Information By Business Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Reportable_Segments	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments			2
Operating revenues	$ 300,812	$ 319,298	$ 697,293	$ 728,659
Resource costs	88,439	105,969	225,786	260,587
Other operating expenses	94,063	88,604	205,060	173,398
Depreciation and amortization	55,634	45,850	104,757	90,764
Income from operations	39,768	53,279	106,839	147,485
Interest expense	25,862	25,472	51,870	50,501
Income taxes	(1,741)	5,209	28,276	15,919
Net income from continuing operations attributable to Avista Corp. shareholders	25,319	25,577	141,113	80,467
Payments to Acquire Other Property, Plant, and Equipment	106,395	101,653	200,172	183,684
Total assets	5,877,928		5,877,928		$ 5,782,576
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	289,808	302,222	667,510	690,976
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	8,743	10,482	19,624	24,145
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,261	6,594	10,159	13,538
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 from operations	0	0	0	0
Interest expense	(197)	(234)	(637)	(399)
Income taxes	0	0	0	0
Net income from continuing operations attributable to Avista Corp. shareholders	0	0	0	0
Payments to Acquire Other Property, Plant, and Equipment	0	0	0	0
Total assets	(28,288)		(28,288)		(35,528)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	298,551	312,704	687,134	715,121
Resource costs	88,439	105,969	225,786	260,587
Other operating expenses	87,731	82,061	191,373	160,031
Depreciation and amortization	55,479	45,651	104,393	90,384
Income from operations	43,994	53,427	110,731	147,694
Interest expense	25,911	25,324	51,771	50,183
Income taxes	(2,567)	5,181	27,340	17,062
Net income from continuing operations attributable to Avista Corp. shareholders	22,295	25,534	137,748	84,846
Payments to Acquire Other Property, Plant, and Equipment	106,373	101,315	199,988	183,132
Total assets	5,798,463		5,798,463		5,731,054
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	289,808	302,222	667,510	690,976
Resource costs	88,506	103,022	227,218	254,687
Other operating expenses	84,602	78,848	185,185	153,987
Depreciation and amortization	53,070	44,186	99,577	87,453
Income from operations	40,978	50,848	101,202	138,993
Interest expense	24,316	24,428	48,580	48,393
Income taxes	(2,947)	4,735	25,597	15,152
Net income from continuing operations attributable to Avista Corp. shareholders	21,219	24,252	133,120	79,792
Payments to Acquire Other Property, Plant, and Equipment	103,297	97,963	195,606	179,139
Total assets	5,520,529		5,520,529		5,458,104
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	8,743	10,482	19,624	24,145
Resource costs	(67)	2,947	(1,432)	5,900
Other operating expenses	3,129	3,213	6,188	6,044
Depreciation and amortization	2,409	1,465	4,816	2,931
Income from operations	3,016	2,579	9,529	8,701
Interest expense	1,595	896	3,191	1,790
Income taxes	380	446	1,743	1,910
Net income from continuing operations attributable to Avista Corp. shareholders	1,076	1,282	4,628	5,054
Payments to Acquire Other Property, Plant, and Equipment	3,076	3,352	4,382	3,993
Total assets	277,934		277,934		272,950
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,261	6,594	10,159	13,538
Resource costs	0	0	0	0
Other operating expenses	6,332	6,543	13,687	13,367
Depreciation and amortization	155	199	364	380
Income from operations	(4,226)	(148)	(3,892)	(209)
Interest expense	148	382	736	717
Income taxes	826	28	936	(1,143)
Net income from continuing operations attributable to Avista Corp. shareholders	3,024	43	3,365	(4,379)
Payments to Acquire Other Property, Plant, and Equipment	22	$ 338	184	$ 552
Total assets	$ 107,753		$ 107,753		$ 87,050