Business Acquisitions Business Acquisitions Pro Forma Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended			30 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	Dec. 31, 2015
Business Acquisition [Line Items]
Revenues Excluding Acquired Entity									$ 1,439,807	$ 1,450,918	$ 1,441,744
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
Total pro forma revenues									1,484,776	1,497,385	1,483,338
Actual AERC revenues included in Avista Corp. revenues (1)									44,969	21,644	0
Income Loss From Continuing Operations Excluding Acquired Entity									111,772	116,665	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
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
Total pro forma net income									123,249	198,565	119,513
Actual AERC net income included in Avista Corp. net income (1)									6,308	3,152	0
Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Operating revenues from continuing operations									44,969	46,467	41,594
Supplemental pro forma AERC net income (1)									6,308	8,806	9,328
Avista Utilities [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs												$ (3,000)
Avista Utilities [Member] | Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs									$ (22)	$ (870)	$ (892)