Long-Term Debt (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended			9 Months Ended									3 Months Ended			9 Months Ended		3 Months Ended
	Dec. 31, 1998	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013	Dec. 31, 2013		Sep. 30, 2014 2032 [Member] Secured Debt [Member]	Sep. 30, 2014 2034 [Member] Secured Debt [Member]	Aug. 18, 1998 AIDEA [Member]	Sep. 30, 2014 Alaska Electric Light & Power [Member]	Sep. 30, 2014 Alaska Electric Light & Power [Member] Capital Lease Obligations [Member]	Sep. 30, 2014 Alaska Electric Light & Power [Member]	Sep. 30, 2013 Alaska Electric Light & Power [Member]	Sep. 30, 2014 Alaska Electric Light & Power [Member]	Sep. 30, 2013 Alaska Electric Light & Power [Member]	Sep. 30, 2014 Power purchase agreement [Member] Alaska Electric Light & Power [Member]	Sep. 30, 2014 Capital Lease Interest [Member] Alaska Electric Light & Power [Member]	Sep. 30, 2014 Capital Lease Amortization [Member] Alaska Electric Light & Power [Member]	Aug. 18, 1998 Minimum [Member] AIDEA [Member]	Aug. 18, 1998 Maximum [Member] AIDEA [Member]
Debt Instrument [Line Items]
Long Term Revenue Bonds												$ 100,000,000
Capital Lease Obligations														70,481,000
Long-term Pollution Control Bond, Noncurrent		(83,700,000)	[1]		(83,700,000)	[1]		(83,700,000)	[1]	66,700,000	17,000,000
Debt instrument, interest rate, stated percentage	8.45%
Amount borrowed to acquire a long-term fixed rate electric capacity contract	145,000,000
Funds held in trust account which are used to secure long-term debt		1,600,000			1,600,000
Capital Leased Assets, Gross													71,000,000
Capital Leases Assets Accumulated Depreciation													(900,000)
Utilities Operating Expense, Products and Services		131,588,000		131,136,000	481,007,000		487,277,000								2,997,000	0	2,997,000	0	10,600,000	1,000,000	900,000
Long Term Revenue Bonds Stated Interest Rate																						4.85%	6.00%
Capital Lease Obligations Annual Minimum Payments of Principal and Interest														$ 5,900,000

[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.