Bradley Lake Hydroelectric Project (Narrative) (Details) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Aug. 31, 2010 Bradley Lake Hydroelectric Project [Member]	Dec. 31, 2012 Bradley Lake Hydroelectric Project [Member] MW	Dec. 31, 2011 Bradley Lake Hydroelectric Project [Member]	Dec. 31, 2010 Bradley Lake Hydroelectric Project [Member]	Aug. 31, 2010 Alaska Energy Authority [Member] Bradley Lake Hydroelectric Project [Member]	Dec. 31, 2012 Revenue Bonds [Member] Alaska Energy Authority [Member] Bradley Lake Hydroelectric Project [Member]	Jul. 31, 2010 Power Revenue Refunding Bonds, Sixth Series [Member] Alaska Energy Authority [Member] Bradley Lake Hydroelectric Project [Member]	Aug. 31, 2010 Fifth Series Bonds [Member] Alaska Energy Authority [Member] Bradley Lake Hydroelectric Project [Member]	Dec. 31, 2012 Forecast [Member] Bradley Lake Hydroelectric Project [Member]	Aug. 31, 2010 Forecast [Member] Alaska Energy Authority [Member] Bradley Lake Hydroelectric Project [Member]	Dec. 31, 2012 Maximum [Member] Forecast [Member] Bradley Lake Hydroelectric Project [Member] MWh
Unrecorded Unconditional Purchase Obligation [Line Items]
Bonds, face value									$ 166,000,000	$ 28,800,000
Percentage share of power purchased					30.40%
Amount of committed purchased power					27.4
Portion of outstanding debt					28,700,000
Bonds payable	491,916,666	264,333,333
Refunding bonds											30,600,000
Threshold percentage for increasing plant costs					25.00%
Term of debt service payments								11 years
Aggregate debt service cost savings													3,300,000
Economic gain				700,000				2,400,000
Estimated increase in annual energy output														40,000
Estimated entitled additional energy output percentage												30.40%
Purchased power	$ 22,104,687	$ 25,861,814	$ 26,691,968		$ 4,223,784	$ 4,643,641	$ 5,120,958					$ 5,100,000