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Property, Plant And Equipment (Major Classifications Of Property, Plant And Equipment) (Details) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Public Utility, Property, Plant and Equipment [Line Items] |  |
Public Utilities, Property, Plant and Equipment, Plant in Service | $ 6,462,993 | $ 6,209,968
Construction work-in-progress (CWIP) and other | 164,941 | 160,598
Total | 6,627,934 | 6,370,566
Other Property | 257,092 | 114,697
Total | 6,656,129 | 6,409,711
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation | 1,830,927 | 1,721,636
Net Utility Property | 4,797,007 | 4,648,930
Avista Utilities [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Total | 6,462,326 | 6,140,790
Common Plant | 681,711 | 641,465
Avista Utilities [Member] | Electricity [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Production | 1,445,017 | 1,426,961
Transmission | 802,546 | 761,156
Distribution | 1,847,273 | 1,726,410
Construction work-in-progress (CWIP) and other | 350,331 | 341,041
Total | 4,445,167 | 4,255,568
Avista Utilities [Member] | Natural Gas [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Distribution | 1,203,186 | 1,118,720
Construction work-in-progress (CWIP) and other | 81,245 | 76,488
Natural gas underground storage | 51,017 | 48,549
Total | 1,335,448 | 1,243,757
Alaska Electric Light & Power [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Total | 165,608 | 229,776
Common Plant | 9,525 | 8,173
Alaska Electric Light & Power [Member] | Electricity [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Production | 100,448 | 99,803
Transmission | 22,000 | 21,347
Distribution | 24,096 | 22,374
Capital Leased Assets, Gross | 0 | 71,007
Construction work-in-progress (CWIP) and other | 9,539 | 7,072
Total | 156,083 | 221,603
Corporate and Other [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Other Property | 28,195 | 39,145
Accumulated depreciation | $ 5,400 | $ 12,400

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