Summary of Consolidation and Significant Accounting Policy (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) mi²	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Summary of Consolidation Policy
Allowance for Credit Losses, Beginning Balance			$ 20,080	$ 8,294
Provision for Credit Loss	$ 26,424	$ 14,660
Receivables Charged-Off	(8,728)	(9,065)
Allowance for Credit Loss, Ending Balance	37,776	13,889
Variable Interest Entity [Line Items]
Bad Debt Deferral, COVID 19	$ 8,500
Subsidiaries [Member]
Summary of Consolidation Policy
Area of Service Territory (in sqmi) | mi²	6,000
Variable Interest Entity [Line Items]
Contract Length, PPA	20 years
Variable Interest Entity, Measure of Activity, Expense	$ 12,300
Variable Interest Entity, Payable	$ 2,600
Subsidiaries [Member] | Tacoma LNG [Member]
Summary of Consolidation Policy
Jointly Owned Non-Utility Plant Share	43.00%
Construction in Progress, Gross	$ 232,800		207,700
Puget LNG [Member]
Summary of Consolidation Policy
Jointly Owned Non-Utility Plant Share	57.00%
Construction in Progress, Gross	$ 238,800		$ 231,600
Puget LNG [Member]
Summary of Consolidation Policy
Operating Costs and Expenses	$ 900	$ 500