Regulatory Matters (Details) Mcf in Millions										1 Months Ended					12 Months Ended
	Mar. 16, 2017 $ / Mcfe Mcf	Nov. 18, 2016 USD ($)	Aug. 29, 2016	Aug. 12, 2016	Jul. 08, 2016 USD ($)	Jul. 01, 2016 USD ($)	Dec. 04, 2015 MMcf	Feb. 13, 2015 USD ($)	Jan. 30, 2015 MMcf	Jan. 31, 2017 USD ($)	Aug. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Jul. 31, 2015 a	Apr. 30, 2015	Dec. 31, 2016 USD ($) $ / Mcfe MMcf
Other Commitments [Line Items]
Proposed percentage increase (decrease) in rates						4.20%		20.00%
Proposed increase (decrease) in rates						$ 4,800,000		$ 21,300,000							$ (5,900,000)
Approved percentage increase (decrease) in rates				4.20%								(0.50%)
Approved increase (decrease) in rates												$ (600,000)
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		$ 11,400,000
Beluga Power Plant, Unit 1 [Member] | Beluga Power Plant [Member]
Other Commitments [Line Items]
Recovery requested		$ 300,000
Amortization period of regulatory asset		30 months
Beluga Power Plant, Unit 2 [Member] | Beluga Power Plant [Member]
Other Commitments [Line Items]
Recovery requested		$ 11,100,000
Amortization period of regulatory asset		108 months
Matanuska Electric Association, Inc. [Member]
Other Commitments [Line Items]
Power contracts extension date															Apr. 30, 2015
City Of Seward [Member]
Other Commitments [Line Items]
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]
Other Commitments [Line Items]
Term to finalize agreementerm to finalize agreement										1 year
Estimated cost reductions										$ 16,000,000
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%
Furie Operating Alaska, LLC [Member] | Subsequent Event [Member]
Other Commitments [Line Items]
Minimum purchase requirement | Mcf	1.8
Term of purchase commitment	16 years
Furie Operating Alaska, LLC [Member] | Subsequent Event [Member] | Firm Purchases [Member]
Other Commitments [Line Items]
Commencement date of natural gas purchases	Apr. 01, 2023
Expiration date of natural gas purchases	Mar. 31, 2033
Furie Operating Alaska, LLC [Member] | Subsequent Event [Member] | Interruptible Gas Purchases [Member]
Other Commitments [Line Items]
Expiration date of natural gas purchases	Mar. 31, 2033
Furie Operating Alaska, LLC [Member] | Subsequent Event [Member] | Minimum [Member]
Other Commitments [Line Items]
Price of natural gas purchases | $ / Mcfe	7.16
Percentage of projected natural gas requirements	20.00%
Furie Operating Alaska, LLC [Member] | Subsequent Event [Member] | Maximum [Member]
Other Commitments [Line Items]
Price of natural gas purchases | $ / Mcfe	7.98
Percentage of projected natural gas requirements	25.00%
Beluga River Unit [Member]
Other Commitments [Line Items]
Date of Purchase and Sale Agreement															Feb. 04, 2016
Initial gas transfer price | $ / Mcfe															5.88
Deferred cost of acquisition															$ 1,500,000