Long-Term Debt Long-Term Debt (Details) $ in Millions	9 Months Ended
Sep. 30, 2019 USD ($) Caontracts	Apr. 30, 2014 USD ($)
Debt Instrument [Line Items]
Payments for (proceeds from) derivative instrument operating activities	$ 13.3
Avista Utilities [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 400.0
Long-term Line of Credit, Noncurrent	87.7
Avista Utilities [Member] \| First Mortgage [Member] \| Two Thousand Forty Nine Three Point Four Three Percent [Member]
Debt Instrument [Line Items]
Secured Debt	$ 180.0
Interest Rate	3.43%
Long-term Debt, Maturity Date	Dec. 31, 2049
Avista Utilities [Member] \| First Mortgage [Member] \| 2019
Debt Instrument [Line Items]
Secured Debt	$ 90.0
Interest Rate Swap [Member] \| 2019
Debt Instrument [Line Items]
Number of Interest Rate Swaps Settled \| Caontracts	6
Settled Derivative Notional Amount	$ 70.0

Number of Interest Rate Swaps Settled

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Payments for (proceeds from) derivative instrument operating activities

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Settled Derivative Notional Amount

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Maturity date of long-term debt, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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The carrying value as of the balance sheet date of the noncurrent portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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