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				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Total gains or losses (realized/unrealized):
Included in regulatory assets/liabilities	$ (4,611)	[1]	$ 5,978	[1]	$ (3,557)	[1]	$ (5,261)	[1]
Liabilities
Beginning Balance	(19,654)		(21,913)		(22,551)		(12,858)
Total gains or losses (realized/unrealized):
Included in net income	0		0		0		0
Included in other comprehensive income	0		0		0		0
Purchases	0		0		0		0
Issuances	0		0		0		0
Settlements	468		1,014		2,311		3,198
Transfers from other categories	0		0		0		0
Ending Balance	(23,797)		(14,921)		(23,797)		(14,921)
Natural Gas Exchange Agreements [Member]
Total gains or losses (realized/unrealized):
Included in regulatory assets/liabilities	1,057	[1]	(162)	[1]	1,807	[1]	13	[1]
Liabilities
Beginning Balance	(1,991)		(2,354)		(2,379)		(1,688)
Total gains or losses (realized/unrealized):
Included in net income	0		0		0		0
Included in other comprehensive income	0		0		0		0
Purchases	0		0		0		0
Issuances	0		0		0		0
Settlements	(88)		(211)		(450)		(1,052)
Transfers from other categories	0		0		0		0
Ending Balance	(1,022)		(2,727)		(1,022)		(2,727)
Power Exchange Agreements [Member]
Total gains or losses (realized/unrealized):
Included in regulatory assets/liabilities	(6,272)	[1]	6,909	[1]	(6,248)	[1]	(4,778)	[1]
Liabilities
Beginning Balance	(16,463)		(18,572)		(18,692)		(9,910)
Total gains or losses (realized/unrealized):
Included in net income	0		0		0		0
Included in other comprehensive income	0		0		0		0
Purchases	0		0		0		0
Issuances	0		0		0		0
Settlements	556		1,225		2,761		4,250
Transfers from other categories	0		0		0		0
Ending Balance	(22,179)		(10,438)		(22,179)		(10,438)
Power Option Agreement [Member]
Total gains or losses (realized/unrealized):
Included in regulatory assets/liabilities	604	[1]	(769)	[1]	884	[1]	(496)	[1]
Liabilities
Beginning Balance	(1,200)		(987)		(1,480)		(1,260)
Total gains or losses (realized/unrealized):
Included in net income	0		0		0		0
Included in other comprehensive income	0		0		0		0
Purchases	0		0		0		0
Issuances	0		0		0		0
Settlements	0		0		0		0
Transfers from other categories	0		0		0		0
Ending Balance	$ (596)		$ (1,756)		$ (596)		$ (1,756)

[1] (1)The UTC 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 rates cases.