Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Weighted average capital interest percentage	4.30%	4.30%	4.30%
Impairment on investments	$ 0	$ 0	$ 0
Investment maturity period	18 months
Minimum number of days past balances reviewed	90 days
Accounts receivable	$ 33,000,919	28,232,930
Fuel stock	6,321,676	7,063,541
Fuel cost over-recovery	3,824,722	5,135,745
Consumer deposits	3,300,000	3,100,000
Customer credits	1,900,000	1,900,000
Grant proceeds included in public utilities property, plant and equipment carrying amount	600,000	1,600,000
Cash provided by operating activities	32,494,336	52,096,436	58,766,300
Cash used in financing activities	46,040,387	(20,486,734)	$ (34,061,334)
NRECA Retirement Security Plan [Member]
Significant Accounting Policies [Line Items]
Multiemployer plan, Prepayment amount	$ 7,900,000
Multiemployer plan, Prepayment amortization period	11 years
ML&P For Fuel And South Central Power Project Costs [Member]
Significant Accounting Policies [Line Items]
Accounts receivable	$ 1,400,000	1,100,000
Alaska Energy Authority For Grant [Member]
Significant Accounting Policies [Line Items]
Accounts receivable	0	200,000
BRU Operations For Gas Sales [Member]
Significant Accounting Policies [Line Items]
Accounts receivable	700,000
Unbilled Retail Revenues [Member]
Significant Accounting Policies [Line Items]
Accounts receivable	10,940,274	10,531,377
Concentration Account [Member]
Significant Accounting Policies [Line Items]
Average balance of cash account	5,897,767	6,218,015
Funds On Deposit [Member]
Significant Accounting Policies [Line Items]
Restricted cash equivalents	$ 800,000	$ 1,700,000
Maximum [Member] | CoBank, ACB (CoBank) And National Rural Utilities Cooperative Finance Corporation (NRUCFC) [Member]
Significant Accounting Policies [Line Items]
Cost ownership percentage	1.00%