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Revenue Revenue Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues | $ 364,559 | $ 283,770 | $ 300,812 | $ 396,481 | $ 372,221 | $ 296,013 | $ 319,298 | $ 409,361 | $ 1,345,622 | $ 1,396,893 | $ 1,445,929
Residential Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 386,236 | 387,259 |
Commercial and Governmental Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 336,980 | 340,521 |
Industrial Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 105,802 | 109,846 |
Public Street and Highway Lighting Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 7,702 | 7,802 |
Total Retail Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 836,720 | 845,428 |
Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 18,180 | 17,864 |
Other Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 26,969 | 27,364 |
Total Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 881,869 | 890,656 |
Avista Utilities [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 1,152,125 | 1,147,935 |
Operating revenues |  |  |  |  |  |  |  |  | 1,295,873 | 1,325,966 |
Avista Utilities [Member] | Residential Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 369,102 | 368,753 |
Avista Utilities [Member] | Commercial and Governmental Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 317,589 | 314,532 |
Avista Utilities [Member] | Industrial Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 105,802 | 109,846 |
Avista Utilities [Member] | Public Street and Highway Lighting Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 7,448 | 7,539 |
Avista Utilities [Member] | Total Retail Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 799,941 | 800,670 |
Avista Utilities [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 18,180 | 17,864 |
Avista Utilities [Member] | Other Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 26,969 | 27,364 |
Avista Utilities [Member] | Total Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 845,090 | 845,898 |
Avista Utilities [Member] | Residential Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 196,430 | 194,340 |
Avista Utilities [Member] | Commercial Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 92,168 | 89,341 |
Avista Utilities [Member] | Industrial and Interruptible Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 5,263 | 4,753 |
Avista Utilities [Member] | Total Retail Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 293,861 | 288,434 |
Avista Utilities [Member] | Transportation Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 8,674 | 9,103 |
Avista Utilities [Member] | Other Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 4,500 | 4,500 |
Avista Utilities [Member] | Total Natural Gas [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 307,035 | 302,037 |
Avista Utilities [Member] | Derivative Revenues [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 118,741 | 186,459 |
Avista Utilities [Member] | Alternative Revenue Programs [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 9,614 | 908 |
Avista Utilities [Member] | Provision for Rate Refunds [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 4,509 | (18,241) |
Avista Utilities [Member] | Other Utility Revenues [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 10,884 | 8,905 |
Alaska Electric Light & Power [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 36,779 | 44,758 |
Operating revenues |  |  |  |  |  |  |  |  | 37,265 | 43,599 |
Alaska Electric Light & Power [Member] | Residential Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 17,134 | 18,506 |
Alaska Electric Light & Power [Member] | Commercial and Governmental Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 19,391 | 25,989 |
Alaska Electric Light & Power [Member] | Industrial Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 0 | 0 |
Alaska Electric Light & Power [Member] | Public Street and Highway Lighting Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 254 | 263 |
Alaska Electric Light & Power [Member] | Total Retail Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 36,779 | 44,758 |
Alaska Electric Light & Power [Member] | Electric Transmission [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 0 | 0 |
Alaska Electric Light & Power [Member] | Other Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 0 | 0 |
Alaska Electric Light & Power [Member] | Total Electric [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 36,779 | 44,758 |
Alaska Electric Light & Power [Member] | Provision for Rate Refunds [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | (190) | (1,753) |
Alaska Electric Light & Power [Member] | Other Utility Revenues [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | 676 | 594 |
Corporate and Other [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax |  |  |  |  |  |  |  |  | 11,286 | 26,154 |
Operating revenues |  |  |  |  |  |  |  |  | 12,484 | 27,328 |
Corporate and Other [Member] | Other Revenues [Member] |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  |  |  |  |  |  |  |  | $ 1,198 | $ 1,174 |

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