Committed Lines of Credit (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Jul. 01, 2014	Apr. 30, 2014
Short-term Debt [Line Items]
Document Period End Date	Mar. 31, 2020
Avista Utilities [Member]
Short-term Debt [Line Items]
Line of Credit, Current	$ 185,000	$ 182,300
Line of Credit Facility, Maximum Borrowing Capacity				$ 400,000
Letters of credit outstanding at end of period	$ 32,983	$ 21,473
Average interest rate at end of period	1.66%	2.64%
Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of Credit, Current	$ 0	$ 3,500
Line of Credit Facility, Maximum Borrowing Capacity			$ 25,000
Letters of credit outstanding at end of period	$ 0	$ 0