Information By Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 411,846		$ 301,558	$ 312,580	$ 446,578	$ 404,280		$ 289,477	$ 307,488	$ 440,499	$ 1,472,562		$ 1,441,744		$ 1,391,338
Resource costs											678,244		689,586		693,127
Other operating expenses											317,250		314,879		314,821
Depreciation and amortization											130,180		117,755		112,883
Income from continuing operations	66,753		32,762	62,731	90,342	64,154		29,827	54,970	82,138	252,588		231,089		187,098
Interest expense											75,752		77,585		75,645
Income taxes											72,240		58,014		39,764
Payments to Acquire Other Property, Plant, and Equipment											325,922		294,734		271,853
Total assets	4,712,331					4,361,923					4,712,331		4,361,923
Income (Loss) from Continuing Operations Attributable to Parent	30,581		10,506	31,254	47,476	30,391		8,450	24,212	41,220	119,817		104,273		76,719
Avista Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues											1,413,499		1,403,995		1,354,185
Resource costs											672,344		689,586		693,127
Other operating expenses											280,964		276,228		276,780
Depreciation and amortization											126,987		117,174		112,091
Income from continuing operations											239,976		232,572		188,778
Interest expense											73,750		75,663		72,552
Income taxes											67,634		60,472		42,842
Payments to Acquire Other Property, Plant, and Equipment											323,931		294,363		271,187
Total assets	4,367,926					3,940,998					4,367,926		3,940,998
Income (Loss) from Continuing Operations Attributable to Parent											113,263		108,598		81,704
Alaska Electric Light & Power [Member]
Segment Reporting Information [Line Items]
Operating revenues											21,644		0		0
Resource costs											5,900		0		0
Other operating expenses											5,868		0		0
Depreciation and amortization											2,583		0		0
Income from continuing operations											6,221		0		0
Interest expense											1,382		0		0
Income taxes											1,816		0		0
Payments to Acquire Other Property, Plant, and Equipment											1,585		0		0
Total assets	264,195					0					264,195		0
Income (Loss) from Continuing Operations Attributable to Parent											3,152		0		0
Total Utility [Member]
Segment Reporting Information [Line Items]
Operating revenues											1,435,143		1,403,995		1,354,185
Resource costs											678,244		689,586		693,127
Other operating expenses											286,832		276,228		276,780
Depreciation and amortization											129,570		117,174		112,091
Income from continuing operations											246,197		232,572		188,778
Interest expense											75,132		75,663		72,552
Income taxes											69,450		60,472		42,842
Payments to Acquire Other Property, Plant, and Equipment											325,516		294,363		271,187
Total assets	4,632,121					3,940,998					4,632,121		3,940,998
Income (Loss) from Continuing Operations Attributable to Parent											116,415		108,598		81,704
Ecova [Member]
Segment Reporting Information [Line Items]
Total assets						339,600							339,600
Other Business Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues											39,219		39,549		38,953
Resource costs											0		0		0
Other operating expenses											32,218		40,451		39,841
Depreciation and amortization											610		581		792
Income from continuing operations											6,391		(1,483)		(1,680)
Interest expense											1,004		2,247		3,437
Income taxes											2,790		(2,458)		(3,078)
Payments to Acquire Other Property, Plant, and Equipment											406	[1]	371	[1]	666	[1]
Total assets	80,210					81,282					80,210		81,282
Income (Loss) from Continuing Operations Attributable to Parent											3,236		(4,650)		(5,319)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues											(1,800)	[2]	(1,800)	[2]	(1,800)	[2]
Resource costs											0	[2]	0	[2]	0	[2]
Other operating expenses											(1,800)	[2]	(1,800)	[2]	(1,800)	[2]
Depreciation and amortization											0	[2]	0	[2]	0	[2]
Income from continuing operations											0	[2]	0	[2]	0	[2]
Interest expense											(384)	[2]	(325)	[2]	(344)	[2]
Income taxes											0	[2]	0	[2]	0	[2]
Payments to Acquire Other Property, Plant, and Equipment											0	[2]	0	[2]	0	[2]
Total assets	0	[2]				0	[2]				0	[2]	0	[2]
Income (Loss) from Continuing Operations Attributable to Parent											166	[2]	325	[2]	334	[2]
Utility and Other (Excluding Ecova) [Member]
Segment Reporting Information [Line Items]
Total assets						$ 4,022,280	[3]						$ 4,022,280	[3]

[1] The capital expenditures for the other businesses are included as other capital expenditures on the Consolidated Statements of Cash Flows. The remainder of the balance included in other capital expenditures on the Consolidated Statements of Cash Flows are related to Ecova.

[2] Intersegment eliminations reported as operating revenues and resource costs represent intercompany purchases and sales of electric capacity and energy between Avista Utilities and Spokane Energy (included in other). Intersegment eliminations reported as interest expense and net income (loss) attributable to Avista Corp. shareholders represent intercompany interest.

[3] The consolidated total assets presented here as of December 31, 2013 exclude total assets at Ecova of $339.6 million.