Regulatory Matters (Details)									1 Months Ended				9 Months Ended	12 Months Ended
	Nov. 08, 2016	Aug. 29, 2016	Aug. 12, 2016	Jul. 08, 2016 USD ($)	Jul. 01, 2016 USD ($)	Dec. 04, 2015 MMcf	Feb. 13, 2015 USD ($)	Jan. 30, 2015 MMcf	Aug. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Jul. 31, 2015 a	Apr. 30, 2015	Sep. 30, 2016 USD ($) $ / Mcfe MMcf	Dec. 31, 2015
Other Commitments [Line Items]
Proposed increase (decrease) in rates					$ 4,800,000		$ 21,300,000						$ (5,900,000)
Proposed percentage increase (decrease) in rates					4.20%		20.00%
Approved percentage increase (decrease) in rates			4.20%							(0.50%)
Times interest earned ratio										1.35				1.30
Times interest earned ratio margin increase per year										$ 1,000,000
Beluga Power Plant [Member]
Other Commitments [Line Items]
Recovery requested													$ 11,000,000
Matanuska Electric Association, Inc. [Member]
Other Commitments [Line Items]
Term of dispatch services													1 year
Expiration date of Dispatch Services Agreement													Mar. 31, 2016
Commencement date of Gas Dispatch Agreement													Apr. 01, 2016
Expiration date of Gas Dispatch Agreement													Mar. 31, 2017
Extension date of Gas Dispatch Agreement													Mar. 31, 2018
Optional extension date of Gas Dispatch Agreement													Mar. 31, 2019
Power contracts expiration date													Apr. 30, 2015
City Of Seward [Member]
Other Commitments [Line Items]
Power contracts expiration date													Dec. 31, 2016
Power contracts extension date													Dec. 31, 2021
Automatic extension term													5 years
Written notice period prior to expiration date													1 year
Proposed percentage increase (decrease) in rates													(4.60%)
Refunds issued				$ 28,000
City Of Seward [Member] | Total Customer Bill Basis [Member]
Other Commitments [Line Items]
Proposed percentage increase (decrease) in rates													(1.90%)
Retail Customers [Member]
Other Commitments [Line Items]
Proposed percentage increase (decrease) in rates					2.50%								(4.70%)
Refunds issued									$ 750,000
Retail Customers [Member] | Total Customer Bill Basis [Member]
Other Commitments [Line Items]
Proposed percentage increase (decrease) in rates													(3.20%)
ConocoPhillips (COP) [Member]
Other Commitments [Line Items]
Acres of exploration prospects | a											5,700
Minimum [Member]
Other Commitments [Line Items]
Approved percentage increase (decrease) in rates												2.00%
Minimum [Member] | Transmission Wheeling And Ancillary Services [Member]
Other Commitments [Line Items]
Proposed percentage increase (decrease) in rates		(9.50%)
Maximum [Member]
Other Commitments [Line Items]
Approved percentage increase (decrease) in rates												5.00%
Maximum [Member] | Transmission Wheeling And Ancillary Services [Member]
Other Commitments [Line Items]
Proposed percentage increase (decrease) in rates		(14.40%)
Subsequent Event [Member] | Beluga Power Plant [Member]
Other Commitments [Line Items]
Amortization period of regulatory asset	10 years
CINGSA [Member]
Other Commitments [Line Items]
Total volume of natural gas found | MMcf								14,500
Approved volume of natural gas for commercial sale | MMcf						2,000
Percentage of proceeds allocated						13.00%
Term of notice preceding gas sales													30 days
CINGSA [Member] | Minimum [Member]
Other Commitments [Line Items]
Proposed volume of natural gas for commercial sale | MMcf													2,000
FSS [Member]
Other Commitments [Line Items]
Percentage of proceeds allocated						87.00%
Beluga River Unit [Member]
Other Commitments [Line Items]
Date of Purchase and Sale Agreement													Feb. 04, 2016
Initial gas transfer price | $ / Mcfe													5.88