Information By Business Segments (Details) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2015 USD ($)		Sep. 30, 2014 USD ($)		Sep. 30, 2015 USD ($) Reportable_Segments	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | Reportable_Segments						2
Operating revenues		$ 313,649		$ 301,558		$ 1,097,471	$ 1,060,716
Resource costs		138,210		131,588		488,886	481,007
Other operating expenses		80,777		82,760		243,523	227,709
Depreciation and amortization		36,481		33,448		106,791	95,652
Income from operations		35,912		32,762		182,847	185,835
Interest expense	[1]	20,071		18,755		60,066	56,269
Income taxes		6,115		7,301		47,378	51,274
Income (Loss) from Continuing Operations Attributable to Parent		12,722		10,506		84,221	89,236
Payments to Acquire Other Property, Plant, and Equipment		95,397	[2]	93,444	[2]	273,653	230,060
Total assets		4,739,206				4,739,206		$ 4,712,331
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	[3]	0		(450)		(550)	(1,350)
Resource costs	[3]	0		0		0	0
Other operating expenses	[3]	0		(450)		(550)	(1,350)
Depreciation and amortization	[3]	0		0		0	0
Income from operations	[3]	0		0		0	0
Interest expense	[1],[3]	(29)		(163)		(81)	(330)
Income taxes	[3]	0		0		0	0
Income (Loss) from Continuing Operations Attributable to Parent	[3]	0		0		0	167
Payments to Acquire Other Property, Plant, and Equipment	[3]	0		0		0	0
Total assets	[3]	0				0		0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		307,405		291,712		1,075,192	1,032,841
Resource costs		138,210		131,588		488,886	481,007
Other operating expenses		74,315		72,509		220,599	207,195
Depreciation and amortization		36,303		33,294		106,279	95,200
Income from operations		36,308		33,321		184,004	178,926
Interest expense	[1]	19,950		18,732		59,686	55,700
Income taxes		6,209		7,475		48,004	48,397
Income (Loss) from Continuing Operations Attributable to Parent		12,919		10,860		85,340	85,541
Payments to Acquire Other Property, Plant, and Equipment	[2]	95,049		93,250		272,801	229,764
Total assets		4,688,009				4,688,009		4,632,121
Operating Segments [Member] | Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues		298,132		282,555		1,042,913	1,023,684
Resource costs		135,048		128,591		479,604	478,010
Other operating expenses		71,536		69,403		212,293	204,089
Depreciation and amortization		34,986		32,006		102,334	93,912
Income from operations		34,800		32,048		175,003	177,653
Interest expense	[1]	19,054		18,247		56,991	55,215
Income taxes		5,980		7,146		45,500	48,068
Income (Loss) from Continuing Operations Attributable to Parent		12,525		10,349		81,387	85,030
Payments to Acquire Other Property, Plant, and Equipment		92,271		92,197		264,283	228,711
Total assets		4,422,431				4,422,431		4,367,926
Operating Segments [Member] | Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues		9,273		9,157		32,279	9,157
Resource costs		3,162		2,997		9,282	2,997
Other operating expenses		2,779		3,106		8,306	3,106
Depreciation and amortization		1,317		1,288		3,945	1,288
Income from operations		1,508		1,273		9,001	1,273
Interest expense	[1]	896		485		2,695	485
Income taxes		229		329		2,504	329
Income (Loss) from Continuing Operations Attributable to Parent		394		511		3,953	511
Payments to Acquire Other Property, Plant, and Equipment		2,778		1,053		8,518	1,053
Total assets		265,578				265,578		264,195
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating revenues		6,244		10,296		22,829	29,225
Resource costs		0		0		0	0
Other operating expenses		6,462		10,701		23,474	21,864
Depreciation and amortization		178		154		512	452
Income from operations		(396)		(559)		(1,157)	6,909
Interest expense	[1]	150		186		461	899
Income taxes		(94)		(174)		(626)	2,877
Income (Loss) from Continuing Operations Attributable to Parent		(197)		(354)		(1,119)	3,528
Payments to Acquire Other Property, Plant, and Equipment		348	[2]	$ 194	[2]	852	$ 296
Total assets		$ 51,197				$ 51,197		$ 80,210

[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 in 2014 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.