Long-Term Debt (Narrative) (Details) - USD ($) $ in Thousands			3 Months Ended		9 Months Ended
		Oct. 01, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Aug. 31, 2015	Dec. 31, 2014	Aug. 18, 1998
Debt Instrument [Line Items]
Capital Lease Obligations			$ 69,331		$ 69,331			$ 74,149
Long-term Pollution Control Bond, Noncurrent	[1]		$ (83,700)		$ (83,700)			$ (83,700)
Debt Instrument, Interest Rate, Stated Percentage			1.20%		1.20%			1.11%
Utilities Operating Expense, Products and Services			$ 138,210	$ 131,588	$ 488,886	$ 481,007
Payments for (Proceeds from) Derivative Instrument, Financing Activities					(9,326)	$ 0
Secured Debt			1,511,700		1,511,700			$ 1,511,700
2032 [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent			66,700		66,700
2034 [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent			17,000		17,000
AIDEA [Member]
Debt Instrument [Line Items]
Long Term Revenue Bonds							$ 65,700		$ 100,000
Avista Utilities [Member]
Debt Instrument [Line Items]
Secured Debt			1,436,700		1,436,700			1,436,700
Avista Utilities [Member] | 2032 [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent	[1]		66,700		$ 66,700			66,700
Maturity Year	[1]				2032
Avista Utilities [Member] | 2034 [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent	[1]		$ 17,000		$ 17,000			17,000
Maturity Year	[1]				2034
Avista Utilities [Member] | 2047 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.23%		4.23%
Secured Debt			$ 80,000		$ 80,000			80,000
Maturity Year					2047
Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Capital Leased Assets, Gross			71,007		$ 71,007			71,007
Capital Leases Assets Accumulated Depreciation			4,552		4,552			1,821
Alaska Electric Light & Power [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital Lease Obligations			64,967		64,967
Capital Lease Obligations Annual Minimum Payments of Principal and Interest					5,500
Power purchase agreement [Member] | Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Utilities Operating Expense, Products and Services					10,200
Minimum [Member] | AIDEA [Member] | Long-Term Revenue Bonds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage							4.00%		4.90%
Maximum [Member] | AIDEA [Member] | Long-Term Revenue Bonds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage							5.00%		6.00%
Interest Rate Swap [Member] | 2015 [Member]
Debt Instrument [Line Items]
Settled Derivative, Notional Amount			$ 75,000		$ 75,000
Derivative, Notional Amount								$ 75,000
Subsequent Event [Member] | Avista Utilities [Member] | 2045 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.37%
Secured Debt		$ 100,000
Maturity Year		12/31/2045

[1] In December 2010, $66.7 million and $17.0 million of the City of Forsyth, Montana Pollution Control Revenue Refunding Bonds (Avista Corporation Colstrip Project) due in 2032 and 2034, respectively, which had been held by Avista Corp. since 2008 and 2009, respectively, were refunded by new bond issues (Series 2010A and Series 2010B). The new bonds were not offered to the public and were purchased by Avista Corp. due to market conditions. The Company expects that at a later date, subject to market conditions, these bonds may be remarketed to unaffiliated investors. So long as Avista Corp. is the holder of these bonds, the bonds will not be reflected as an asset or a liability on Avista Corp.'s Condensed Consolidated Balance Sheets.