Information By Business Segments (Information By Business Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenues	$ 452,257		$ 476,586
Resource costs	211,012		248,121
Other operating expenses	107,059		90,928
Depreciation and amortization	30,322		27,719
Income (loss) from operations	78,722		84,825
Interest expense	19,277	[1]	18,591	[1]
Income taxes	21,138		23,637
Net income attributable to Avista Corporation	38,388		41,918
Capital expenditures	58,915		50,128
Total Assets	4,254,004				4,214,531
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	405,910		438,147
Resource costs	211,012		248,121
Other operating expenses	63,357		59,682
Depreciation and amortization	27,318		25,852
Income (loss) from operations	79,081		79,499
Interest expense	18,046	[1]	17,356	[1]
Income taxes	21,726		22,255
Net income attributable to Avista Corporation	39,477		40,117
Capital expenditures	57,771		49,654
Total Assets	3,758,726				3,809,446
Ecova [Member]
Segment Reporting Information [Line Items]
Operating revenues	37,010		29,158
Other operating expenses	35,774		24,008
Depreciation and amortization	2,836		1,664
Income (loss) from operations	(1,600)		3,486
Interest expense	360	[1]	11	[1]
Income taxes	(381)		1,254
Net income attributable to Avista Corporation	(826)		1,707
Capital expenditures	1,142		315
Total Assets	389,782				292,940
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,787		9,731
Other operating expenses	8,378		7,688
Depreciation and amortization	168		203
Income (loss) from operations	1,241		1,840
Interest expense	965	[1]	1,597	[1]
Income taxes	(207)		128
Net income attributable to Avista Corporation	(263)		94
Capital expenditures	2		159
Total Assets	105,496				112,145
Total Non-Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	46,797		38,889
Other operating expenses	44,152		31,696
Depreciation and amortization	3,004		1,867
Income (loss) from operations	(359)		5,326
Interest expense	1,325	[1]	1,608	[1]
Income taxes	(588)		1,382
Net income attributable to Avista Corporation	(1,089)		1,801
Capital expenditures	1,144		474
Total Assets	495,278				405,085
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(450)	[2]	(450)	[2]
Other operating expenses	(450)	[2]	(450)	[2]
Interest expense	$ (94)	[1],[2]	$ (373)	[1],[2]

[1] Including interest expense to affiliated trusts.

[2] Intersegment eliminations reported as operating revenues and resource costs represent intercompany purchases and sales of electric capacity and energy. Intersegment eliminations reported as interest expense represent intercompany interest.