Derivatives And Risk Management (Energy Commodity Derivatives) (Details)	12 Months Ended
	Dec. 31, 2012 Volt
Purchases [Member] | Physical [Member] | Gas Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	18,523,000
2014	6,394,000
2015	3,390,000
2016	1,365,000
2017	0
Thereafter	0
Purchases [Member] | Physical [Member] | Electric Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	713,000	[1]
2014	397,000	[1]
2015	379,000	[1]
2016	367,000	[1]
2017	366,000	[1]
Thereafter	583,000	[1]
Purchases [Member] | Financial [Member] | Gas Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	88,391,000
2014	55,407,000
2015	42,930,000
2016	455,000
2017	0
Thereafter	0
Purchases [Member] | Financial [Member] | Electric Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	3,365,000	[1]
2014	801,000	[1]
2015	614,000	[1]
2016	0	[1]
2017	0	[1]
Thereafter	0	[1]
Sales [Member] | Physical [Member] | Gas Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	7,252,000
2014	1,786,000
2015	0
2016	0
2017	0
Thereafter	0
Sales [Member] | Physical [Member] | Electric Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	264,000
2014	377,000
2015	286,000
2016	287,000
2017	286,000
Thereafter	443,000
Sales [Member] | Financial [Member] | Gas Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	91,962,000
2014	33,623,000
2015	35,575,000
2016	0
2017	0
Thereafter	0
Sales [Member] | Financial [Member] | Electric Derivatives [Member]
Energy Commodity Derivative Volumes [Line Items]
2013	2,712,000
2014	1,844,000
2015	982,000
2016	0
2017	0
Thereafter	0

[1] Physical transactions represent commodity transactions where Avista will take delivery of either electricity or natural gas and financial transactions represent derivative instruments with no physical delivery, such as futures, swaps, options, or forward contracts.