Fair Value (Reconciliation For All Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) (USD $) In Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Assets
Beginning balance	$ 17,032		$ 33,851		$ 19,739		$ 57,276
Total gains or losses (realized/unrealized):
Included in net income
Included in other comprehensive income
Included in regulatory assets/liabilities	(4,644)	[1]	(22,105)	[1]	(7,351)	[1]	(43,181)	[1]
Purchases
Issuances
Settlements							(2,349)
Transfers from other categories						[2]		[2]
Ending balance	12,388		11,746		12,388		11,746
Liabilities
Beginning Balance	(9,687)		(4,381)		(6,280)		(7,806)
Total gains or losses (realized/unrealized):
Included in net income
Included in other comprehensive income
Included in regulatory assets/liabilities	(2,461)	[1]	(2,788)	[1]	(3,409)	[1]	556	[1]
Purchases
Issuances
Settlements					1,945		81
Transfers from other categories					(4,404)	[2]		[2]
Ending Balance	$ (12,148)		$ (7,169)		$ (12,148)		$ (7,169)

[1] The WUTC and the IPUC issued accounting orders authorizing Avista Utilities to offset commodity derivative assets or liabilities with a regulatory asset or liability. This accounting treatment is intended to defer the recognition of mark-to-market gains and losses on energy commodity transactions until the period of settlement. The orders provide for Avista Utilities to not recognize the unrealized gain or loss on utility derivative commodity instruments in the Condensed Consolidated Statements of Income. Realized gains or losses are recognized in the period of settlement, subject to approval for recovery through retail rates. Realized gains and losses, subject to regulatory approval, result in adjustments to retail rates through purchased gas cost adjustments, the ERM in Washington, the PCA mechanism in Idaho, and periodic general rate cases.

[2] A derivative contract was reclassified from Level 2 to Level 3 during the nine months ended September 30, 2011 due to a particular unobservable input becoming more significant to the fair value measurement.