Information by Business Segments - Schedule of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 298,255	$ 278,592	$ 711,125	$ 668,822
Resource costs	90,678	67,965	225,257	197,512
Other operating expenses	95,212	86,863	183,951	182,719
Depreciation and amortization	56,139	64,096	111,487	115,752
Income (loss) from operations	31,752	34,926	133,647	117,119
Interest expense	26,237	25,832	52,650	52,450
Income taxes	2,398	(7,919)	14,562	613
Net income (loss)	14,074	17,453	82,091	65,877
Capital expenditures	117,161	94,431	214,392	190,066
Total Assets	6,646,301		6,646,301		$ 6,402,097
Operating Segments [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	298,107	278,337	710,788	667,744
Resource costs	90,678	67,965	225,257	197,512
Other operating expenses	94,053	86,204	181,608	180,700
Depreciation and amortization	56,066	63,908	111,287	115,329
Income (loss) from operations	32,836	35,519	135,853	118,483
Interest expense	26,131	25,749	52,456	52,320
Income taxes	1,053	(7,524)	13,104	1,181
Net income (loss)	9,016	18,933	76,550	68,307
Capital expenditures	116,624	93,954	213,827	189,480
Total Assets	6,542,984		6,542,984		6,304,311
Operating Segments [Member] | Avista Utilities [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	287,560	268,340	687,420	645,545
Resource costs	89,515	67,069	223,355	196,625
Other operating expenses	90,728	83,140	175,327	174,420
Depreciation and amortization	53,569	61,462	106,293	110,436
Income (loss) from operations	29,561	32,217	126,254	108,935
Interest expense	24,608	24,188	49,408	49,171
Income taxes	585	(8,004)	11,303	600
Net income (loss)	7,717	17,605	71,775	63,584
Capital expenditures	114,441	91,867	210,835	185,923
Total Assets	6,272,062		6,272,062		6,035,340
Operating Segments [Member] | Alaska Electric Light & Power [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,547	9,997	23,368	22,199
Resource costs	1,163	896	1,902	(887)
Other operating expenses	3,325	3,064	6,281	6,280
Depreciation and amortization	2,497	2,446	4,994	4,893
Income (loss) from operations	3,275	3,302	9,599	9,548
Interest expense	1,523	1,561	3,048	3,149
Income taxes	468	480	1,801	1,781
Net income (loss)	1,299	1,328	4,775	4,723
Capital expenditures	2,183	2,087	2,992	3,557
Total Assets	270,922		270,922		268,971
Other [Member] | Non-Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	148	255	337	1,078
Resource costs	0	0	0	0
Other operating expenses	1,159	659	2,343	2,019
Depreciation and amortization	73	188	200	423
Income (loss) from operations	1,084	(593)	2,206	(1,364)
Interest expense	131	130	260	262
Income taxes	1,345	(395)	1,458	568
Net income (loss)	5,058	(1,480)	5,541	2,430
Capital expenditures	537	477	565	586
Total Assets	116,654		116,654		109,658
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	25	(47)	66	(132)
Income taxes	0	0	0	0
Net income (loss)	0	0	0	0
Capital expenditures	0	$ 0	0	$ 0
Total Assets	$ (13,337)		$ (13,337)		$ (11,872)