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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations Attributable to Parent	$ 30,581	$ 10,506	$ 31,254	$ 47,476	$ 30,391	$ 8,450	$ 24,212	$ 41,220	$ 119,817	$ 104,273	$ 76,719
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	1,639	(55)	69,617	1,023	1,275	2,963	1,445	1,121	72,224	6,804	1,491
Numerator:
Net income attributable to Avista Corporation shareholders	32,220	10,451	100,871	48,499	31,666	11,413	25,657	42,341	192,041	111,077	78,210
Subsidiary earnings adjustment for dilutive securities (discontinued operations)									5	(229)	(38)
Adjusted net income from discontinued operations attributable to Avista Corp. shareholders for computation of diluted earnings per common share									$ 72,229	$ 6,575	$ 1,453
Denominator:
Weighted-average number of common shares outstanding-basic	62,290	63,934	60,184	60,122	60,037	59,994	59,937	59,866	61,632	59,960	59,028
Performance and restricted stock awards									255	37	162
Incremental Common Shares Attributable To Stock Options									0	0	11
Weighted-average number of common shares outstanding-diluted	62,671	64,244	60,463	60,168	60,087	60,032	59,962	59,898	61,887	59,997	59,201
Income (Loss) from Continuing Operations, Per Basic Share									$ 1.94	$ 1.74	$ 1.30
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									$ 1.18	$ 0.11	$ 0.02