Information by Business Segments - Schedule of Business Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Operating revenues	$ 1,321,891	$ 1,345,622	$ 1,396,893
Resource costs	398,509	439,817	494,736
Other operating expenses	359,958	383,770	350,073
Depreciation and amortization	224,223	205,994	183,676
Income (loss) from operations	232,700	210,389	261,113
Interest expense	105,061	104,354	100,936
Income taxes	7,051	31,374	26,060
Net income (loss) from continuing operations attributable to Avista Corp. shareholders	129,488	196,979	136,429
Capital expenditures	405,674	443,345	425,241
Total Assets	6,402,097	6,082,456	5,782,576
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,277,468	1,295,873	1,325,966
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	42,809	37,265	43,599
Operating Segments [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,320,277	1,333,138	1,369,565
Resource costs	398,509	439,817	494,736
Other operating expenses	354,614	364,887	321,992
Depreciation and amortization	223,507	205,365	182,877
Income (loss) from operations	237,146	217,417	262,665
Interest expense	104,723	104,251	100,322
Income taxes	7,932	31,179	28,353
Net income (loss) from continuing operations attributable to Avista Corp. shareholders	132,905	191,435	143,166
Capital expenditures	404,306	442,510	424,350
Total Assets	6,304,311	5,984,661	5,731,054
Operating Segments [Member] | Avista Utilities [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,277,468	1,295,873	1,325,966
Resource costs	396,543	442,471	485,231
Other operating expenses	341,709	352,170	309,501
Depreciation and amortization	213,701	195,697	177,006
Income (loss) from operations	220,058	200,994	248,000
Interest expense	98,451	97,866	96,738
Income taxes	4,921	28,363	25,259
Net income (loss) from continuing operations attributable to Avista Corp. shareholders	124,810	183,977	134,874
Capital expenditures	397,292	434,077	418,741
Total Assets	6,035,340	5,713,268	5,458,104
Operating Segments [Member] | Alaska Electric Light & Power [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	42,809	37,265	43,599
Resource costs	1,966	(2,654)	9,505
Other operating expenses	12,905	12,717	12,491
Depreciation and amortization	9,806	9,668	5,871
Income (loss) from operations	17,088	16,423	14,665
Interest expense	6,272	6,385	3,584
Income taxes	3,011	2,816	3,094
Net income (loss) from continuing operations attributable to Avista Corp. shareholders	8,095	7,458	8,292
Capital expenditures	7,014	8,433	5,609
Total Assets	268,971	271,393	272,950
Other [Member] | Non-Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,614	12,484	27,328
Resource costs	0	0	0
Other operating expenses	5,344	18,883	28,081
Depreciation and amortization	716	629	799
Income (loss) from operations	(4,446)	(7,028)	(1,552)
Interest expense	524	1,032	1,694
Income taxes	(881)	195	(2,293)
Net income (loss) from continuing operations attributable to Avista Corp. shareholders	(3,417)	5,544	(6,737)
Capital expenditures	1,368	835	891
Total Assets	109,658	113,390	87,050
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 (loss) from operations	0	0	0
Interest expense	(186)	(929)	(1,080)
Income taxes	0	0	0
Net income (loss) from continuing operations attributable to Avista Corp. shareholders	0	0	0
Capital expenditures	0	0	0
Total Assets	$ (11,872)	$ (15,595)	$ (35,528)