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Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 272,646 | $ 283,770 | $ 941,468 | $ 981,063
Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 88,644 | 81,312 | 285,467 | 279,166
Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 84,824 | 86,209 | 244,355 | 251,488
Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 28,472 | 28,453 | 77,999 | 79,946
Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,910 | 1,915 | 5,659 | 5,836
Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 203,850 | 197,889 | 613,480 | 616,436
Transmission Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 5,938 | 4,058 | 14,121 | 13,460
Other Electric Revenues from Contracts With Customers [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 4,551 | 5,860 | 13,256 | 18,433
Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 214,339 | 207,807 | 640,857 | 648,329
Avista Utilities [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 263,564 | 274,931 | 909,109 | 942,441
Avista Utilities [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 85,494 | 78,548 | 272,231 | 266,826
Avista Utilities [Member] | Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 79,242 | 81,352 | 226,876 | 236,973
Avista Utilities [Member] | Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 28,472 | 28,453 | 77,999 | 79,946
Avista Utilities [Member] | Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,845 | 1,849 | 5,474 | 5,648
Avista Utilities [Member] | Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 195,053 | 190,202 | 582,580 | 589,393
Avista Utilities [Member] | Transmission Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 5,938 | 4,058 | 14,121 | 13,460
Avista Utilities [Member] | Other Electric Revenues from Contracts With Customers [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 4,551 | 5,860 | 13,256 | 18,433
Avista Utilities [Member] | Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 205,542 | 200,120 | 609,957 | 621,286
Avista Utilities [Member] | Residential Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 20,835 | 20,271 | 139,833 | 125,543
Avista Utilities [Member] | Commercial and Governmental Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 9,340 | 10,093 | 62,883 | 60,056
Avista Utilities [Member] | Industrial and Interruptible Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,538 | 1,000 | 5,276 | 3,730
Avista Utilities [Member] | Retail Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 31,713 | 31,364 | 207,992 | 189,329
Avista Utilities [Member] | Transmission Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,656 | 1,925 | 5,747 | 6,448
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 | 1,125 | 1,125 | 3,375 | 3,375
Avista Utilities [Member] | Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 34,494 | 34,414 | 217,114 | 199,152
Avista Utilities [Member] | Revenue from Contracts with Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 240,036 | 234,534 | 827,071 | 820,438
Avista Utilities [Member] | Derivative revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 24,075 | 33,372 | 79,361 | 99,628
Avista Utilities [Member] | Alternative Revenue Programs [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (3,972) | 6,038 | (4,023) | 11,105
Avista Utilities [Member] | Deferrals and Amortizations for Rate Refunds to Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1,742 | (927) | 1,216 | 3,720
Avista Utilities [Member] | Other Utility Revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1,683 | 1,914 | 5,484 | 7,550
Alaska Electric Light & Power [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 8,815 | 7,790 | 31,014 | 27,414
Alaska Electric Light & Power [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 3,150 | 2,764 | 13,236 | 12,340
Alaska Electric Light & Power [Member] | Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 5,582 | 4,857 | 17,479 | 14,515
Alaska Electric Light & Power [Member] | Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 0 | 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 | 65 | 66 | 185 | 188
Alaska Electric Light & Power [Member] | Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 8,797 | 7,687 | 30,900 | 27,043
Alaska Electric Light & Power [Member] | Transmission Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 0 | 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 | 0
Alaska Electric Light & Power [Member] | Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 8,797 | 7,687 | 30,900 | 27,043
Alaska Electric Light & Power [Member] | Revenue from Contracts with Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 8,797 | 7,687 | 30,900 | 27,043
Alaska Electric Light & Power [Member] | Deferrals and Amortizations for Rate Refunds to Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (48) | (48) | (143) | (143)
Alaska Electric Light & Power [Member] | Other Utility Revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 66 | 151 | 257 | 514
Corporate and Other [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 267 | 1,049 | 1,345 | 11,208
Corporate and Other [Member] | Revenue from Contracts with Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 3 | 731 | 521 | 10,402
Corporate and Other [Member] | Other Revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 264 | $ 318 | $ 824 | $ 806

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