Business Acquisitions Business Acquisitions Pro Forma Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended			42 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Business Acquisition [Line Items]
Revenues Excluding Acquired Entity									$ 1,395,989	$ 1,439,807	$ 1,450,918
Operating revenues	$ 402,123	$ 303,349	$ 318,838	$ 418,173	$ 387,305	$ 313,649	$ 337,332	$ 446,490	1,442,483	1,484,776	1,472,562
Total pro forma revenues									1,442,483	1,484,776	1,497,385
Actual AERC revenues included in Avista Corp. revenues (1)									46,494	44,969	21,644
Income Loss From Continuing Operations Excluding Acquired Entity									129,505	111,772	116,665
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent					4,662	289	196	0	0	5,147	72,224
Supplemental pro forma AERC net income (1)	$ 40,091	$ 12,234	$ 27,254	$ 57,649	$ 38,521	$ 13,011	$ 25,246	$ 46,449	137,228	123,227	192,041
Total pro forma net income									137,228	123,249	198,565
Actual AERC net income included in Avista Corp. net income (1)									7,723	6,308	3,152
Alaska Energy Resources Company [Member]
Business Acquisition [Line Items]
Operating revenues									46,494	44,969	46,467
Supplemental pro forma AERC net income (1)									7,723	6,308	8,806
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									$ 0	$ 22	$ 870