Business Acquisitions Business Acquisitions Assets Acquired Liabilities Assumed (Details) - USD ($) $ 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	Jul. 01, 2014
Business Acquisition [Line Items]
Acquired cash												$ 19,704
Goodwill	$ 57,672				$ 57,976				$ 57,672	$ 57,976	$ 76,257	52,426
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
Accounts receivable - gross totals $3,928												3,851
Materials and supplies												2,017
Other current assets												999
Total current assets												26,571
Utility plant in service												113,964
Utility property under long-term capital lease												71,007
Construction work in progress												3,440
Total utility property												188,411
Non-utility property												6,660
Electric plant held for future use												3,711
Other deferred charges and non-current assets												5,368
Total other non-current assets												68,165
Total assets												283,147
Accounts payable												700
Current portion of long-term debt and capital lease obligations												3,773
Other current liabilities (1)												2,807
Total current liabilities												7,280
Long-term debt												37,227
Capital lease obligations												68,840
Other non-current liabilities and deferred credits (1)												14,889
Total liabilities												128,236
Total net assets acquired												$ 154,911
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