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Long-Term Debt - Schedule Of Long-Term Debt Instruments (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019
Debt Instrument [Line Items] |  |
Secured Debt | $ 2,092,200 | $ 1,979,200
Secured and Unsecured Debt | 2,107,200 | 1,994,200
Unamortized debt discount | (710) | (788)
Unamortized Debt Issuance Expense | (14,256) | (13,944)
Total | 2,092,234 | 1,979,468
Current portion of long-term debt |  | (52,000)
Long-term debt | 2,008,534 | 1,843,768
Secured Debt [Member] |  |
Debt Instrument [Line Items] |  |
Pollution Control Bonds | (83,700) | (83,700)
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 | $ 2,017,200 | 1,904,200
Avista Utilities [Member] | 2020 [Member] | First Mortgage [Member] |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2020 |
Debt Instrument, Interest Rate, Stated Percentage | 3.89% |
Secured Debt |  | 52,000
Avista Utilities [Member] | 2022 [Member] | 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] | 2023 7.18% - 7.54% | Minimum [Member] | Secured Debt [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 7.18% |
Avista Utilities [Member] | 2023 7.18% - 7.54% | Maximum [Member] | Secured Debt [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 7.54% |
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 | 180,000
Avista Utilities [Member] | 2050 3.07% | First Mortgage [Member] |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2050 |
Debt Instrument, Interest Rate, Stated Percentage | 3.07% |
Secured Debt | $ 165,000 |
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] | 2024 | Unsecured Debt [Member] |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2024 |
Debt Instrument, Interest Rate, Stated Percentage | 3.44% |
Unsecured Debt | $ 15,000 | $ 15,000

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