Committed Lines of Credit - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Apr. 30, 2014
Avista Utilities [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity			$ 400,000,000.0
Line of credit facility, expiration date	2022-04
Line of credit facility additional expiration period	1 year
Line of credit facility, covenant terms, maximum debt to equity ratio	65.00%
Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 25,000,000.0
Line of credit facility, covenant terms, maximum debt to equity ratio	67.50%