Long-Term Debt (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014	Dec. 31, 2014		Aug. 18, 1998
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent	$ (83,700,000)	[1]		$ (83,700,000)	[1]
Utilities Operating Expense, Products and Services	209,560,000		220,497,000
2032 [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent	66,700,000
2034 [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Pollution Control Bond, Noncurrent	17,000,000
AIDEA [Member]
Debt Instrument [Line Items]
Long Term Revenue Bonds						100,000,000
Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Capital Leased Assets, Gross	71,007,000			71,007,000
Capital Leases Assets Accumulated Depreciation	(2,731,000)			(1,821,000)
Utilities Operating Expense, Products and Services	2,900,000		0
Alaska Electric Light & Power [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital Lease Obligations	69,398,000
Capital Lease Obligations Annual Minimum Payments of Principal and Interest	5,900,000
Power purchase agreement [Member] | Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Utilities Operating Expense, Products and Services	10,600,000
Capital Lease Interest [Member] | Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Utilities Operating Expense, Products and Services	923,000		0
Capital Lease Amortization [Member] | Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Utilities Operating Expense, Products and Services	$ 910,000		$ 0
Minimum [Member] | AIDEA [Member]
Debt Instrument [Line Items]
Long Term Revenue Bonds Stated Interest Rate						4.85%
Maximum [Member] | AIDEA [Member]
Debt Instrument [Line Items]
Long Term Revenue Bonds Stated Interest Rate						6.00%

[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.