Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Summary Of Significant Accounting Policies [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount		$ 3,400,000		$ 8,000,000
Investment portfolio percentage rated AA or higher			95.00%		97.00%
Sale and maturity of securities available for sale	1,825,000	32,053,000	16,955,000	103,545,000
Ecova [Member]
Summary Of Significant Accounting Policies [Line Items]
Owners percentage interest	78.90%		78.90%
Employee Severance [Member]
Summary Of Significant Accounting Policies [Line Items]
Severance costs					7,300,000
Restructuring number of positions eliminated					55
Other Intangible Assets [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life			1 year
Other Intangible Assets [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life			10 years
Software and Software Development Costs [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life			3 years
Software and Software Development Costs [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life			7 years
Customer Relationships [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life			2 years
Customer Relationships [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life			12 years
Other operating expenses [Member] | Avista Utilities [Member]
Summary Of Significant Accounting Policies [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount		2,000,000		5,400,000
Other operating expenses [Member] | Other Business Segment [Member]
Summary Of Significant Accounting Policies [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount		1,400,000		2,500,000
Utility operating expenses, taxes [Member] | Avista Utilities [Member]
Summary Of Significant Accounting Policies [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount		$ 0		$ 100,000