Balance Sheet Components - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Regulated Asset Liability [Line Items]
Regulatory assets	$ 210,097	$ 193,787
Non-current regulatory assets	839,272	833,328
Regulatory liabilities	85,462	95,665
Non-current regulatory liabilities	840,211	840,837
Income Tax Related Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	58,931	73,267
Non-current regulatory liabilities	372,765	390,734
Decoupling Rebate [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	11,032	9,469
Non-current regulatory liabilities	31,754	20,476
Utility Plant Retirement Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	383,743	376,817
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	23,191	24,204
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	0	0
Non-current regulatory liabilities	11,637	11,874
Other Regulatory Liabilities [Member]
Regulated Asset Liability [Line Items]
Regulatory liabilities	15,499	12,929
Non-current regulatory liabilities	17,121	16,732
Energy Commodity Derivatives [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	73,968	112,090
Non-current regulatory assets	10,769	18,185
Decoupling Surcharge [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	4,362	6,250
Non-current regulatory assets	787	5,449
Deferred Natural Gas Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	94,653	52,091
Non-current regulatory assets	0	0
Deferred Power Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	37,114	23,356
Non-current regulatory assets	24,143	24,043
Deferred Income Taxes [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	237,263	240,325
Pension and Other Postretirement Benefit Plans [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	133,837	135,337
Interest Rate Swaps [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	184,784	185,919
AFUDC Above FERC Allowed Rate [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	50,973	51,649
Settlement with Coeur d'Alene Tribe [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	37,530	37,809
Advanced Meter Infrastructure [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	31,622	32,381
Utility Plant Abandoned [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	32,794	24,389
Deferred Climate Commitment Act Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	19,019	0
COVID-19 Deferrals [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	9,797	9,793
Unamortized Debt Repurchase Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	6,057	6,177
Demand Side Management Programs [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	451	3,683
Other Regulatory Assets [Member]
Regulated Asset Liability [Line Items]
Regulatory assets	0	0
Non-current regulatory assets	$ 59,446	$ 58,189