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Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 296,007 | $ 272,646 | $ 1,007,132 | $ 941,468
Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 97,883 | 88,644 | 306,093 | 285,467
Commercial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 92,148 | 84,824 | 262,138 | 244,355
Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 28,843 | 28,472 | 80,983 | 77,999
Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,942 | 1,910 | 5,782 | 5,659
Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 220,816 | 203,850 | 654,996 | 613,480
Transmission Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 7,372 | 5,938 | 15,668 | 14,121
Other Electric Revenues from Contracts With Customers [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 11,610 | 4,551 | 24,282 | 13,256
Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 239,798 | 214,339 | 694,946 | 640,857
Avista Utilities [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 286,752 | 263,564 | 974,172 | 909,109
Avista Utilities [Member] | Revenue from Contracts with Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 266,789 | 240,036 | 886,078 | 827,071
Avista Utilities [Member] | Derivative revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 28,087 | 24,075 | 91,151 | 79,361
Avista Utilities [Member] | Alternative Revenue Programs [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (10,499) | (3,972) | (13,069) | (4,023)
Avista Utilities [Member] | Deferrals and Amortizations for Rate Refunds to Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (156) | 1,742 | 2,664 | 1,216
Avista Utilities [Member] | Other Utility Revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,531 | 1,683 | 7,348 | 5,484
Alaska Electric Light & Power [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 9,147 | 8,815 | 32,515 | 31,014
Alaska Electric Light & Power [Member] | Revenue from Contracts with Customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 9,065 | 8,797 | 32,331 | 30,900
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 | 130 | 66 | 327 | 257
Corporate and Other [Member] | Other Revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 108 | 267 | 445 | 1,345
Avista Utilities [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 94,803 | 85,494 | 292,714 | 272,231
Avista Utilities [Member] | Commercial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 86,228 | 79,242 | 243,370 | 226,876
Avista Utilities [Member] | Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 28,843 | 28,472 | 80,983 | 77,999
Avista Utilities [Member] | Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,877 | 1,845 | 5,598 | 5,474
Avista Utilities [Member] | Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 211,751 | 195,053 | 622,665 | 582,580
Avista Utilities [Member] | Transmission Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 7,372 | 5,938 | 15,668 | 14,121
Avista Utilities [Member] | Other Electric Revenues from Contracts With Customers [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 11,610 | 4,551 | 24,282 | 13,256
Avista Utilities [Member] | Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 230,733 | 205,542 | 662,615 | 609,957
Avista Utilities [Member] | Residential Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 21,197 | 20,835 | 142,401 | 139,833
Avista Utilities [Member] | Commercial Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 10,055 | 9,340 | 65,428 | 62,883
Avista Utilities [Member] | Industrial and Interruptible Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,477 | 1,538 | 5,520 | 5,276
Avista Utilities [Member] | Retail Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 32,729 | 31,713 | 213,349 | 207,992
Avista Utilities [Member] | Transportation Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 1,921 | 1,656 | 6,177 | 5,747
Avista Utilities [Member] | Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 36,056 | 34,494 | 223,463 | 217,114
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 | 1,406 | 1,125 | 3,937 | 3,375
Alaska Electric Light & Power [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 3,080 | 3,150 | 13,379 | 13,236
Alaska Electric Light & Power [Member] | Commercial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 5,920 | 5,582 | 18,768 | 17,479
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 | 65 | 184 | 185
Alaska Electric Light & Power [Member] | Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from contract with customer including assessed tax | 9,065 | 8,797 | 32,331 | 30,900
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 | $ 9,065 | $ 8,797 | $ 32,331 | $ 30,900

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