Property, Plant And Equipment (Major Classifications Of Property, Plant And Equipment) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 6,209,968	$ 5,853,308
Construction work-in-progress (CWIP) and other	160,598	157,839
Total	6,370,566	6,011,147
Other intangibles, property and investments-net	114,697	101,317
Total	6,409,711	6,047,930
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	1,721,636	1,612,337
Net Utility Property	4,648,930	4,398,810
Avista Utilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	6,140,790	5,783,918
Avista Utilities [Member] | Electricity [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	1,426,961	1,392,017
Transmission	761,156	726,240
Distribution	1,726,410	1,617,451
Construction work-in-progress (CWIP) and other	341,041	322,144
Total	4,255,568	4,057,852
Avista Utilities [Member] | Natural Gas [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Distribution	1,118,720	1,027,197
Construction work-in-progress (CWIP) and other	76,488	63,803
Natural gas underground storage	48,549	46,233
Total	1,243,757	1,137,233
Avista Utilities [Member] | Common Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	641,465	588,833
Alaska Electric Light & Power [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Capital Leased Assets, Gross	71,007	71,007
Total	229,776	227,229
Alaska Electric Light & Power [Member] | Electricity [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Production	99,803	97,883
Transmission	21,347	21,413
Distribution	22,374	21,061
Capital Leased Assets, Gross	71,007	71,007
Construction work-in-progress (CWIP) and other	7,072	7,341
Total	221,603	218,705
Alaska Electric Light & Power [Member] | Common Plant [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total	8,173	8,524
Corporate and Other [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Other intangibles, property and investments-net	39,145	36,783
Accumulated depreciation	$ 12,400	$ 11,600