Commitments and Contingencies Commitments and Contingencies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) employee
2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual	$ 3.6
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 Bargaining Unit Employees Oregon | employee	50
Minimum [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 3.6
Maximum [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	77.0
Electricity [Member] | Maximum [Member] | 2015 Washington General Rate Case [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 20.0