Commitments and Contingencies Commitments and Contingencies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) employee	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Litigation Settlement, Amount	$ 15,000
Owners percentage interest	15.00%
Regulatory Assets	$ 579,632	$ 579,000
Market Manipulation Lawsuit [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Maximum	16,000
WASHINGTON
Loss Contingencies [Line Items]
Public Utilities Property Plant And Equipment Proposed Amount Of Disallowed Costs For Recently Completed Plant	12,700
IDAHO
Loss Contingencies [Line Items]
Public Utilities Property Plant And Equipment Proposed Amount Of Disallowed Costs For Recently Completed Plant	$ 1,200
Avista Utilities [Member]
Loss Contingencies [Line Items]
Percentage Of Employees, Collective Bargaining Agreement	45.00%
Majority Of Bargaining Unit Employees, Percentage	90.00%
Number Of Employees Covering Two Agreements | employee	50
Alaska Electric Light & Power [Member]
Loss Contingencies [Line Items]
Percentage Of Employees, Collective Bargaining Agreement	54.00%