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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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