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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net Income (Loss) Attributable to Parent	$ 45,843	$ 10,119	$ 25,577	$ 54,890	$ 27,578	$ 4,451	$ 21,771	$ 62,116	$ 136,429	$ 115,916	$ 137,228
Denominator:
Weighted-average number of common shares outstanding-basic	65,688	65,688	65,677	65,639	64,809	64,412	64,401	64,362	65,673	64,496	63,508
Performance and restricted stock awards									273	310	412
Weighted-average number of common shares outstanding-diluted	65,846	66,026	65,983	65,931	65,308	64,892	64,553	64,469	65,946	64,806	63,920
Earnings Per Share, Basic									$ 2.08	$ 1.80	$ 2.16
Earnings Per Share, Diluted	$ 0.70	$ 0.15	$ 0.39	$ 0.83	$ 0.42	$ 0.07	$ 0.34	$ 0.96	$ 2.07	$ 1.79	$ 2.15