Avista Utilities Regulatory Matters (Schedule Of Energy Recovery Mechanism) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Within plus/minus $0 to $4 million (deadband) [Member]
Regulated Asset Liability [Line Items]
Deferred for future surcharge or rebate to customers percentage	0.00%
Expense or benefit to the company	100.00%
Within plus/minus $0 to $4 million (deadband) [Member] | Minimum [Member]
Regulated Asset Liability [Line Items]
Annual power supply cost variability	0
Within plus/minus $0 to $4 million (deadband) [Member] | Maximum [Member]
Regulated Asset Liability [Line Items]
Annual power supply cost variability	4.0
Higher by $4 million to $10 million [Member]
Regulated Asset Liability [Line Items]
Deferred for future surcharge or rebate to customers percentage	50.00%
Expense or benefit to the company	50.00%
Higher by $4 million to $10 million [Member] | Minimum [Member]
Regulated Asset Liability [Line Items]
Annual power supply cost variability	4.0
Higher by $4 million to $10 million [Member] | Maximum [Member]
Regulated Asset Liability [Line Items]
Annual power supply cost variability	10.0
Lower by $4 million to $10 million [Member]
Regulated Asset Liability [Line Items]
Deferred for future surcharge or rebate to customers percentage	75.00%
Expense or benefit to the company	25.00%
Lower by $4 million to $10 million [Member] | Minimum [Member]
Regulated Asset Liability [Line Items]
Annual power supply cost variability	4.0
Lower by $4 million to $10 million [Member] | Maximum [Member]
Regulated Asset Liability [Line Items]
Annual power supply cost variability	10.0
Higher or lower by over $10 million [Member]
Regulated Asset Liability [Line Items]
Deferred for future surcharge or rebate to customers percentage	90.00%
Expense or benefit to the company	10.00%
Annual power supply cost variability	10.0