Revenue Revenue Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Operating revenues	$ 364,559	$ 283,770	$ 300,812	$ 396,481	$ 372,221	$ 296,013	$ 319,298	$ 409,361	$ 1,345,622	$ 1,396,893	$ 1,445,929
Residential Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									386,236	387,259
Commercial and Governmental Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									336,980	340,521
Industrial Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									105,802	109,846
Public Street and Highway Lighting Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									7,702	7,802
Total Retail Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									836,720	845,428
Electric Transmission [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									18,180	17,864
Other Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									26,969	27,364
Total Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									881,869	890,656
Avista Utilities [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									1,152,125	1,147,935
Operating revenues									1,295,873	1,325,966
Avista Utilities [Member] | Residential Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									369,102	368,753
Avista Utilities [Member] | Commercial and Governmental Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									317,589	314,532
Avista Utilities [Member] | Industrial Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									105,802	109,846
Avista Utilities [Member] | Public Street and Highway Lighting Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									7,448	7,539
Avista Utilities [Member] | Total Retail Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									799,941	800,670
Avista Utilities [Member] | Electric Transmission [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									18,180	17,864
Avista Utilities [Member] | Other Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									26,969	27,364
Avista Utilities [Member] | Total Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									845,090	845,898
Avista Utilities [Member] | Residential Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									196,430	194,340
Avista Utilities [Member] | Commercial Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									92,168	89,341
Avista Utilities [Member] | Industrial and Interruptible Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									5,263	4,753
Avista Utilities [Member] | Total Retail Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									293,861	288,434
Avista Utilities [Member] | Transportation Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									8,674	9,103
Avista Utilities [Member] | Other Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									4,500	4,500
Avista Utilities [Member] | Total Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									307,035	302,037
Avista Utilities [Member] | Derivative Revenues [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									118,741	186,459
Avista Utilities [Member] | Alternative Revenue Programs [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									9,614	908
Avista Utilities [Member] | Provision for Rate Refunds [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									4,509	(18,241)
Avista Utilities [Member] | Other Utility Revenues [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									10,884	8,905
Alaska Electric Light & Power [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									36,779	44,758
Operating revenues									37,265	43,599
Alaska Electric Light & Power [Member] | Residential Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									17,134	18,506
Alaska Electric Light & Power [Member] | Commercial and Governmental Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									19,391	25,989
Alaska Electric Light & Power [Member] | Industrial Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									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									254	263
Alaska Electric Light & Power [Member] | Total Retail Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									36,779	44,758
Alaska Electric Light & Power [Member] | Electric Transmission [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0
Alaska Electric Light & Power [Member] | Other Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									0	0
Alaska Electric Light & Power [Member] | Total Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									36,779	44,758
Alaska Electric Light & Power [Member] | Provision for Rate Refunds [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									(190)	(1,753)
Alaska Electric Light & Power [Member] | Other Utility Revenues [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									676	594
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									11,286	26,154
Operating revenues									12,484	27,328
Corporate and Other [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Operating revenues									$ 1,198	$ 1,174