Information by Business Segments - Schedule of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 296,007	$ 272,646	$ 1,007,132	$ 941,468
Resource costs	102,133	78,785	327,390	276,297
Other operating expenses	86,468	87,248	270,419	269,967
Depreciation and amortization	57,752	54,099	169,239	169,851
Income (loss) from operations	24,214	28,498	157,861	145,617
Interest expense	26,649	25,940	79,299	78,390
Income taxes	(5,432)	859	9,130	1,472
Net income (loss)	14,366	4,876	96,457	70,753
Capital expenditures	109,354	109,157	323,746	299,223
Total Assets	6,731,478		6,731,478		$ 6,402,097
Operating Segments [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	295,899	272,379	1,006,687	940,123
Resource costs	102,133	78,785	327,390	276,297
Other operating expenses	85,625	85,551	267,233	266,251
Depreciation and amortization	57,722	53,953	169,009	169,282
Income (loss) from operations	24,979	30,074	160,832	148,556
Interest expense	26,538	25,838	78,994	78,158
Income taxes	(6,353)	1,119	6,751	2,300
Net income (loss)	9,127	5,814	85,677	74,121
Capital expenditures	108,981	108,354	322,808	297,834
Total Assets	6,614,097		6,614,097		6,304,311
Operating Segments [Member] | Avista Utilities [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	286,752	263,564	974,172	909,109
Resource costs	101,109	77,843	324,464	274,468
Other operating expenses	82,006	82,151	257,333	256,570
Depreciation and amortization	55,039	51,499	161,332	161,934
Income (loss) from operations	23,416	28,284	149,670	137,219
Interest expense	25,015	24,277	74,423	73,449
Income taxes	(6,371)	1,060	4,932	460
Net income (loss)	9,086	5,546	80,861	69,130
Capital expenditures	107,519	105,494	318,354	291,417
Total Assets	6,345,036		6,345,036		6,035,340
Operating Segments [Member] | Alaska Electric Light & Power [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,147	8,815	32,515	31,014
Resource costs	1,024	942	2,926	(1,829)
Other operating expenses	3,619	3,400	9,900	9,681
Depreciation and amortization	2,683	2,454	7,677	7,348
Income (loss) from operations	1,563	1,790	11,162	11,337
Interest expense	1,523	1,561	4,571	4,709
Income taxes	18	59	1,819	1,840
Net income (loss)	41	268	4,816	4,991
Capital expenditures	1,462	2,860	4,454	6,417
Total Assets	269,061		269,061		268,971
Other [Member] | Non-Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	108	267	445	1,345
Resource costs	0	0	0	0
Other operating expenses	843	1,697	3,186	3,716
Depreciation and amortization	30	146	230	569
Income (loss) from operations	(765)	(1,576)	(2,971)	(2,939)
Interest expense	132	131	392	393
Income taxes	921	(260)	2,379	(828)
Net income (loss)	5,239	(938)	10,780	(3,368)
Capital expenditures	373	803	938	1,389
Total Assets	123,355		123,355		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	(21)	(29)	(87)	(161)
Income taxes	0	0	0	0
Net income (loss)	0	0	0	0
Capital expenditures	0	$ 0	0	$ 0
Total Assets	$ (5,974)		$ (5,974)		$ (11,872)