Earnings Per Share Attributable To Avista Corporation (Computation Of Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Numerator:
Net income attributable to Avista Corporation shareholders	$ 15,858	$ 5,786	$ 18,178	$ 38,388	$ 24,603	$ 10,702	$ 23,001	$ 41,918	$ 78,210		$ 100,224		$ 92,425
Subsidiary earnings adjustment for dilutive securities									(38)		(473)		(226)
Adjusted net income attributable to Avista Corporation shareholders for computation of diluted earnings per common share									$ 78,172		$ 99,751		$ 92,199
Denominator:
Weighted-average number of common shares outstanding-basic	59,774	59,047	58,702	58,581	58,304	58,057	57,787	57,342	59,028		57,872		55,595
Effect of dilutive securities:
Performance and restricted stock awards									162		172		157
Stock options									11		48		72
Weighted-average number of common shares outstanding-diluted	59,826	59,123	58,924	58,950	58,583	58,232	58,143	57,414	59,201		58,092		55,824
Potential shares excluded in calculation									0	[1]	0	[1]	0	[1]
Earnings per common share attributable to Avista Corporation:
Basic									$ 1.32		$ 1.73		$ 1.66
Diluted (usd per share)	$ 0.26	$ 0.10	$ 0.31	$ 0.65	$ 0.42	$ 0.18	$ 0.39	$ 0.73	$ 1.32		$ 1.72		$ 1.65

[1] There were no shares excluded from the calculation because they were antidilutive. All stock options had exercise prices which were less than the average market price of Avista Corp. common stock during the respective period.