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Summary of Significant Accounting Policies - Summary of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Goodwill [Line Items] |  |
Balance as of January 1, 2019 | $ 52,426 | $ 57,672
Goodwill sold during the year |  | (5,246)
Balance as of December 2019 | 52,426 | 52,426
Alaska Electric Light & Power [Member] |  |
Goodwill [Line Items] |  |
Balance as of January 1, 2019 | 52,426 | 52,426
Goodwill sold during the year |  | 0
Balance as of December 2019 | 52,426 | 52,426
Corporate and Other [Member] |  |
Goodwill [Line Items] |  |
Balance as of January 1, 2019 | 0 | 12,979
Goodwill sold during the year |  | (12,979)
Balance as of December 2019 | 0 | 0
Accumulated Impairment Losses [Member] |  |
Goodwill [Line Items] |  |
Balance as of January 1, 2019 | 0 | (7,733)
Goodwill sold during the year |  | 7,733
Balance as of December 2019 | $ 0 | $ 0

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(10)(1)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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