Property, Plant And Equipment (Major Classifications Of Property, Plant And Equipment) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 6,462,993	$ 6,209,968
Construction work-in-progress (CWIP) and other	164,941	160,598
Total	6,627,934	6,370,566
Other Property	257,092	114,697
Total	6,656,129	6,409,711
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	1,830,927	1,721,636
Net Utility Property	4,797,007	4,648,930
Avista Utilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	6,462,326	6,140,790
Common Plant	681,711	641,465
Avista Utilities [Member] | Electricity [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	1,445,017	1,426,961
Transmission	802,546	761,156
Distribution	1,847,273	1,726,410
Construction work-in-progress (CWIP) and other	350,331	341,041
Total	4,445,167	4,255,568
Avista Utilities [Member] | Natural Gas [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	1,203,186	1,118,720
Construction work-in-progress (CWIP) and other	81,245	76,488
Natural gas underground storage	51,017	48,549
Total	1,335,448	1,243,757
Alaska Electric Light & Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	165,608	229,776
Common Plant	9,525	8,173
Alaska Electric Light & Power [Member] | Electricity [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	100,448	99,803
Transmission	22,000	21,347
Distribution	24,096	22,374
Capital Leased Assets, Gross	0	71,007
Construction work-in-progress (CWIP) and other	9,539	7,072
Total	156,083	221,603
Corporate and Other [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Other Property	28,195	39,145
Accumulated depreciation	$ 5,400	$ 12,400