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Revenue Revenue Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 296,013 | $ 297,096 | $ 1,024,672 | $ 1,048,067
Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 85,457 |  | 285,721 |
Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 87,290 |  | 257,246 |
Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 30,806 |  | 83,910 |
Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,926 |  | 5,815 |
Total Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 205,479 |  | 632,692 |
Electric Transmission [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 4,832 |  | 12,833 |
Other Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 8,564 |  | 18,774 |
Total Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 218,875 |  | 664,299 |
Residential Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 19,247 |  | 130,668 |
Commercial Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 9,437 |  | 61,477 |
Industrial and Interruptible Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,006 |  | 3,767 |
Total Retail Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 29,690 |  | 195,912 |
Transportation Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 2,007 |  | 6,795 |
Other Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,125 |  | 3,375 |
Total Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 32,822 |  | 206,082 |
Avista Utilities [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 279,549 |  | 970,525 |
Avista Utilities [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 82,470 |  | 272,041 |
Avista Utilities [Member] | Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 80,744 |  | 236,115 |
Avista Utilities [Member] | Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 30,806 |  | 83,910 |
Avista Utilities [Member] | Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,860 |  | 5,618 |
Avista Utilities [Member] | Total Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 195,880 |  | 597,684 |
Avista Utilities [Member] | Electric Transmission [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 4,832 |  | 12,833 |
Avista Utilities [Member] | Other Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 8,564 |  | 18,774 |
Avista Utilities [Member] | Total Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 209,276 |  | 629,291 |
Avista Utilities [Member] | Residential Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 19,247 |  | 130,668 |
Avista Utilities [Member] | Commercial Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 9,437 |  | 61,477 |
Avista Utilities [Member] | Industrial and Interruptible Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,006 |  | 3,767 |
Avista Utilities [Member] | Total Retail Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 29,690 |  | 195,912 |
Avista Utilities [Member] | Transportation Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 2,007 |  | 6,795 |
Avista Utilities [Member] | Other Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,125 |  | 3,375 |
Avista Utilities [Member] | Total Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 32,822 |  | 206,082 |
Avista Utilities [Member] | Revenue from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 242,098 |  | 835,373 |
Avista Utilities [Member] | Derivative revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 32,718 |  | 147,467 |
Avista Utilities [Member] | Alternative revenue programs |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 606 |  | (1,763) |
Avista Utilities [Member] | Deferrals and amortizations for rate refunds to customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 1,940 |  | (16,900) |
Avista Utilities [Member] | Other utility revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,187 |  | 6,348 |
Alaska Electric Light & Power [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 9,570 |  | 33,715 |
Alaska Electric Light & Power [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 2,987 |  | 13,680 |
Alaska Electric Light & Power [Member] | Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 6,546 |  | 21,131 |
Alaska Electric Light & Power [Member] | Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 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 | 66 |  | 197 |
Alaska Electric Light & Power [Member] | Total Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 9,599 |  | 35,008 |
Alaska Electric Light & Power [Member] | Electric Transmission [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Other Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Total Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 9,599 |  | 35,008 |
Alaska Electric Light & Power [Member] | Residential Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Commercial Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Industrial and Interruptible Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Total Retail Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Transportation Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Other Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Total Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 0 |  | 0 |
Alaska Electric Light & Power [Member] | Revenue from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 9,599 |  | 35,008 |
Alaska Electric Light & Power [Member] | Deferrals and amortizations for rate refunds to customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (156) |  | (1,705) |
Alaska Electric Light & Power [Member] | Other utility revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 127 |  | 412 |
Corporate and Other [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 6,894 |  | 20,432 |
Corporate and Other [Member] | Revenue from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 6,580 |  | 19,633 |
Corporate and Other [Member] | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 314 |  | $ 799 |

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