Commitments and Contingencies - Additional Information (Details)	1 Months Ended	12 Months Ended
	Aug. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Sep. 02, 2020 a Building	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Regulatory liabilities		$ 46,435,000			$ 51,715,000
Boyds Fire [Member] | Damage from Fire [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Loss contingency, damages sought, value	$ 4,400,000
Labor Day Windstorm [Member] | Damage from Fire [Member]
Loss Contingencies [Line Items]
Wildfire covered area | a			22,000
Number of residential, commercial and other structures impacted | Building			230
Provision for Rate Refunds [Member]
Loss Contingencies [Line Items]
Regulatory liabilities				$ 8,500,000	$ 3,600,000
Provision for Rate Refunds [Member] | Electricity [Member]
Loss Contingencies [Line Items]
Regulatory liabilities				4,900,000
Provision for Rate Refunds [Member] | Natural Gas [Member]
Loss Contingencies [Line Items]
Regulatory liabilities				$ 3,600,000
Avista Utilities [Member]
Loss Contingencies [Line Items]
Percentage Of Employees, Collective Bargaining Agreement		40.00%
Majority Of Bargaining Unit Employees, Percentage		90.00%