Information By Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 301,558		$ 289,477		$ 1,060,716		$ 1,037,464
Resource costs	131,588		131,136		481,007		487,277
Other operating expenses	82,760		79,808		227,709		229,796
Depreciation and amortization	33,448		29,994		95,652		87,319
Income from operations	32,762		29,827		185,835		166,935
Interest expense	18,755	[1]	19,285	[1]	56,269	[1]	58,206	[1]
Income taxes	7,301		3,367		51,274		41,929
Net income (loss) attributable to Avista Corporation	10,451		11,413		159,821		79,411
Income (Loss) from Continuing Operations Attributable to Parent	10,506		8,450		89,236		73,882
Payments to Acquire Other Property, Plant, and Equipment	93,444		75,392		230,060		220,851
Total assets	4,336,346				4,336,346				4,361,923
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	282,555		278,923		1,023,684		1,008,669
Resource costs	128,591		131,136		478,010		487,277
Other operating expenses	69,403		69,596		204,089		200,824
Depreciation and amortization	32,006		29,823		93,912		86,783
Income from operations	32,048		29,657		177,653		167,648
Interest expense	18,247	[1]	18,837	[1]	55,215	[1]	56,635	[1]
Income taxes	7,146		3,945		48,068		43,278
Net income (loss) attributable to Avista Corporation	10,349		9,447		85,030		76,265
Payments to Acquire Other Property, Plant, and Equipment	92,197		75,368		228,711		220,712
Total assets	3,991,330				3,991,330				3,940,998
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,157		0		9,157		0
Resource costs	2,997		0		2,997		0
Other operating expenses	3,106		0		3,106		0
Depreciation and amortization	1,288		0		1,288		0
Income from operations	1,273		0		1,273		0
Interest expense	485	[1]	0	[1]	485	[1]	0	[1]
Income taxes	329		0		329		0
Net income (loss) attributable to Avista Corporation	511		0		511		0
Payments to Acquire Other Property, Plant, and Equipment	1,053		0		1,053		0
Total assets	261,402				261,402				0
Total Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	291,712		278,923		1,032,841		1,008,669
Resource costs	131,588		131,136		481,007		487,277
Other operating expenses	72,509		69,596		207,195		200,824
Depreciation and amortization	33,294		29,823		95,200		86,783
Income from operations	33,321		29,657		178,926		167,648
Interest expense	18,732	[1]	18,837	[1]	55,700	[1]	56,635	[1]
Income taxes	7,475		3,945		48,397		43,278
Net income (loss) attributable to Avista Corporation	10,860		9,447		85,541		76,265
Payments to Acquire Other Property, Plant, and Equipment	93,250	[2]	75,368	[2]	229,764	[2]	220,712	[2]
Total assets	4,252,732				4,252,732				3,940,998
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,296		11,004		29,225		30,145
Resource costs	0		0		0		0
Other operating expenses	10,701		10,662		21,864		30,322
Depreciation and amortization	154		171		452		536
Income from operations	(559)		170		6,909		(713)
Interest expense	186	[1]	525	[1]	899	[1]	1,801	[1]
Income taxes	(174)		(578)		2,877		(1,349)
Net income (loss) attributable to Avista Corporation	(354)		(1,074)		3,528		(2,613)
Payments to Acquire Other Property, Plant, and Equipment	194		24		296		139
Total assets	83,614				83,614				81,282
Ecova [Member]
Segment Reporting Information [Line Items]
Total assets									339,600
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(450)	[3]	(450)	[3]	(1,350)	[3]	(1,350)	[3]
Resource costs	0	[3]	0	[3]	0	[3]	0	[3]
Other operating expenses	(450)	[3]	(450)	[3]	(1,350)	[3]	(1,350)	[3]
Depreciation and amortization	0	[3]	0	[3]	0	[3]	0	[3]
Income from operations	0	[3]	0	[3]	0	[3]	0	[3]
Interest expense	(163)	[1],[3]	(77)	[1],[3]	(330)	[1],[3]	(230)	[1],[3]
Income taxes	0	[3]	0	[3]	0	[3]	0	[3]
Net income (loss) attributable to Avista Corporation	0	[3]	77	[3]	167	[3]	230	[3]
Payments to Acquire Other Property, Plant, and Equipment	0	[3]	0	[3]	0	[3]	0	[3]
Total assets	0	[3]			0	[3]			0	[3]
Avista Utilities and Other Businesses [Member]
Segment Reporting Information [Line Items]
Total assets									$ 4,022,280	[4]

[1] Including interest expense to affiliated trusts.

[2] The capital expenditures for the other businesses are included as other capital expenditures on the Condensed Consolidated Statements of Cash Flows. The remainder of the balance included in other capital expenditures on the Condensed Consolidated Statements of Cash Flows are related to Ecova.

[3] 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 and net income (loss) attributable to Avista Corp. shareholders represent intercompany interest.

[4] The consolidated total assets presented here as of December 31, 2013 exclude total assets at Ecova of $339.6 million.