Property, Plant And Equipment - Schedule of Major Classifications of Property, Plant And Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Public Utility, Property, Plant and Equipment [Line Items]
Construction work-in-progress (CWIP) and other	$ 175,767	$ 164,941
Total	6,985,564	6,627,934
Other Property	263,639	257,092
Total	7,001,958	6,656,129
Avista Utilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	6,815,891	6,462,326
Common Plant	712,609	681,711
Avista Utilities [Member] | Electricity [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	1,457,497	1,445,017
Transmission	862,987	802,546
Distribution	1,978,868	1,847,273
Construction work-in-progress (CWIP) and other	384,372	350,331
Total	4,683,724	4,445,167
Avista Utilities [Member] | Natural Gas [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	1,282,563	1,203,186
Construction work-in-progress (CWIP) and other	83,644	81,245
Total	1,419,558	1,335,448
Natural gas underground storage	53,351	51,017
Alaska Electric Light & Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	169,673	165,608
Common Plant	9,687	9,525
Alaska Electric Light & Power [Member] | Electricity [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	105,076	100,448
Transmission	22,419	22,000
Distribution	25,814	24,096
Construction work-in-progress (CWIP) and other	6,677	9,539
Total	159,986	156,083
Corporate and Other [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Other Property	$ 16,394	$ 28,195