Information By Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 446,490		$ 446,578
Resource costs	209,560		220,497
Other operating expenses	82,988		76,720
Depreciation and amortization	34,469		30,873
Income from operations	89,575		90,342
Interest expense	20,014	[1]	18,855	[1]
Income taxes	26,247		27,282
Net income (loss) attributable to Avista Corporation	46,449		48,499
Income (Loss) from Continuing Operations Attributable to Parent	46,449		47,476
Payments to Acquire Other Property, Plant, and Equipment	82,009	[2]	59,771	[2]
Total assets	4,689,029				4,712,331
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	424,083		437,574
Resource costs	206,660		220,497
Other operating expenses	70,409		67,337
Depreciation and amortization	32,997		30,726
Income from operations	84,788		90,868
Interest expense	18,968	[1]	18,546	[1]
Income taxes	24,888		27,620
Net income (loss) attributable to Avista Corporation	44,384		47,996
Payments to Acquire Other Property, Plant, and Equipment	81,212		59,725
Total assets	4,345,988				4,367,926
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues	12,774		0
Resource costs	2,900		0
Other operating expenses	2,763		0
Depreciation and amortization	1,303		0
Income from operations	5,139		0
Interest expense	904	[1]	0	[1]
Income taxes	1,684		0
Net income (loss) attributable to Avista Corporation	2,634		0
Payments to Acquire Other Property, Plant, and Equipment	385		0
Total assets	267,590				264,195
Total Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues	436,857		437,574
Resource costs	209,560		220,497
Other operating expenses	73,172		67,337
Depreciation and amortization	34,300		30,726
Income from operations	89,927		90,868
Interest expense	19,872	[1]	18,546	[1]
Income taxes	26,572		27,620
Net income (loss) attributable to Avista Corporation	47,018		47,996
Payments to Acquire Other Property, Plant, and Equipment	81,597	[2]	59,725	[2]
Total assets	4,613,578				4,632,121
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,083		9,454
Resource costs	0		0
Other operating expenses	10,266		9,833
Depreciation and amortization	169		147
Income from operations	(352)		(526)
Interest expense	164	[1]	397	[1]
Income taxes	(325)		(338)
Net income (loss) attributable to Avista Corporation	(569)		(608)
Payments to Acquire Other Property, Plant, and Equipment	412	[2]	46	[2]
Total assets	75,451				80,210
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(450)	[3]	(450)	[3]
Resource costs	0	[3]	0	[3]
Other operating expenses	(450)	[3]	(450)	[3]
Depreciation and amortization	0	[3]	0	[3]
Income from operations	0	[3]	0	[3]
Interest expense	(22)	[1],[3]	(88)	[1],[3]
Income taxes	0	[3]	0	[3]
Net income (loss) attributable to Avista Corporation	0	[3]	88	[3]
Payments to Acquire Other Property, Plant, and Equipment	0	[3]	0	[3]
Total assets	$ 0	[3]			$ 0	[3]

[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.