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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income from continuing operations attributable to Avista Corp. shareholders	$ 10,119	$ 4,451	$ 90,586	$ 88,338
Denominator:
Weighted-average number of common shares outstanding-basic	65,688	64,412	65,668	64,392
Performance and restricted stock awards	338	480	312	246
Weighted-average number of common shares outstanding-diluted	66,026	64,892	65,980	64,638
Earnings Per Share, Basic [Abstract]
Basic	$ 0.15	$ 0.07	$ 1.38	$ 1.37
Earnings Per Share, Diluted [Abstract]
Diluted	$ 0.15	$ 0.07	$ 1.37	$ 1.37