Balance Sheet Components - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Regulated Asset Liability [Line Items]
Regulatory assets	$ 59,573	$ 43,783
Non-current regulatory assets	836,538	860,626
Regulatory liabilities	98,081	77,149
Non-current regulatory liabilities	845,495	861,515
Income Tax Related Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	77,689	56,331
Non-current regulatory liabilities	402,464	458,789
Deferred Power Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	6,457
Non-current regulatory liabilities	2,287	5,434
Decoupling Rebate [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	7,504	3,049
Non-current regulatory liabilities	17,748	6,259
Utility Plant Retirement Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	370,232	350,190
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	23,556	15,062
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	12,032	12,500
Other Regulatory Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	12,888	11,312
Non-current regulatory liabilities	17,176	13,281
Energy Commodity Derivatives [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	8,374	12,447
Non-current regulatory assets	4,201	2,938
Decoupling Surcharge [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	6,674	9,907
Non-current regulatory assets	5,346	14,625
Deferred Natural Gas Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	38,674	14,095
Non-current regulatory assets	0	6,932
Deferred Power Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	4,413	7,334
Non-current regulatory assets	0	3,501
Deferred Income Taxes [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	251,033	244,154
Pension and Other Postretirement Benefit Plans [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	161,665	165,696
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	187,607	199,754
AFUDC Above FERC Allowed Rate [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	50,956	48,455
Settlement with Coeur d'Alene Tribe [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	38,088	38,926
Advanced Meter Infrastructure [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	33,288	36,008
Utility Plant Abandoned [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	24,937	26,771
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	13,497	13,591
Unamortized Debt Repurchase Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	6,305	6,768
Demand Side Management Programs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	5,144	3,974
Other Regulatory Assets [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	1,438	0
Non-current regulatory assets	$ 54,471	$ 48,533