilities and deferred credits 12,532 (27,555 ) 3,936 (11,087 ) Total derivative instruments recorded on the balance sheet $ 46,766 $ (144,548 ) $ 51,337 $ (46,445 ) The following table presents the fair values and locations of derivative instruments recorded on the Condensed Consolidated Balance Sheet as of December 31, 2016 (in thousands): Fair Value as of December 31, 2016 Derivative and Balance Sheet Location Gross Asset Gross Liability Collateral Net Asset Foreign currency exchange derivatives Other current liabilities $ 5 $ (28 ) $ — $ (23 ) Interest rate swap derivatives Other current assets 3,393 — — 3,393 Other property and investments-net and other non-current assets 5,754 (397 ) — 5,357 Current interest rate swap derivative liabilities — (15,756 ) 9,731 (6,025 ) Non-current interest rate swap derivative liabilities 3,951 (57,825 ) 25,169 (28,705 ) Energy commodity derivatives Other current assets 18,682 (16,787 ) — 1,895 Current energy commodity derivative liabilities 16,335 (29,598 ) 6,228 (7,035 ) Other non-current liabilities, regulatory liabilities and deferred credits 13,071 (29,990 ) 3,630 (13,289 ) Total derivative instruments recorded on the balance sheet $ 61,191 $ (150,381 ) $ 44,758 $ (44,432 ) Exposure to Demands for Collateral Avista Corp.'s derivative contracts often require collateral (in the form of cash or letters of credit) or other credit enhancements, or reductions or terminations of a portion of the contract through cash settlement. In the event of a downgrade in Avista Corp.'s credit ratings or changes in market prices, additional collateral may be required. In periods of price volatility, the level of exposure can change significantly. As a result, sudden and significant demands may be made against Avista Corp.'s credit facilities and cash. Avista Corp. actively monitors the exposure to possible collateral calls and takes steps to mitigate capital requirements. The following table presents Avista Corp.'s collateral outstanding related to its derivative instruments as of June 30, 2017 and December 31, 2016 (in thousands): June 30, December 31, 2017 2016 Energy commodity derivatives Cash collateral posted $ 15,924 $ 17,134 Letters of credit outstanding 37,250 24,400 Balance sheet offsetting (cash collateral against net derivative positions) 9,767 9,858 Interest rate swap derivatives Cash collateral posted 41,570 34,900 Letters of credit outstanding 13,100 3,600 Balance sheet offsetting (cash collateral against net derivative positions) 41,570 34,900 Certain of Avista Corp.’s derivative instruments contain provisions that require Avista Corp. to maintain an "investment grade" credit rating from the major credit rating agencies. If Avista Corp.’s credit ratings were to fall below "investment grade," it would be in violation of these provisions, and the counterparties to the derivative instruments could request immediate payment or demand immediate and ongoing collateralization on derivative instruments in net liability positions. The following table presents the aggregate fair value of all derivative instruments with credit-risk-related contingent features that are in a liability position and the amount of additional collateral Avista Corp. could be required to post as of June 30, 2017 and December 31, 2016 (in thousands): June 30, December 31, 2017 2016 Energy commodity derivatives Liabilities with credit-risk-related contingent features $ 648 $ 1,124 Additional collateral to post 648 1,046 Interest rate swap derivatives Liabilities with credit-risk-related contingent features 80,266 73,978 Additional collateral to post 11,210 21,100

Pension Plans And Other Postret

Pension Plans And Other Postretirement Benefit Plans	6 Months Ended
	Jun. 30, 2017
General Discussion of Pension and Other Postretirement Benefits [Abstract]
Pension Plans and Other Postretirement Benefit Plans	PENSION PLANS AND OTHER POSTRETIREMENT BENEFIT PLANS Avista Utilities Avista Utilities’ pension and other postretirement plans have not changed during the six months ended June 30, 2017 . The Company’s funding policy is to contribute at least the minimum amounts that are required to be funded under the Employee Retirement Income Security Act, but not more than the maximum amounts that are currently deductible for income tax purposes. The Company contributed $14.8 million in cash to the pension plan for the six months ended June 30, 2017 and expects to contribute a total of $22.0 million in 2017. The Company contributed $12.0 million in cash to the pension plan in 2016 . The Company uses a December 31 measurement date for its defined benefit pension and other postretirement benefit plans. The following table sets forth the components of net periodic benefit costs for the three and six months ended June 30 (dollars in thousands): Pension Benefits Other Post-retirement Benefits 2017 2016 2017 2016 Three months ended June 30: Service cost $ 5,092 $ 4,569 $ 799 $ 804 Interest cost 6,976 6,900 1,374 1,534 Expected return on plan assets (7,900 ) (6,875 ) (475 ) (475 ) Amortization of prior service cost — — (312 ) (312 ) Net loss recognition 2,317 2,201 1,320 1,494 Net periodic benefit cost $ 6,485 $ 6,795 $ 2,706 $ 3,045 Six months ended June 30: Service cost $ 10,134 $ 9,088 $ 1,623 $ 1,583 Interest cost 13,927 13,800 2,773 3,093 Expected return on plan assets (15,800 ) (13,625 ) (950 ) (950 ) Amortization of prior service cost — — (624 ) (624 ) Net loss recognition 4,863 4,091 2,593 2,859 Net periodic benefit cost $ 13,124 $ 13,354 $ 5,415 $ 5,961 Total net periodic benefit costs in the table above are recorded to the same accounts as labor expense. Labor and benefits expense is recorded to various projects based on whether the work is a capital project or an operating expense. Approximately 40 percent of all labor and benefits is capitalized to utility property and 60 percent is expensed to other operating expenses.

Committed Lines of Credit

Committed Lines of Credit	6 Months Ended
	Jun. 30, 2017
Short-term Debt [Abstract]
Committed Lines of Credit	COMMITTED LINES OF CREDIT Avista Corp. Avista Corp. has a committed line of credit with various financial institutions in the total amount of $400.0 million that expires in April 2021 . The committed line of credit is secured by non-transferable first mortgage bonds of the Company issued to the agent bank that would only become due and payable in the event, and then only to the extent, that the Company defaults on its obligations under the committed line of credit. Borrowings outstanding and interest rates of borrowings (excluding letters of credit) under the Company’s revolving committed line of credit were as follows as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Borrowings outstanding at end of period $ 136,000 $ 120,000 Letters of credit outstanding at end of period $ 56,703 $ 34,353 Average interest rates at end of period 1.99 % 1.50 % As of June 30, 2017 and December 31, 2016 , the borrowings outstanding under Avista Corp.'s committed line of credit were classified as short-term borrowings on the Condensed Consolidated Balance Sheet. The additional short-term borrowings outstanding as of June 30, 2017 on the Condensed Consolidated Balance Sheet relate to a short-term note payable by a subsidiary for the acquisition of land that will be repaid in early 2018. AEL&P AEL&P has a committed line of credit in the amount of $25.0 million that expires in November 2019 . As of June 30, 2017 and December 31, 2016 , there were no borrowings or letters of credit outstanding under this committed line of credit. The committed line of credit is secured by non-transferable first mortgage bonds of AEL&P issued to the agent bank that would only become due and payable in the event, and then only to the extent, that AEL&P defaults on its obligations under the committed line of credit.

Long-Term Debt and Capital Leas

Long-Term Debt and Capital Leases Long-Term Debt and Capital Leases (Notes)	6 Months Ended
	Jun. 30, 2017
Debt Disclosure [Abstract]
Debt and Capital Leases Disclosures [Text Block]	LONG-TERM DEBT AND CAPITAL LEASES The following details long-term debt outstanding as of June 30, 2017 and December 31, 2016 (dollars in thousands): Maturity Year Description Interest Rate June 30, December 31, Avista Corp. Secured Long-Term Debt 2018 First Mortgage Bonds 5.95% $ 250,000 $ 250,000 2018 Secured Medium-Term Notes 7.39%-7.45% 22,500 22,500 2019 First Mortgage Bonds 5.45% 90,000 90,000 2020 First Mortgage Bonds 3.89% 52,000 52,000 2022 First Mortgage Bonds 5.13% 250,000 250,000 2023 Secured Medium-Term Notes 7.18%-7.54% 13,500 13,500 2028 Secured Medium-Term Notes 6.37% 25,000 25,000 2032 Secured Pollution Control Bonds (1) (1) 66,700 66,700 2034 Secured Pollution Control Bonds (1) (1) 17,000 17,000 2035 First Mortgage Bonds 6.25% 150,000 150,000 2037 First Mortgage Bonds 5.70% 150,000 150,000 2040 First Mortgage Bonds 5.55% 35,000 35,000 2041 First Mortgage Bonds 4.45% 85,000 85,000 2044 First Mortgage Bonds 4.11% 60,000 60,000 2045 First Mortgage Bonds 4.37% 100,000 100,000 2047 First Mortgage Bonds 4.23% 80,000 80,000 2051 First Mortgage Bonds 3.54% 175,000 175,000 Total Avista Corp. secured long-term debt 1,621,700 1,621,700 Alaska Electric Light and Power Company Secured Long-Term Debt 2044 First Mortgage Bonds 4.54% 75,000 75,000 Total secured long-term debt 1,696,700 1,696,700 Alaska Energy and Resources Company Unsecured Long-Term Debt 2019 Unsecured Term Loan 3.85% 15,000 15,000 Total secured and unsecured long-term debt 1,711,700 1,711,700 Other Long-Term Debt Components Capital lease obligations 63,791 65,435 Unamortized debt discount (709 ) (792 ) Unamortized long-term debt issuance costs (10,204 ) (10,639 ) Total 1,764,578 1,765,704 Secured Pollution Control Bonds held by Avista Corporation (1) (83,700 ) (83,700 ) Current portion of long-term debt and capital leases (277,814 ) (3,287 ) Total long-term debt and capital leases $ 1,403,064 $ 1,678,717 (1) In December 2010, $66.7 million and $17.0 million of the City of Forsyth, Montana Pollution Control Revenue Refunding Bonds (Avista Corporation Colstrip Project) due in 2032 and 2034 , respectively, which had been held by Avista Corp. since 2008 and 2009, respectively, were refunded by new variable rate bond issues (Series 2010A and Series 2010B). The new bonds were not offered to the public and were purchased by Avista Corp. due to market conditions. The Company expects that at a later date, subject to market conditions, these bonds may be remarketed to unaffiliated investors. So long as Avista Corp. is the holder of these bonds, the bonds will not be reflected as an asset or a liability on Avista Corp.'s Consolidated Balance Sheets.

Long- Term Debt to Affiliated T

Long- Term Debt to Affiliated Trust Long-Term Debt to Affiliated Trust (Notes)	6 Months Ended
	Jun. 30, 2017
Long-Term Debt to Affiliated Trust [Abstract]
Long Term Debt To Affiliated Trusts Disclosure [Text Block]	LONG-TERM DEBT TO AFFILIATED TRUSTS In 1997, the Company issued Floating Rate Junior Subordinated Deferrable Interest Debentures, Series B, with a principal amount of $51.5 million to Avista Capital II, an affiliated business trust formed by the Company. Avista Capital II issued $50.0 million of Preferred Trust Securities with a floating distribution rate of LIBOR plus 0.875 percent , calculated and reset quarterly. The distribution rates paid were as follows during the six months ended June 30, 2017 and the year ended December 31, 2016 : June 30, December 31, 2017 2016 Low distribution rate 1.81 % 1.29 % High distribution rate 2.08 % 1.81 % Distribution rate at the end of the period 2.08 % 1.81 % Concurrent with the issuance of the Preferred Trust Securities, Avista Capital II issued $1.5 million of Common Trust Securities to the Company. These debt securities may be redeemed at the option of Avista Capital II at any time and mature on June 1, 2037. In December 2000, the Company purchased $10.0 million of these Preferred Trust Securities. The Company owns 100 percent of Avista Capital II and has solely and unconditionally guaranteed the payment of distributions on, and redemption price and liquidation amount for, the Preferred Trust Securities to the extent that Avista Capital II has funds available for such payments from the respective debt securities. Upon maturity or prior redemption of such debt securities, the Preferred Trust Securities will be mandatorily redeemed. The Company does not include these capital trusts in its consolidated financial statements as Avista Corp. is not the primary beneficiary. As such, the sole assets of the capital trusts are $51.5 million of junior subordinated deferrable interest debentures of Avista Corp., which are reflected on the Condensed Consolidated Balance Sheets. Interest expense to affiliated trusts in the Condensed Consolidated Statements of Income represents interest expense on these debentures.

Fair Value

Fair Value	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value	FAIR VALUE The carrying values of cash and cash equivalents, accounts and notes receivable, accounts payable, and short-term borrowings are reasonable estimates of their fair values. Long-term debt (including current portion and material capital leases) and long-term debt to affiliated trusts are reported at carrying value on the Condensed Consolidated Balance Sheets. The fair value hierarchy prioritizes the inputs 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 measurement) and the lowest priority to fair values derived from unobservable inputs (Level 3 measurement). The three levels of the fair value hierarchy are defined as follows: Level 1 – Quoted prices are available in active markets for identical assets or liabilities. Active markets are those in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 – Pricing inputs are other than quoted prices in active markets included in Level 1, but which are either directly or indirectly observable as of the reporting date. Level 2 includes those financial instruments that are valued using models or other valuation methodologies. These models are primarily industry-standard models that consider various assumptions, including quoted forward prices for commodities, time value, volatility factors, and current market and contractual prices for the underlying instruments, as well as other relevant economic measures. Substantially all of these assumptions are observable in the marketplace throughout the full term of the instrument, can be derived from observable data or are supported by observable levels at which transactions are executed in the marketplace. Level 3 – Pricing inputs include significant inputs that are generally unobservable from objective sources. These inputs may be used with internally developed methodologies that result in management’s best estimate of fair value. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of fair value assets and liabilities and their placement within the fair value hierarchy levels. The determination of the fair values incorporates various factors that not only include the credit standing of the counterparties involved and the impact of credit enhancements (such as cash deposits and letters of credit), but also the impact of Avista Corp.’s nonperformance risk on its liabilities. The following table sets forth the carrying value and estimated fair value of the Company’s financial instruments not reported at estimated fair value on the Condensed Consolidated Balance Sheets as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, 2017 December 31, 2016 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Long-term debt (Level 2) $ 951,000 $ 1,076,925 $ 951,000 $ 1,048,661 Long-term debt (Level 3) 677,000 701,924 677,000 675,251 Snettisham capital lease obligation (Level 3) 60,953 62,600 62,160 62,800 Long-term debt to affiliated trusts (Level 3) 51,547 43,042 51,547 38,660 These estimates of fair value of long-term debt and long-term debt to affiliated trusts were primarily based on available market information, which generally consists of estimated market prices from third party brokers for debt with similar risk and terms. The price ranges obtained from the third party brokers consisted of par values of 83.50 to 128.87 , where a par value of 100.0 represents the carrying value recorded on the Condensed Consolidated Balance Sheets. Level 2 long-term debt represents publicly issued bonds with quoted market prices; however, due to their limited trading activity, they are classified as Level 2 because brokers must generate quotes and make estimates if there is no trading activity near a period end. Level 3 long-term debt consists of private placement bonds and debt to affiliated trusts, which typically have no secondary trading activity. Fair values in Level 3 are estimated based on market prices from third party brokers using secondary market quotes for debt with similar risk and terms to generate quotes for Avista Corp. bonds. Due to the unique nature of the Snettisham capital lease obligation, the estimated fair value of these items was determined based on a discounted cash flow model using available market information. The Snettisham capital lease obligation was discounted to present value using the Morgan Markets A Ex-Fin discount rate as published on June 30, 2017 . The following table discloses by level within the fair value hierarchy the Company’s assets and liabilities measured and reported on the Condensed Consolidated Balance Sheets as of June 30, 2017 and December 31, 2016 at fair value on a recurring basis (dollars in thousands): Level 1 Level 2 Level 3 Counterparty Total June 30, 2017 Assets: Energy commodity derivatives $ — $ 35,198 $ — $ (35,041 ) $ 157 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 79 (79 ) — Foreign currency exchange derivatives — 187 — — 187 Interest rate swap derivatives — 11,302 — (1,853 ) 9,449 Deferred compensation assets: Fixed income securities (2) 1,716 — — — 1,716 Equity securities (2) 6,067 — — — 6,067 Total $ 7,783 $ 46,687 $ 79 $ (36,973 ) $ 17,576 Liabilities: Energy commodity derivatives $ — $ 46,203 $ — $ (44,808 ) $ 1,395 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 4,252 (79 ) 4,173 Power exchange agreement — — 13,784 — 13,784 Power option agreement — — 43 — 43 Interest rate swap derivatives — 80,266 — (43,423 ) 36,843 Total $ — $ 126,469 $ 18,079 $ (88,310 ) $ 56,238 Level 1 Level 2 Level 3 Counterparty Total December 31, 2016 Assets: Energy commodity derivatives $ — $ 47,994 $ — $ (46,099 ) $ 1,895 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 69 (69 ) — Power exchange agreement — — 25 (25 ) — Foreign currency exchange derivatives — 5 — (5 ) — Interest rate swap derivatives — 13,098 — (4,348 ) 8,750 Deferred compensation assets: Fixed income securities (2) 1,789 — — — 1,789 Equity securities (2) 5,481 — — — 5,481 Total $ 7,270 $ 61,097 $ 94 $ (50,546 ) $ 17,915 Liabilities: Energy commodity derivatives $ — $ 56,871 $ — $ (55,957 ) $ 914 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 5,954 (69 ) 5,885 Power exchange agreement — — 13,474 (25 ) 13,449 Power option agreement — — 76 — 76 Foreign currency exchange derivatives — 28 — (5 ) 23 Interest rate swap derivatives — 73,978 — (39,248 ) 34,730 Total $ — $ 130,877 $ 19,504 $ (95,304 ) $ 55,077 (1) The Company is permitted to net derivative assets and derivative liabilities with the same counterparty when a legally enforceable master netting agreement exists. In addition, the Company nets derivative assets and derivative liabilities against any payables and receivables for cash collateral held or placed with these same counterparties. (2) These assets are trading securities and are included in other property and investments-net and other non-current assets on the Condensed Consolidated Balance Sheets. The difference between the amount of derivative assets and liabilities disclosed in respective levels in the table above and the amount of derivative assets and liabilities disclosed on the Condensed Consolidated Balance Sheets is due to netting arrangements with certain counterparties. See Note 3 for additional discussion of derivative netting. To establish fair value for energy commodity derivatives, the Company uses quoted market prices and forward price curves to estimate the fair value of energy commodity derivative instruments included in Level 2. In particular, electric derivative valuations are performed using market quotes, adjusted for periods in between quotable periods. Natural gas derivative valuations are estimated using New York Mercantile Exchange (NYMEX) pricing for similar instruments, adjusted for basin differences, using market quotes. Where observable inputs are available for substantially the full term of the contract, the derivative asset or liability is included in Level 2. To establish fair values for interest rate swap derivatives, the Company uses forward market curves for interest rates for the term of the swaps and discounts the cash flows back to present value using an appropriate discount rate. The discount rate is calculated by third party brokers according to the terms of the swap derivatives and evaluated by the Company for reasonableness, with consideration given to the potential non-performance risk by the Company. Future cash flows of the interest rate swap derivatives are equal to the fixed interest rate in the swap compared to the floating market interest rate multiplied by the notional amount for each period. To establish fair value for foreign currency derivatives, the Company uses forward market curves for Canadian dollars against the US dollar and multiplies the difference between the locked-in price and the market price by the notional amount of the derivative. Forward foreign currency market curves are provided by third party brokers. The Company's credit spread is factored into the locked-in price of the foreign exchange contracts. Deferred compensation assets and liabilities represent funds held by the Company in a Rabbi Trust for an executive deferral plan. These funds consist of actively traded equity and bond funds with quoted prices in active markets. The balance disclosed in the table above excludes cash and cash equivalents of $0.2 million as of June 30, 2017 and $0.4 million as of December 31, 2016 . Level 3 Fair Value Under the power exchange agreement the Company purchases power at a price that is based on the average operating and maintenance (O&M) charges from three surrogate nuclear power plants around the country. To estimate the fair value of this agreement the Company estimates the difference between the purchase price based on the future O&M charges and forward prices for energy. The Company compares the Level 2 brokered quotes and forward price curves described above to an internally developed forward price which is based on the average O&M charges from the three surrogate nuclear power plants for the current year. Because the nuclear power plant O&M charges are only known for one year, all forward years are estimated assuming an annual escalation. In addition to the forward price being estimated using unobservable inputs, the Company also estimates the volumes of the transactions that will take place in the future based on historical average transaction volumes per delivery year (November to April). Significant increases or decreases in any of these inputs in isolation would result in a significantly higher or lower fair value measurement. Generally, a change in the current year O&M charges for the surrogate plants is accompanied by a directionally similar change in O&M charges in future years. There is generally not a correlation between external market prices and the O&M charges used to develop the internal forward price. For the power commodity option agreement, the Company uses the Black-Scholes-Merton valuation model to estimate the fair value, and this model includes significant inputs not observable or corroborated in the market. These inputs include: 1) the strike price (which is an internally derived price based on a combination of generation plant heat rate factors, natural gas market pricing, delivery and other O&M charges) and 2) estimated delivery volumes. Significant increases or decreases in these inputs in isolation would result in a significantly higher or lower fair value measurement. Generally, changes in overall commodity market prices are accompanied by directionally similar changes in the strike price assumptions used in the calculation. For the natural gas commodity exchange agreement, the Company uses the same Level 2 brokered quotes described above; however, the Company also estimates the purchase and sales volumes (within contractual limits) as well as the timing of those transactions. Changing the timing of volume estimates changes the timing of purchases and sales, impacting which brokered quote is used. Because the brokered quotes can vary significantly from period to period, the unobservable estimates of the timing and volume of transactions can have a significant impact on the calculated fair value. The Company currently estimates volumes and timing of transactions based on a most likely scenario using historical data. Historically, the timing and volume of transactions have not been highly correlated with market prices and market volatility. The following table presents the quantitative information which was used to estimate the fair values of the Level 3 assets and liabilities above as of June 30, 2017 (dollars in thousands): Fair Value (Net) at June 30, 2017 Valuation Technique Unobservable Input Range Power exchange agreement $ (13,784 ) Surrogate facility pricing O&M charges $33.59-$49.15/MWh (1) Escalation factor 3% - 2017 to 2019 Transaction volumes 396,984 MWhs Power option agreement $ (43 ) Black-Scholes- Merton Strike price $35.92/MWh - 2019 $48.39/MWh - 2018 Delivery volumes 128,611 - 254,363 MWhs Natural gas exchange agreement $ (4,173 ) Internally derived Forward purchase prices $1.66 - $2.38/mmBTU Forward sales prices $1.67 - $3.29/mmBTU Purchase volumes 115,000 - 310,000 mmBTUs Sales volumes 60,000 - 310,000 mmBTUs (1) The average O&M charges for the delivery year beginning in November 2016 are $39.22 per MWh. For ratemaking purposes the average O&M charges to be included for recovery in retail rates vary slightly between regulatory jurisdictions. The average O&M charges for the delivery year beginning in 2016 are $44.33 for Washington and $39.22 for Idaho. The valuation methods, significant inputs and resulting fair values described above were developed by the Company's management and are reviewed on at least a quarterly basis to ensure they provide a reasonable estimate of fair value each reporting period. The following table presents activity for energy commodity derivative assets (liabilities) measured at fair value using significant unobservable inputs (Level 3) for the three and six months ended June 30 (dollars in thousands): Natural Gas Exchange Agreement Power Exchange Agreement Power Option Agreement Total Three months ended June 30, 2017: Balance as of April 1, 2017 $ (4,278 ) $ (14,419 ) $ (266 ) $ (18,963 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) (195 ) (672 ) 223 (644 ) Settlements 300 1,307 — 1,607 Ending balance as of June 30, 2017 (2) $ (4,173 ) $ (13,784 ) $ (43 ) $ (18,000 ) Three months ended June 30, 2016: Balance as of April 1, 2016 $ (6,006 ) $ (20,193 ) $ (97 ) $ (26,296 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) (1,551 ) 4,400 (8 ) 2,841 Settlements 700 1,179 — 1,879 Ending balance as of June 30, 2016 (2) $ (6,857 ) $ (14,614 ) $ (105 ) $ (21,576 ) Six months ended June 30, 2017: Balance as of January 1, 2017 $ (5,885 ) $ (13,449 ) $ (76 ) $ (19,410 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) 1,817 (5,165 ) 33 (3,315 ) Settlements (105 ) 4,830 — 4,725 Ending balance as of June 30, 2017 (2) $ (4,173 ) $ (13,784 ) $ (43 ) $ (18,000 ) Six months ended June 30, 2016: Balance as of January 1, 2016 $ (5,039 ) $ (21,961 ) $ (124 ) $ (27,124 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) (3,296 ) 1,968 19 (1,309 ) Settlements 1,478 5,379 — 6,857 Ending balance as of June 30, 2016 (2) $ (6,857 ) $ (14,614 ) $ (105 ) $ (21,576 ) (1) All gains and losses are included in other regulatory assets and liabilities. There were no gains and losses included in either net income or other comprehensive income during any of the periods presented in the table above. (2) There were no purchases, issuances or transfers from other categories of any derivatives instruments during the periods presented in the table above.

Common Stock Common Stock (Note

Common Stock Common Stock (Notes)	6 Months Ended
	Jun. 30, 2017
Stockholders' Equity Note [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	COMMON STOCK In March 2016, the Company entered into four separate sales agency agreements under which Avista Corp.'s sales agents may offer and sell up to 3.8 million new shares of Avista Corp.'s common stock, no par value, from time to time. The sales agency agreements expire on February 29, 2020. As of June 30, 2017 , 1.6 million shares have been issued under these agreements, leaving 2.2 million shares remaining to be issued. No shares were issued under these agreements in the six months ended June 30, 2017 . In the six months ended June 30, 2017 , Avista Corp. issued 0.2 million shares of common stock, most of which were under employee incentive plans. The Company also issued a small number of shares under the 401(k) employee investment plan. Total net proceeds for all issuances were $1.2 million .

Earnings Per Common Share Attri

Earnings Per Common Share Attributable To Avista Corporation	6 Months Ended
	Jun. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share Attributable To Avista Corporation Shareholders	EARNINGS PER COMMON SHARE ATTRIBUTABLE TO AVISTA CORP. SHAREHOLDERS The following table presents the computation of basic and diluted earnings per common share attributable to Avista Corp. shareholders for the three and six months ended June 30 (in thousands, except per share amounts): Three months ended June 30, Six months ended June 30, 2017 2016 2017 2016 Numerator: Net income attributable to Avista Corp. shareholders $ 21,771 $ 27,254 $ 83,887 $ 84,903 Denominator: Weighted-average number of common shares outstanding-basic 64,401 63,386 64,382 62,995 Effect of dilutive securities: Performance and restricted stock awards 152 397 129 373 Weighted-average number of common shares outstanding-diluted 64,553 63,783 64,511 63,368 Earnings per common share attributable to Avista Corp. shareholders: Basic $ 0.34 $ 0.43 $ 1.30 $ 1.35 Diluted $ 0.34 $ 0.43 $ 1.30 $ 1.34 There were no shares excluded from the calculation because they were antidilutive.

Commitments And Contingencies

Commitments And Contingencies	6 Months Ended
	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	COMMITMENTS AND CONTINGENCIES In the course of its business, the Company becomes involved in various claims, controversies, disputes and other contingent matters, including the items described in this Note. Some of these claims, controversies, disputes and other contingent matters involve litigation or other contested proceedings. For all such matters, the Company intends to vigorously protect and defend its interests and pursue its rights. However, no assurance can be given as to the ultimate outcome of any particular matter because litigation and other contested proceedings are inherently subject to numerous uncertainties. For matters that affect Avista Utilities’ or AEL&P's operations, the Company intends to seek, to the extent appropriate, recovery of incurred costs through the ratemaking process. California Refund Proceeding In February 2016, APX, a market maker in the California Refund Proceedings in whose markets Avista Energy participated in the summer of 2000, asserted that Avista Energy and its other customer/participants may be responsible for a share of the disgorgement penalty APX may be found to owe to the California Parties (as defined in the 2016 Form 10-K). The penalty arises as a result of the Federal Energy and Regulatory Commission's (FERC) finding that APX committed violations in the California market in the summer of 2000. APX is making these assertions despite Avista Energy having been dismissed in FERC Opinion No. 536 from the on-going administrative proceeding at the FERC regarding potential wrongdoing in the California markets in the summer of 2000. APX has identified Avista Energy’s share of APX’s exposure to be as much as $16.0 million even though no wrongdoing allegations are specifically attributable to Avista Energy. Avista Energy believes its 2014 settlement with the California Parties insulates it from any such liability and that as a dismissed party it cannot be drawn back into the litigation. Avista Energy intends to vigorously dispute APX’s assertions of indirect liability, but cannot at this time predict the eventual outcome. Cabinet Gorge Total Dissolved Gas Abatement Plan Dissolved atmospheric gas levels (referred to as "Total Dissolved Gas" or "TDG") in the Clark Fork River exceed state of Idaho and federal water quality numeric standards downstream of Cabinet Gorge particularly during periods when excess river flows must be diverted over the spillway. Under the terms of the Clark Fork Settlement Agreement (CFSA) as incorporated in Avista Corp.’s FERC license for the Clark Fork Project, Avista Corp. has worked in consultation with agencies, tribes and other stakeholders to address this issue. Under the terms of a gas supersaturation mitigation plan, Avista is reducing TDG by constructing spill crest modifications on spill gates at the dam, and the Company expects to continue spill crest modifications over the next several years, in ongoing consultation with key stakeholders. Avista Corp. cannot at this time predict the outcome or estimate a range of costs associated with this contingency; however, the Company will continue to seek recovery, through the ratemaking process, of all operating and capitalized costs related to this issue. Fish Passage at Cabinet Gorge and Noxon Rapids In 1999, the United States Fish and Wildlife Service (USFWS) listed bull trout as threatened under the Endangered Species Act. In 2010, the USFWS issued a revised designation of critical habitat for bull trout, which includes the lower Clark Fork River. The USFWS issued a final recovery plan in October 2015. The CFSA describes programs intended to help restore bull trout populations in the project area. Using the concept of adaptive management and working closely with the USFWS, the Company evaluated the feasibility of fish passage at Cabinet Gorge and Noxon Rapids. The results of these studies led, in part, to the decision to move forward with development of permanent facilities, among other bull trout enhancement efforts. Parties to the CFSA are working to resolve several issues. The Company believes its ongoing efforts through the CFSA continue to effectively address issues related to bull trout. Avista Corp. cannot at this time predict the outcome or estimate a range of costs associated with this contingency; however, the Company will continue to seek recovery, through the ratemaking process, of all operating and capitalized costs related to fish passage at Cabinet Gorge and Noxon Rapids. Other Contingencies In the normal course of business, the Company has various other legal claims and contingent matters outstanding. The Company believes that any ultimate liability arising from these actions will not have a material impact on its financial condition, results of operations or cash flows. It is possible that a change could occur in the Company’s estimates of the probability or amount of a liability being incurred. Such a change, should it occur, could be significant. See "Note 19 of the Notes to Consolidated Financial Statements" in the 2016 Form 10-K for additional discussion regarding other contingencies.

Information By Business Segment

Information By Business Segments	6 Months Ended
	Jun. 30, 2017
Segment Reporting [Abstract]
Information by Business Segments	INFORMATION BY BUSINESS SEGMENTS The business segment presentation reflects the basis used by the Company's management to analyze performance and determine the allocation of resources. The Company's management evaluates performance based on income (loss) from operations before income taxes as well as net income (loss) attributable to Avista Corp. shareholders. The accounting policies of the segments are the same as those described in the summary of significant accounting policies. Avista Utilities' business is managed based on the total regulated utility operation; therefore, it is considered one segment. AEL&P is a separate reportable business segment as it has separate financial reports that are reviewed in detail by the Chief Operating Decision Maker and its operations and risks are sufficiently different from Avista Utilities and the other businesses at AERC that it cannot be aggregated with any other operating segments. The Other category, which is not a reportable segment, includes other investments and operations of various subsidiaries, as well as certain other operations of Avista Capital. The following table presents information for each of the Company’s business segments (dollars in thousands): Avista Utilities Alaska Electric Light and Power Company Total Utility Other Intersegment Eliminations (1) Total For the three months ended June 30, 2017: Operating revenues $ 296,747 $ 11,982 $ 308,729 $ 5,772 $ — $ 314,501 Resource costs 99,461 3,290 102,751 — — 102,751 Other operating expenses 78,970 2,995 81,965 7,086 — 89,051 Depreciation and amortization 41,195 1,448 42,643 157 — 42,800 Income (loss) from operations 53,971 3,597 57,568 (1,471 ) — 56,097 Interest expense (2) 22,826 895 23,721 176 (27 ) 23,870 Income taxes 12,892 1,075 13,967 (916 ) — 13,051 Net income (loss) attributable to Avista Corp. shareholders 21,765 1,681 23,446 (1,675 ) — 21,771 Capital expenditures (3) 88,612 2,339 90,951 134 — 91,085 Avista Utilities Alaska Electric Light and Power Company Total Utility Other Intersegment Eliminations (1) Total For the three months ended June 30, 2016: Operating revenues $ 302,641 $ 10,247 $ 312,888 $ 5,950 $ — $ 318,838 Resource costs 106,607 3,208 109,815 — — 109,815 Other operating expenses 75,790 2,876 78,666 6,281 — 84,947 Depreciation and amortization 38,351 1,327 39,678 192 — 39,870 Income (loss) from operations 59,862 2,252 62,114 (523 ) — 61,591 Interest expense (2) 20,462 895 21,357 149 (34 ) 21,472 Income taxes 16,349 676 17,025 (315 ) — 16,710 Net income (loss) attributable to Avista Corp. shareholders 26,771 1,058 27,829 (575 ) — 27,254 Capital expenditures (3) 88,048 5,889 93,937 46 — 93,983 For the six months ended June 30, 2017: Operating revenues $ 712,128 $ 27,138 $ 739,266 $ 11,705 $ — $ 750,971 Resource costs 262,074 6,263 268,337 — — 268,337 Other operating expenses 150,682 5,767 156,449 13,265 — 169,714 Depreciation and amortization 81,733 2,895 84,628 345 — 84,973 Income (loss) from operations 162,606 10,782 173,388 (1,905 ) — 171,483 Interest expense (2) 45,509 1,789 47,298 343 (41 ) 47,600 Income taxes 43,909 3,538 47,447 (1,052 ) — 46,395 Net income (loss) attributable to Avista Corp. shareholders 80,204 5,534 85,738 (1,851 ) — 83,887 Capital expenditures (3) 174,015 3,699 177,714 169 — 177,883 For the six months ended June 30, 2016: Operating revenues $ 702,788 $ 22,893 $ 725,681 $ 11,330 $ — $ 737,011 Resource costs 265,685 5,849 271,534 — — 271,534 Other operating expenses 149,046 5,399 154,445 12,106 — 166,551 Depreciation and amortization 76,217 2,653 78,870 380 — 79,250 Income (loss) from operations 161,107 7,725 168,832 (1,156 ) — 167,676 Interest expense (2) 40,880 1,790 42,670 310 (97 ) 42,883 Income taxes 45,021 2,571 47,592 (537 ) — 47,055 Net income (loss) attributable to Avista Corp. shareholders 81,758 4,019 85,777 (874 ) — 84,903 Capital expenditures (3) 172,483 10,332 182,815 165 — 182,980 Total Assets: As of June 30, 2017: $ 5,034,778 $ 278,470 $ 5,313,248 $ 59,756 $ — $ 5,373,004 As of December 31, 2016: $ 4,975,555 $ 273,770 $ 5,249,325 $ 60,430 $ — $ 5,309,755 (1) Intersegment eliminations reported as interest expense represent intercompany interest. (2) Including interest expense to affiliated trusts. (3) The capital expenditures for the other businesses are included in other investing activities on the Condensed Consolidated Statements of Cash Flows.

Subsequent Event Subsequent Eve

Subsequent Event Subsequent Event (Notes)	6 Months Ended
	Jun. 30, 2017
Subsequent Events [Abstract]
Subsequent Events [Text Block]	SUBSEQUENT EVENT On July 19, 2017, Avista Corp. entered into an Agreement and Plan of Merger (Merger Agreement), by and among Hydro One Limited (Hydro One), Olympus Holding Corp., a wholly owned subsidiary of Hydro One (US parent), and Olympus Corp., a wholly owned subsidiary of US parent (Merger Sub). Hydro One, based in Toronto, is Ontario’s largest electricity transmission and distribution provider with more than 1.3 million customers, C $25.0 billion in assets and annual revenues of over C $6.5 billion . The Merger Agreement provides for Avista Corp. to become an indirect, wholly-owned subsidiary of Hydro One. At the effective time of the merger, each share of Avista Corp. Common Stock issued and outstanding, other than Dissenting Shareholder Shares (as defined in the Merger Agreement) and shares of Avista Corp. Common Stock that are owned by Hydro One, US Parent or Merger Sub or any of their respective subsidiaries, will be converted automatically into the right to receive an amount in cash equal to $53.00 , without interest. Consummation of the merger is subject to the satisfaction or waiver of specified closing conditions, including, but not limited to, (i) the approval of the merger by the holders of a majority of the outstanding shares of Avista Corp. Common Stock, (ii) the receipt of regulatory approvals required to consummate the Merger, including approval from the FERC, the Committee on Foreign Investment in the United States (CFIUS), the Federal Communications Commission (FCC), the UTC, IPUC, Public Service Commission of the State of Montana (MPSC), OPUC, and the RCA, and (iii) the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. Avista Corp. expects to file for all necessary approvals within 45 to 60 days from the date of the Merger Agreement and the merger is expected to close during the second half of 2018. The Merger Agreement also contains customary representations, warranties and covenants of Avista Corp., Hydro One, US Parent and Merger Sub. These covenants include, among others, an obligation on behalf of Avista Corp. to operate its business in the ordinary course until the Merger is consummated, subject to certain exceptions. In addition, the parties are required to use reasonable best efforts to obtain any required regulatory approvals. Avista Corp. has made certain additional customary covenants, including, among others, and subject to certain exceptions, (a) causing a meeting of Avista Corp.’s shareholders to be held to consider approval of the Merger Agreement and (b) a customary non-solicitation covenant prohibiting Avista Corp. from soliciting, providing non-public information or entering into discussions or negotiations concerning proposals relating to alternative business combination transactions, except as and to the extent permitted under the Merger Agreement with respect to an unsolicited written Takeover Proposal (as defined in the Merger Agreement) made prior to the approval of the Merger by Avista Corp.'s shareholders if, among other things, Avista Corp.'s board of directors determines in good faith that such Takeover Proposal is or could be reasonably expected to lead to a Superior Proposal (as defined in the Merger Agreement) and that failure to take such actions would reasonably be expected to be inconsistent with its fiduciary duties under applicable law. The Merger Agreement may be terminated by Avista Corp. and Hydro One by mutual consent and by either Avista Corp. or Hydro One under certain circumstances, including if the Merger is not consummated by September 30, 2018 (subject to an extension of up to six months by either party if all of the conditions to closing, other than the conditions related to obtaining required regulatory approvals, the absence of a law or injunction preventing the consummation of the Merger and the absence of a Burdensome Condition (as defined in the Merger Agreement) in any required regulatory approval, have been satisfied). The Merger Agreement also provides for certain additional termination rights for each of Avista Corp. and Hydro One. Upon termination of the Merger Agreement under certain specified circumstances, including (i) termination by Avista Corp. in order to enter into a definitive agreement with respect to a Superior Proposal, or (ii) termination by Hydro One following a withdrawal by Avista Corp.'s board or directors of its recommendation of the Merger Agreement, Avista Corp. will be required to pay Hydro One a termination fee of $103.0 million (Company Termination Fee). Avista Corp. will also be required to pay Hydro One the Company Termination Fee in the event Avista Corp. signs or consummates any specified alternative transaction within twelve months following the termination of the Merger Agreement under certain circumstances. In addition, if the Merger Agreement is terminated under certain circumstances due to the failure to obtain required regulatory approvals, the imposition of a Burdensome Condition with respect to a required regulatory approval, or the breach by Hydro One, US Parent or Merger Sub of their obligations in respect of obtaining regulatory approvals, Hydro One will be required to pay Avista Corp. a termination fee of $103.0 million .
Business Combination Disclosure [Text Block]	SUBSEQUENT EVENT On July 19, 2017, Avista Corp. entered into an Agreement and Plan of Merger (Merger Agreement), by and among Hydro One Limited (Hydro One), Olympus Holding Corp., a wholly owned subsidiary of Hydro One (US parent), and Olympus Corp., a wholly owned subsidiary of US parent (Merger Sub). Hydro One, based in Toronto, is Ontario’s largest electricity transmission and distribution provider with more than 1.3 million customers, C $25.0 billion in assets and annual revenues of over C $6.5 billion . The Merger Agreement provides for Avista Corp. to become an indirect, wholly-owned subsidiary of Hydro One. At the effective time of the merger, each share of Avista Corp. Common Stock issued and outstanding, other than Dissenting Shareholder Shares (as defined in the Merger Agreement) and shares of Avista Corp. Common Stock that are owned by Hydro One, US Parent or Merger Sub or any of their respective subsidiaries, will be converted automatically into the right to receive an amount in cash equal to $53.00 , without interest. Consummation of the merger is subject to the satisfaction or waiver of specified closing conditions, including, but not limited to, (i) the approval of the merger by the holders of a majority of the outstanding shares of Avista Corp. Common Stock, (ii) the receipt of regulatory approvals required to consummate the Merger, including approval from the FERC, the Committee on Foreign Investment in the United States (CFIUS), the Federal Communications Commission (FCC), the UTC, IPUC, Public Service Commission of the State of Montana (MPSC), OPUC, and the RCA, and (iii) the expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. Avista Corp. expects to file for all necessary approvals within 45 to 60 days from the date of the Merger Agreement and the merger is expected to close during the second half of 2018. The Merger Agreement also contains customary representations, warranties and covenants of Avista Corp., Hydro One, US Parent and Merger Sub. These covenants include, among others, an obligation on behalf of Avista Corp. to operate its business in the ordinary course until the Merger is consummated, subject to certain exceptions. In addition, the parties are required to use reasonable best efforts to obtain any required regulatory approvals. Avista Corp. has made certain additional customary covenants, including, among others, and subject to certain exceptions, (a) causing a meeting of Avista Corp.’s shareholders to be held to consider approval of the Merger Agreement and (b) a customary non-solicitation covenant prohibiting Avista Corp. from soliciting, providing non-public information or entering into discussions or negotiations concerning proposals relating to alternative business combination transactions, except as and to the extent permitted under the Merger Agreement with respect to an unsolicited written Takeover Proposal (as defined in the Merger Agreement) made prior to the approval of the Merger by Avista Corp.'s shareholders if, among other things, Avista Corp.'s board of directors determines in good faith that such Takeover Proposal is or could be reasonably expected to lead to a Superior Proposal (as defined in the Merger Agreement) and that failure to take such actions would reasonably be expected to be inconsistent with its fiduciary duties under applicable law. The Merger Agreement may be terminated by Avista Corp. and Hydro One by mutual consent and by either Avista Corp. or Hydro One under certain circumstances, including if the Merger is not consummated by September 30, 2018 (subject to an extension of up to six months by either party if all of the conditions to closing, other than the conditions related to obtaining required regulatory approvals, the absence of a law or injunction preventing the consummation of the Merger and the absence of a Burdensome Condition (as defined in the Merger Agreement) in any required regulatory approval, have been satisfied). The Merger Agreement also provides for certain additional termination rights for each of Avista Corp. and Hydro One. Upon termination of the Merger Agreement under certain specified circumstances, including (i) termination by Avista Corp. in order to enter into a definitive agreement with respect to a Superior Proposal, or (ii) termination by Hydro One following a withdrawal by Avista Corp.'s board or directors of its recommendation of the Merger Agreement, Avista Corp. will be required to pay Hydro One a termination fee of $103.0 million (Company Termination Fee). Avista Corp. will also be required to pay Hydro One the Company Termination Fee in the event Avista Corp. signs or consummates any specified alternative transaction within twelve months following the termination of the Merger Agreement under certain circumstances. In addition, if the Merger Agreement is terminated under certain circumstances due to the failure to obtain required regulatory approvals, the imposition of a Burdensome Condition with respect to a required regulatory approval, or the breach by Hydro One, US Parent or Merger Sub of their obligations in respect of obtaining regulatory approvals, Hydro One will be required to pay Avista Corp. a termination fee of $103.0 million .

Summary Of Significant Accoun22

Summary Of Significant Accounting Policies (Policy)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Nature Of Business	Nature of Business Avista Corp. is primarily an electric and natural gas utility with certain other business ventures. Avista Utilities is an operating division of Avista Corp., comprising the regulated utility operations in the Pacific Northwest. Avista Utilities provides electric distribution and transmission, and natural gas distribution services in parts of eastern Washington and northern Idaho. Avista Utilities also provides natural gas distribution service in parts of northeastern and southwestern Oregon. Avista Utilities has electric generating facilities in Washington, Idaho, Oregon and Montana. Avista Utilities also supplies electricity to a small number of customers in Montana, most of whom are employees who operate Avista Utilities' Noxon Rapids generating facility. Alaska Energy and Resources Company (AERC) is a wholly-owned subsidiary of Avista Corp. The primary subsidiary of AERC is Alaska Electric Light and Power Company (AEL&P), which comprises Avista Corp.'s regulated utility operations in Alaska. Avista Capital, Inc. (Avista Capital), a wholly owned non-regulated subsidiary of Avista Corp., is the parent company of all of the subsidiary companies in the non-utility businesses, with the exception of AJT Mining Properties, Inc., which is a subsidiary of AERC.
Basis Of Reporting	Basis of Reporting The condensed consolidated financial statements include the assets, liabilities, revenues and expenses of the Company and its subsidiaries and other majority owned subsidiaries and variable interest entities for which the Company or its subsidiaries are the primary beneficiaries. Intercompany balances were eliminated in consolidation. The accompanying condensed consolidated financial statements include the Company’s proportionate share of utility plant and related operations resulting from its interests in jointly owned plants.
Taxes Other Than Income Taxes	Taxes Other Than Income Taxes Taxes other than income taxes include state excise taxes, city occupational and franchise taxes, real and personal property taxes and certain other taxes not based on income. These taxes are generally based on revenues or the value of property. Utility related taxes collected from customers (primarily state excise taxes and city utility taxes) are recorded as operating revenue and expense. Taxes other than income taxes consisted of the following items for the three and six months ended June 30 (dollars in thousands): Three months ended June 30, Six months ended June 30, 2017 2016 2017 2016 Utility related taxes $ 13,552 $ 12,573 $ 35,136 $ 30,938 Property taxes 9,432 9,290 19,838 19,710 Other taxes 818 752 1,490 1,352 Total $ 23,802 $ 22,615 $ 56,464 $ 52,000
Materials And Supplies, Fuel Stock And Natural Gas Stored	Materials and Supplies, Fuel Stock and Stored Natural Gas Inventories of materials and supplies, fuel stock and stored natural gas are recorded at average cost for our regulated operations and the lower of cost or net realizable value for our non-regulated operations and consisted of the following as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Materials and supplies $ 41,492 $ 40,700 Fuel stock 5,921 4,585 Stored natural gas 13,774 8,029 Total $ 61,187 $ 53,314
Derivative Assets And Liabilities	Derivative Assets and Liabilities Derivatives are recorded as either assets or liabilities on the Condensed Consolidated Balance Sheets measured at estimated fair value. The Washington Utilities and Transportation Commission (UTC) and the Idaho Public Utilities Commission (IPUC) issued accounting orders authorizing Avista Corp. to offset energy commodity derivative assets or liabilities with a regulatory asset or liability. This accounting treatment is intended to defer the recognition of mark-to-market gains and losses on energy commodity transactions until the period of delivery. Realized benefits and costs result in adjustments to retail rates through purchased gas cost adjustments, the Energy Recovery Mechanism (ERM) in Washington, the Power Cost Adjustment (PCA) mechanism in Idaho, and periodic general rate cases. The resulting regulatory assets have been concluded to be probable of recovery through future rates. Substantially all forward contracts to purchase or sell power and natural gas are recorded as derivative assets or liabilities at estimated fair value with an offsetting regulatory asset or liability. Contracts that are not considered derivatives are accounted for on the accrual basis until they are settled or realized unless there is a decline in the fair value of the contract that is determined to be other-than-temporary. For interest rate swap derivatives, Avista Corp. records all mark-to-market gains and losses in each accounting period as assets and liabilities, as well as offsetting regulatory assets and liabilities, such that there is no income statement impact. The interest rate swap derivatives are risk management tools similar to energy commodity derivatives. Upon settlement of interest rate swap derivatives, the regulatory asset or liability is amortized as a component of interest expense over the term of the associated debt. The Company records an offset of interest rate swap derivative assets and liabilities with regulatory assets and liabilities, based on the prior practice of the commissions to provide recovery through the ratemaking process. As of June 30, 2017 , the Company has multiple master netting agreements with a variety of entities that allow for cross-commodity netting of derivative agreements with the same counterparty (i.e. power derivatives can be netted with natural gas derivatives). In addition, some master netting agreements allow for the netting of commodity derivatives and interest rate swap derivatives for the same counterparty. The Company does not have any agreements which allow for cross-affiliate netting among multiple affiliated legal entities. The Company nets all derivative instruments when allowed by the agreement for presentation in the Condensed Consolidated Balance Sheets.
Fair Value Measurements	Fair Value Measurements Fair value represents the price that would be received when selling an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. Energy commodity derivative assets and liabilities, deferred compensation assets, as well as derivatives related to interest rate swaps and foreign currency exchange contracts, are reported at estimated fair value on the Condensed Consolidated Balance Sheets. See Note 8 for the Company’s fair value disclosures.
Contingencies	Contingencies The Company has unresolved regulatory, legal and tax issues which have inherently uncertain outcomes. The Company accrues a loss contingency if it is probable that a liability has been incurred and the amount of the loss or impairment can be reasonably estimated. The Company also discloses loss contingencies that do not meet these conditions for accrual if there is a reasonable possibility that a material loss may be incurred. As of June 30, 2017 , the Company has not recorded any significant amounts related to unresolved contingencies. See Note 11 for further discussion of the Company's commitments and contingencies.
Stockholders' Equity, Policy	Accumulated Other Comprehensive Loss Accumulated other comprehensive loss, net of tax, consisted of the following as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Unfunded benefit obligation for pensions and other postretirement benefit plans - net of taxes of $3,878 and $4,075, respectively $ 7,202 $ 7,568 The following table details the reclassifications out of accumulated other comprehensive loss by component for the three and six months ended June 30 (dollars in thousands). Amounts Reclassified from Accumulated Other Comprehensive Loss Three months ended June 30, Six months ended June 30, Details about Accumulated Other Comprehensive Loss Components 2017 2016 2017 2016 Affected Line Item in Statement of Income Amortization of defined benefit pension items Amortization of net prior service cost $ (299 ) $ (311 ) $ (598 ) $ (622 ) (a) Amortization of net loss 3,638 3,642 $ 7,276 $ 7,284 (a) Adjustment due to effects of regulation (3,057 ) (3,115 ) (6,115 ) (8,338 ) (a) (b) 282 216 563 (1,676 ) Total before tax (99 ) (76 ) (197 ) 587 Tax benefit (expense) $ 183 $ 140 $ 366 $ (1,089 ) Net of tax (a) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 4 for additional details). (b) The adjustment for the effects of regulation during the six months ended June 30, 2016 includes approximately $2.1 million related to the reclassification of a pension regulatory asset associated with one of our jurisdictions into accumulated other comprehensive loss.

Summary Of Significant Accoun23

Summary Of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Loss Accumulated other comprehensive loss, net of tax, consisted of the following as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Unfunded benefit obligation for pensions and other postretirement benefit plans - net of taxes of $3,878 and $4,075, respectively $ 7,202 $ 7,568
Reclassifications Out of Accumulated Other Comprehensive Loss by Component	The following table details the reclassifications out of accumulated other comprehensive loss by component for the three and six months ended June 30 (dollars in thousands). Amounts Reclassified from Accumulated Other Comprehensive Loss Three months ended June 30, Six months ended June 30, Details about Accumulated Other Comprehensive Loss Components 2017 2016 2017 2016 Affected Line Item in Statement of Income Amortization of defined benefit pension items Amortization of net prior service cost $ (299 ) $ (311 ) $ (598 ) $ (622 ) (a) Amortization of net loss 3,638 3,642 $ 7,276 $ 7,284 (a) Adjustment due to effects of regulation (3,057 ) (3,115 ) (6,115 ) (8,338 ) (a) (b) 282 216 563 (1,676 ) Total before tax (99 ) (76 ) (197 ) 587 Tax benefit (expense) $ 183 $ 140 $ 366 $ (1,089 ) Net of tax (a) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 4 for additional details).
Utility Taxes	Utility related taxes collected from customers (primarily state excise taxes and city utility taxes) are recorded as operating revenue and expense. Taxes other than income taxes consisted of the following items for the three and six months ended June 30 (dollars in thousands): Three months ended June 30, Six months ended June 30, 2017 2016 2017 2016 Utility related taxes $ 13,552 $ 12,573 $ 35,136 $ 30,938 Property taxes 9,432 9,290 19,838 19,710 Other taxes 818 752 1,490 1,352 Total $ 23,802 $ 22,615 $ 56,464 $ 52,000
Materials And Supplies Fuel Stock And Natural Gas Stored	Inventories of materials and supplies, fuel stock and stored natural gas are recorded at average cost for our regulated operations and the lower of cost or net realizable value for our non-regulated operations and consisted of the following as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Materials and supplies $ 41,492 $ 40,700 Fuel stock 5,921 4,585 Stored natural gas 13,774 8,029 Total $ 61,187 $ 53,314

Derivatives And Risk Manageme24

Derivatives And Risk Management (Tables)	6 Months Ended
	Jun. 30, 2017
Derivative Instruments and Hedges, Assets [Abstract]
Energy Commodity Derivatives	The following table presents the underlying energy commodity derivative volumes as of June 30, 2017 that are expected to be delivered in each respective year (in thousands of MWhs and mmBTUs): Purchases Sales Electric Derivatives Gas Derivatives Electric Derivatives Gas Derivatives Year Physical (1) MWH Financial (1) MWH Physical (1) mmBTUs Financial (1) mmBTUs Physical (1) Financial (1) Physical (1) Financial (1) Remainder 2017 185 999 7,418 63,423 154 1,129 3,378 43,940 2018 397 307 — 78,488 254 1,244 1,360 46,805 2019 235 737 610 42,775 158 982 1,345 26,590 2020 — — 910 3,635 — — 1,430 — 2021 — — — — — — 1,049 — Thereafter — — — — — — — — The following table presents the underlying energy commodity derivative volumes as of December 31, 2016 that are expected to be delivered in each respective year (in thousands of MWhs and mmBTUs): Purchases Sales Electric Derivatives Gas Derivatives Electric Derivatives Gas Derivatives Year Physical (1) MWH Financial (1) MWH Physical (1) mmBTUs Financial (1) mmBTUs Physical (1) Financial (1) Physical (1) Financial (1) 2017 510 907 15,475 110,380 316 1,552 4,165 73,110 2018 397 — — 52,755 286 1,244 1,360 15,113 2019 235 — 610 29,475 158 982 1,345 4,020 2020 — — 910 2,725 — — 1,430 — 2021 — — — — — — 1,060 — Thereafter — — — — — — — —
Foreign Currency Exchange Contracts	The following table summarizes the foreign currency exchange derivatives that Avista Corp. has outstanding as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Number of contracts 24 21 Notional amount (in United States dollars) $ 7,588 $ 2,819 Notional amount (in Canadian dollars) 10,075 3,754
Interest Rate Swap Agreements	The following table summarizes the unsettled interest rate swap derivatives that Avista Corp. has outstanding as of June 30, 2017 and December 31, 2016 (dollars in thousands): Balance Sheet Date Number of Contracts Notional Amount Mandatory Cash Settlement Date June 30, 2017 6 $ 75,000 2017 14 275,000 2018 6 70,000 2019 3 30,000 2020 5 60,000 2022 December 31, 2016 6 $ 75,000 2017 14 275,000 2018 6 70,000 2019 2 20,000 2020 5 60,000 2022
Derivative Instruments Summary	The following table presents the fair values and locations of derivative instruments recorded on the Condensed Consolidated Balance Sheet as of June 30, 2017 (in thousands): Fair Value as of June 30, 2017 Derivative and Balance Sheet Location Gross Asset Gross Liability Collateral Netted Net Asset (Liability) on Balance Sheet Foreign currency exchange derivatives Other current assets $ 187 $ — $ — $ 187 Interest rate swap derivatives Other current assets 5,626 (208 ) — 5,418 Other property and investments-net and other non-current assets 5,676 (1,645 ) — 4,031 Current interest rate swap derivative liabilities — (78,077 ) 41,570 (36,507 ) Non-current interest rate swap derivative liabilities — (336 ) — (336 ) Energy commodity derivatives Other current assets 168 (11 ) — 157 Current energy commodity derivative liabilities 22,577 (36,716 ) 5,831 (8,308 ) Other non-current liabilities, regulatory liabilities and deferred credits 12,532 (27,555 ) 3,936 (11,087 ) Total derivative instruments recorded on the balance sheet $ 46,766 $ (144,548 ) $ 51,337 $ (46,445 ) The following table presents the fair values and locations of derivative instruments recorded on the Condensed Consolidated Balance Sheet as of December 31, 2016 (in thousands): Fair Value as of December 31, 2016 Derivative and Balance Sheet Location Gross Asset Gross Liability Collateral Net Asset Foreign currency exchange derivatives Other current liabilities $ 5 $ (28 ) $ — $ (23 ) Interest rate swap derivatives Other current assets 3,393 — — 3,393 Other property and investments-net and other non-current assets 5,754 (397 ) — 5,357 Current interest rate swap derivative liabilities — (15,756 ) 9,731 (6,025 ) Non-current interest rate swap derivative liabilities 3,951 (57,825 ) 25,169 (28,705 ) Energy commodity derivatives Other current assets 18,682 (16,787 ) — 1,895 Current energy commodity derivative liabilities 16,335 (29,598 ) 6,228 (7,035 ) Other non-current liabilities, regulatory liabilities and deferred credits 13,071 (29,990 ) 3,630 (13,289 ) Total derivative instruments recorded on the balance sheet $ 61,191 $ (150,381 ) $ 44,758 $ (44,432 )
Schedule of Assets Pledged as Collateral and Related Offsets [Table Text Block]	The following table presents Avista Corp.'s collateral outstanding related to its derivative instruments as of June 30, 2017 and December 31, 2016 (in thousands): June 30, December 31, 2017 2016 Energy commodity derivatives Cash collateral posted $ 15,924 $ 17,134 Letters of credit outstanding 37,250 24,400 Balance sheet offsetting (cash collateral against net derivative positions) 9,767 9,858 Interest rate swap derivatives Cash collateral posted 41,570 34,900 Letters of credit outstanding 13,100 3,600 Balance sheet offsetting (cash collateral against net derivative positions) 41,570 34,900 Certain of Avista Corp.’s derivative instruments contain provisions that require Avista Corp. to maintain an "investment grade" credit rating from the major credit rating agencies. If Avista Corp.’s credit ratings were to fall below "investment grade," it would be in violation of these provisions, and the counterparties to the derivative instruments could request immediate payment or demand immediate and ongoing collateralization on derivative instruments in net liability positions. The following table presents the aggregate fair value of all derivative instruments with credit-risk-related contingent features that are in a liability position and the amount of additional collateral Avista Corp. could be required to post as of June 30, 2017 and December 31, 2016 (in thousands): June 30, December 31, 2017 2016 Energy commodity derivatives Liabilities with credit-risk-related contingent features $ 648 $ 1,124 Additional collateral to post 648 1,046 Interest rate swap derivatives Liabilities with credit-risk-related contingent features 80,266 73,978 Additional collateral to post 11,210 21,100

Pension Plans And Other Postr25

Pension Plans And Other Postretirement Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2017
Components of Net Periodic Benefit Cost	Pension Benefits Other Post-retirement Benefits 2017 2016 2017 2016 Three months ended June 30: Service cost $ 5,092 $ 4,569 $ 799 $ 804 Interest cost 6,976 6,900 1,374 1,534 Expected return on plan assets (7,900 ) (6,875 ) (475 ) (475 ) Amortization of prior service cost — — (312 ) (312 ) Net loss recognition 2,317 2,201 1,320 1,494 Net periodic benefit cost $ 6,485 $ 6,795 $ 2,706 $ 3,045 Six months ended June 30: Service cost $ 10,134 $ 9,088 $ 1,623 $ 1,583 Interest cost 13,927 13,800 2,773 3,093 Expected return on plan assets (15,800 ) (13,625 ) (950 ) (950 ) Amortization of prior service cost — — (624 ) (624 ) Net loss recognition 4,863 4,091 2,593 2,859 Net periodic benefit cost $ 13,124 $ 13,354 $ 5,415 $ 5,961

Committed Lines of Credit (Tabl

Committed Lines of Credit (Tables)	6 Months Ended
	Jun. 30, 2017
Short-term Debt [Abstract]
Schedule of Line of Credit Facilities [Table Text Block]	Borrowings outstanding and interest rates of borrowings (excluding letters of credit) under the Company’s revolving committed line of credit were as follows as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, December 31, 2017 2016 Borrowings outstanding at end of period $ 136,000 $ 120,000 Letters of credit outstanding at end of period $ 56,703 $ 34,353 Average interest rates at end of period 1.99 % 1.50 %

Long-Term Debt and Capital Le27

Long-Term Debt and Capital Leases Long-Term Debt and Capital Leases (Tables)	6 Months Ended
	Jun. 30, 2017
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table Text Block]	The following details long-term debt outstanding as of June 30, 2017 and December 31, 2016 (dollars in thousands): Maturity Year Description Interest Rate June 30, December 31, Avista Corp. Secured Long-Term Debt 2018 First Mortgage Bonds 5.95% $ 250,000 $ 250,000 2018 Secured Medium-Term Notes 7.39%-7.45% 22,500 22,500 2019 First Mortgage Bonds 5.45% 90,000 90,000 2020 First Mortgage Bonds 3.89% 52,000 52,000 2022 First Mortgage Bonds 5.13% 250,000 250,000 2023 Secured Medium-Term Notes 7.18%-7.54% 13,500 13,500 2028 Secured Medium-Term Notes 6.37% 25,000 25,000 2032 Secured Pollution Control Bonds (1) (1) 66,700 66,700 2034 Secured Pollution Control Bonds (1) (1) 17,000 17,000 2035 First Mortgage Bonds 6.25% 150,000 150,000 2037 First Mortgage Bonds 5.70% 150,000 150,000 2040 First Mortgage Bonds 5.55% 35,000 35,000 2041 First Mortgage Bonds 4.45% 85,000 85,000 2044 First Mortgage Bonds 4.11% 60,000 60,000 2045 First Mortgage Bonds 4.37% 100,000 100,000 2047 First Mortgage Bonds 4.23% 80,000 80,000 2051 First Mortgage Bonds 3.54% 175,000 175,000 Total Avista Corp. secured long-term debt 1,621,700 1,621,700 Alaska Electric Light and Power Company Secured Long-Term Debt 2044 First Mortgage Bonds 4.54% 75,000 75,000 Total secured long-term debt 1,696,700 1,696,700 Alaska Energy and Resources Company Unsecured Long-Term Debt 2019 Unsecured Term Loan 3.85% 15,000 15,000 Total secured and unsecured long-term debt 1,711,700 1,711,700 Other Long-Term Debt Components Capital lease obligations 63,791 65,435 Unamortized debt discount (709 ) (792 ) Unamortized long-term debt issuance costs (10,204 ) (10,639 ) Total 1,764,578 1,765,704 Secured Pollution Control Bonds held by Avista Corporation (1) (83,700 ) (83,700 ) Current portion of long-term debt and capital leases (277,814 ) (3,287 ) Total long-term debt and capital leases $ 1,403,064 $ 1,678,717 (1) In December 2010, $66.7 million and $17.0 million of the City of Forsyth, Montana Pollution Control Revenue Refunding Bonds (Avista Corporation Colstrip Project) due in 2032 and 2034 , respectively, which had been held by Avista Corp. since 2008 and 2009, respectively, were refunded by new variable rate bond issues (Series 2010A and Series 2010B). The new bonds were not offered to the public and were purchased by Avista Corp. due to market conditions. The Company expects that at a later date, subject to market conditions, these bonds may be remarketed to unaffiliated investors. So long as Avista Corp. is the holder of these bonds, the bonds will not be reflected as an asset or a liability on Avista Corp.'s Consolidated Balance Sheets.

Long- Term Debt to Affiliated28

Long- Term Debt to Affiliated Trust Long-Term Debt to Affiliated Trust (Tables)	6 Months Ended
	Jun. 30, 2017
Long-Term Debt to Affiliated Trust [Abstract]
Schedule Of Distribution Rates Paid [Table Text Block]	The distribution rates paid were as follows during the six months ended June 30, 2017 and the year ended December 31, 2016 : June 30, December 31, 2017 2016 Low distribution rate 1.81 % 1.29 % High distribution rate 2.08 % 1.81 % Distribution rate at the end of the period 2.08 % 1.81 %

Fair Value (Tables)

Fair Value (Tables)	6 Months Ended
	Jun. 30, 2017
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Liabilities, Quantitative Information [Table Text Block]	The following table presents the quantitative information which was used to estimate the fair values of the Level 3 assets and liabilities above as of June 30, 2017 (dollars in thousands): Fair Value (Net) at June 30, 2017 Valuation Technique Unobservable Input Range Power exchange agreement $ (13,784 ) Surrogate facility pricing O&M charges $33.59-$49.15/MWh (1) Escalation factor 3% - 2017 to 2019 Transaction volumes 396,984 MWhs Power option agreement $ (43 ) Black-Scholes- Merton Strike price $35.92/MWh - 2019 $48.39/MWh - 2018 Delivery volumes 128,611 - 254,363 MWhs Natural gas exchange agreement $ (4,173 ) Internally derived Forward purchase prices $1.66 - $2.38/mmBTU Forward sales prices $1.67 - $3.29/mmBTU Purchase volumes 115,000 - 310,000 mmBTUs Sales volumes 60,000 - 310,000 mmBTUs
Carrying Value and Estimated Fair Value of Financial Instruments	The following table sets forth the carrying value and estimated fair value of the Company’s financial instruments not reported at estimated fair value on the Condensed Consolidated Balance Sheets as of June 30, 2017 and December 31, 2016 (dollars in thousands): June 30, 2017 December 31, 2016 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Long-term debt (Level 2) $ 951,000 $ 1,076,925 $ 951,000 $ 1,048,661 Long-term debt (Level 3) 677,000 701,924 677,000 675,251 Snettisham capital lease obligation (Level 3) 60,953 62,600 62,160 62,800 Long-term debt to affiliated trusts (Level 3) 51,547 43,042 51,547 38,660
Fair Value of Assets And Liabilities Measured on Recurring Basis	Level 1 Level 2 Level 3 Counterparty Total June 30, 2017 Assets: Energy commodity derivatives $ — $ 35,198 $ — $ (35,041 ) $ 157 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 79 (79 ) — Foreign currency exchange derivatives — 187 — — 187 Interest rate swap derivatives — 11,302 — (1,853 ) 9,449 Deferred compensation assets: Fixed income securities (2) 1,716 — — — 1,716 Equity securities (2) 6,067 — — — 6,067 Total $ 7,783 $ 46,687 $ 79 $ (36,973 ) $ 17,576 Liabilities: Energy commodity derivatives $ — $ 46,203 $ — $ (44,808 ) $ 1,395 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 4,252 (79 ) 4,173 Power exchange agreement — — 13,784 — 13,784 Power option agreement — — 43 — 43 Interest rate swap derivatives — 80,266 — (43,423 ) 36,843 Total $ — $ 126,469 $ 18,079 $ (88,310 ) $ 56,238 Level 1 Level 2 Level 3 Counterparty Total December 31, 2016 Assets: Energy commodity derivatives $ — $ 47,994 $ — $ (46,099 ) $ 1,895 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 69 (69 ) — Power exchange agreement — — 25 (25 ) — Foreign currency exchange derivatives — 5 — (5 ) — Interest rate swap derivatives — 13,098 — (4,348 ) 8,750 Deferred compensation assets: Fixed income securities (2) 1,789 — — — 1,789 Equity securities (2) 5,481 — — — 5,481 Total $ 7,270 $ 61,097 $ 94 $ (50,546 ) $ 17,915 Liabilities: Energy commodity derivatives $ — $ 56,871 $ — $ (55,957 ) $ 914 Level 3 energy commodity derivatives: Natural gas exchange agreement — — 5,954 (69 ) 5,885 Power exchange agreement — — 13,474 (25 ) 13,449 Power option agreement — — 76 — 76 Foreign currency exchange derivatives — 28 — (5 ) 23 Interest rate swap derivatives — 73,978 — (39,248 ) 34,730 Total $ — $ 130,877 $ 19,504 $ (95,304 ) $ 55,077 (1) The Company is permitted to net derivative assets and derivative liabilities with the same counterparty when a legally enforceable master netting agreement exists. In addition, the Company nets derivative assets and derivative liabilities against any payables and receivables for cash collateral held or placed with these same counterparties. (2) These assets are trading securities and are included in other property and investments-net and other non-current assets on the Condensed Consolidated Balance Sheets.
Reconciliation for All Assets Measured At Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3)	Natural Gas Exchange Agreement Power Exchange Agreement Power Option Agreement Total Three months ended June 30, 2017: Balance as of April 1, 2017 $ (4,278 ) $ (14,419 ) $ (266 ) $ (18,963 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) (195 ) (672 ) 223 (644 ) Settlements 300 1,307 — 1,607 Ending balance as of June 30, 2017 (2) $ (4,173 ) $ (13,784 ) $ (43 ) $ (18,000 ) Three months ended June 30, 2016: Balance as of April 1, 2016 $ (6,006 ) $ (20,193 ) $ (97 ) $ (26,296 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) (1,551 ) 4,400 (8 ) 2,841 Settlements 700 1,179 — 1,879 Ending balance as of June 30, 2016 (2) $ (6,857 ) $ (14,614 ) $ (105 ) $ (21,576 ) Six months ended June 30, 2017: Balance as of January 1, 2017 $ (5,885 ) $ (13,449 ) $ (76 ) $ (19,410 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) 1,817 (5,165 ) 33 (3,315 ) Settlements (105 ) 4,830 — 4,725 Ending balance as of June 30, 2017 (2) $ (4,173 ) $ (13,784 ) $ (43 ) $ (18,000 ) Six months ended June 30, 2016: Balance as of January 1, 2016 $ (5,039 ) $ (21,961 ) $ (124 ) $ (27,124 ) Total gains or (losses) (realized/unrealized): Included in regulatory assets/liabilities (1) (3,296 ) 1,968 19 (1,309 ) Settlements 1,478 5,379 — 6,857 Ending balance as of June 30, 2016 (2) $ (6,857 ) $ (14,614 ) $ (105 ) $ (21,576 ) (1) All gains and losses are included in other regulatory assets and liabilities. There were no gains and losses included in either net income or other comprehensive income during any of the periods presented in the table above. (2) There were no purchases, issuances or transfers from other categories of any derivatives instruments during the periods presented in the table above.

Earnings Per Common Share Att30

Earnings Per Common Share Attributable To Avista Corporation (Tables)	6 Months Ended
	Jun. 30, 2017
Earnings Per Share [Abstract]
Computations Of Earnings Per Share	The following table presents the computation of basic and diluted earnings per common share attributable to Avista Corp. shareholders for the three and six months ended June 30 (in thousands, except per share amounts): Three months ended June 30, Six months ended June 30, 2017 2016 2017 2016 Numerator: Net income attributable to Avista Corp. shareholders $ 21,771 $ 27,254 $ 83,887 $ 84,903 Denominator: Weighted-average number of common shares outstanding-basic 64,401 63,386 64,382 62,995 Effect of dilutive securities: Performance and restricted stock awards 152 397 129 373 Weighted-average number of common shares outstanding-diluted 64,553 63,783 64,511 63,368 Earnings per common share attributable to Avista Corp. shareholders: Basic $ 0.34 $ 0.43 $ 1.30 $ 1.35 Diluted $ 0.34 $ 0.43 $ 1.30 $ 1.34 There were no shares excluded from the calculation because they were antidilutive.

Information By Business Segme31

Information By Business Segments (Tables)	6 Months Ended
	Jun. 30, 2017
Segment Reporting [Abstract]
Information by Business Segments	The following table presents information for each of the Company’s business segments (dollars in thousands): Avista Utilities Alaska Electric Light and Power Company Total Utility Other Intersegment Eliminations (1) Total For the three months ended June 30, 2017: Operating revenues $ 296,747 $ 11,982 $ 308,729 $ 5,772 $ — $ 314,501 Resource costs 99,461 3,290 102,751 — — 102,751 Other operating expenses 78,970 2,995 81,965 7,086 — 89,051 Depreciation and amortization 41,195 1,448 42,643 157 — 42,800 Income (loss) from operations 53,971 3,597 57,568 (1,471 ) — 56,097 Interest expense (2) 22,826 895 23,721 176 (27 ) 23,870 Income taxes 12,892 1,075 13,967 (916 ) — 13,051 Net income (loss) attributable to Avista Corp. shareholders 21,765 1,681 23,446 (1,675 ) — 21,771 Capital expenditures (3) 88,612 2,339 90,951 134 — 91,085 Avista Utilities Alaska Electric Light and Power Company Total Utility Other Intersegment Eliminations (1) Total For the three months ended June 30, 2016: Operating revenues $ 302,641 $ 10,247 $ 312,888 $ 5,950 $ — $ 318,838 Resource costs 106,607 3,208 109,815 — — 109,815 Other operating expenses 75,790 2,876 78,666 6,281 — 84,947 Depreciation and amortization 38,351 1,327 39,678 192 — 39,870 Income (loss) from operations 59,862 2,252 62,114 (523 ) — 61,591 Interest expense (2) 20,462 895 21,357 149 (34 ) 21,472 Income taxes 16,349 676 17,025 (315 ) — 16,710 Net income (loss) attributable to Avista Corp. shareholders 26,771 1,058 27,829 (575 ) — 27,254 Capital expenditures (3) 88,048 5,889 93,937 46 — 93,983 For the six months ended June 30, 2017: Operating revenues $ 712,128 $ 27,138 $ 739,266 $ 11,705 $ — $ 750,971 Resource costs 262,074 6,263 268,337 — — 268,337 Other operating expenses 150,682 5,767 156,449 13,265 — 169,714 Depreciation and amortization 81,733 2,895 84,628 345 — 84,973 Income (loss) from operations 162,606 10,782 173,388 (1,905 ) — 171,483 Interest expense (2) 45,509 1,789 47,298 343 (41 ) 47,600 Income taxes 43,909 3,538 47,447 (1,052 ) — 46,395 Net income (loss) attributable to Avista Corp. shareholders 80,204 5,534 85,738 (1,851 ) — 83,887 Capital expenditures (3) 174,015 3,699 177,714 169 — 177,883 For the six months ended June 30, 2016: Operating revenues $ 702,788 $ 22,893 $ 725,681 $ 11,330 $ — $ 737,011 Resource costs 265,685 5,849 271,534 — — 271,534 Other operating expenses 149,046 5,399 154,445 12,106 — 166,551 Depreciation and amortization 76,217 2,653 78,870 380 — 79,250 Income (loss) from operations 161,107 7,725 168,832 (1,156 ) — 167,676 Interest expense (2) 40,880 1,790 42,670 310 (97 ) 42,883 Income taxes 45,021 2,571 47,592 (537 ) — 47,055 Net income (loss) attributable to Avista Corp. shareholders 81,758 4,019 85,777 (874 ) — 84,903 Capital expenditures (3) 172,483 10,332 182,815 165 — 182,980 Total Assets: As of June 30, 2017: $ 5,034,778 $ 278,470 $ 5,313,248 $ 59,756 $ — $ 5,373,004 As of December 31, 2016: $ 4,975,555 $ 273,770 $ 5,249,325 $ 60,430 $ — $ 5,309,755 (1) Intersegment eliminations reported as interest expense represent intercompany interest. (2) Including interest expense to affiliated trusts. (3) The capital expenditures for the other businesses are included in other investing activities on the Condensed Consolidated Statements of Cash Flows.

Summary Of Significant Accoun32

Summary Of Significant Accounting Policies (Utility Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounting Policies [Abstract]
Utility related taxes	$ 13,552	$ 12,573	$ 35,136	$ 30,938
Property taxes	9,432	9,290	19,838	19,710
Other taxes	818	752	1,490	1,352
Utilities Operating Expense, Taxes	$ 23,802	$ 22,615	$ 56,464	$ 52,000

Summary Of Significant Accoun33

Summary Of Significant Accounting Policies (Materials And Supplies Fuel Stock And Natural Gas Stored) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Materials and supplies	$ 41,492	$ 40,700
Fuel stock	5,921	4,585
Natural gas stored	13,774	8,029
Total	$ 61,187	$ 53,314

Summary Of Significant Accoun34

Summary Of Significant Accounting Policies Summary of Significant Accounting Policies (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans Net Unamortized (Gain) Loss, Tax	$ 3,878	$ 4,075
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	7,202	7,568
Accumulated other comprehensive loss	$ (7,202)	$ (7,568)

Summary Of Significant Accoun35

Summary Of Significant Accounting Policies (Reclassifications Out of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	$ (13,051)	$ (16,710)	$ (46,395)	$ (47,055)
Total other comprehensive loss	183	140	366	(1,089)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net prior service cost	(299)	(311)	(598)	(622)
Amortization of net loss	3,638	3,642	7,276	7,284
Adjustment due to effects of regulation	(3,057)	(3,115)	(6,115)	(8,338)
Total before tax	282	216	563	(1,676)
Income tax expense	(99)	(76)	(197)	587
Total other comprehensive loss	$ 183	140	$ 366	$ (1,089)
OREGON | Reclassification Out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Adjustment due to effects of regulation		$ (2,100)

New Accounting Standards New Ac

New Accounting Standards New Accounting Standards (Details) $ in Millions	6 Months Ended
	Jun. 30, 2016USD ($)
Accounting Changes and Error Corrections [Abstract]
Excess Tax Benefit Realized from Exercise of Stock Compensation Instruments	$ 1.6

Derivatives And Risk Manageme37

Derivatives And Risk Management (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	$ 51,337	$ 44,758
Commodity Contracts [Member]
Derivative [Line Items]
Cash deposited as collateral	15,924	17,134
Letters of credit outstanding	37,250	24,400
Derivative, Fair Value, Amount Offset Against Collateral, Net	9,767	9,858
Liability position at aggregate fair value	648	1,124
Additional Collateral, Aggregate Fair Value	648	1,046
Interest Rate Swap [Member]
Derivative [Line Items]
Cash deposited as collateral	41,570	34,900
Letters of credit outstanding	13,100	3,600
Derivative, Fair Value, Amount Offset Against Collateral, Net	41,570	34,900
Liability position at aggregate fair value	80,266	73,978
Additional Collateral, Aggregate Fair Value	$ 11,210	$ 21,100

Derivatives And Risk Manageme38

Derivatives And Risk Management (Energy Commodity Derivatives) (Details) frequency in Thousands, Volt in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017Voltfrequency	Dec. 31, 2016Voltfrequency
Sales [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2,017	154	316
2,018	254	286
2,019	158	158
2,020	0	0
2,021	0	0
Thereafter	0	0
Sales [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	3,378	4,165
2018 | Volt	1,360	1,360
2019 | Volt	1,345	1,345
2,020	1,430	1,430
2,021	1,049	1,060
Thereafter | Volt	0	0
Sales [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2,017	1,129	1,552
2,018	1,244	1,244
2,019	982	982
2,020	0	0
2,021	0	0
Thereafter	0	0
Sales [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	43,940	73,110
2018 | Volt	46,805	15,113
2019 | Volt	26,590	4,020
2020 | Volt	0	0
2,021	0	0
Thereafter | Volt	0	0
Purchase [Member] | Physical [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2,017	185	510
2,018	397	397
2,019	235	235
2,020	0	0
2,021	0	0
Thereafter	0	0
Purchase [Member] | Physical [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	7,418	15,475
2018 | Volt	0	0
2019 | Volt	610	610
2020 | Volt	910	910
2021 | Volt	0	0
Thereafter | Volt	0	0
Purchase [Member] | Financial [Member] | Electric Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2,017	999	907
2,018	307	0
2,019	737	0
2,020	0	0
2,021	0	0
Thereafter	0	0
Purchase [Member] | Financial [Member] | Gas Derivative [Member]
Energy Commodity Derivative Volumes [Line Items]
2017 | Volt	63,423	110,380
2018 | Volt	78,488	52,755
2019 | Volt	42,775	29,475
2020 | Volt	3,635	2,725
2021 | Volt	0	0
Thereafter | Volt	0	0

Derivatives And Risk Manageme39

Derivatives And Risk Management Derivatives and Risk Management (Foreign Currency Exchange Contracts) (Details) CAD in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2017CADderivative_contracts	Jun. 30, 2017USD ($)derivative_contracts	Dec. 31, 2016CADderivative_contracts	Dec. 31, 2016USD ($)derivative_contracts
Foreign Currency Fair Value Hedge Derivative [Line Items]
Number Of Days Canadian Currency Prices Are Settled With U.S. Dollars	60 days
Number of Foreign Currency Derivatives Held | derivative_contracts	24	24	21	21
United States of America, Dollars | Foreign Exchange Contract [Member]
Foreign Currency Fair Value Hedge Derivative [Line Items]
Derivative, Notional Amount | $		$ 7,588		$ 2,819
Canada, Dollars | Foreign Exchange Contract [Member]
Foreign Currency Fair Value Hedge Derivative [Line Items]
Derivative, Notional Amount | CAD	CAD 10,075		CAD 3,754

Derivatives And Risk Manageme40

Derivatives And Risk Management (Interest Rate Swap Agreements) (Details) - Interest Rate Swap [Member] $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017USD ($)Caontracts	Dec. 31, 2016USD ($)Caontracts
2,017
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts	6	6
Derivative, Notional Amount | $	$ 75,000	$ 75,000
Derivative, Maturity Date	Dec. 31, 2017	Dec. 31, 2017
2,018
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts	14	14
Derivative, Notional Amount | $	$ 275,000	$ 275,000
Derivative, Maturity Date	Dec. 31, 2018	Dec. 31, 2018
2,019
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts	6	6
Derivative, Notional Amount | $	$ 70,000	$ 70,000
Derivative, Maturity Date	Dec. 31, 2019	Dec. 31, 2019
2,020
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts	3	2
Derivative, Notional Amount | $	$ 30,000	$ 20,000
Derivative, Maturity Date	Dec. 31, 2020	Dec. 31, 2020
2,022
Derivatives, Fair Value [Line Items]
Number of contracts | Caontracts	5	5
Derivative, Notional Amount | $	$ 60,000	$ 60,000
Derivative, Maturity Date	Dec. 31, 2022	Dec. 31, 2022

Derivatives And Risk Manageme41

Derivatives And Risk Management (Derivative Instruments Summary) (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Asset	$ 46,766,000	$ 61,191,000
Gross Liability	(144,548,000)	(150,381,000)
Collateral Netted	51,337,000	44,758,000
Net Asset (Liability) on Balance Sheet	(46,445,000)	(44,432,000)
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	41,570,000	34,900,000
Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Collateral Netted	9,767,000	9,858,000
Other Current Liabilities [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset		5,000
Gross Liability		(28,000)
Collateral Netted		0
Net Asset (Liability) on Balance Sheet		(23,000)
Other Current Assets [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	187,000
Gross Liability	0
Collateral Netted	0
Net Asset (Liability) on Balance Sheet	187,000
Other Current Assets [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	5,626,000	3,393,000
Gross Liability	(208,000)	0
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	5,418,000	3,393,000
Other Current Assets [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	168,000	18,682,000
Gross Liability	(11,000)	(16,787,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	157,000	1,895,000
Other Current Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	0	0
Gross Liability	(78,077,000)	(15,756,000)
Collateral Netted	41,570,000	9,731,000
Net Asset (Liability) on Balance Sheet	(36,507,000)	(6,025,000)
Non-Current Interest Rate Swap Derivative Liabilities [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	0	3,951,000
Gross Liability	(336,000)	(57,825,000)
Collateral Netted	0	25,169,000
Net Asset (Liability) on Balance Sheet	(336,000)	(28,705,000)
Other Property And Investments Net and Other Non-current Assets[Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	5,676,000	5,754,000
Gross Liability	(1,645,000)	(397,000)
Collateral Netted	0	0
Net Asset (Liability) on Balance Sheet	4,031,000	5,357,000
Current Utility Energy Commodity Derivative Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	22,577,000	16,335,000
Gross Liability	(36,716,000)	(29,598,000)
Collateral Netted	5,831,000	6,228,000
Net Asset (Liability) on Balance Sheet	(8,308,000)	(7,035,000)
Other Noncurrent Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	12,532,000	13,071,000
Gross Liability	(27,555,000)	(29,990,000)
Collateral Netted	3,936,000	3,630,000
Net Asset (Liability) on Balance Sheet	$ (11,087,000)	$ (13,289,000)

Derivatives And Risk Manageme42

Derivatives And Risk Management Derivatives and Risk Management (Collateral) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	$ 51,337	$ 44,758
Commodity Contracts [Member]
Derivative [Line Items]
Liability position at aggregate fair value	648	1,124
Additional Collateral, Aggregate Fair Value	648	1,046
Collateral Already Posted, Aggregate Fair Value	15,924	17,134
Letters of credit outstanding	37,250	24,400
Derivative, Fair Value, Amount Offset Against Collateral, Net	9,767	9,858
Foreign Exchange Contract [Member]
Derivative [Line Items]
Collateral Already Posted, Aggregate Fair Value	0	0
Letters of credit outstanding	$ 0	$ 0

Pension Plans And Other Postr43

Pension Plans And Other Postretirement Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions	$ 14,800	$ 8,000	$ 12,000
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated Pension Contributions in Next Fiscal Year	$ (22,000)

Pension Plans And Other Postr44

Pension Plans And Other Postretirement Benefit Plans (Components Of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of Net Periodic Benefit Costs Capitalized to Utility Property			40.00%
Percentage of Net Periodic Benefit Costs Recorded to Operating Expenses			60.00%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,092	$ 4,569	$ 10,134	$ 9,088
Interest cost	6,976	6,900	13,927	13,800
Expected return on plan assets	(7,900)	(6,875)	(15,800)	(13,625)
Amortization of prior service cost	0	0	0	0
Net loss recognition	2,317	2,201	4,863	4,091
Net periodic benefit cost	6,485	6,795	13,124	13,354
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	799	804	1,623	1,583
Interest cost	1,374	1,534	2,773	3,093
Expected return on plan assets	(475)	(475)	(950)	(950)
Amortization of prior service cost	(312)	(312)	(624)	(624)
Net loss recognition	1,320	1,494	2,593	2,859
Net periodic benefit cost	$ 2,706	$ 3,045	$ 5,415	$ 5,961

Committed Lines of Credit (Deta

Committed Lines of Credit (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jul. 01, 2014	Apr. 30, 2014
Short-term Debt [Line Items]
Line of Credit, Current	$ 136,398	$ 120,000
Avista Utilities [Member]
Short-term Debt [Line Items]
Line of Credit, Current	136,000	120,000
Letters of credit outstanding at end of period	$ 56,703	$ 34,353
Average interest rate at end of period	1.99%	1.50%
Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of Credit, Current	$ 0	$ 0
Letters of credit outstanding at end of period	$ 0	$ 0
Line of Credit [Member] | Avista Utilities [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 400,000
Line of Credit [Member] | Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 25,000

Long-Term Debt and Capital Le46

Long-Term Debt and Capital Leases Long-Term Debt and Capital Leases (Schedule of Long-Term Debt Instruments) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent	$ (83,700)	$ (83,700)
Interest Rate at End of Period	2.08%	1.81%
Secured Debt	$ 1,696,700	$ 1,696,700
Secured and Unsecured Debt	1,711,700	1,711,700
Capital Lease Obligations	63,791	65,435
Debt Instrument, Unamortized Discount	(709)	(792)
Unamortized Debt Issuance Expense	(10,204)	(10,639)
Long-Term Debt, Before Current Portion And Bonds Held by Company	1,764,578	1,765,704
Long-term Debt and Capital Lease Obligations, Current	(277,814)	(3,287)
Long-term debt and capital leases	$ 1,403,064	$ 1,678,717
Minimum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	1.81%	1.29%
Maximum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	2.08%	1.81%
Avista Utilities [Member]
Debt Instrument [Line Items]
Secured Debt	$ 1,621,700	$ 1,621,700
Avista Utilities [Member] | First Mortgage [Member] | 2018 5.95%
Debt Instrument [Line Items]
Maturity Year	2,018
Interest Rate at End of Period	5.95%
Secured Debt	$ 250,000	250,000
Avista Utilities [Member] | First Mortgage [Member] | 2019
Debt Instrument [Line Items]
Maturity Year	2,019
Interest Rate at End of Period	5.45%
Secured Debt	$ 90,000	90,000
Avista Utilities [Member] | First Mortgage [Member] | 2020
Debt Instrument [Line Items]
Maturity Year	2,020
Interest Rate at End of Period	3.89%
Secured Debt	$ 52,000	52,000
Avista Utilities [Member] | First Mortgage [Member] | 2022
Debt Instrument [Line Items]
Maturity Year	2,022
Interest Rate at End of Period	5.13%
Secured Debt	$ 250,000	250,000
Avista Utilities [Member] | First Mortgage [Member] | 2035
Debt Instrument [Line Items]
Maturity Year	2,035
Interest Rate at End of Period	6.25%
Secured Debt	$ 150,000	150,000
Avista Utilities [Member] | First Mortgage [Member] | 2037
Debt Instrument [Line Items]
Maturity Year	2,037
Interest Rate at End of Period	5.70%
Secured Debt	$ 150,000	150,000
Avista Utilities [Member] | First Mortgage [Member] | 2040
Debt Instrument [Line Items]
Maturity Year	2,040
Interest Rate at End of Period	5.55%
Secured Debt	$ 35,000	35,000
Avista Utilities [Member] | First Mortgage [Member] | 2041
Debt Instrument [Line Items]
Maturity Year	2,041
Interest Rate at End of Period	4.45%
Secured Debt	$ 85,000	85,000
Avista Utilities [Member] | First Mortgage [Member] | 2044
Debt Instrument [Line Items]
Maturity Year	2,044
Interest Rate at End of Period	4.11%
Secured Debt	$ 60,000	60,000
Avista Utilities [Member] | First Mortgage [Member] | 2045
Debt Instrument [Line Items]
Maturity Year	2,045
Interest Rate at End of Period	4.37%
Secured Debt	$ 100,000	100,000
Avista Utilities [Member] | First Mortgage [Member] | 2047
Debt Instrument [Line Items]
Maturity Year	2,047
Interest Rate at End of Period	4.23%
Secured Debt	$ 80,000	80,000
Avista Utilities [Member] | First Mortgage [Member] | 2051
Debt Instrument [Line Items]
Maturity Year	2,051
Interest Rate at End of Period	3.54%
Secured Debt	$ 175,000	175,000
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% to 7.45%
Debt Instrument [Line Items]
Maturity Year	2,018
Medium-term Notes, Noncurrent	$ 22,500	22,500
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% to 7.45% | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.39%
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% to 7.45% | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.45%
Avista Utilities [Member] | Secured Debt [Member] | 2023 7.18% to 7.54%
Debt Instrument [Line Items]
Maturity Year	2,023
Medium-term Notes, Noncurrent	$ 13,500	13,500
Avista Utilities [Member] | Secured Debt [Member] | 2028
Debt Instrument [Line Items]
Maturity Year	2,028
Medium-term Notes, Noncurrent	$ 25,000	25,000
Interest Rate at End of Period	6.37%
Avista Utilities [Member] | Secured Debt [Member] | 2032
Debt Instrument [Line Items]
Maturity Year	2,032
Long-term Pollution Control Bond, Noncurrent	$ 66,700	66,700
Avista Utilities [Member] | Secured Debt [Member] | 2034
Debt Instrument [Line Items]
Maturity Year	2,034
Long-term Pollution Control Bond, Noncurrent	$ 17,000	17,000
Avista Utilities [Member] | Secured Debt [Member] | Two Thousand Twenty Three Seven Point One Eight Percentage To Seven Point Five Four Percentage [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.18%
Avista Utilities [Member] | Secured Debt [Member] | Two Thousand Twenty Three Seven Point One Eight Percentage To Seven Point Five Four Percentage [Member] | Maximum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	7.54%
Alaska Electric Light & Power [Member] | First Mortgage [Member] | 2044
Debt Instrument [Line Items]
Maturity Year	2,044
Interest Rate at End of Period	4.54%
Secured Debt	$ 75,000	75,000
Alaska Energy Resources Company [Member] | Unsecured Debt [Member] | 2019
Debt Instrument [Line Items]
Maturity Year	2,019
Interest Rate at End of Period	3.85%
Unsecured Debt	$ 15,000	$ 15,000

Long- Term Debt to Affiliated47

Long- Term Debt to Affiliated Trust Long-Term Debt to Affiliated Trust (Schedule of Distribution Rates Paid) (Details)	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Interest Rate at End of Period	2.08%	1.81%
Minimum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	1.81%	1.29%
Maximum [Member]
Debt Instrument [Line Items]
Interest Rate at End of Period	2.08%	1.81%

Long- Term Debt to Affiliated48

Long- Term Debt to Affiliated Trust Long-Term Debt to Affiliated Trust (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2000	Dec. 31, 1997
Debt Instrument [Line Items]
Payments for Repurchase of Trust Preferred Securities		$ 10
Equity Method Investment, Ownership Percentage	100.00%
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	$ 51.5		$ 51.5
Trust Preferred Securities Subject to Mandatory Redemption [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Trust Preferred Securities			50
Debt Instrument, Description of Variable Rate Basis	LIBOR
Debt Instrument, Basis Spread on Variable Rate	0.875%
Common Trust Securities [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Trust Preferred Securities			$ 1.5

Fair Value (Carrying Value And

Fair Value (Carrying Value And Estimated Fair Value Of Financial Instruments) (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Capital Lease Obligations	$ 63,791	$ 65,435
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	1,076,925	1,048,661
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	951,000	951,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	701,924	675,251
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 677,000	677,000
Secured and Unsecured Debt [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Inputs, Offered Quotes	$ 100
Alaska Electric Light & Power [Member] | Capital Lease Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Capital Lease Obligations	$ 62,600	62,800
Alaska Electric Light & Power [Member] | Capital Lease Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Capital Lease Obligations	60,953	62,160
Affiliated Entity [Member] | Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	43,042	38,660
Affiliated Entity [Member] | Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 51,547	$ 51,547
Minimum [Member] | Secured and Unsecured Debt [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Inputs, Offered Quotes	$ 83.50
Maximum [Member] | Secured and Unsecured Debt [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Inputs, Offered Quotes	$ 128.87

Fair Value (Fair Value Of Asset

Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	$ 46,766	$ 61,191
Liability	144,548	150,381
Cash and cash equivalents	13,410	8,507	$ 13,522	$ 10,484
Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	200	400
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(36,973)	(50,546)
Interest rate swaps	9,449	8,750
Total	17,576	17,915
Counterparty and collateral netting, liabilities	(88,310)	(95,304)
Interest rate swaps	36,843	34,730
Total	56,238	55,077
Fair Value, Measurements, Recurring [Member] | Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(79)	(69)
Derivative Asset	0	0
Counterparty and collateral netting, liabilities	(79)	(69)
Derivative Liability	4,173	5,885
Fair Value, Measurements, Recurring [Member] | Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets		(25)
Derivative Asset		0
Counterparty and collateral netting, liabilities	0	(25)
Derivative Liability	13,784	13,449
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(1,853)	(4,348)
Counterparty and collateral netting, liabilities	(43,423)	(39,248)
Fair Value, Measurements, Recurring [Member] | Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	(35,041)	(46,099)
Derivative Asset	157	1,895
Counterparty and collateral netting, liabilities	(44,808)	(55,957)
Derivative Liability	1,395	914
Fair Value, Measurements, Recurring [Member] | Power Option Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, liabilities	0	0
Derivative Liability	43	76
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Counterparty and collateral netting, assets	0	(5)
Derivative Asset	187	0
Counterparty and collateral netting, liabilities		(5)
Derivative Liability		23
Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	1,716	1,789
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	6,067	5,481
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	7,783	7,270
Total	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Fixed Income Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	1,716	1,789
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets:	6,067	5,481
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps	11,302	13,098
Total	46,687	61,097
Interest rate swaps	80,266	73,978
Total	126,469	130,877
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Energy commodity derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	35,198	47,994
Liability	46,203	56,871
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Exchange Contract [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	187	5
Liability		28
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total	79	94
Total	18,079	19,504
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Natural Gas Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset	79	69
Liability	4,252	5,954
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Power Exchange Agreements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Asset		25
Liability	13,784	13,474
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Power Option Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability	$ 43	$ 76

Fair Value (Quantitative Inform

Fair Value (Quantitative Information) (Details) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2017USD ($)$ / MWHMMBTUMWh$ / shares$ / MmBtu	Dec. 31, 2016USD ($)
Power Exchange Agreements [Member] | Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Average operation and maintenance charges	39.22
Minimum [Member] | Power Exchange Agreements [Member] | Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions Operation And Maintenance Charges	33.59
Transaction/Delivery Volumes | MWh	396,984
Minimum [Member] | Power Option Agreement [Member] | Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Transaction/Delivery Volumes | MWh	128,611
Maximum [Member] | Power Exchange Agreements [Member] | Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions Operation And Maintenance Charges	49.15
Transaction/Delivery Volumes | MWh	396,984
Maximum [Member] | Power Option Agreement [Member] | Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Transaction/Delivery Volumes | MWh	254,363
Fair Value, Measurements, Recurring [Member] | Power Exchange Agreements [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability | $	$ (13,784)	$ (13,449)
Fair Value, Measurements, Recurring [Member] | Power Option Agreement [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability | $	(43)	(76)
Fair Value, Measurements, Recurring [Member] | Natural Gas Exchange Agreements [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability | $	$ (4,173)	$ (5,885)
WASHINGTON | Power Exchange Agreements [Member] | Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Average operation and maintenance charges	44.33
IDAHO | Power Exchange Agreements [Member] | Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Average operation and maintenance charges	39.22
Sales [Member] | Minimum [Member] | Natural Gas Exchange Agreements [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price | $ / MmBtu	1.67
Transaction/Delivery Volumes | MMBTU	60,000
Sales [Member] | Maximum [Member] | Natural Gas Exchange Agreements [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price | $ / MmBtu	3.29
Transaction/Delivery Volumes | MMBTU	310,000
Purchase [Member] | Minimum [Member] | Natural Gas Exchange Agreements [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price | $ / MmBtu	1.66
Transaction/Delivery Volumes | MMBTU	115,000
Purchase [Member] | Maximum [Member] | Natural Gas Exchange Agreements [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price | $ / MmBtu	2.38
Transaction/Delivery Volumes | MMBTU	310,000
2017 to 2019 [Member] | Power Exchange Agreements [Member] | Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Escalation Factor	3.00%
2019 | Power Option Agreement [Member] | Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Exercise Price | $ / shares	$ 35.92
2018 | Power Option Agreement [Member] | Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Exercise Price | $ / shares	$ 48.39

Fair Value (Reconciliation For

Fair Value (Reconciliation For All Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (18,963)	$ (26,296)	$ (19,410)	$ (27,124)
Included in regulatory assets/liabilities	(644)	2,841	(3,315)	(1,309)
Settlements	1,607	1,879	4,725	6,857
Ending Balance	(18,000)	(21,576)	(18,000)	(21,576)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(4,278)	(6,006)	(5,885)	(5,039)
Included in regulatory assets/liabilities	(195)	(1,551)	1,817	(3,296)
Settlements	300	700	(105)	1,478
Ending Balance	(4,173)	(6,857)	(4,173)	(6,857)
Power Option Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(266)	(97)	(76)	(124)
Included in regulatory assets/liabilities	223	(8)	33	19
Settlements	0	0	0	0
Ending Balance	(43)	(105)	(43)	(105)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(14,419)	(20,193)	(13,449)	(21,961)
Included in regulatory assets/liabilities	(672)	4,400	(5,165)	1,968
Settlements	1,307	1,179	4,830	5,379
Ending Balance	$ (13,784)	$ (14,614)	$ (13,784)	$ (14,614)

Common Stock Common Stock (Deta

Common Stock Common Stock (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Shares Issued During Period, Value, Share-based Compensation	$ 1.2
Sales Agency Agreements Common Stock, Shares Authorized	200,000,000	200,000,000
Document Period End Date	Jun. 30, 2017
Shares Issued During Period, Share-based Compensation	200,000
Sales Agency Agreement [Member]
Class of Stock [Line Items]
Shares issued		1,600,000
Sales Agency Agreements Common Stock, Shares Authorized	3,800,000
Common Stock Shares Authorized Under Sales Agency Agreements Remaining Shares Authorized To Sell	2,200,000

Earnings Per Share Attributable

Earnings Per Share Attributable To Avista Corporation (Computation Of Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income from continuing operations attributable to Avista Corp. shareholders	$ 21,771	$ 27,254	$ 83,887	$ 84,903
Denominator:
Weighted-average number of common shares outstanding-basic	64,401	63,386	64,382	62,995
Performance and restricted stock awards	152	397	129	373
Weighted-average number of common shares outstanding-diluted	64,553	63,783	64,511	63,368
Earnings Per Share, Basic [Abstract]
Basic	$ 0.34	$ 0.43	$ 1.30	$ 1.35
Earnings Per Share, Diluted [Abstract]
Diluted	$ 0.34	$ 0.43	$ 1.30	$ 1.34

Commitments And Contingencies (

Commitments And Contingencies (Details) $ in Millions	Jun. 30, 2017USD ($)
Maximum [Member] | Market Manipulation Lawsuit [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimated Potential Loss	$ 16

Information By Business Segme56

Information By Business Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2017USD ($)Reportable_Segments	Jun. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments			2
Operating revenues	$ 314,501	$ 318,838	$ 750,971	$ 737,011
Resource costs	102,751	109,815	268,337	271,534
Other operating expenses	89,051	84,947	169,714	166,551
Depreciation and amortization	42,800	39,870	84,973	79,250
Income from operations	56,097	61,591	171,483	167,676
Interest expense	23,870	21,472	47,600	42,883
Income taxes	13,051	16,710	46,395	47,055
Net income from continuing operations attributable to Avista Corp. shareholders	21,771	27,254	83,887	84,903
Payments to Acquire Other Property, Plant, and Equipment	91,085	93,983	177,883	182,980
Total assets	5,373,004		5,373,004		$ 5,309,755
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Resource costs	0	0	0	0
Other operating expenses	0	0	0	0
Depreciation and amortization	0	0	0	0
Income from operations	0	0	0	0
Interest expense	(27)	(34)	(41)	(97)
Income taxes	0	0	0	0
Net income from continuing operations attributable to Avista Corp. shareholders	0	0	0	0
Payments to Acquire Other Property, Plant, and Equipment	0	0	0	0
Total assets	0		0		0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	308,729	312,888	739,266	725,681
Resource costs	102,751	109,815	268,337	271,534
Other operating expenses	81,965	78,666	156,449	154,445
Depreciation and amortization	42,643	39,678	84,628	78,870
Income from operations	57,568	62,114	173,388	168,832
Interest expense	23,721	21,357	47,298	42,670
Income taxes	13,967	17,025	47,447	47,592
Net income from continuing operations attributable to Avista Corp. shareholders	23,446	27,829	85,738	85,777
Payments to Acquire Other Property, Plant, and Equipment	90,951	93,937	177,714	182,815
Total assets	5,313,248		5,313,248		5,249,325
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	296,747	302,641	712,128	702,788
Resource costs	99,461	106,607	262,074	265,685
Other operating expenses	78,970	75,790	150,682	149,046
Depreciation and amortization	41,195	38,351	81,733	76,217
Income from operations	53,971	59,862	162,606	161,107
Interest expense	22,826	20,462	45,509	40,880
Income taxes	12,892	16,349	43,909	45,021
Net income from continuing operations attributable to Avista Corp. shareholders	21,765	26,771	80,204	81,758
Payments to Acquire Other Property, Plant, and Equipment	88,612	88,048	174,015	172,483
Total assets	5,034,778		5,034,778		4,975,555
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,982	10,247	27,138	22,893
Resource costs	3,290	3,208	6,263	5,849
Other operating expenses	2,995	2,876	5,767	5,399
Depreciation and amortization	1,448	1,327	2,895	2,653
Income from operations	3,597	2,252	10,782	7,725
Interest expense	895	895	1,789	1,790
Income taxes	1,075	676	3,538	2,571
Net income from continuing operations attributable to Avista Corp. shareholders	1,681	1,058	5,534	4,019
Payments to Acquire Other Property, Plant, and Equipment	2,339	5,889	3,699	10,332
Total assets	278,470		278,470		273,770
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	5,772	5,950	11,705	11,330
Resource costs	0	0	0	0
Other operating expenses	7,086	6,281	13,265	12,106
Depreciation and amortization	157	192	345	380
Income from operations	(1,471)	(523)	(1,905)	(1,156)
Interest expense	176	149	343	310
Income taxes	(916)	(315)	(1,052)	(537)
Net income from continuing operations attributable to Avista Corp. shareholders	(1,675)	(575)	(1,851)	(874)
Payments to Acquire Other Property, Plant, and Equipment	134	$ 46	169	$ 165
Total assets	$ 59,756		$ 59,756		$ 60,430

Subsequent Event Subsequent E57

Subsequent Event Subsequent Event (Details) $ / shares in Units, $ in Thousands, customers in Millions, CAD in Billions	Jul. 19, 2017CADcustomers	Jun. 30, 2017USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2016USD ($)	Jul. 19, 2017USD ($)customers$ / shares	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Hydro One Total Assets		$ 5,373,004		$ 5,373,004			$ 5,309,755
Hydro One Total Annual Revenues		$ 314,501	$ 318,838	$ 750,971	$ 737,011
Subsequent Event [Member] | Hydro One [Member]
Business Acquisition [Line Items]
Hydro One Number of Customers | customers	1.3					1.3
Business Acquisition, Share Price | $ / shares						$ 53
Termination Fee Payable By Company						$ 103,000
Subsequent Event [Member] | Canada, Dollars | Hydro One [Member]
Business Acquisition [Line Items]
Hydro One Total Assets | CAD	CAD 25
Hydro One Total Annual Revenues | CAD	CAD 6.5