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								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations Attributable to Parent	$ 33,859	$ 12,722	$ 25,050	$ 46,449	$ 30,581	$ 10,506	$ 31,254	$ 47,476	$ 118,080	$ 119,817	$ 104,273
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	4,662	289	196	0	1,639	(55)	69,617	1,023	5,147	72,224	6,804
Numerator:
Supplemental pro forma AERC net income (1)	$ 38,521	$ 13,011	$ 25,246	$ 46,449	$ 32,220	$ 10,451	$ 100,871	$ 48,499	123,227	192,041	111,077
Subsidiary earnings adjustment for dilutive securities (discontinued operations)									0	5	(229)
Adjusted net income from discontinued operations attributable to Avista Corp. shareholders for computation of diluted earnings per common share									$ 5,147	$ 72,229	$ 6,575
Denominator:
Weighted-average number of common shares outstanding-basic	62,308	62,299	62,281	62,318	62,290	63,934	60,184	60,122	62,301	61,632	59,960
Performance and restricted stock awards									407	255	37
Weighted-average number of common shares outstanding-diluted	62,758	62,688	62,600	62,889	62,671	64,244	60,463	60,168	62,708	61,887	59,997
Income (Loss) from Continuing Operations, Per Basic Share									$ 1.90	$ 1.94	$ 1.74
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share									0.08	1.18	0.11
Earnings Per Share, Basic									1.98	3.12	1.85
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.54	$ 0.21	$ 0.40	$ 0.74	$ 0.48	$ 0.16	$ 0.52	$ 0.79	1.89	1.93	1.74
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.07	0.00	0.00	0.00	0.03	0.00	1.15	0.02	0.08	1.17	0.11
Earnings Per Share, Diluted	$ 0.61	$ 0.21	$ 0.40	$ 0.74	$ 0.51	$ 0.16	$ 1.67	$ 0.81	$ 1.97	$ 3.10	$ 1.85