Information By Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 490,962		$ 482,906
Resource costs	220,497		229,630
Other operating expenses	114,597		110,779
Depreciation and amortization	34,582		31,618
Income from operations	93,140		85,062
Interest expense	19,195	[1]	19,810	[1]
Income taxes	28,176		25,236
Net income (loss) attributable to Avista Corporation	48,499		42,341
Payments to Acquire Other Property, Plant, and Equipment	63,654		71,464
Total assets	4,316,078				4,361,923
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	437,574		431,577
Resource costs	220,497		229,630
Other operating expenses	67,337		65,444
Depreciation and amortization	30,726		27,935
Income from operations	90,868		82,751
Interest expense	18,546	[1]	18,770	[1]
Income taxes	27,620		24,780
Net income (loss) attributable to Avista Corporation	47,996		42,250
Payments to Acquire Other Property, Plant, and Equipment	59,725		70,645
Total assets	3,893,474				3,940,998
Ecova [Member]
Segment Reporting Information [Line Items]
Operating revenues	44,384		42,407
Resource costs	0		0
Other operating expenses	37,877		35,990
Depreciation and amortization	3,709		3,493
Income from operations	2,798		2,924
Interest expense	340	[1]	444	[1]
Income taxes	894		984
Net income (loss) attributable to Avista Corporation	1,111		1,198
Payments to Acquire Other Property, Plant, and Equipment	3,883		794
Total assets	344,828				339,643
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,454		9,372
Resource costs	0		0
Other operating expenses	9,833		9,795
Depreciation and amortization	147		190
Income from operations	(526)		(613)
Interest expense	397	[1]	673	[1]
Income taxes	(338)		(528)
Net income (loss) attributable to Avista Corporation	(608)		(1,107)
Payments to Acquire Other Property, Plant, and Equipment	46		25
Total assets	77,776				81,282
Total Non-Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	53,838		51,779
Resource costs	0		0
Other operating expenses	47,710		45,785
Depreciation and amortization	3,856		3,683
Income from operations	2,272		2,311
Interest expense	737	[1]	1,117	[1]
Income taxes	556		456
Net income (loss) attributable to Avista Corporation	503		91
Payments to Acquire Other Property, Plant, and Equipment	3,929		819
Total assets	422,604				420,925
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(450)	[2]	(450)	[2]
Resource costs	0	[2]	0	[2]
Other operating expenses	(450)	[2]	(450)	[2]
Depreciation and amortization	0	[2]	0	[2]
Income from operations	0	[2]	0	[2]
Interest expense	(88)	[1],[2]	(77)	[1],[2]
Income taxes	0	[2]	0	[2]
Net income (loss) attributable to Avista Corporation	0	[2]	0	[2]
Payments to Acquire Other Property, Plant, and Equipment	0	[2]	0	[2]
Total assets	$ 0	[2]			$ 0	[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.