Derivatives And Risk Management (Derivative Instruments Summary) (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Gross Asset	$ 94,598,000		$ 89,297,000
Gross Liability	(115,001,000)		(143,766,000)
Collateral Netting	10,413,000		9,707,000
Net Asset (Liability) in Balance Sheet	(9,990,000)		(44,762,000)
Gross Assets Not Offset	0		0
Gross Liabilities Not Offset	0		0
Net Asset (Liability)	(9,990,000)		(44,762,000)
Other Current Liabilities [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset			7,000
Gross Liability			(34,000)
Collateral Netting			0
Net Asset (Liability) in Balance Sheet			(27,000)
Gross Assets Not Offset			0
Gross Liabilities Not Offset			0
Net Asset (Liability)			(27,000)
Other Current Liabilities [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset			0
Gross Liability			(1,406,000)
Collateral Netting			0
Net Asset (Liability) in Balance Sheet			(1,406,000)
Gross Assets Not Offset			0
Gross Liabilities Not Offset			0
Net Asset (Liability)			(1,406,000)
Other Current Liabilities [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	19,000
Gross Liability	(1,000)
Collateral Netting	0
Net Asset (Liability) in Balance Sheet	18,000
Gross Assets Not Offset	0
Gross Liabilities Not Offset	0
Net Asset (Liability)	18,000
Other Property and Investments-Net [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	25,178,000		7,265,000
Gross Liability	0		0
Collateral Netting	0		0
Net Asset (Liability) in Balance Sheet	25,178,000		7,265,000
Gross Assets Not Offset	0		0
Gross Liabilities Not Offset	0		0
Net Asset (Liability)	25,178,000		7,265,000
Current Utility Energy Commodity Derivative Assets [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	4,078,000	[1]	10,772,000	[1]
Gross Liability	(648,000)	[1]	(6,633,000)	[1]
Collateral Netting	0	[1]	0	[1]
Net Asset (Liability) in Balance Sheet	3,430,000	[1]	4,139,000	[1]
Gross Assets Not Offset	0	[1]	(9,678,000)	[1]
Gross Liabilities Not Offset	0	[1]	6,572,000	[1]
Net Asset (Liability)	3,430,000	[1]	1,033,000	[1]
Non-Current Utility Energy Commodity Derivative Assets [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	7,191,000	[1]	18,779,000	[1]
Gross Liability	(6,898,000)	[1]	(17,686,000)	[1]
Collateral Netting	0	[1]	0	[1]
Net Asset (Liability) in Balance Sheet	293,000	[1]	1,093,000	[1]
Gross Assets Not Offset	0	[1]	0	[1]
Gross Liabilities Not Offset	0	[1]	0	[1]
Net Asset (Liability)	293,000	[1]	1,093,000	[1]
Current Utility Energy Commodity Derivative Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	34,858,000	[1]	50,227,000	[1]
Gross Liability	(58,687,000)	[1]	(89,449,000)	[1]
Collateral Netting	5,121,000	[1]	9,707,000	[1]
Net Asset (Liability) in Balance Sheet	(18,708,000)	[1]	(29,515,000)	[1]
Gross Assets Not Offset	0	[1]	9,678,000	[1]
Gross Liabilities Not Offset	0	[1]	(6,572,000)	[1]
Net Asset (Liability)	(18,708,000)	[1]	(26,409,000)	[1]
Other Noncurrent Liabilities [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	0
Gross Liability	(471,000)
Collateral Netting	0
Net Asset (Liability) in Balance Sheet	(471,000)
Gross Assets Not Offset	0
Gross Liabilities Not Offset	0
Net Asset (Liability)	(471,000)
Other Noncurrent Liabilities [Member] | Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Asset	23,274,000	[1]	2,247,000	[1]
Gross Liability	(48,296,000)	[1]	(28,558,000)	[1]
Collateral Netting	5,292,000	[1]	0	[1]
Net Asset (Liability) in Balance Sheet	(19,730,000)	[1]	(26,311,000)	[1]
Gross Assets Not Offset	0	[1]	0	[1]
Gross Liabilities Not Offset	0	[1]	0	[1]
Net Asset (Liability)	$ (19,730,000)	[1]	$ (26,311,000)	[1]

[1] Avista Corp. has a master netting agreement that governs the transactions of multiple affiliated legal entities under this single master netting agreement. This master netting agreement allows for cross-commodity netting (i.e. netting physical power, physical natural gas, and financial transactions) and cross-affiliate netting for the parties to the agreement. Avista Corp. performs cross-commodity netting for each legal entity that is a party to the master netting agreement for presentation in the Condensed Consolidated Balance Sheets; however, Avista Corp. does not perform cross-affiliate netting because the Company believes that cross-affiliate netting may not be enforceable. Therefore, the requirements for cross-affiliate netting under ASC 210-20-45 are not applicable for Avista Corp. As of September 30, 2013, all derivatives for each affiliated entity under this master netting agreement were in a net liability position. As such, there is no additional netting which requires disclosure.