Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 272,646	$ 283,770	$ 941,468	$ 981,063
Residential Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	88,644	81,312	285,467	279,166
Commercial and Governmental Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	84,824	86,209	244,355	251,488
Industrial Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	28,472	28,453	77,999	79,946
Public Street and Highway Lighting Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	1,910	1,915	5,659	5,836
Retail Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	203,850	197,889	613,480	616,436
Transmission Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	5,938	4,058	14,121	13,460
Other Electric Revenues from Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	4,551	5,860	13,256	18,433
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	214,339	207,807	640,857	648,329
Avista Utilities [Member]
Disaggregation of Revenue [Line Items]
Revenues	263,564	274,931	909,109	942,441
Avista Utilities [Member] \| Residential Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	85,494	78,548	272,231	266,826
Avista Utilities [Member] \| Commercial and Governmental Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	79,242	81,352	226,876	236,973
Avista Utilities [Member] \| Industrial Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	28,472	28,453	77,999	79,946
Avista Utilities [Member] \| Public Street and Highway Lighting Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	1,845	1,849	5,474	5,648
Avista Utilities [Member] \| Retail Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	195,053	190,202	582,580	589,393
Avista Utilities [Member] \| Transmission Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	5,938	4,058	14,121	13,460
Avista Utilities [Member] \| Other Electric Revenues from Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	4,551	5,860	13,256	18,433
Avista Utilities [Member] \| Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	205,542	200,120	609,957	621,286
Avista Utilities [Member] \| Residential Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	20,835	20,271	139,833	125,543
Avista Utilities [Member] \| Commercial and Governmental Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	9,340	10,093	62,883	60,056
Avista Utilities [Member] \| Industrial and Interruptible Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	1,538	1,000	5,276	3,730
Avista Utilities [Member] \| Retail Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	31,713	31,364	207,992	189,329
Avista Utilities [Member] \| Transmission Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	1,656	1,925	5,747	6,448
Avista Utilities [Member] \| Other Natural Gas Revenues from Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	1,125	1,125	3,375	3,375
Avista Utilities [Member] \| Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	34,494	34,414	217,114	199,152
Avista Utilities [Member] \| Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues	240,036	234,534	827,071	820,438
Avista Utilities [Member] \| Derivative revenues
Disaggregation of Revenue [Line Items]
Revenues	24,075	33,372	79,361	99,628
Avista Utilities [Member] \| Alternative Revenue Programs [Member]
Disaggregation of Revenue [Line Items]
Revenues	(3,972)	6,038	(4,023)	11,105
Avista Utilities [Member] \| Deferrals and Amortizations for Rate Refunds to Customers
Disaggregation of Revenue [Line Items]
Revenues	1,742	(927)	1,216	3,720
Avista Utilities [Member] \| Other Utility Revenues
Disaggregation of Revenue [Line Items]
Revenues	1,683	1,914	5,484	7,550
Alaska Electric Light & Power [Member]
Disaggregation of Revenue [Line Items]
Revenues	8,815	7,790	31,014	27,414
Alaska Electric Light & Power [Member] \| Residential Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	3,150	2,764	13,236	12,340
Alaska Electric Light & Power [Member] \| Commercial and Governmental Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	5,582	4,857	17,479	14,515
Alaska Electric Light & Power [Member] \| Industrial Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	0	0	0	0
Alaska Electric Light & Power [Member] \| Public Street and Highway Lighting Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	65	66	185	188
Alaska Electric Light & Power [Member] \| Retail Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	8,797	7,687	30,900	27,043
Alaska Electric Light & Power [Member] \| Transmission Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	0	0	0	0
Alaska Electric Light & Power [Member] \| Other Electric Revenues from Contracts With Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	0	0	0	0
Alaska Electric Light & Power [Member] \| Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contract with customer including assessed tax	8,797	7,687	30,900	27,043
Alaska Electric Light & Power [Member] \| Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues	8,797	7,687	30,900	27,043
Alaska Electric Light & Power [Member] \| Deferrals and Amortizations for Rate Refunds to Customers
Disaggregation of Revenue [Line Items]
Revenues	(48)	(48)	(143)	(143)
Alaska Electric Light & Power [Member] \| Other Utility Revenues
Disaggregation of Revenue [Line Items]
Revenues	66	151	257	514
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	267	1,049	1,345	11,208
Corporate and Other [Member] \| Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues	3	731	521	10,402
Corporate and Other [Member] \| Other Revenues
Disaggregation of Revenue [Line Items]
Revenues	$ 264	$ 318	$ 824	$ 806