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Evaluated Power Capacity

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

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The charge for the use of long-lived depreciable capital leased assets for the period.

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The financing charge for leasing arrangements meeting the criteria for capitalization.

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The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of operating expense for products and services of regulated operation.

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Long-Term Debt and Capital Leases Long-Term Debt and Capital Leases (Capital Lease Obligations) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) MW	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Aug. 31, 2015 USD ($)	Aug. 18, 1998 USD ($)
Debt Instrument [Line Items]
Capital Lease Obligations	$ 62,148	$ 65,435
Debt Instrument, Interest Rate, Stated Percentage	2.36%	1.81%	1.29%
Utilities Operating Expense, Products and Services	$ 524,566	$ 551,366	$ 656,964
Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Capital Leased Assets, Gross	71,007	71,007
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	12,745	9,104
Alaska Electric Light & Power [Member] \| Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital Lease Obligations	59,745
Capital Lease Obligations Annual Minimum Payments of Principal and Interest	$ 5,500
Alaska Electric Light & Power [Member] \| Power purchase agreement [Member]
Debt Instrument [Line Items]
Evaluated Power Capacity \| MW	78
Carrying Value [Member] \| Fair Value, Inputs, Level 3 [Member] \| Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Capital Lease Obligations	$ 59,745	62,160
Operating Expense [Member] \| Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Capital Leases, Income Statement, Interest Expense	3,042	3,157
Capital Leases, Income Statement, Amortization Expense	$ 3,641	$ 3,642
AIDEA [Member]
Debt Instrument [Line Items]
Long Term Revenue Bonds				$ 65,700	$ 100,000
Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.81%	1.29%	1.11%
Minimum [Member] \| AIDEA [Member] \| Long-Term Revenue Bonds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				4.00%	4.90%
Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.36%	1.81%	1.29%
Maximum [Member] \| AIDEA [Member] \| Long-Term Revenue Bonds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				5.00%	6.00%
Power purchase agreement [Member] \| Minimum [Member] \| Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Utilities Operating Expense, Products and Services	$ 10,700
Power purchase agreement [Member] \| Maximum [Member] \| Alaska Electric Light & Power [Member]
Debt Instrument [Line Items]
Utilities Operating Expense, Products and Services	$ 13,200