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Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disaggregation of Revenue [Line Items] |  |  |
Revenues | $ 1,321,891 | $ 1,345,622 | $ 1,396,893
Residential Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 396,403 | 386,236 | 387,259
Commercial and Governmental Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 327,726 | 336,980 | 340,521
Industrial Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 103,103 | 105,802 | 109,846
Public Street and Highway Lighting Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 7,555 | 7,702 | 7,802
Retail Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 834,787 | 836,720 | 845,428
Transmission Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 18,236 | 18,180 | 17,864
Other Electric Revenues from Contracts With Customers [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 19,252 | 26,969 | 27,364
Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 872,275 | 881,869 | 890,656
Avista Utilities [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,277,468 | 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 | 377,785 | 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 | 303,972 | 317,589 | 314,532
Avista Utilities [Member] | Industrial Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 103,103 | 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 | 7,303 | 7,448 | 7,539
Avista Utilities [Member] | Retail Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 792,163 | 799,941 | 800,670
Avista Utilities [Member] | Transmission Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 18,236 | 18,180 | 17,864
Avista Utilities [Member] | Other Electric Revenues from Contracts With Customers [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 19,252 | 26,969 | 27,364
Avista Utilities [Member] | Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 829,651 | 845,090 | 845,898
Avista Utilities [Member] | Residential Natural Gas [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 213,612 | 196,430 | 194,340
Avista Utilities [Member] | Commercial Natural Gas [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 94,937 | 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 | 7,128 | 5,263 | 4,753
Avista Utilities [Member] | Retail Natural Gas [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 315,677 | 293,861 | 288,434
Avista Utilities [Member] | Transportation Natural Gas [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 7,917 | 8,674 | 9,103
Avista Utilities [Member] | Other Natural Gas Revenues from Contracts With Customers [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 4,501 | 4,500 | 4,500
Avista Utilities [Member] | Natural Gas [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 328,095 | 307,035 | 302,037
Avista Utilities [Member] | Revenue from Contracts with Customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,157,746 | 1,152,125 | 1,147,935
Avista Utilities [Member] | Derivative revenues |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 110,313 | 118,741 | 186,459
Avista Utilities [Member] | Alternative Revenue Programs [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | (3,814) | 9,614 | 908
Avista Utilities [Member] | Deferrals and Amortizations for Rate Refunds to Customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 5,335 | 4,509 | (18,241)
Avista Utilities [Member] | Other Utility Revenues |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 7,888 | 10,884 | 8,905
Alaska Electric Light & Power [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 42,809 | 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 | 18,618 | 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 | 23,754 | 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 | 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 | 252 | 254 | 263
Alaska Electric Light & Power [Member] | Retail Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 42,624 | 36,779 | 44,758
Alaska Electric Light & Power [Member] | Transmission Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 0 | 0 | 0
Alaska Electric Light & Power [Member] | Other Electric Revenues from Contracts With Customers [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 0 | 0 | 0
Alaska Electric Light & Power [Member] | Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenue from contract with customer including assessed tax | 42,624 | 36,779 | 44,758
Alaska Electric Light & Power [Member] | Revenue from Contracts with Customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 42,624 | 36,779 | 44,758
Alaska Electric Light & Power [Member] | Deferrals and Amortizations for Rate Refunds to Customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | (190) | (190) | (1,753)
Alaska Electric Light & Power [Member] | Other Utility Revenues |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 375 | 676 | 594
Corporate and Other [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,614 | 12,484 | 27,328
Corporate and Other [Member] | Revenue from Contracts with Customers |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 564 | 11,286 | 26,154
Corporate and Other [Member] | Other Revenues |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | $ 1,050 | $ 1,198 | $ 1,174

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