Information By Business Segments (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Reportable_Segments	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments									2
Operating revenues	$ 372,221	$ 296,013	$ 319,298	$ 409,361	$ 397,862	$ 297,096	$ 314,501	$ 436,470	$ 1,396,893	$ 1,445,929	$ 1,442,483
Resource costs									494,736	524,566	551,366
Other operating expenses									350,073	350,411	331,238
Depreciation and amortization									183,676	172,021	161,283
Income from operations	77,184	$ 36,444	$ 53,279	$ 94,206	83,907	32,899	57,946	117,427	261,113	292,179	299,861
Interest expense									100,936	96,192	87,130
Total income tax expense									26,060	82,758	78,086
Payments to Acquire Other Property, Plant, and Equipment									425,241	416,619	406,997
Total assets	5,782,576				5,514,732				5,782,576	5,514,732	5,309,755
Income (Loss) from Continuing Operations Attributable to Parent									136,429	115,916	137,228
Acquisition costs									3,718	14,618	0
Non-service portion of pension and other postretirement benefit expenses					2,000	$ 1,900	$ 1,800	$ 2,000	5,156	7,670	10,058
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,325,966
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues									43,599
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues									27,328
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,369,565	1,423,386	1,418,914
Resource costs									494,736	524,566	551,366
Other operating expenses									321,992	324,761	305,737
Depreciation and amortization									182,877	171,281	160,514
Income from operations									262,665	296,026	302,562
Interest expense									100,322	95,600	86,654
Total income tax expense									28,353	83,098	79,442
Payments to Acquire Other Property, Plant, and Equipment									424,350	412,339	406,644
Total assets	5,731,054				5,456,566				5,731,054	5,456,566	5,249,325
Income (Loss) from Continuing Operations Attributable to Parent									143,166	123,770	140,458
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues									1,325,966	1,370,359	1,372,638
Resource costs									485,231	511,163	539,352
Other operating expenses									309,501	312,229	294,586
Depreciation and amortization									177,006	165,478	155,162
Income from operations									248,000	278,079	287,128
Interest expense									96,738	92,019	83,070
Total income tax expense									25,259	77,583	74,121
Payments to Acquire Other Property, Plant, and Equipment									418,741	405,938	390,690
Total assets	5,458,104				5,177,878				5,458,104	5,177,878	4,975,555
Income (Loss) from Continuing Operations Attributable to Parent									134,874	114,716	132,490
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues									43,599	53,027	46,276
Resource costs									9,505	13,403	12,014
Other operating expenses									12,491	12,532	11,151
Depreciation and amortization									5,871	5,803	5,352
Income from operations									14,665	17,947	15,434
Interest expense									3,584	3,581	3,584
Total income tax expense									3,094	5,515	5,321
Payments to Acquire Other Property, Plant, and Equipment									5,609	6,401	15,954
Total assets	272,950				278,688				272,950	278,688	273,770
Income (Loss) from Continuing Operations Attributable to Parent									8,292	9,054	7,968
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues									27,328	22,543	23,569
Resource costs									0	0	0
Other operating expenses									28,081	25,650	25,501
Depreciation and amortization									799	740	769
Income from operations									(1,552)	(3,847)	(2,701)
Interest expense									1,694	781	608
Total income tax expense									(2,293)	(340)	(1,356)
Payments to Acquire Other Property, Plant, and Equipment									891	4,280	353
Total assets	87,050				73,241				87,050	73,241	60,430
Income (Loss) from Continuing Operations Attributable to Parent									(6,737)	(7,854)	(3,230)
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									(1,080)	(189)	(132)
Total income tax expense									0	0	0
Payments to Acquire Other Property, Plant, and Equipment									0	0	0
Total assets	$ (35,528)				$ (15,075)				(35,528)	(15,075)	0
Income (Loss) from Continuing Operations Attributable to Parent									$ 0	$ 0	$ 0