Committed Lines of Credit (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jul. 01, 2014	Apr. 30, 2014
Short-term Debt [Line Items]
Line of Credit, Current	$ 136,398	$ 120,000
Avista Utilities [Member]
Short-term Debt [Line Items]
Line of Credit, Current	136,000	120,000
Letters of credit outstanding at end of period	$ 56,703	$ 34,353
Average interest rate at end of period	1.99%	1.50%
Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of Credit, Current	$ 0	$ 0
Letters of credit outstanding at end of period	$ 0	$ 0
Line of Credit [Member] | Avista Utilities [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 400,000
Line of Credit [Member] | Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 25,000