Bradley Lake Hydroelectric Project (Bradley Lake Project Financials) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 30, 2012 Bradley Lake Hydroelectric Project [Member] Alaska Energy Authority [Member]	Jun. 30, 2012 Bradley Lake Hydroelectric Project [Member] Alaska Energy Authority [Member] Proportionate Share [Member]
Electric plant in service	$ 891,781,509				$ 862,362,243				$ 891,781,509	$ 862,362,243		$ 181,587,000	$ 55,202,000
Long term debt	546,090,108				429,450,318				546,090,108	429,450,318		87,607,000	26,633,000
Interest expense	$ 3,492,044	$ 3,495,865	$ 3,542,676	$ 3,872,346	$ 4,102,750	$ 3,544,204	$ 4,209,482	$ 4,890,541	$ 14,402,931	$ 16,746,977	$ 20,005,698	$ 5,032,000	$ 1,530,000