Committed Lines of Credit (Details) (USD $)	9 Months Ended				9 Months Ended
	Sep. 30, 2014 Avista Corporation [Member]	Dec. 31, 2013 Avista Corporation [Member]	Dec. 31, 2013 Ecova [Member]	Feb. 28, 2011 Line of Credit [Member] Avista Corporation [Member]	Sep. 30, 2014 Line of Credit [Member] Alaska Electric Light & Power [Member]	Jul. 01, 2014 Line of Credit [Member] Alaska Electric Light & Power [Member]	Jul. 31, 2012 Line of Credit [Member] Ecova [Member]	Sep. 30, 2014 Minimum [Member] Line of Credit [Member] Alaska Electric Light & Power [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 400,000,000		$ 14,500,000	$ 125,000,000
Line Of Credit Facility Percentage Below Prime					0.25%
Line of Credit Facility, Commitment Fee Percentage					0.45%
Line of Credit Facility, Covenant Terms	0.65
Balance outstanding at end of period	35,000,000	171,000,000	46,000,000
Letters of credit outstanding at end of period	$ 45,614,000	$ 27,434,000
Average interest rate at end of period	0.92%	1.02%	2.17%					4.00%