Information by Business Segments - Schedule of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 278,592	$ 300,812	$ 668,822	$ 697,293
Resource costs	67,965	88,439	197,512	225,786
Other operating expenses	86,863	94,063	182,719	205,060
Depreciation and amortization	64,096	55,634	115,752	104,757
Income (loss) from operations	34,926	39,768	117,119	106,839
Interest expense	25,832	25,862	52,450	51,870
Income taxes	(7,919)	(1,741)	613	28,276
Net income (loss) attributable to Avista Corp. shareholders	17,453	25,319	65,877	141,113
Capital expenditures	94,431	106,395	190,066	200,172
Total Assets	6,302,624		6,302,624		$ 6,082,456
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	268,339	289,808	645,544	667,510
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,998	8,743	22,200	19,624
Operating Segments [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	278,337	298,551	667,744	687,134
Resource costs	67,965	88,439	197,512	225,786
Other operating expenses	86,204	87,731	180,700	191,373
Depreciation and amortization	63,908	55,479	115,329	104,393
Income (loss) from operations	35,519	43,994	118,483	110,731
Interest expense	25,749	25,911	52,320	51,771
Income taxes	(7,524)	(2,567)	1,181	27,340
Net income (loss) attributable to Avista Corp. shareholders	18,933	22,295	68,307	137,748
Capital expenditures	93,954	106,373	189,480	199,988
Total Assets	6,205,804		6,205,804		5,984,661
Operating Segments [Member] | Avista Utilities [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	268,340	289,808	645,545	667,510
Resource costs	67,069	88,506	196,625	227,218
Other operating expenses	83,140	84,602	174,420	185,185
Depreciation and amortization	61,462	53,070	110,436	99,577
Income (loss) from operations	32,217	40,978	108,935	101,202
Interest expense	24,188	24,316	49,171	48,580
Income taxes	(8,004)	(2,947)	(600)	25,597
Net income (loss) attributable to Avista Corp. shareholders	17,605	21,219	63,584	133,120
Capital expenditures	91,867	103,297	185,923	195,606
Total Assets	5,932,490		5,932,490		5,713,268
Operating Segments [Member] | Alaska Electric Light & Power [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,997	8,743	22,199	19,624
Resource costs	896	(67)	887	(1,432)
Other operating expenses	3,064	3,129	6,280	6,188
Depreciation and amortization	2,446	2,409	4,893	4,816
Income (loss) from operations	3,302	3,016	9,548	9,529
Interest expense	1,561	1,595	3,149	3,191
Income taxes	480	380	1,781	1,743
Net income (loss) attributable to Avista Corp. shareholders	1,328	1,076	4,723	4,628
Capital expenditures	2,087	3,076	3,557	4,382
Total Assets	273,314		273,314		271,393
Other [Member] | Non-Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	255	2,261	1,078	10,159
Resource costs	0	0	0	0
Other operating expenses	659	6,332	2,019	13,687
Depreciation and amortization	188	155	423	364
Income (loss) from operations	(593)	(4,226)	(1,364)	(3,892)
Interest expense	130	148	262	736
Income taxes	(395)	826	(568)	936
Net income (loss) attributable to Avista Corp. shareholders	(1,480)	3,024	(2,430)	3,365
Capital expenditures	477	22	586	184
Total Assets	111,591		111,591		113,390
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Resource costs	0	0	0	0
Other operating expenses	0	0	0	0
Depreciation and amortization	0	0	0	0
Income (loss) from operations	0	0	0	0
Interest expense	(47)	(197)	(132)	(637)
Income taxes	0	0	0	0
Net income (loss) attributable to Avista Corp. shareholders	0	0	0	0
Capital expenditures	0	$ 0	0	$ 0
Total Assets	$ (14,771)		$ (14,771)		$ (15,595)