Bradley Lake Hydroelectric Project (Schedule Of Bradley Lake Information) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Long-term Contract for Purchase of Electric Power [Line Items]
Plant in service	$ 1,210,969,809				$ 1,144,075,666				$ 1,210,969,809		$ 1,144,075,666
Note outstanding balance	470,442,665								470,442,665
Interest expense	$ 5,341,242	$ 5,427,440	$ 5,247,404	$ 5,385,211	$ 5,415,131	$ 5,428,774	$ 5,381,167	$ 5,589,373	$ 21,401,297		$ 21,814,445	$ 22,800,706
Bradley Lake Hydroelectric Project [Member] | Alaska Energy Authority [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant in service			163,531,000							$ 163,531,000
Note outstanding balance			53,495,000							53,495,000
Interest expense										3,177,000
Bradley Lake Hydroelectric Project [Member] | Alaska Energy Authority [Member] | Proportionate Share [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant in service			49,713,000							49,713,000
Note outstanding balance			$ 16,262,000							16,262,000
Interest expense										$ 966,000