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Property, Plant And Equipment - Schedule of Major Classifications of Property, Plant And Equipment (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Public Utility, Property, Plant and Equipment [Line Items] |  |
Construction work-in-progress (CWIP) and other | $ 175,767 | $ 164,941
Total | 6,985,564 | 6,627,934
Other Property | 263,639 | 257,092
Total | 7,001,958 | 6,656,129
Avista Utilities [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Total | 6,815,891 | 6,462,326
Common Plant | 712,609 | 681,711
Avista Utilities [Member] | Electricity [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Production | 1,457,497 | 1,445,017
Transmission | 862,987 | 802,546
Distribution | 1,978,868 | 1,847,273
Construction work-in-progress (CWIP) and other | 384,372 | 350,331
Total | 4,683,724 | 4,445,167
Avista Utilities [Member] | Natural Gas [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Distribution | 1,282,563 | 1,203,186
Construction work-in-progress (CWIP) and other | 83,644 | 81,245
Total | 1,419,558 | 1,335,448
Natural gas underground storage | 53,351 | 51,017
Alaska Electric Light & Power [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Total | 169,673 | 165,608
Common Plant | 9,687 | 9,525
Alaska Electric Light & Power [Member] | Electricity [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Production | 105,076 | 100,448
Transmission | 22,419 | 22,000
Distribution | 25,814 | 24,096
Construction work-in-progress (CWIP) and other | 6,677 | 9,539
Total | 159,986 | 156,083
Corporate and Other [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Other Property | $ 16,394 | $ 28,195

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