Committed Lines of Credit (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2014	Apr. 30, 2014
Avista Utilities [Member]
Short-term Debt [Line Items]
Balance outstanding at end of period	$ 190,000	$ 105,000
Letters of credit outstanding at end of period	$ 10,503	$ 34,420
Average interest rate at end of period	3.18%	2.26%
Line of Credit Facility, Covenant Terms, Maximum Debt to Equity Ratio	65.00%
Avista Utilities [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 400,000
Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Balance outstanding at end of period	$ 0	$ 0
Letters of credit outstanding at end of period	$ 0	$ 0
Line of Credit Facility, Covenant Terms, Maximum Debt to Equity Ratio	67.50%
Alaska Electric Light & Power [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 25,000