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	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (23,758)		$ (16,435)		$ (22,551)		$ (12,858)
Included in net income	0		0		0
Included in other comprehensive income	0		0		0
Included in regulatory assets/liabilities	(5,778)	[1]	4,020	[1]	(15,113)	[1]
Purchases	0		0		0
Issuances	0		0		0
Settlements	(1,545)		2,096		5,420
Transfers to/from other categories	0		0		0
Natural Gas Exchange Agreements [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(35)		(1,219)		(2,379)		(1,688)
Included in net income	0		0		0
Included in other comprehensive income	0		0		0
Included in regulatory assets/liabilities	3,873	[1]	2,298	[1]	343	[1]
Purchases	0		0		0
Issuances	0		0		0
Settlements	(2,689)		(1,138)		(1,034)
Transfers to/from other categories	0		0		0
Power Exchange Agreements [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(23,299)		(14,441)		(18,692)		(9,910)
Included in net income	0		0		0
Included in other comprehensive income	0		0		0
Included in regulatory assets/liabilities	(10,002)	[1]	1,017	[1]	(15,236)	[1]
Purchases	0		0		0
Issuances	0		0		0
Settlements	1,144		3,234		6,454
Transfers to/from other categories	0		0		0
Power Option Agreement [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(424)		(775)		(1,480)		(1,260)
Included in net income	0		0		0
Included in other comprehensive income	0		0		0
Included in regulatory assets/liabilities	351	[1]	705	[1]	(220)	[1]
Purchases	0		0		0
Issuances	0		0		0
Settlements	0		0		0
Transfers to/from other categories	$ 0		$ 0		$ 0

[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 is intended to defer 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 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.