Earnings Per Share Attributable To Avista Corporation (Computation Of Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net Income (Loss) Attributable to Parent	$ 50,776	$ 5,090	$ 25,319	$ 115,794	$ 45,843	$ 10,119	$ 25,577	$ 54,890	$ 196,979	$ 136,429	$ 115,916
Denominator:
Weighted-average number of common shares outstanding-basic	66,929	66,265	65,894	65,733	65,688	65,688	65,677	65,639	66,205	65,673	64,496
Performance and restricted stock awards									124	273	310
Weighted-average number of common shares outstanding-diluted	67,059	66,351	65,963	65,941	65,846	66,026	65,983	65,931	66,329	65,946	64,806
Earnings Per Share, Basic									$ 2.98	$ 2.08	$ 1.80
Earnings Per Share, Diluted	$ 0.76	$ 0.08	$ 0.38	$ 1.76	$ 0.70	$ 0.15	$ 0.39	$ 0.83	$ 2.97	$ 2.07	$ 1.79