Accounting For Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Parenthetical) (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Federal statutory tax rate			21.00%	21.00%	21.00%	21.00%	35.00%
Regulatory liability, current			$ 77,149	$ 46,435
Effective income tax rate reconciliation, excess deferred income tax reversal amount				$ 8,476	$ 5,690
Washington Utilities and Transportation Commission [Member]
Regulatory Liabilities [Line Items]
Effective income tax rate reconciliation, excess deferred income tax reversal amount	$ 8,400
Washington Utilities and Transportation Commission [Member] | Income Tax Related [Member]
Regulatory Liabilities [Line Items]
Regulatory liability, current	$ 10,900
Idaho Public Utilities Commission [Member]
Regulatory Liabilities [Line Items]
Effective income tax rate reconciliation, excess deferred income tax reversal amount		$ 5,100
Idaho Public Utilities Commission [Member] | Income Tax Related [Member]
Regulatory Liabilities [Line Items]
Regulatory liability, current		$ 6,400