Information By Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 312,580		$ 307,488		$ 759,158		$ 747,987
Resource costs	128,922		126,511		349,419		356,141
Other operating expenses	68,229		75,199		144,949		149,988
Depreciation and amortization	31,331		29,200		62,204		57,325
Income from operations	62,731		54,970		153,073		137,108
Interest expense	18,659	[1]	19,555	[1]	37,514	[1]	38,921	[1]
Income taxes	16,691		14,310		43,973		38,562
Net income (loss) attributable to Avista Corporation	100,871		25,657		149,370		67,998
Income (Loss) from Continuing Operations Attributable to Parent	31,254		24,212		78,730		65,432
Payments to Acquire Other Property, Plant, and Equipment	76,845		74,789		136,616		145,459
Total assets	4,202,130				4,202,130				4,361,923
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	303,555		298,169		741,129		729,746
Resource costs	128,922		126,511		349,419		356,141
Other operating expenses	67,349		65,784		134,686		131,228
Depreciation and amortization	31,180		29,025		61,906		56,960
Income from operations	54,737		55,240		145,605		137,991
Interest expense	18,422	[1]	19,028	[1]	36,968	[1]	37,798	[1]
Income taxes	13,302		14,553		40,922		39,333
Net income (loss) attributable to Avista Corporation	26,685		24,568		74,681		66,818
Payments to Acquire Other Property, Plant, and Equipment	76,789		74,699		136,514		145,344
Total assets	4,119,627				4,119,627				3,940,998
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,475		9,769		18,929		19,141
Resource costs	0		0		0		0
Other operating expenses	1,330		9,865		11,163		19,660
Depreciation and amortization	151		175		298		365
Income from operations	7,994		(270)		7,468		(883)
Interest expense	316	[1]	603	[1]	713	[1]	1,276	[1]
Income taxes	3,389		(243)		3,051		(771)
Net income (loss) attributable to Avista Corporation	4,490		(432)		3,882		(1,539)
Payments to Acquire Other Property, Plant, and Equipment	56		90		102		115
Total assets	82,503				82,503				81,282
Ecova [Member]
Segment Reporting Information [Line Items]
Total assets									339,600
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(450)	[2]	(450)	[2]	(900)	[2]	(900)	[2]
Resource costs	0	[2]	0	[2]	0	[2]	0	[2]
Other operating expenses	(450)	[2]	(450)	[2]	(900)	[2]	(900)	[2]
Depreciation and amortization	0	[2]	0	[2]	0	[2]	0	[2]
Income from operations	0	[2]	0	[2]	0	[2]	0	[2]
Interest expense	(79)	[1],[2]	(76)	[1],[2]	(167)	[1],[2]	(153)	[1],[2]
Income taxes	0	[2]	0	[2]	0	[2]	0	[2]
Net income (loss) attributable to Avista Corporation	79	[2]	76	[2]	167	[2]	153	[2]
Payments to Acquire Other Property, Plant, and Equipment	0	[2]	0	[2]	0	[2]	0	[2]
Total assets	0	[2]			0	[2]			0	[2]
Avista Utilities and Other Businesses [Member]
Segment Reporting Information [Line Items]
Total assets									$ 4,022,280

[1] Including interest expense to affiliated trusts.(3)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.(4)The consolidated total assets presented here as of December 31, 2013 exclude total assets at Ecova of $339.6 million.

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