Information By Business Segments (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Reportable_Segments	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments									2
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
Resource costs									439,817	494,736	524,566
Other operating expenses									383,770	350,073	350,411
Depreciation and amortization									205,994	183,676	172,021
Income from operations	73,307	$ 30,243	$ 39,768	$ 67,071	77,184	$ 36,444	$ 53,279	$ 94,206	210,389	261,113	292,179
Interest expense									104,354	100,936	96,192
Total income tax expense									31,374	26,060	82,758
Payments to Acquire Other Property, Plant, and Equipment									443,345	425,241	416,619
Total assets	6,082,456				5,782,576				6,082,456	5,782,576	5,514,732
Income (Loss) from Continuing Operations Attributable to Parent									196,979	136,429	115,916
Non-service portion of pension and other postretirement benefit expenses									8,899	5,156	7,670
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,295,873	1,325,966
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues									37,265	43,599
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues									12,484	27,328
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,333,138	1,369,565	1,423,386
Resource costs									439,817	494,736	524,566
Other operating expenses									364,887	321,992	324,761
Depreciation and amortization									205,365	182,877	171,281
Income from operations									217,417	262,665	296,026
Interest expense									104,251	100,322	95,600
Total income tax expense									31,179	28,353	83,098
Payments to Acquire Other Property, Plant, and Equipment									442,510	424,350	412,339
Total assets	5,984,661				5,731,054				5,984,661	5,731,054	5,456,566
Income (Loss) from Continuing Operations Attributable to Parent									191,435	143,166	123,770
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,295,873	1,325,966	1,370,359
Resource costs									442,471	485,231	511,163
Other operating expenses									352,170	309,501	312,229
Depreciation and amortization									195,697	177,006	165,478
Income from operations									200,994	248,000	278,079
Interest expense									97,866	96,738	92,019
Total income tax expense									28,363	25,259	77,583
Payments to Acquire Other Property, Plant, and Equipment									434,077	418,741	405,938
Total assets	5,713,268				5,458,104				5,713,268	5,458,104	5,177,878
Income (Loss) from Continuing Operations Attributable to Parent									183,977	134,874	114,716
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues									37,265	43,599	53,027
Resource costs									(2,654)	9,505	13,403
Other operating expenses									12,717	12,491	12,532
Depreciation and amortization									9,668	5,871	5,803
Income from operations									16,423	14,665	17,947
Interest expense									6,385	3,584	3,581
Total income tax expense									2,816	3,094	5,515
Payments to Acquire Other Property, Plant, and Equipment									8,433	5,609	6,401
Total assets	271,393				272,950				271,393	272,950	278,688
Income (Loss) from Continuing Operations Attributable to Parent									7,458	8,292	9,054
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues									12,484	27,328	22,543
Resource costs									0	0	0
Other operating expenses									18,883	28,081	25,650
Depreciation and amortization									629	799	740
Income from operations									(7,028)	(1,552)	(3,847)
Interest expense									1,032	1,694	781
Total income tax expense									195	(2,293)	(340)
Payments to Acquire Other Property, Plant, and Equipment									835	891	4,280
Total assets	113,390				87,050				113,390	87,050	73,241
Income (Loss) from Continuing Operations Attributable to Parent									5,544	(6,737)	(7,854)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Resource costs									0	0	0
Other operating expenses									0	0	0
Depreciation and amortization									0	0	0
Income from operations									0	0	0
Interest expense									(929)	(1,080)	(189)
Total income tax expense									0	0	0
Payments to Acquire Other Property, Plant, and Equipment									0	0	0
Total assets	$ (15,595)				$ (35,528)				(15,595)	(35,528)	(15,075)
Income (Loss) from Continuing Operations Attributable to Parent									$ 0	$ 0	$ 0