Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Parenthetical) (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2016 Meter	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018	Dec. 31, 2017
Regulated Asset Liability [Line Items]
Number of electric meters to be replaced | Meter	253,000
Federal statutory tax rate		21.00%	21.00%	21.00%	35.00%
Regulatory liabilities		$ 46,435	$ 51,715
Non-plant excess deferred turnaround, amount		8,476	5,690
WUTC [Member]
Regulated Asset Liability [Line Items]
Non-plant excess deferred turnaround, amount		8,400
IPUC [Member]
Regulated Asset Liability [Line Items]
Non-plant excess deferred turnaround, amount			5,100
Income Tax Related [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities		14,952	23,803
Income Tax Related [Member] | WUTC [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities		$ 10,900
Income Tax Related [Member] | IPUC [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities			$ 6,400
Avista Utilities [Member]
Regulated Asset Liability [Line Items]
Tax cuts and jobs act period to return plant related excess deferred income taxes		36 years
Alaska Electric Light & Power [Member]
Regulated Asset Liability [Line Items]
Tax cuts and jobs act period to return plant related excess deferred income taxes		40 years