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Long-Term Debt (Schedule Of Long-Term Debt Instruments) (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Nov. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Debt Instrument [Line Items] |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 2.79% | 3.61% | 2.36%
Secured Debt |  |  | $ 1,979,200 | $ 1,889,200 |
Secured and Unsecured Debt |  |  | 1,994,200 | 1,904,200 |
Capital Lease Obligations |  |  | 0 | 57,210 |
Unamortized debt discount |  |  | (788) | (882) |
Unamortized Debt Issuance Expense |  |  | (13,944) | (13,654) |
Total |  |  | 1,979,468 | 1,946,874 |
Pollution Control Bonds |  |  | (83,700) | (83,700) |
Long-term Debt and Lease Obligation, Current |  |  | (52,000) | (107,645) |
Long-term debt and capital leases |  |  | 1,843,768 | 1,755,529 |
Payments for (proceeds from) derivative instrument operating activities |  | $ (13,300) |  |  |
2032 | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Pollution Control Bonds |  |  | 66,700 |  |
2034 | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Pollution Control Bonds |  |  | 17,000 |  |
Avista Utilities [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Secured Debt |  |  | $ 1,904,200 | 1,814,200 |
Avista Utilities [Member] | 2019 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2019 |  |
Repayments of Debt | $ 90,000 |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 5.45% |  |
Secured Debt |  |  | $ 0 |  |
Avista Utilities [Member] | 2020 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2020 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.89% |  |
Secured Debt |  |  | $ 52,000 | 52,000 |
Avista Utilities [Member] | 2022 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2022 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 5.13% |  |
Secured Debt |  |  | $ 250,000 | 250,000 |
Avista Utilities [Member] | 2023 7.18% - 7.54% | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2023 |  |
Medium-Term Notes, Noncurrent |  |  | $ 13,500 | 13,500 |
Avista Utilities [Member] | 2028 | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2028 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 6.37% |  |
Medium-Term Notes, Noncurrent |  |  | $ 25,000 | 25,000 |
Avista Utilities [Member] | 2032 | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2032 |  |
Pollution Control Bonds |  |  | $ 66,700 | 66,700 |
Avista Utilities [Member] | 2034 | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2034 |  |
Pollution Control Bonds |  |  | $ 17,000 | 17,000 |
Avista Utilities [Member] | 2035 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2035 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 6.25% |  |
Secured Debt |  |  | $ 150,000 | 150,000 |
Avista Utilities [Member] | 2037 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2037 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 5.70% |  |
Secured Debt |  |  | $ 150,000 | 150,000 |
Avista Utilities [Member] | 2040 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2040 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 5.55% |  |
Secured Debt |  |  | $ 35,000 | 35,000 |
Avista Utilities [Member] | 2041 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2041 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 4.45% |  |
Secured Debt |  |  | $ 85,000 | 85,000 |
Avista Utilities [Member] | 2044 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2044 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 4.11% |  |
Secured Debt |  |  | $ 60,000 | 60,000 |
Avista Utilities [Member] | 2045 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2045 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 4.37% |  |
Secured Debt |  |  | $ 100,000 | 100,000 |
Avista Utilities [Member] | 2047 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2047 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 4.23% |  |
Secured Debt |  |  | $ 80,000 | 80,000 |
Avista Utilities [Member] | 2047 3.91% | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2047 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.91% |  |
Secured Debt |  |  | $ 90,000 | 90,000 |
Avista Utilities [Member] | 2048 4.35% | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2048 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 4.35% |  |
Secured Debt |  |  | $ 375,000 | 375,000 |
Avista Utilities [Member] | 2049 3.43% | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2049 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.43% |  |
Secured Debt |  |  | $ 180,000 | 0 |
Avista Utilities [Member] | 2051 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2051 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.54% |  |
Secured Debt |  |  | $ 175,000 | 175,000 |
Alaska Electric Light & Power [Member] | 2044 | First Mortgage [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2044 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 4.54% |  |
Secured Debt |  |  | $ 75,000 | 75,000 |
Alaska Energy Resources Company [Member] | 2019 | Unsecured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2019 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.85% |  |
Unsecured Debt |  |  | $ 0 | 15,000 |
Alaska Energy Resources Company [Member] | 2024 | Unsecured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maturity Year |  |  | 2024 |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.44% |  |
Unsecured Debt |  |  | $ 15,000 | $ 0 |
Minimum [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 2.79% | 2.36% | 1.81%
Minimum [Member] | Avista Utilities [Member] | 2023 7.18% - 7.54% | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 7.18% |  |
Maximum [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.61% | 3.61% | 2.36%
Maximum [Member] | Avista Utilities [Member] | 2023 7.18% - 7.54% | Secured Debt [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 7.54% |  |

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- Details
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- Details
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Namespace Prefix: |
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