Information By Business Segments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) Reportable_Segments	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments	2
Operating revenues	$ 390,230	$ 396,481
Resource costs	129,547	137,347
Other operating expenses	95,856	110,997
Depreciation and amortization	51,656	49,123
Income from operations	82,193	67,071
Interest expense	26,617	26,008
Income taxes	8,532	30,017
Net income from continuing operations attributable to Avista Corp. shareholders	48,424	115,794
Capital Expenditures	95,635	93,777
Total assets	6,173,999		$ 6,082,456
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	377,205	377,702
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	12,202	10,881
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	823	7,898
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Resource costs	0	0
Other operating expenses	0	0
Depreciation and amortization	0	0
Income from operations	0	0
Interest expense	(86)	(440)
Income taxes	0	0
Net income from continuing operations attributable to Avista Corp. shareholders	0	0
Capital Expenditures	0	0
Total assets	(19,011)		(15,595)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	389,407	388,583
Resource costs	129,547	137,347
Other operating expenses	94,496	103,642
Depreciation and amortization	51,421	48,914
Income from operations	82,780	66,737
Interest expense	26,572	25,860
Income taxes	8,705	29,907
Net income from continuing operations attributable to Avista Corp. shareholders	49,374	115,453
Capital Expenditures	95,526	93,615
Total assets	6,080,797		5,984,661
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	377,205	377,702
Resource costs	129,557	138,712
Other operating expenses	91,279	100,583
Depreciation and amortization	48,974	46,507
Income from operations	76,534	60,224
Interest expense	24,983	24,264
Income taxes	7,404	28,544
Net income from continuing operations attributable to Avista Corp. shareholders	45,979	111,901
Capital Expenditures	94,056	92,309
Total assets	5,808,619		5,713,268
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	12,202	10,881
Resource costs	(10)	(1,365)
Other operating expenses	3,217	3,059
Depreciation and amortization	2,447	2,407
Income from operations	6,246	6,513
Interest expense	1,589	1,596
Income taxes	1,301	1,363
Net income from continuing operations attributable to Avista Corp. shareholders	3,395	3,552
Capital Expenditures	1,470	1,306
Total assets	272,178		271,393
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	823	7,898
Resource costs	0	0
Other operating expenses	1,360	7,355
Depreciation and amortization	235	209
Income from operations	(587)	334
Interest expense	131	588
Income taxes	(173)	110
Net income from continuing operations attributable to Avista Corp. shareholders	(950)	341
Capital Expenditures	109	$ 162
Total assets	$ 112,213		$ 113,390