Regulatory Matters (Schedule Of Asset And Liability) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Regulated Asset Liability [Line Items]
Earning a return, asset	$ 408,184
Not earning a return, asset	235,125
Pending regulatory treatment, asset	49,344
Regulatory Assets, Current	21,851	$ 48,552
Non-current regulatory assets	670,802	614,354
Earning a return, liability	802,285
Not earning a return, liability	20,599
Pending Regulatory Treatment Liability	4,267
Regulatory Liability, Current	51,715	113,209
Non-current regulatory liabilities	775,436	780,701
Excess Deferred Income Taxes Non-plant Related [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities	11,100	18,500
Natural Gas Deferrals [Member]
Regulated Asset Liability [Line Items]
Earning a return, liability	3,189
Not earning a return, liability	0
Pending Regulatory Treatment Liability	0
Regulatory Liability, Current	3,189	40,713
Non-current regulatory liabilities	0	0
Power Deferrals [Member]
Regulated Asset Liability [Line Items]
Earning a return, liability	37,699
Not earning a return, liability	0
Pending Regulatory Treatment Liability	0
Regulatory Liability, Current	14,155	25,072
Non-current regulatory liabilities	23,544	16,933
Removal Costs [Member]
Regulated Asset Liability [Line Items]
Earning a return, liability	312,403
Not earning a return, liability	0
Pending Regulatory Treatment Liability	0
Regulatory Liability, Current	0	0
Non-current regulatory liabilities	312,403	297,379
Deferred Income Tax Charge [Member]
Regulated Asset Liability [Line Items]
Earning a return, liability	416,581
Not earning a return, liability	14,659
Pending Regulatory Treatment Liability	112
Regulatory Liability, Current	23,803	27,997
Non-current regulatory liabilities	$ 407,549	425,613
Decoupling [Member]
Regulated Asset Liability [Line Items]
Remaining amortization period, regulatory liability	2 years
Earning a return, liability	$ 2,653
Not earning a return, liability	0
Pending Regulatory Treatment Liability	0
Regulatory Liability, Current	255	6,782
Non-current regulatory liabilities	2,398	204
Other Regulatory Assets [Member]
Regulated Asset Liability [Line Items]
Earning a return, liability	13,261
Not earning a return, liability	5,940
Pending Regulatory Treatment Liability	3,566
Regulatory Liability, Current	10,313	12,645
Non-current regulatory liabilities	12,454	12,494
AFUDC Above FERC Allowed Rate [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	40,749
Not earning a return, asset	0
Pending regulatory treatment, asset	0
Regulatory Assets, Current	0	0
Non-current regulatory assets	40,749	0
Deferred Income Tax Charge [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	95,752
Not earning a return, asset	0
Pending regulatory treatment, asset	0
Regulatory Assets, Current	0	0
Non-current regulatory assets	95,752	91,188
Pension and Other Postretirement Plans Costs [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	0
Not earning a return, asset	208,754
Pending regulatory treatment, asset	0
Regulatory Assets, Current	0	0
Non-current regulatory assets	208,754	228,062
Unamortized Debt Repurchase Costs [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	8,884
Not earning a return, asset	0
Pending regulatory treatment, asset	0
Regulatory Assets, Current	0	0
Non-current regulatory assets	$ 8,884	10,255
Regulatory Asset For Settlement With Coeur d'Alene Tribe [Member]
Regulated Asset Liability [Line Items]
Remaining amortization period, regulatory assets	40 years
Earning a return, asset	$ 41,332
Not earning a return, asset	0
Pending regulatory treatment, asset	0
Regulatory Assets, Current	0	0
Non-current regulatory assets	41,332	42,643
Demand Side Management Programs [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	0
Not earning a return, asset	12,170
Pending regulatory treatment, asset	0
Regulatory Assets, Current	0	0
Non-current regulatory assets	$ 12,170	19,674
Decoupling [Member]
Regulated Asset Liability [Line Items]
Remaining amortization period, regulatory assets	2 years
Earning a return, asset	$ 26,904
Not earning a return, asset	0
Pending regulatory treatment, asset	0
Regulatory Assets, Current	12,098	3,408
Non-current regulatory assets	14,806	17,501
Asset Impairment for Regulatory Action [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	31,291
Not earning a return, asset	0
Pending regulatory treatment, asset	0
Regulatory Assets, Current	0	0
Non-current regulatory assets	31,291	24,334
Other Regulatory Assets [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	41,096
Not earning a return, asset	7,627
Pending regulatory treatment, asset	2,926
Regulatory Assets, Current	3,443	3,716
Non-current regulatory assets	$ 48,206	29,977
Avista Utilities [Member]
Regulated Asset Liability [Line Items]
Tax Cuts and Jobs Act Period to Return Plant Related Excess Deferred Income Taxes	36 years
Alaska Electric Light & Power [Member]
Regulated Asset Liability [Line Items]
Tax Cuts and Jobs Act Period to Return Plant Related Excess Deferred Income Taxes	40 years
Commodity Contract [Member] \| Deferred Derivative Gain (Loss) [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	$ 0
Not earning a return, asset	6,574
Pending regulatory treatment, asset	0
Regulatory Assets, Current	6,310	41,428
Non-current regulatory assets	264	16,866
Interest Rate Swap [Member] \| Deferred Derivative Gain (Loss) [Member]
Regulated Asset Liability [Line Items]
Earning a return, liability	16,499
Not earning a return, liability	0
Pending Regulatory Treatment Liability	589
Regulatory Liability, Current	0	0
Non-current regulatory liabilities	17,088	28,078
Interest Rate Swap [Member] \| Deferred Derivative Gain (Loss) [Member]
Regulated Asset Liability [Line Items]
Earning a return, asset	122,176
Not earning a return, asset	0
Pending regulatory treatment, asset	46,418
Regulatory Assets, Current	0	0
Non-current regulatory assets	168,594	133,854
IDAHO \| Power Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities		7,600
IDAHO \| Revenue Subject to Refund [Member]
Regulated Asset Liability [Line Items]
Regulatory Liabilities	686	774
IDAHO \| Power Deferrals Regulatory Asset [Member]
Regulated Asset Liability [Line Items]
Total, asset	300
IDAHO \| Decoupling [Member]
Regulated Asset Liability [Line Items]
Total, asset	$ 2,549	$ 2,150

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Regulated Asset Liability [Line Items]

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Earning a return includes either interest on the regulatory asset, or a return on the investment as a component of rate base or the weighted cost of capital.

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Earning a return includes either interest on the regulatory liability, or a return on the investment as a component of rate base or the weighted cost of capital.

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Remaining amounts of regulatory liabilities for which no interest during recovery period is provided.

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Tax Cuts and Jobs Act estimated period to return plant related excess deferred income taxes using the Average Rate Assumption Method.

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Amount of regulatory costs not yet approved by the regulatory authority.

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Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amortization period for the recovery of regulatory liability, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base.

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