Committed Lines of Credit (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Jul. 01, 2014	Apr. 30, 2014
Short-term Debt [Line Items]
Document Period End Date	Sep. 30, 2019
Avista Utilities [Member]
Short-term Debt [Line Items]
Long-term Line of Credit	$ 207,000
Line of Credit, Current	119,300	$ 190,000
Long-term Line of Credit, Noncurrent	87,700
Line of Credit Facility, Maximum Borrowing Capacity				$ 400,000
Letters of credit outstanding at end of period	$ 13,503	$ 10,503
Average interest rate at end of period	2.94%	3.18%
Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of Credit, Current	$ 0	$ 0
Line of Credit Facility, Maximum Borrowing Capacity			$ 25,000
Letters of credit outstanding at end of period	$ 0	$ 0