Information By Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 352,048		$ 343,585		$ 834,954		$ 795,842
Resource costs	126,511		135,992		356,141		347,004
Other operating expenses	112,915	[1]	109,813	[1]	223,694	[1]	219,176	[1]
Depreciation and amortization	33,272		31,325		64,890		61,647
Income from operations	57,742	[1]	46,020	[1]	142,804	[1]	122,414	[1]
Interest expense	19,978	[2]	19,325	[2]	39,788	[2]	38,602	[2]
Income taxes	15,412		10,360		40,648		31,498
Net income (loss) attributable to Avista Corporation	25,657		18,178		67,998		56,566
Capital expenditures	75,224		63,827		146,688		122,742
Total assets	4,347,796				4,347,796				4,313,179
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	298,169		293,765		729,746		699,675
Resource costs	126,511		135,992		356,141		347,004
Other operating expenses	65,784	[1]	64,981	[1]	131,228	[1]	130,303	[1]
Depreciation and amortization	29,025		27,754		56,960		55,072
Income from operations	55,240	[1]	44,603	[1]	137,991	[1]	121,695	[1]
Interest expense	19,028	[2]	18,101	[2]	37,798	[2]	36,147	[2]
Income taxes	14,553		10,108		39,333		31,835
Net income (loss) attributable to Avista Corporation	24,568		18,020		66,818		57,497
Capital expenditures	74,699		62,705		145,344		120,476
Total assets	3,911,203				3,911,203				3,894,821
Ecova [Member]
Segment Reporting Information [Line Items]
Operating revenues	44,560		40,080		86,967		77,090
Resource costs	0		0		0		0
Other operating expenses	37,716	[1]	34,750	[1]	73,706	[1]	70,524	[1]
Depreciation and amortization	4,072		3,359		7,565		6,195
Income from operations	2,772	[1]	1,971	[1]	5,696	[1]	371	[1]
Interest expense	423	[2]	411	[2]	867	[2]	771	[2]
Income taxes	1,102		805		2,086		423
Net income (loss) attributable to Avista Corporation	1,521		1,149		2,719		322
Capital expenditures	435		1,083		1,229		2,225
Total assets	346,424				346,424				322,720
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,769		10,190		19,141		19,977
Resource costs	0		0		0		0
Other operating expenses	9,865	[1]	10,532	[1]	19,660	[1]	19,249	[1]
Depreciation and amortization	175		212		365		380
Income from operations	(270)	[1]	(554)	[1]	(883)	[1]	348	[1]
Interest expense	603	[2]	902	[2]	1,276	[2]	1,867	[2]
Income taxes	(243)		(553)		(771)		(760)
Net income (loss) attributable to Avista Corporation	(432)		(991)		(1,539)		(1,253)
Capital expenditures	90		39		115		41
Total assets	90,169				90,169				95,638
Total Non-Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	54,329		50,270		106,108		97,067
Resource costs	0		0		0		0
Other operating expenses	47,581	[1]	45,282	[1]	93,366	[1]	89,773	[1]
Depreciation and amortization	4,247		3,571		7,930		6,575
Income from operations	2,502	[1]	1,417	[1]	4,813	[1]	719	[1]
Interest expense	1,026	[2]	1,313	[2]	2,143	[2]	2,638	[2]
Income taxes	859		252		1,315		(337)
Net income (loss) attributable to Avista Corporation	1,089		158		1,180		(931)
Capital expenditures	525		1,122		1,344		2,266
Total assets	436,593				436,593				418,358
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(450)	[3]	(450)	[3]	(900)	[3]	(900)	[3]
Resource costs	0	[3]	0	[3]	0	[3]	0	[3]
Other operating expenses	(450)	[1],[3]	(450)	[1],[3]	(900)	[1],[3]	(900)	[1],[3]
Depreciation and amortization	0	[3]	0	[3]	0	[3]	0	[3]
Income from operations	0	[1],[3]	0	[1],[3]	0	[1],[3]	0	[1],[3]
Interest expense	(76)	[2],[3]	(89)	[2],[3]	(153)	[2],[3]	(183)	[2],[3]
Income taxes	0	[3]	0	[3]	0	[3]	0	[3]
Net income (loss) attributable to Avista Corporation	0	[3]	0	[3]	0	[3]	0	[3]
Capital expenditures	0	[3]	0	[3]	0	[3]	0	[3]
Total assets	$ 0	[3]			$ 0	[3]			$ 0	[3]

[1] Includes a correction of an immaterial error related to the reclassification of certain operating expenses from other expense-net to utility and non-utility other operating expenses and utility taxes other than income taxes. This correction did not have an impact on net income or earnings per share. See Note 1 for further information regarding this reclassification.

[2] (2)Including interest expense to affiliated trusts.

[3] (1)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.