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Long-Term Debt and Capital Leases Long-Term Debt and Capital Leases (Details) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2018 USD ($) Caontracts | Dec. 31, 2017 USD ($)
Debt Instrument [Line Items] |  |
Long-term Pollution Control Bond, Noncurrent | $ (83,700) | $ (83,700)
First Mortgage Bonds | 1,889,200 | 1,786,700
Secured and Unsecured Debt | 1,904,200 | 1,801,700
Capital Lease Obligations | 57,844 | 62,148
Unamortized Discount | (905) | (626)
Unamortized Long-Term Debt Issuance Costs | (13,866) | (10,285)
Long-Term Debt, Before Current Portion And Bonds Held by Company | 1,947,273 | 1,852,937
Current portion of long-term debt | (2,629) | (277,438)
Long-term debt and capital leases | 1,860,944 | 1,491,799
Payments for (proceeds from) settlement of derivative instruments | (26,600) |
Avista Utilities [Member] |  |
Debt Instrument [Line Items] |  |
First Mortgage Bonds | $ 1,814,200 | 1,711,700
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% To 7.45% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2018 |
Secured Medium-term Notes | $ 0 | 22,500
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% To 7.45% | Minimum [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 7.39% |
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% To 7.45% | Maximum [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 7.45% |
Avista Utilities [Member] | Secured Debt [Member] | 2023 7.18% To 7.54% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2023 |
Secured Medium-term Notes | $ 13,500 | 13,500
Avista Utilities [Member] | Secured Debt [Member] | 2023 7.18% To 7.54% | Minimum [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 7.18% |
Avista Utilities [Member] | Secured Debt [Member] | 2023 7.18% To 7.54% | Maximum [Member] |  |
Debt Instrument [Line Items] |  |
Debt Instrument, Interest Rate, Stated Percentage | 7.54% |
Avista Utilities [Member] | Secured Debt [Member] | 2028 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2028 |
Secured Medium-term Notes | $ 25,000 | 25,000
Debt Instrument, Interest Rate, Stated Percentage | 6.37% |
Avista Utilities [Member] | Secured Debt [Member] | 2032 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2032 |
Long-term Pollution Control Bond, Noncurrent | $ 66,700 | 66,700
Avista Utilities [Member] | Secured Debt [Member] | 2034 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2034 |
Long-term Pollution Control Bond, Noncurrent | $ 17,000 | 17,000
Avista Utilities [Member] | First Mortgage [Member] | 2018 5.95% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2018 |
Debt Instrument, Interest Rate, Stated Percentage | 5.95% |
First Mortgage Bonds | $ 0 | 250,000
Avista Utilities [Member] | First Mortgage [Member] | 2019 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2019 |
Debt Instrument, Interest Rate, Stated Percentage | 5.45% |
First Mortgage Bonds | $ 90,000 | 90,000
Avista Utilities [Member] | First Mortgage [Member] | 2020 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2020 |
Debt Instrument, Interest Rate, Stated Percentage | 3.89% |
First Mortgage Bonds | $ 52,000 | 52,000
Avista Utilities [Member] | First Mortgage [Member] | 2022 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2022 |
Debt Instrument, Interest Rate, Stated Percentage | 5.13% |
First Mortgage Bonds | $ 250,000 | 250,000
Avista Utilities [Member] | First Mortgage [Member] | 2035 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2035 |
Debt Instrument, Interest Rate, Stated Percentage | 6.25% |
First Mortgage Bonds | $ 150,000 | 150,000
Avista Utilities [Member] | First Mortgage [Member] | 2037 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2037 |
Debt Instrument, Interest Rate, Stated Percentage | 5.70% |
First Mortgage Bonds | $ 150,000 | 150,000
Avista Utilities [Member] | First Mortgage [Member] | 2040 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2040 |
Debt Instrument, Interest Rate, Stated Percentage | 5.55% |
First Mortgage Bonds | $ 35,000 | 35,000
Avista Utilities [Member] | First Mortgage [Member] | 2041 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2041 |
Debt Instrument, Interest Rate, Stated Percentage | 4.45% |
First Mortgage Bonds | $ 85,000 | 85,000
Avista Utilities [Member] | First Mortgage [Member] | 2044 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2044 |
Debt Instrument, Interest Rate, Stated Percentage | 4.11% |
First Mortgage Bonds | $ 60,000 | 60,000
Avista Utilities [Member] | First Mortgage [Member] | 2045 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2045 |
Debt Instrument, Interest Rate, Stated Percentage | 4.37% |
First Mortgage Bonds | $ 100,000 | 100,000
Avista Utilities [Member] | First Mortgage [Member] | 2047 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2047 |
Debt Instrument, Interest Rate, Stated Percentage | 4.23% |
First Mortgage Bonds | $ 80,000 | 80,000
Avista Utilities [Member] | First Mortgage [Member] | 2047 3.91% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2047 |
Debt Instrument, Interest Rate, Stated Percentage | 3.91% |
First Mortgage Bonds | $ 90,000 | 90,000
Avista Utilities [Member] | First Mortgage [Member] | 2048 4.35% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2048 |
Debt Instrument, Interest Rate, Stated Percentage | 4.35% |
First Mortgage Bonds | $ 375,000 | 0
Avista Utilities [Member] | First Mortgage [Member] | 2051 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2051 |
Debt Instrument, Interest Rate, Stated Percentage | 3.54% |
First Mortgage Bonds | $ 175,000 | 175,000
Alaska Electric Light & Power [Member] | First Mortgage [Member] | 2044 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2044 |
Debt Instrument, Interest Rate, Stated Percentage | 4.54% |
First Mortgage Bonds | $ 75,000 | 75,000
Interest Rate Swap [Member] | 2018 |  |
Debt Instrument [Line Items] |  |
Number of interest rate swaps settled | Caontracts | 14 |
Settled derivative notional amount | $ 275,000 |
Alaska Energy Resources Company [Member] | Unsecured Debt [Member] | 2019 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2019 |
Debt Instrument, Interest Rate, Stated Percentage | 3.85% |
Unsecured Term Loan | $ 15,000 | $ 15,000

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