Summary of Significant Accounting Policies - Summary of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	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