Information by Business Segments - Schedule of Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 272,646	$ 283,770	$ 941,468	$ 981,063
Resource costs	78,785	98,324	276,297	324,110
Other operating expenses	87,248	81,562	269,967	286,622
Depreciation and amortization	54,099	50,186	169,851	154,943
Income (loss) from operations	28,498	30,243	145,617	137,082
Interest expense	25,940	26,193	78,390	78,063
Income taxes	859	(131)	1,472	28,145
Net income (loss) attributable to Avista Corp. shareholders	4,876	5,090	70,753	146,203
Capital expenditures	109,157	121,897	299,223	322,069
Total Assets	6,283,131		6,283,131		$ 6,082,456
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	263,564	274,931	909,109	942,441
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	8,815	7,790	31,014	27,414
Operating Segments [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	272,379	282,721	940,123	969,855
Resource costs	78,785	98,324	276,297	324,110
Other operating expenses	85,551	80,112	266,251	271,485
Depreciation and amortization	53,953	50,052	169,282	154,445
Income (loss) from operations	30,074	30,778	148,556	141,509
Interest expense	25,838	26,230	78,158	78,001
Income taxes	1,119	207	2,300	27,547
Net income (loss) attributable to Avista Corp. shareholders	5,814	6,163	74,121	143,911
Capital expenditures	108,354	120,977	297,834	320,965
Total Assets	6,186,397		6,186,397		5,984,661
Operating Segments [Member] | Avista Utilities [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	263,564	274,931	909,109	942,441
Resource costs	77,843	98,397	274,468	325,615
Other operating expenses	82,151	76,749	256,570	261,934
Depreciation and amortization	51,499	47,631	161,934	147,208
Income (loss) from operations	28,284	28,998	137,219	130,200
Interest expense	24,277	24,634	73,449	73,214
Income taxes	1,060	125	460	25,722
Net income (loss) attributable to Avista Corp. shareholders	5,546	5,966	69,130	139,086
Capital expenditures	105,494	118,141	291,417	313,747
Total Assets	5,916,490		5,916,490		5,713,268
Operating Segments [Member] | Alaska Electric Light & Power [Member] | Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	8,815	7,790	31,014	27,414
Resource costs	942	(73)	1,829	(1,505)
Other operating expenses	3,400	3,363	9,681	9,551
Depreciation and amortization	2,454	2,421	7,348	7,237
Income (loss) from operations	1,790	1,780	11,337	11,309
Interest expense	1,561	1,596	4,709	4,787
Income taxes	59	82	1,840	1,825
Net income (loss) attributable to Avista Corp. shareholders	268	197	4,991	4,825
Capital expenditures	2,860	2,836	6,417	7,218
Total Assets	269,907		269,907		271,393
Other [Member] | Non-Utility Revenue [Member]
Segment Reporting Information [Line Items]
Operating revenues	267	1,049	1,345	11,208
Resource costs	0	0	0	0
Other operating expenses	1,697	1,450	3,716	15,137
Depreciation and amortization	146	134	569	498
Income (loss) from operations	(1,576)	(535)	(2,939)	(4,427)
Interest expense	131	149	393	885
Income taxes	(260)	(338)	(828)	598
Net income (loss) attributable to Avista Corp. shareholders	(938)	(1,073)	(3,368)	2,292
Capital expenditures	803	920	1,389	1,104
Total Assets	108,681		108,681		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	(29)	(186)	(161)	(823)
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	$ (11,947)		$ (11,947)		$ (15,595)