Committed Lines of Credit (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2014	Apr. 30, 2014
Avista Utilities [Member]
Short-term Debt [Line Items]
Balance outstanding at end of period	$ 105,000	$ 105,000
Letters of credit outstanding at end of period	$ 44,595	$ 32,579
Average interest rate at end of period	1.18%	0.93%
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	68.00%
Alaska Electric Light & Power [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 25,000