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Revenue Revenue Disaggregation of Revenue (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 319,298 | $ 314,501 | $ 728,659 | $ 750,971
Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 78,973 |  | 200,264 |
Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 83,003 |  | 169,956 |
Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 27,985 |  | 53,104 |
Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,962 |  | 3,889 |
Total Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 191,923 |  | 427,213 |
Electric Transmission [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 4,171 |  | 8,001 |
Other Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 3,919 |  | 10,210 |
Total Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 200,013 |  | 445,424 |
Residential Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 30,767 |  | 111,421 |
Commercial Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 14,668 |  | 52,040 |
Industrial and Interruptible Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,078 |  | 2,761 |
Total Retail Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 46,513 |  | 166,222 |
Transportation Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 2,221 |  | 4,788 |
Other Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,125 |  | 2,250 |
Total Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 49,859 |  | 173,260 |
Avista Utilities [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 302,222 |  | 690,976 |
Avista Utilities [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 74,818 |  | 189,571 |
Avista Utilities [Member] | Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 76,462 |  | 155,371 |
Avista Utilities [Member] | Industrial Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 27,985 |  | 53,104 |
Avista Utilities [Member] | Public Street and Highway Lighting Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,899 |  | 3,758 |
Avista Utilities [Member] | Total Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 181,164 |  | 401,804 |
Avista Utilities [Member] | Electric Transmission [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 4,171 |  | 8,001 |
Avista Utilities [Member] | Other Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 3,919 |  | 10,210 |
Avista Utilities [Member] | Total Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 189,254 |  | 420,015 |
Avista Utilities [Member] | Residential Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 30,767 |  | 111,421 |
Avista Utilities [Member] | Commercial Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 14,668 |  | 52,040 |
Avista Utilities [Member] | Industrial and Interruptible Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,078 |  | 2,761 |
Avista Utilities [Member] | Total Retail Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 46,513 |  | 166,222 |
Avista Utilities [Member] | Transportation Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 2,221 |  | 4,788 |
Avista Utilities [Member] | Other Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 1,125 |  | 2,250 |
Avista Utilities [Member] | Total Natural Gas [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 49,859 |  | 173,260 |
Avista Utilities [Member] | Revenue from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 239,113 |  | 593,275 |
Avista Utilities [Member] | Derivative revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 56,357 |  | 114,749 |
Avista Utilities [Member] | Alternative revenue programs |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 3,570 |  | (2,369) |
Avista Utilities [Member] | Deferrals and amortizations for rate refunds to customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 982 |  | (18,840) |
Avista Utilities [Member] | Other utility revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 2,200 |  | 4,161 |
Alaska Electric Light & Power [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 10,482 |  | 24,145 |
Alaska Electric Light & Power [Member] | Residential Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 4,155 |  | 10,693 |
Alaska Electric Light & Power [Member] | Commercial and Governmental Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 6,541 |  | 14,585 |
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 | 63 |  | 131 |
Alaska Electric Light & Power [Member] | Total Retail Electric [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer, Including Assessed Tax | 10,759 |  | 25,409 |
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 | 10,759 |  | 25,409 |
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 | 10,759 |  | 25,409 |
Alaska Electric Light & Power [Member] | Deferrals and amortizations for rate refunds to customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | (427) |  | (1,549) |
Alaska Electric Light & Power [Member] | Other utility revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 150 |  | 285 |
Corporate and Other [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 6,594 |  | 13,538 |
Corporate and Other [Member] | Revenue from contracts with customers |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | 6,324 |  | 13,053 |
Corporate and Other [Member] | Other revenues |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenues | $ 270 |  | $ 485 |

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