Fair Value (Reconciliation For All Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) (Fair Value, Inputs, Level 3 [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (23,758)		$ (16,435)
Included in net income	0		0
Included in other comprehensive income	0		0
Included in regulatory assets/liabilities	(5,431)	[1]	4,222	[1]
Purchases	0		0
Issuances	0		0
Settlements	3,852		(4,257)
Transfers from other categories	0		0
Ending Balance	(25,337)		(16,470)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(35)		(1,219)
Included in net income	0		0
Included in other comprehensive income	0		0
Included in regulatory assets/liabilities	777	[1]	1,849	[1]
Purchases	0		0
Issuances	0		0
Settlements	75		(3,048)
Transfers from other categories	0		0
Ending Balance			(2,418)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	817
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(23,299)		(14,441)
Included in net income	0		0
Included in other comprehensive income	0		0
Included in regulatory assets/liabilities	(6,381)	[1]	2,026	[1]
Purchases	0		0
Issuances	0		0
Settlements	3,777		(1,209)
Transfers from other categories	0		0
Ending Balance	(25,903)		(13,624)
Power Option Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(424)		(775)
Included in net income	0		0
Included in other comprehensive income	0		0
Included in regulatory assets/liabilities	173	[1]	347	[1]
Purchases	0		0
Issuances	0		0
Settlements	0		0
Transfers from other categories	0		0
Ending Balance	$ (251)		$ (428)

[1] (1)The UTC and the IPUC issued accounting orders authorizing Avista Corp. to offset commodity derivative assets or liabilities with a regulatory asset or liability. This accounting treatment defers the recognition of mark-to-market gains and losses on energy commodity transactions until the period of delivery. The orders provide for Avista Corp. 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 delivery, 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 rates cases.