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Long-Term Debt and Capital Leases Long-Term Debt and Capital Leases (Schedule of Long-Term Debt Instruments) (Details) - USD ($) $ in Thousands | 6 Months Ended |
--- | --- | ---
Jun. 30, 2017 | Dec. 31, 2016
Debt Instrument [Line Items] |  |
Long-term Pollution Control Bond, Noncurrent | $ (83,700) | $ (83,700)
Interest Rate at End of Period | 2.08% | 1.81%
Secured Debt | $ 1,696,700 | $ 1,696,700
Secured and Unsecured Debt | 1,711,700 | 1,711,700
Capital Lease Obligations | 63,791 | 65,435
Debt Instrument, Unamortized Discount | (709) | (792)
Unamortized Debt Issuance Expense | (10,204) | (10,639)
Long-Term Debt, Before Current Portion And Bonds Held by Company | 1,764,578 | 1,765,704
Long-term Debt and Capital Lease Obligations, Current | (277,814) | (3,287)
Long-term debt and capital leases | $ 1,403,064 | $ 1,678,717
Minimum [Member] |  |
Debt Instrument [Line Items] |  |
Interest Rate at End of Period | 1.81% | 1.29%
Maximum [Member] |  |
Debt Instrument [Line Items] |  |
Interest Rate at End of Period | 2.08% | 1.81%
Avista Utilities [Member] |  |
Debt Instrument [Line Items] |  |
Secured Debt | $ 1,621,700 | $ 1,621,700
Avista Utilities [Member] | First Mortgage [Member] | 2018 5.95% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2018 |
Interest Rate at End of Period | 5.95% |
Secured Debt | $ 250,000 | 250,000
Avista Utilities [Member] | First Mortgage [Member] | 2019 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2019 |
Interest Rate at End of Period | 5.45% |
Secured Debt | $ 90,000 | 90,000
Avista Utilities [Member] | First Mortgage [Member] | 2020 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2020 |
Interest Rate at End of Period | 3.89% |
Secured Debt | $ 52,000 | 52,000
Avista Utilities [Member] | First Mortgage [Member] | 2022 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2022 |
Interest Rate at End of Period | 5.13% |
Secured Debt | $ 250,000 | 250,000
Avista Utilities [Member] | First Mortgage [Member] | 2035 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2035 |
Interest Rate at End of Period | 6.25% |
Secured Debt | $ 150,000 | 150,000
Avista Utilities [Member] | First Mortgage [Member] | 2037 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2037 |
Interest Rate at End of Period | 5.70% |
Secured Debt | $ 150,000 | 150,000
Avista Utilities [Member] | First Mortgage [Member] | 2040 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2040 |
Interest Rate at End of Period | 5.55% |
Secured Debt | $ 35,000 | 35,000
Avista Utilities [Member] | First Mortgage [Member] | 2041 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2041 |
Interest Rate at End of Period | 4.45% |
Secured Debt | $ 85,000 | 85,000
Avista Utilities [Member] | First Mortgage [Member] | 2044 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2044 |
Interest Rate at End of Period | 4.11% |
Secured Debt | $ 60,000 | 60,000
Avista Utilities [Member] | First Mortgage [Member] | 2045 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2045 |
Interest Rate at End of Period | 4.37% |
Secured Debt | $ 100,000 | 100,000
Avista Utilities [Member] | First Mortgage [Member] | 2047 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2047 |
Interest Rate at End of Period | 4.23% |
Secured Debt | $ 80,000 | 80,000
Avista Utilities [Member] | First Mortgage [Member] | 2051 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2051 |
Interest Rate at End of Period | 3.54% |
Secured Debt | $ 175,000 | 175,000
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% to 7.45% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2018 |
Medium-term Notes, Noncurrent | $ 22,500 | 22,500
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% to 7.45% | Minimum [Member] |  |
Debt Instrument [Line Items] |  |
Interest Rate at End of Period | 7.39% |
Avista Utilities [Member] | Secured Debt [Member] | 2018 7.39% to 7.45% | Maximum [Member] |  |
Debt Instrument [Line Items] |  |
Interest Rate at End of Period | 7.45% |
Avista Utilities [Member] | Secured Debt [Member] | 2023 7.18% to 7.54% |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2023 |
Medium-term Notes, Noncurrent | $ 13,500 | 13,500
Avista Utilities [Member] | Secured Debt [Member] | 2028 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2028 |
Medium-term Notes, Noncurrent | $ 25,000 | 25,000
Interest Rate at End of Period | 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] | Secured Debt [Member] | Two Thousand Twenty Three Seven Point One Eight Percentage To Seven Point Five Four Percentage [Member] | Minimum [Member] |  |
Debt Instrument [Line Items] |  |
Interest Rate at End of Period | 7.18% |
Avista Utilities [Member] | Secured Debt [Member] | Two Thousand Twenty Three Seven Point One Eight Percentage To Seven Point Five Four Percentage [Member] | Maximum [Member] |  |
Debt Instrument [Line Items] |  |
Interest Rate at End of Period | 7.54% |
Alaska Electric Light & Power [Member] | First Mortgage [Member] | 2044 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2044 |
Interest Rate at End of Period | 4.54% |
Secured Debt | $ 75,000 | 75,000
Alaska Energy Resources Company [Member] | Unsecured Debt [Member] | 2019 |  |
Debt Instrument [Line Items] |  |
Maturity Year | 2019 |
Interest Rate at End of Period | 3.85% |
Unsecured Debt | $ 15,000 | $ 15,000

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- Definition Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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