Commitments and Contingencies Commitments and Contingencies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) employee
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	50.00%
Maximum [Member] | Market Manipulation Lawsuit [Member]
Loss Contingencies [Line Items]
Loss Contingency, Maximum	$ 16.0
Maximum [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Maximum	35.2
Electricity [Member] | Maximum [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Maximum	28.3
Natural Gas [Member] | Maximum [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Maximum	$ 6.9