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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net income attributable to Avista Corporation shareholders	$ 25,657	$ 18,178	$ 67,998	$ 56,566
Subsidiary earnings adjustment for dilutive securities	(39)	(47)	(82)	(9)
Adjusted net income attributable to Avista Corporation shareholders for computation of diluted earnings per common share	$ 25,618	$ 18,131	$ 67,916	$ 56,557
Denominator:
Weighted-average number of common shares outstanding-basic	59,937	58,702	59,926	58,642
Effect of dilutive securities:
Performance and restricted stock awards	25	211	28	277
Stock options	0	11	0	18
Weighted-average number of common shares outstanding-diluted	59,962	58,924	59,954	58,937
Earnings per common share attributable to Avista Corporation:
Basic	$ 0.43	$ 0.31	$ 1.13	$ 0.96
Diluted (usd per share)	$ 0.43	$ 0.31	$ 1.13	$ 0.96