Earnings Per Share Attributable To Avista Corporation (Computation Of Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010		Sep. 30, 2011	Sep. 30, 2010
Numerator:
Net income attributable to Avista Corporation	$ 10,702	$ 12,346		$ 75,621	$ 66,696
Subsidiary earnings adjustment for dilutive securities	(170)	(92)		(340)	(170)
Adjusted net income attributable to Avista Corporation for computation of diluted earnings per common share	$ 10,532	$ 12,254		$ 75,281	$ 66,526
Denominator:
Weighted-average number of common shares outstanding-basic	58,057	55,616		57,731	55,175
Effect of dilutive securities
Contingent stock awards	131	113		149	134
Stock options	44	72		54	75
Weighted-average number of common shares outstanding-diluted	58,232	55,801		57,934	55,384
Potential shares excluded in calculation		198	[1]		198	[1]
Basic	$ 0.18	$ 0.22		$ 1.31	$ 1.21
Diluted	$ 0.18	$ 0.22		$ 1.30	$ 1.20

[1] Certain stock options were excluded from the calculation because they were antidilutive, as the exercise price of the stock options was higher than the average market price of Avista Corp. common stock during the respective period.