Selected Quarterly Financial Data (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
Selected Quarterly Financial Information [Abstract]
Operating revenues from continuing operations	$ 387,305	$ 313,649	$ 337,332	$ 446,490	$ 411,846	$ 301,558	$ 312,580	$ 446,578	$ 1,484,776	$ 1,472,562	$ 1,441,744
Operating expenses	316,938	277,737	279,972	356,915	345,093	268,796	249,849	356,236	1,231,562	1,219,974	1,210,655
Income from operations	70,367	35,912	57,360	89,575	66,753	32,762	62,731	90,342	253,214	252,588	231,089
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	33,876	12,754	25,078	46,462	30,604	10,526	31,270	47,466	118,170	119,866	104,333
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	4,662	289	196	0	1,639	(55)	69,312	1,515	5,147	72,411	7,961
Net income	38,538	13,043	25,274	46,462	32,243	10,471	100,582	48,981	123,317	192,277	112,294
Net income attributable to noncontrolling interests	(17)	(32)	(28)	(13)	(23)	(20)	289	(482)
Net income attributable to Avista Corp. shareholders	38,521	13,011	25,246	46,449	32,220	10,451	100,871	48,499	123,227	192,041	111,077
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
Weighted average, basic	62,308	62,299	62,281	62,318	62,290	63,934	60,184	60,122	62,301	61,632	59,960
Weighted average, 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 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