Information By Business Segments (Details) (USD $) In Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010		Dec. 31, 2010
Segment Reporting Information [Line Items]
Operating revenues	$ 343,710		$ 367,172		$ 1,180,853		$ 1,184,320
Resource costs	171,393		201,113		575,290		628,864
Other operating expenses	92,305		85,823		284,542		254,068
Depreciation and amortization	28,305		26,650		84,273		79,192
Income from operations	34,878		37,744		175,227		167,317
Interest expense	18,855	[1]	19,005	[1]	55,870	[1]	57,538	[1]
Income taxes	3,717		5,030		40,937		38,732
Net income (loss) attributable to Avista Corporation	10,702		12,346		75,621		66,696
Capital expenditures	70,846		58,148		172,328		139,383
Total assets	3,968,586				3,968,586				3,940,095
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	302,001		331,542		1,060,571		1,081,690
Resource costs	171,393		201,113		575,290		628,864
Other operating expenses	60,579		59,961		188,961		174,044
Depreciation and amortization	26,341		24,918		78,600		73,890
Income from operations	26,859		29,708		156,199		150,013
Interest expense	17,639	[1]	17,708	[1]	52,134	[1]	53,415	[1]
Income taxes	1,546		2,616		35,857		34,243
Net income (loss) attributable to Avista Corporation	7,582		9,058		68,733		60,898
Capital expenditures	69,716		57,798		169,598		138,083
Total assets	3,607,397				3,607,397				3,589,235
Ecova [Member]
Segment Reporting Information [Line Items]
Operating revenues	32,228		25,568		91,207		74,725
Other operating expenses	23,790		18,021		72,220		57,732
Depreciation and amortization	1,784		1,498		5,086		4,522
Income from operations	6,654		6,049		13,901		12,471
Interest expense	71	[1]	15	[1]	206	[1]	68	[1]
Income taxes	2,416		2,238		5,005		4,576
Net income (loss) attributable to Avista Corporation	3,467		2,936		7,016		5,895
Capital expenditures	897		293		2,173		994
Total assets	246,220				246,220				221,086
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,931		16,813		30,425		47,337
Other operating expenses	8,386		14,592		24,711		41,724
Depreciation and amortization	180		234		587		780
Income from operations	1,365		1,987		5,127		4,833
Interest expense	1,150	[1]	1,348	[1]	3,912	[1]	4,243	[1]
Income taxes	(245)		176		75		(87)
Net income (loss) attributable to Avista Corporation	(347)		352		(128)		(97)
Capital expenditures	233		57		557		306
Total assets	114,969				114,969				129,774
Total Non-Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	42,159		42,381		121,632		122,062
Other operating expenses	32,176		32,613		96,931		99,456
Depreciation and amortization	1,964		1,732		5,673		5,302
Income from operations	8,019		8,036		19,028		17,304
Interest expense	1,221	[1]	1,363	[1]	4,118	[1]	4,311	[1]
Income taxes	2,171		2,414		5,080		4,489
Net income (loss) attributable to Avista Corporation	3,120		3,288		6,888		5,798
Capital expenditures	1,130		350		2,730		1,300
Total assets	361,189				361,189				350,860
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(450)	[2]	(6,751)	[2]	(1,350)	[2]	(19,432)	[2]
Other operating expenses	(450)	[2]	(6,751)	[2]	(1,350)	[2]	(19,432)	[2]
Interest expense	$ (5)	[1],[2]	$ (66)	[1],[2]	$ (382)	[1],[2]	$ (188)	[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.